View Full Version here: : How to hone observing sensitivity and accuracy
22-09-2011, 10:17 PM
In responding to one of my recent observation reports, some very experienced observers - Rob_K, madbadgalaxyman and pgc hunter have put in some very good tips about how to be sure that some faint features seen are real and also how to see faint features more clearly. I learned heaps from what they had to say.
As many people may miss that thread and there are clearly a lot more people out there with valuable tips for how to enhance visual observing, some of us thought that it would be good to start a thread on the topic.
So all ideas, questions and tips are welcome on how to see more clearly. There is a lot to share and learn from each other.
For those who've not read the original thread, http://www.iceinspace.com.au/forum/showthread.php?t=80800 is the link - there are many gems to be mined!
If there is enough interest, maybe it could be a sticky
22-09-2011, 11:43 PM
A very good idea on a sticky for observational techniques and tips, Paddy. I'd be happy to contribute a few words too. It all helps.
22-09-2011, 11:46 PM
Top idea Paddy, no doubt it'll help many other observers aswell :thumbsup:
Some tips for getting the best out of limit-of-vision objects as requested:
- if possible, seek out your targets in the early morning hours.... not only because light pollution will be at a minimum as business are closed, vehicle traffic is at a minimum and most people are long asleep, but you'll have been dark adapted for several hours already (if you started observing in the evening).
-use a dark shroud over your head and keep both eyes open, covering the unused eye with your hand. You'll avoid the discomfort which occurs from unnaturally squeezing one eye closed for long periods and the associated eyestrain which will result. Works wonders and really helps with visibility of faint objects. I live by this.
-Jiggling the scope may help spotting faint low surface brightness objects.
-take a break every couple of hours and have a snack/drink.. keeps you alert and full so you won't have distracting thoughts of a midnight maccas run ;) Taking regular snack breaks helps you relax and relieve any eyestrain etc and allows you to hit the next object refreshed and invigorated.
-use magnification...if seeing is good, high power is your friend. It darkens background sky so increases contrast of faint galaxies and stellar objects. Recently, my best views of Neptune's moon Triton and Uranus's moons was at 600x with an 8" scope. Ofcourse, experiment and find out what works best for you.
-Study the FOV for several minutes...if something is really at the limit of vision and popping in and out of sight, verify that it is not "averted imagination" by observing the field intensely, noting each time the object "pops" into view it is in the same location using nearby stars/objects. If you get that dust mote sighted 5-10 times and each time it correlates to its correct position relative to nearby objects.... that to me is a hit.
-no booze! I'm normally the last person on earth to knock back grog....but it stuffs with your night vision, body temperature, makes you tired and lose concentration and you just won't be at 100% if you're a bit tipsy
23-09-2011, 10:21 AM
In a forthcoming post, I shall try to summarize the many good suggestions that have been made so far, as to how to improve our ability to see faint objects in the telescope.
I am glad the active observers are chipping in, with many suggestions.
We have got a lot of worthwile techiques together, in a short period of time!
Of course, moving to a binocular telescope is another good way to see more. In a side by side comparison, for example, I found that an 8 inch binocular telescope was about equivalent to a 10 inch "monocular" telescope, and there were types of objects where the binocular improvement over a standard 8 inch monocular telescope was even greater:
- angular resolution significantly improved
- Dark nebula observing becomes a really major event, for people with binocular telescopes!
I have not done any detailed assessment of how binocular vision deals with very low surface brightness light at the edge of detectability, as compared to monocular vision.
But I did have a period when I used only 10by50s , and my impression was that there are times when you see low surface brightness nebulosity in binos that would be too hard to see in a monocular telescope of the same design and aperture.
I have found that billberry's seem to work quite well to improve your night vision and faint object viewing.
They were used in the second world war by the British bomber pilots to enhance their night vision. Taking them as a dried fruit, jam or tablet seem to have the same effect.
I tried it as an experiment and observed faint PN's without taking billberry tablets and then tried the same PN's again after taking Billberry tablets for about six weeks. I was happy to see that I was actually observing fainter details but the effect does drop off very quickly if you stop taking them.
These results may not be the same for everyone, but at the very least you are getting a nice dose of antioxidants into your system.
23-09-2011, 08:23 PM
great thread guy's,it's been awhile since iv'e posted a report.i should have my replacement scope on wednesday so i'm very very keen to get back in the pod it's been quite a few months.like some of your tips so far especially the hand over the eye..stops that squinting.
most of my observing is done after midnight darker skies,no cars and i feel better after a few hours sleep (especially after laying bricks all day in the summer sun) i feel refreshed...also that evening cloud has disappeared...
heading on a boat cruise in about 10 days and heading to noumea so i'm going to take my bino's and do some seeing to the north let's hope the seas not to big :lol::lol: try and see some objects not visable from home..
23-09-2011, 10:12 PM
This is a repeat of my last post in the "Observation Reports" forum, which had to be put there because it follows on from mental4astro's post regarding Observing techniques. However, it now belongs to this forum on how best to observe faint deep sky objects.
