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  #21  
Old 01-11-2018, 07:40 AM
Jethro777 (Jethro)
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Right.

So, here's some adjustments I'll try. Let me know if there are more, if I have them right or if I have missed something else.

Forum suggested

- Switch off noise reduction. Since I am shooting in raw, it's pointless anyway.
- Aperture should be 2-2.8 from what that lens date looks like - not 1.4 or 8, lol.
- Increase number of frames taken from 9 to 16 or 32 for stacking.
- Make a 'dark' shot (I guess same length as the normal frames I am taking but with the lens on? Is that how I make one?)

My ideas

- Start building a barn door tracker, lol.
- Maybe drop down from 10 seconds to 8, as I can still see star trailing.
- Mozzie repellant. I paid for each final frame with three bites last night.

Questions

1. If the pictures I take look quite 'bright' (light), will DSS 'darken' them so I get a black sky? - Sorry for the stupid question.) If it is quite 'bright' - what should I be adjusting then? For example, I am going to do f/2.0 on a f/1.4 lens at 1600 ISO at 10 seconds. That's going to result in a bright image - right? In my head, I'm thinking "That isn't right!" - but it is, as DSS adjusts it?
2. Also, does the fact that I have a 'bright' object, like Mars mean that the camera is less able to pick up the stars around it? Would I have gotten better results if I hadn't chosen mars?
3. What ISO is best for my particular situation? From what I was reading, some are doing anything up to 12,000+ and claiming it doesn't matter, while others go for 400-800, or 1200. I'm thinking I should go 1600.
4. Is the best focus actually just short of infinity, or infinity?

Next up will be the Southern Cross with modifications applied.

Edit

Ok, several (e.g.16/32) 'dark shots'. Good for one night.

Last edited by Jethro777; 01-11-2018 at 08:09 AM.
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  #22  
Old 01-11-2018, 07:58 AM
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You should take the same number of darks and lights...
DSS will create "master dark", you can use that one for more photos on the same night.



"Black sky" is obtained by post processing of resulting tiff file, I am using DPP (Canon software) for that.

Last edited by bojan; 01-11-2018 at 08:14 AM.
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  #23  
Old 01-11-2018, 09:29 AM
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Quote:
Originally Posted by Jethro777 View Post
What do you guys think? If you were to invest in something (why not, I'll save for something!) what should it be? A star tracker like the iOptron or Vixen Polarie? A proper mount?

Love to hear your thoughts!
I do most of my AP with DSLR from regular tripod, no trackers, no barndoor mounts etc. Its definitely doable and can take a bit of fiddling to fine tune. First I suggest ignoring your lenses unless you want to use for wide angle shots, instead find a good quality fast (f2.8) lens around 150-200mm. Prime not zoom. And work around this being your astro setup.

First do tests with manual settings (its all manual setting really) adjusting just f-stop to find your combos optimimal sharp sweet spot with stars (with a f2.8 lens f4 tends to be much sharper, but an f4 lens it'll be more f5.6/6.3. Once you find that you have one manual setting to stay put on. Next use the "500 rule" as a guidline. divide 500 by the focal length of the lens to get your starting test exposure time. eg 150mm lens is 500/150 = 3.333s call it 3 sec. now set exposure time to 3sec and point at night sky (pick random direction each time as linear rates change and take a test shot each time and zoom in on the pics to see the stars should be more round than little streaks, adjust shutter speed one increment on your camera and repeat until the stars are a good roundness and not streaking . It'll be close to the initial 500 rule value. Note the stars will distort anyway in a camera lens but the more they start to streak the harder it becomes to align and stack images. So you've now got the second manual setting value you need, th third and final is ISO, set your camera with the first two values and take shots at each iso setting until the images are obviously too noisy on the lcd. decide which are starting to get too noisy to work with. Too much noise and again aligning is problematic. as you work you improve your workflow in time so can revise iso to try to capture fainter nebulosity by capturing a lot more shots. but basically those three settings you can lock off on the camera and are about the limit of the gear combo for capture.

use a remote trigger or intervalometer to take say batches of 100 shots, after that you'll need to reframe your camera as the stars will have moved. I take about 500 shots in batches of 100 which pretty much fills one memory card and drains one battery. when you register/align the images the movement and rotation is taken care of and stacking a lot of shots takes care of the iso noise giving you a good snr integrated image to start stretching etc.

next purchase should be a tracking mount, like an EQ6. something good that will last and can take a scope when budget allows. you will need to find a suitable dovetail plate for the mount that lets you attach a camera to it. You then use live view etc to do star alignment of the mount so it can track and slew to nonvisible targets. This means you can retest your maximum shutter speed to maintain round stars and iso too for cleaner subs. this will open up a whole lot more shooting opportunities for you. every mount has limitations and if you aren't precise with alignment, especially cheap travel options like polarie you are often limitied to little better than a static tripod anyway. A quality mount will give you the chance to go for longer telephoto lenses as well as scope OTA and imaging cam options. If you skimp on the mount it will be less stable and less flexible for options in the long run, best to save and wait until you can get the right long term mount rather than a quick disappointing stopgap.
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  #24  
Old 01-11-2018, 10:02 AM
Jasp05 (Aaron)
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Quote:
Originally Posted by Jethro777 View Post
Right.

So, here's some adjustments I'll try. Let me know if there are more, if I have them right or if I have missed something else.

Forum suggested

- Switch off noise reduction. Since I am shooting in raw, it's pointless anyway.
- Aperture should be 2-2.8 from what that lens date looks like - not 1.4 or 8, lol.
- Increase number of frames taken from 9 to 16 or 32 for stacking.
- Make a 'dark' shot (I guess same length as the normal frames I am taking but with the lens on? Is that how I make one?)

My ideas

- Start building a barn door tracker, lol.
- Maybe drop down from 10 seconds to 8, as I can still see star trailing.
- Mozzie repellant. I paid for each final frame with three bites last night.

Questions

1. If the pictures I take look quite