In visually observing a faint galaxy or faint HII region, or observing a faint feature within a galaxy or HII region, I would probably do a combination of the following things:
- looking fixedly, just to one side of the target object, while concentrating on the object itself, for 5-10 seconds, thereby allowing the exposure time of the rods to be used, and thereby allowing an image to build up.
- moving my eyes randomly and rapidly around the field, in order to relax or reset them
- looking fixedly just to one side of the target object again (but looking at the opposite side of the object to the side I looked at first), while still concentrating on the object itself. (again, for 5-10 seconds)
- looking straight at the object, for comparison with the views that I get using averted vision
- moving the telescope, just a very little, from time to time (as mentioned in mental4astro's post), which can make the object more obvious.
I repeat all of these steps when I observe a vanishingly faint Diffuse object, often repeating them many times, and I find that I do gradually build up a better idea about the morphology of the "very very faint object" in the eyepiece. This seems to be an additive process, and the various glimpses that I get of the object (or of features within the object) can be used to build up a better picture of it.
I have been known to persist for up to one hour on a single object, at which point my eyes are thoroughly fatigued.
If I am not sure whether or not I have seen something, I resort to some of the stratagems in my previous post within this thread ("When the eye+brain sees an intermittent feature - is it real?).
There have been some studies done of how far away from the object, in degrees, your gaze should be centred, in order to put the light from the object onto the most sensitive part of the retina. But there is some individual variation, and this is something that is worth studying!
An important point, as per my above description of observing technique, is that both staring fixedly and (at other times) moving the telescope a tiny bit, are probably necessary to see all that we can see in a very faint object.
26-09-2011, 10:34 AM
Sab, a question about your shroud technique. When I've tried this, my breath increases the humidity under the shroud and the eyepiece fogs up. How do you avoid this?
26-09-2011, 10:37 AM
Conversely, Robert, I reckon an layman's understanding of how our eyes work, then how to exploit this, is important too:
One thing I've read so far that is being hinted at is what I call "light saturation" of our eyes. We typically sit on an object, and as the observation time elapses we begin to actually see less in the object than we noticed at the start of the observation. We are not imagining this. What is needed here is to restimulate our eyes. This is somewhat akin to how our nose looses its sensitivity to a particular odor when exposed to an odor for an extended period of time.
Another part to this is how our eyes are made to detect motion. Here's an example: You're looking across a peaceful valley. We see nothing moving, other than a few leaves on the trees (due to the breeze). Unconsciously our eyes begin to dart around, looking for movement (from a possible threat). We spot something out of the corner of our eye, a rabbit shooting off from a stand-still - we didn't see it at first even though it was in plain sight, as it wasn't moving, and the sudden change in light conditions, small as they were, was instantly picked up by our eyes when the bunny moved.
Where I'm heading to here is that a still, unmoving telescope is our biggest impediment. Our eye (or eyes if you're using a bino viewer), darts over the image the eyepiece presents. Low light quickly saturates the rods in our eyes, and we no longer see as much detail.
Solution: give the scope a little tap to set off a vibration, and all of a sudden our eyes begin to see detail! The induced movement restimulates the natural reactivation mechanism in our eyes.
This is something that I had noticed for many years, but wasn't aware that it was of the physiological reason behind it until it was explained to me. I had struggled on occasions to spot very faint objects at times, even though the charts said the object SHOULD be there. Yet, I only noticed it when there was a brisk movement or vibration induced in the scope, otherwise the object seemed to be totally invisible.
This is one reason why I've decided not to motorise my dobs. The constant shifting of the scope I actually now find is most benificial to my productivity.
Robert, your observing method is most thorough! Uncanny too how my own method has developed similar to yours. BUT what I hadn't done was attempt to exploit more of the rod-rich areas of my eye. I've settled into my own pattern, but you've inspired me to attempt a new stratergy.
Having an observing stratergy that is based on understanding the physiology of how our eyes work is probably the best way of making the most of our obseving time. The flexability in developing your own stratergy is the key here too. What I hadn't mentioned was the crucial importance of averted vision in the physiology. It will be a most interesting thread if Paddy succeeds in getting a sticky on this going. Most interesting.
26-09-2011, 10:58 AM
Thanks for your comments, Mr mental4astro,
It is hard to know what is the very best technique to adopt, when using the eye+brain+telescope system.
I hope that some of the other very experienced observers will make a serious attempt to clearly codify (hopefully in English, and not in Klingon) "what they do" at the eyepiece, and then write up the results in this thread.
It would be really nice to compare techniques between a large number of experienced observers.
Somewhat more objective could be the results of an experiment, in which we line up 10 experienced observers, behind 10 identical optical/mechanical systems, and then we get them to do several different and defined sequences of things with their "eye and mind and telescope";
in order to compare and contrast what can be seen with each sequence of activities.
26-09-2011, 01:35 PM
That's a good point you raise.... the shroud is simply a black sheet of fabric draped over my head, rather than a tight fitting hood or anything like that so there is still ample room for body heat to escape. I still get fogging, but tends to be a problem only on really cold dewy nights. With the shroud, the problem is no worse than if I simply cup my face with my hands (infact the latter tends to create more fog problems).
26-09-2011, 10:10 PM
I think I must be trying too vigorously to exclude light and holding the shroud too close around my ugly mug. I'll keep trying. Not breathing did not seem to be a sustainable option.
28-09-2011, 07:34 AM
A very interesting thread and great tips.
I have a question though not deep sky related I hope this is okay.
In a lot of observing reports I see mentions of Apparant size of an object and was just wondering how to do this myself is it plainly estimations on your knowledge of your Eps TFOV or is it more complicated than that.
Thanks in advance
28-09-2011, 08:19 AM
same here! I think they probably use the eyepiece TFOV as a reference like you say. Still, it would be just dead reckoning. The only other way I can think of is using an astrometric / reticle eyepiece.
28-09-2011, 09:14 AM
Don't know about everyone else, but I use a few methods:
- First, knowing the FOV. If you've got a 1-deg FOV and a big object spans a third of it, then it's about 20' across.
- Sometimes in generating charts for small, faint objects, I obtain the distance between an obvious, reasonably tight pair of stars that will be close to the object in the field (many planetarium programs like Starry Night have this 'ruler' function).
- Also, having done that many times, you can get a fair gauge on distances between close star pairs in the field at a certain magnification and use that to estimate size.
Now finding north to add 'directions' to an observation is a different problem, using a reflector & an alt-az mount! :mad2: ;)
28-09-2011, 09:52 AM
The way I mostly do it is mentally divide the FOV. So my 13mm Nagler gives me a TFOV of 28', I find the centre of the field to get 14' to the edge, then half way from there to the edge is 7' etc. It's a bit hit and miss - sometimes I'm close to what's recorded in my books and sometimes a long way off. I did buy an illuminated reticle eyepiece, but find that the red light is so bright even on lowest setting that it blots out whatever I'm trying to see. I cope with this by shining a faint red light on the secondary (benefit of a truss scope) to faintly illuminate the reticle. But it's so much mucking around that I mostly just go back to my mental reticle method with my usual eps. I like Rob's idea of comparing size to distances between close stars.
I'd love to hear Steve Gottlieb's approach...
This is a great thread Paddy!
I will go and ask Steve Gotlieb and Ray Cash for some input into this thread. They are friends of mine on facebook, and have to say, they are amongst the nicest people out there, & so helpful. :D I was in fact going to ask Steve before you mentioned his name anyway. :P:lol:
Orestis, you've asked the same question that has been plaguing me- thank you!
Okay, done- sent messages to both Steve G and Ray Cash, so we'll wait and see if they are able to help us. ;)
28-09-2011, 07:51 PM
Might I also add, "practice makes perfect"? Persistent years of observing seems to have improved my night vision over the years (or is it I am a persistent astronomer due to my night vision? *ponders*). I was a below average marksman during my time in the RAAF, but achieved perfect scores on night shoots while those around me failed to even hit the target once. :)
29-09-2011, 11:35 AM
This will be my first post. Invited by Suzy. . . Looks like a great community under the greatest of skies! Lots of great advice by experienced observers already on this thread. . . But, at the risk of repeating what some of you have already said, I'll post a list that works for me, in no particular order, off the top of my (bald-ass) head:
1) Be relaxed and rested. A comfortable position at the eyepiece cannot be over emphasized. If caffeine makes you jumpy, don't do it, or do it in moderation. If alcohol makes you drowsy. . . Have snacks on hand, but don't eat a full-blown dinner shortly before observing. Take breaks as necessary: this is not work, it is PLAY!
2) Go at your own pace. Again, relax. Trying too hard, moving from object to object too quickly savors little.
3) Observe with friends! Sharing with novices is always great, but having a buddy with similar equipment and experience to share views with always benefits both (or more) of you!
4) Linger on the view(s). Photons will accumulate on your eye/brain whether the object is bright or dim. Quite remarkable and rewarding to experience this.
5) Definitely use higher power (once you find your object)--your eye/brain will make more sense and see more detail from a more magnified image, even if the lower power image is more aesthetically pleasing.
6) Fine tune the art of averted vision: Don't try too hard. Relax. Massage your eyes . . Jiggle the scope.
7) Make an "eyepiece chart" for really dim objects with your Astro software--that way you can be certain you are in the correct FOV, even if the object itself is too dim/conditions are not ideal and skunks you.
8) Take notes, at the very least. Sketch if you like. Both will force you to see more.
9) Be honest with yourself--don't always trust what you see! I've experienced "averted imagination" in myself as well as with others (especially susceptible in the wee hours when extremely tired). . . Look again. Confirm difficult sightings with others.
And, of course, all the basic stuff: Dim red lights, observing list(s), resource books/charts, play with different filters. . .
29-09-2011, 11:49 AM
Thanks for your contribution, Ray, it is much appreciated by the "locals", many of whom are Australians, but some of whom are far flung all over the world.
Happy to have you join our community.
Experienced observers such as yourself have worked out what works best for them.
Thanks to contributions such as yours, we are building up quite a store of knowledge as to how best to observe the deep sky.
29-09-2011, 01:00 PM
I'll just copy some of my stuff across from the other thread:
For really faint objects on the limits of detectability (rather than faint details in galaxies) where I might get odd flickerings of something in the position, I usually repeat the process in another or even several parts of the field. You quite often get a similar response. Sometimes when you move your eyes back to the target position you get a much stronger response that can be held in averted vision even if intermittently, almost like the exercise sharpened your vision. But if I get the same flickerings of something (all too often!), I'm fairly satisfied that I'm not seeing anything other than a trick of the eye. You really have to hold it, even briefly.
Spending time is essential, and movement helps greatly (tap the eyepiece or jiggle the controls). Provided your eyes are fully light-adapted, I find that coming back to the field later on in the observing session doesn't help all that much unless there is a change in transparency, because you have to pretty much repeat the teasing-out process all over again. May as well spend quality time first-up.
Generally: find a dark place and shield any extraneous light (eg put street lights behind trees). Get light-adapted - never go for really faint objects first. Have (generate) charts that position a faint object precisely in the field - as part of pre-planning pick 'asterisms' or star alignments that you will be able to recognise in the FOV (eg a little triangle of stars or a line of four stars etc etc). Above all, have fun.
While increasing magnification may help by increasing contrast, in a little scope like mine it doesn't generally work - not enough light. Things just disappear!
Anyway, some great tips, thanks to those who've posted. Must admit though, this tip by Doug Snyder has me a little confused! :confused2: :P
"double averted vision ( you back off from the eyepiece a little, cross your eyes and let each of your eyes view the opposite edge of the field)"
What if the wind changes? ;)
29-09-2011, 02:42 PM
Welcome to our vibrant little community, Ray, and many thanks for your very useful tips. I really like your emphasis on taking time and having a spirit of play. It is tempting to try to see more objects rather than fully appreciate the one already in view. Also easy to get so focused on the technical that it's possible to lose the magic of observing.
Observing with friends is also such a great tip. I usually observe on my own and really appreciate the several star camps that I go to each year as an opportunity to have friends let me know what they are seeing - opens up whole new vistas, as does comparing the view through different scopes. I think the conversation over the eyepiece also means more coming and going, the revisits revealing more each time.
And thanks Rob for your tips, which I notice you added to - good stuff. And a very good point about the limitations of trying to use high power with a small scope. The double averted vision thing is going to take a bit of thinking about. Does it imply a binoviewer?
29-09-2011, 03:28 PM
Some great tips here ,thanks to everyone who has posted.
I only have a couple to add to the list
My favourite is a dark cloth or hood,I think it can give you maybe a quarter or half a mag brighter as it blocks any stray llight or even the normal sky glow from the millions of stars.
Don't try to see deep sky objects after using the computer for a little while, even with the red screen as dull as it will effect your night vision, wait a few minutes or don't use the computer at all.
Even using a dull red light can can take a few seconds for my eyes to adjust when I am using a star chart.
Print off some charts and use them at the scope with the dullest red light you can see by.
I have an ArgoNavis DTC and set to the bare minimum brightness when observing.
Averted Vision is one of my main tools as well as moving the scope especialy for faint Nebulae which are not much brighter than the background sky.
Put as many stars as possible out of the field if trying to see very faint object as even 10th mag stars can make a difference when trying to tease out very faint galaxies.
Time spent on the object has been mentioned but I think this is one of the main things I get out of observing, trying to tease as much information out of the object as possible .
Try using different eyepieces on each object,it helps you to make up a picture in your brain as you go deeper in magnification.
Have some images handy to see if you have anyobjects in the field that don't belong there Ie Supenova.
And always try to enjoy your observing as it will make you want to come back and observe again and again,as if you dont enjoy it you will soon become an imager
30-09-2011, 07:11 AM
Thanks for the responses guys,
I'll try it out and see how close i can get.
Regarding the double averted vision,I can't think of any way that will work without it implying a binoviewer unless by crossing your eyes,the one eye on the eyepiece will be in averted vision.Though crossing my eyes hurts my brain.
Thanks for the tips
30-09-2011, 08:44 AM
30-09-2011, 10:28 AM
Way to go Patrick! Marvelous thread topic now with it's deserved status.
Now, if only the clouds would clear we could apply these pearls of wisdom... :lol::sadeyes:
01-10-2011, 12:05 PM
It is a tough task to put in writing "what we do" when we are at the telescope, in order to tease out that ultra-faint detail within objects; but I think Ron and Ray and Paddy and Rob K are doing a good job of describing the procedures that advanced visual observers actually do use.
Author's preliminary warning:
(regarding this post , and regarding my next post in this thread)
My comments reflect the approach that I have taken in my own visual observations of diffuse (= extended)(= non-stellar) deep sky objects, such as emission nebulae and galaxies, which is based on my own qualitative observations of what happens when the eye and brain are put behind the astronomical telescope.
In no way have I actually put any hard numbers to the various important factors that affect how well we see a diffuse object or feature which is near to the fringes of visibility (e.g. surface brightness, contrast, angular resolution at low light levels, feature recognition by the brain, etc.).
As such, everything that I say is very preliminary, and "disprovable".
The Human Brain is the Deep Sky observer's Camera :
Ron and Ray have made the important point (in their recent posts in this thread) that Deep Sky Observers - when they are viewing a very faint nebula or galaxy - are actually trying to gradually build up an image of the object in the human brain. Which is why Ray's point about the utility of sketching (and/or a detailed prose description of what is seen) is so important; the process of sketching and describing an object implies that we are transferring the things that the human brain/mind sees at various times and moments.......onto a piece of paper, which serves as an “accumulator” for the things the brain perceives.
Putting together a mental image of an object :
I do agree with Ron that many and various magnifications should be tried on a diffuse object, because the final result of a deep sky observation is a sort of composite “mental image” of an object, made up of multiple individual views or glimpses of the object.
Therefore, a good approach is to put together, into a single "mental image" and/or a sketch and/or a prose description:
the details that the observer sees over a prolonged period of viewing at a single magnification
the details that she/he sees when viewing at various magnifications
the details seen on various nights
As experienced observers will tell you, some of the galaxy images which are very large in angular terms, such as M101, M31, M33,
NGC 4565, NGC 891, NGC 6744, NGC 5128, NGC 1365, NGC 1313, NGC 253, NGC 55, M83, etc., do contain substantial amounts of detail that is visible to the eye at the telescope, at least if these objects are observed in a dark sky. However, the details within these galaxy images tend to be fleeting, and these details are often seen haltingly because they may be near to the eye's limit. So this is why the approach of "gradually building up a mental image of the target object" can eventually result in the observer getting a really good idea of the structure of the image of an object.
06-10-2011, 10:27 PM
OTA modification that may help at the eyepiece
Tips and techniques that can help I see as a big part of this thread. I posted this originally in the DIY section where I had started a thread on the DIY dob mount that this 8" f/4 OTA.
As I use this scope a lot from home, the ambient light is a real pain in the neck reflecting off the white tube. I had some foam rubber left over from the stuff I used to wrap around the poles of my 17.5", so I used it to cover the top half of the 8" OTA. I cut out the necessary openings to accomodate the focuser, finder shoe and spider nuts. The white markings were done to position these openings.
The foam rubber sheet is wrapped around the OTA and only glued onto itself, not the tube. The holes that the various components poke out from hold the thing in place so it doesn't slip. I made it a snug fit which helps too.
The result works really well to tone down the reflections, ;). An added bonus was the insulative effect it had on the secondary mirror, protecting it from dewing up for a longer time than before. A bit of a surprise that was. I might consider making a dew shield for it out of thicker foam, much like the ones used on SCTs. Even at a dark site, this simple mod has improved the reflection attenuation off the OTA.
This stuff weighs bugger all, so it doesn't upset the balance.
Below are a couple of pics showing before and after.
Another thing I've done was paint the focuser board of my 17.5" matt black, specifically using black coloured blackboard paint. This was considered from the planning stages of the scope, and I've never had the same problem of reflections coming off the board.
Some food for thought.
07-10-2011, 01:55 PM
Nice modification there, and undoubtedly it puts the unwanted light somewhere away from your eye! Anything that increases the image light and decreases other light reaching the eye is a wonderful thing. (for instance, I am all for getting the the highest reflectivity mirror coatings that I can afford)
I have heard it said by experienced observers and telescope makers that the apparent contrast advantage of traditional (F10 to F15) refractors over newtonian reflectors is simply caused by the traditional refractors having longer tubes and tubes which are well baffled....leading to there being actually less light all over the observed field, and thereby explaining the slight edge that these long-tube refractors had for visual observation of deep sky objects.
10-10-2011, 06:22 AM
Suzy asked if I would contribute some suggestions as I always include size or dimension estimates in my observing notes, so for what it's worth, here are my techniques.
The first method was just mentioned above. I keep a printed page in my notebooks (and sometimes attached near the eyepiece) that includes my various eyepiece focal lengths, magnification and actual field. Using the actual field as a ruler works reasonably well for large objects, such as large open clusters, that take up a significant fraction of the field. Just estimate the percent of the entire field (or the radius) and multiply by the field diameter. I find that this is easier, though, with small to moderate apparent field eyepiece designs such as Plossls or Orthoscopics. Now, I'm using Ethos eyepieces with a 100° apparent field that require peering around to see the edge, and this method is less accurate.
A second technique that's probably rarely used among amateurs is to let the object drift through the field, either by placing it just off the east edge or just on the west edge, and time (using a stopwatch) the number of seconds to enter or leave the field. With a scientific calculator (using a little trig) the seconds can be easily converted into arc minutes (hey, I'm a math teacher ;-)
A third method uses nearby field stars and works well with galaxies and nebulae between say 1' and 5' in size. Often, besides my written notes, I make a rough sketch (I'm bad at accurate sketching) of the object and include some nearby field stars. Then I'll add a comment such as "extends 2/3 the distance between the two 10th mag stars just south". Later when I'm home at my computer, I'll look up the separation of these stars using a program such as Megastar or online with a program such as Aladin. Even this method sometimes fails, though, with compact planetaries and galaxies that are smaller than 1'.
The 4th method is to calibrate your eyepieces to estimate small sizes under 1'. How so? Well, I often start an observing session by taking a look at a few well known double stars that I can find instantly and observe them with the same eyepieces I often use for small galaxies. With my 18" scope, I often use 225x and 285x, and I'll quickly observe 2 or 3 doubles that I know the separations to calibrate my eyes. For example, in the summer/fall northern skies of California, I'll look at Albireo (35" separation), Polaris (18" separation) and Gamma Delphinus (10" separation). By doing this I have a pretty decent sense of these separations using those two eyepieces and feel comfortable making an estimate for a small planetary or galaxy as say 30" diameter. If the object is elongated roughly 2:1, then I log it as 30"x15". My experience is that at 285x, a galaxy that is just 30" or 40" diameter appears larger than most amateurs would probably guess, so it's easy to overestimate sizes.
Hope some of these ideas help!
10-10-2011, 12:43 PM
Hi Steve,thanks for your input.
There are some good suggestions there :).
I use the drift method myself.
11-10-2011, 10:24 PM
Thanks for those tips Steve. More to add to the repertoire, especially for the small DSOs. I particularly like the sound of the double star method. I might have to revisit long-forgotten maths for the drift method. A useful mental challenge in itself!
16-10-2011, 10:21 AM
Thanks, SteveG, for some interesting and useful techniques for visual observers.
Wow! As an amateur astronomer, I am always deeply impressed by people who "measure things and put numbers to them".
(a professional astronomer would probably adopt a serious and weighty and grave tone, intoning the phrase "it was a cogent quantitative analysis", very much in the tone and manner of a medieval doctor pompously reciting in Latin, but - in my view - "quantitative vs qualitative" is exclusive language that serves mainly to confirm the membership of a scientist in a secret elite of "those who know".)
17-10-2011, 08:37 PM
I was having a look at some SMC objects last night and was musing on how slowly objects close to the pole move through the eyepiece, which prompted me to wonder about whether there is a need to correct for declination if using transit time to estimate angular size of a DSO and if so how this is done. Steve....?
18-11-2011, 06:52 PM
First of all Hello SteveG and I think I know who you are ... ;)
I am only now transcribing some field recordings of Abell Planetaries
and assorted Herschel 2 list objects and ran across a case where I
wish I had drawn a crude drawing (yet again). I was trying to describe in words the position of 5 stars in and around Abell 75 so that if one of them were the central star I could then say that it had been noted. I have no idea if one of them was it or not.
Well due to not having a drawing and perhaps poor DSS image back home
I for the life of me cannot figure out what the heck I was talking about.
The observation was from 3am on the 3rd day of a big star party (CalStar in California, USA) so perhaps fatigue caused the description to 'suffer' as well. :lol:
Some of my Australia trip from a year and a half ago were also rather difficult to follow. Ever try to verbally describe with some detail the area around the keyhole nebula? Or the whole Eta Car nebula for that matter. Difficult to do with words, very complex but amazing just the same and I hope I get back there again in a year or two.
Anyway, a little drawing sure would prove useful when the description takes more than 20 words or so.
I have heard SteveG in the past discuss the trick of mentioning size relative to nearby stars in the field for tiny objects and that was a nice tip to be sure.
Besides that great set of tips Steve mentions I'll add a tiny bit about one way to increase accuracy on length measurements I tend to use. I'll often bring an object to the edge of the field keeping in mind where I felt it's edge was when it was in the center. I bring it to the side of the view so it's main axis (if elongatted) is radial towards the center then a measurement that is a fraction of the half-field-of-view is noted. This method breaks down when the object is really small. I favor a 7mmNagler or 5mmNagler and the 7 gives about an 18' diameter of fov. So down to 1' is about where it breaks down in accuracy.
Another thing is I have stopped doing the math in my head on fov (too many 3am stupid math errors) and instead I now always note fraction of field of view in my field descriptions to recorder. Then I have a chart (got tired of calculator/head) and this chart is a spreadsheet with eyepieces along the left and across the top I write 1 2 3 ... 20 for the fraction (denominator) So for 7mm 1/8fov I later when transcribing say just that but use square braces and in those place the calculated value which for me I find 7 on the left and 8 on the top and drop down and get 2.21'. Of course before I got lazy I would run the math for 17.7'/8 but I find the spreadsheet printed on a paper at my desk is far more easy to lookup than fumbling with a calculator as I transcribe my recordings.
Anyway, I am sure it is the SteveG I am thinking of, rest assured that he knows basically all 'of the tricks' (or at least 10x more than I will every know).
Mark (Hint to SteveG: I am Marko)
19-11-2011, 11:38 AM
Thanks for your interesting and useful contribution, Mark. It is always good to hear from our "foreign correspondents", as so many of us are Aussies.
There are quite a lot of active contributors to our forum, but it sometimes "goes quiet" because all of us are busy.
19-11-2011, 09:39 PM
Thanks Mark, that's quite a handy way of estimating size. I tend to do something similar, but I can only feel confident with a couple of my eyepieces as I keep forgetting what the TFOV is with the others. a little table would be a very good idea and could sit in the cover of one of my books.
I laugh when I read of your difficulty in deciphering some of your recorded observations - I experience this quite often when trying to transcribe a few days later and wonder what on earth I was rabbiting on about.
19-11-2011, 10:21 PM
I will share how I became able to see super faint fuzzies. It works for me but I can't say it will work for everyone.
What makes this even more amazing is that I suffer night blindness :eyepop:
For the many years I was a full-time Visual Observer (yes, I used to be one). I had 'Trained' my eyes.
Brains and eyes can be trained to know what to look for.
I achieved this by going to an object (or where I believed it should be) and looking, and looking,
and I kept looking.
Then I would walk away from the scope but never look up at any distant light or even the sky, but walk around looking down at the ground for about 2 - 3 minutes, then go back to the scope and keep looking.
Because I was determined to see those faint fuzzies that I saw in books I would do this several times, and eventually I would start to notice things.
Usually (but not always) by the 3rd look I could make out some detail in tiny super faint objects.
Then I would go look at another object (one that I knew well, like NGC 253 or 55 etc, but not a bright object) for about 5 minutes, than go back to the elusive faint fuzzy again and you would be amazed at how instantly you recognise the detail you saw before.
Look for a few minutes then do the walk again, then return to the scope and by looking for another few minutes you will start to see even MORE detail that you thought wasn't even possible with a super faint fuzzy!
If I found that I couldn't quite make out a particular detail I would attempt to sketch the object.
As an artistic person I tend to notice more detail this way.
I would stay on this object off and on all night and each time I went back to it I found it easier to recognise it and any detail in it.
The following night I would start with another object but go back to ones I have 'learnt' on the previous nights. The more I went back to others the more I saw in them.
I did this with many hundreds of super faint fuzzies and after years at it I could recognise then within seconds.
It's not a gift, or a trick.
It is training, and it takes practice, Lots of it. :thumbsup:
The many long nights I spent doing this was enjoyable to me as tiny super faint fuzzies are my 'thing' :)
Even though I don't do visual any more, it pleases me when I do look through Eric's scope about every 2 or 3 months, or look through a scope at camp, and I can still recognise and 'see' detail in very faint fuzzies that many people only see as a very faint blob. It's like recognising an old friend. My eyes still remember what to look for.
Practice, practice and practice.
and then some practice ;)
20-11-2011, 07:23 AM
Some years back in doing some reading on averted vision and following a few links on the web I became aware of the veins we all have on the back of our eyes naturally lead to 'sweet spots' that may vary in each individual to some extent. For averted of course the rods are great for low level light and are the most dense away from the central vision as we know.
So to better understand where my averted vision sweet spots were I found that in the eyepiece go to some starfield that is not very populated (not in the milky way for example) and find an area that has a star or two that are at the very limits of your perception in averted vision.
Now move your eyes relative to that tiny dot and you will fine that the star disappears and re-appears. Try to note the fraction of the field of view and if you are for example looking 'up and to the right 1/6 fov' for example for the very best and widest sweet spot. (I am a right-eyed observer).
You will find sweet spots in different places. It is well worth the time and from time to time I refresh my memory as to where they are. I tend to favor about 3 of them (sometimes below object as well so try all over the place but of course away from the object just a bit)
Too far away and of course averted looses it's ability to form an image, too close and you loose it entirely (The star starts to image on your central eye which means the image is on higher and higher density of cones that are lousy for dim light)
One really nice and detailed discussion of the effect of cones/rods is here
So learn about your observing eye(s). It will pay off to be sure.
For extreme challange objects I first identify the field and set my big dob to track. (if you cannot track then just sit near your scope and take a few seconds a couple times a minute to push your scope to the field while doing the next bit. Next I cover my entire head in a dark blanket for 10 minutes and hope nobody comes by to make fun of me ... :lol:
Then I find you will have that extra edge that is sometimes required for extremely dim objects. While viewing I wrap the light/dark blanket that is over my head already around the eyepiece so that my mouth has an open area and I don't breath into this tiny cone I have formed to see the eyepiece.
This may sound very funny but I can assure you it works and is sometimes even required for extremely dim objects.
25-05-2012, 02:43 PM
I had a marvelous experience a month ago to do with "blinking".
Blinking is a technique where you look for an object by switching between a neat image through the EP and then switch to a view with a filter, and back and forth, and so one. This technique is useful for finding very tiny DSO's that on their own are drowned out by the surrounding stars or background skyglow. Planetary nebulae respond very well to Blinking using an OIII filter.
Our mate erick showed me his DIY Blinking paddle. It is a $1 plastic paint spatula with a hole drilled in it and an OIII filter threaded into it. The spatula is also painted matt black. Such a marvelously simple and effective tool! Blinking is such an easy task as you hold the paddle in one hand and flick the filter between your eye and the eyepiece as needed.
I'm hoping to make a little paddle for myself now after a clumsy but successful blinking session to find one of the three planetary nebulae that lie within the boundaries of the giant open cluster M7 three nights ago. Clumsy as I had to hold the OIII filter between my fat fingers making the blinking process rather trying. Still, I managed to track down on of them.
Eric, thanks for showing me the paddle! Great and effective tool that is sooooo simple to make, :thumbsup: . As soon as I make mine I'll post a picture of it, unless eric beats me to it.
By the way, Blinking was the method used to discover Pluto back in 1930. Then, the blinking process was done by switching between two photos taken a few days apart of the same patch of sky time and time again to spot a tiny 'dot' that had moved between each of the exposures.
If observing with a group and the object you are trying to locate is proving challenging,
if a friend in the group has a larger aperture scope, offer them a Tim Tam and
ask them when they have a moment if they could please dial up the object and point their scope to it.
Once you see it in a larger aperture, sometimes when you go back to a more
modest aperture, it suddenly "pops out" and becomes self evident.
I have sometimes been flabbergasted that an object that requires a reasonably
experienced eye in say a 20" may suddenly also become observable in an 8"
simply because you now know what to look for.
We have all done this from time to time. It is such an obvious tip and for that
reason was probably overlooked on this thread.
If you are observing alone or if you have the biggest scope on the field, then Plan B
is to use the other valuable tips that appear on this thread. :lol:
08-06-2012, 09:28 PM
Might be stating the obvious here but my biggest lesson was learning to use my non-preferred eye. My natural sighter is my right eye, I use it to wink, site a rifle, it is my primary seeing eye when I'm talking to someone and it was my natural ep eye when I first started observational viewing, but it's not my best eye. I have been told it's 18/20 due to some metal that got lodged in it when I was 21, the metal had to be scraped out with a scalpel and it has never been the same. My left eye is 20/20 and I use this eye for all my viewing, even if it doesn't come naturally and still feels uncomfortable after extended viewing. The problem with using my secondary eye is that while it might provide clearer vision it was much weaker than my primary eye, so I needed to train it and develop it. My first reaction is still to look in any ep with my right eye, but it's important to know your best eye, or pick your best eye for the best results.
Strange but true. :eyepop:
09-06-2012, 01:56 PM
When observing galaxies, I find using a dark hood draped over my head works wonders. It eliminates all stray light that may be reflecting off the eyepiece lens and removes the need to cup your face with your hands in an attempt to shield your eyes from surrounding light pollution. It does really enhance the visibility of faint objects. Only issue I've found is that the eyepiece tends to fog up easily, as your body heat is sort of "trapped" under the hood.
10-06-2012, 06:45 PM
Gary, so true about seeing as much with a smaller aperture as with a larger. I've notice that in switching between my own scopes. Sometimes the only difference is just subtle texture.
John, I have a preference for my right eye, but some nights I find I'm using my left. Not a conscience decision either. Just happens :shrug:. And it's difficult to swap mid-session too.
Sab, I've tried the cloak too, but the problem of fogging killed that. Heating the eyepiece is an option, but the density of H20 in our breath overcomes this too. I can only cup my observing eye, trying to keep my nose out of the cocoon to reduce the amount of exhaled breath that enters.
Well, I've finished this PN Blinking Paddle. I used a piece of MDF I had left over from making a couple of bullroarers for my son, hence its shape. Turns out to be just fine for my purposes - long enough to just need a small flick of the wrist to move it into and out of place, and its ovoid shape good to accomodate the shape of one's face. Its thin profile will help deal with eyerelief distance. I'm not sure if to paint it or not. At most I may just give it a once over with some acrylic paint as I don't want paint fumes in my eyepiece case.
12-06-2012, 10:42 PM
Very interesting John. I also use the eye that I am less likely to use for other purposes, but still find switching from eye to eye useful at the eyepiece. Like you Alex at present I find a cloak makes my ep fog up so I cup my hands around the ep. I found Sab'a suggestion does make quite a difference. Maybe a mini-cloak just over the ep and not my nose might work. Like the blinking paddle too.
06-07-2012, 06:19 PM
I am sold on use of the cloak for limit objects. I allow the cloak to cover head but keep my mouth and noise exposed to air by careful adjustment of cloak all about the eye but allowing the mouth to be breathing if not to open air at least to an area of the cloak that is not going to leak much into the eyepiece area. Have to hold the cloak for this sort of approach. I think you could make some odd cyborg sort of full head hat that covers one eye like the borg in Star Trek but perhaps that is taking things a bit far ... :rofl:
I also use a heated eyepiece in 'dew season' as I find just the heat off of the face/eye can fog an eyepiece when it's real cold.
vBulletin® v3.8.7, Copyright ©2000-2013, vBulletin Solutions, Inc.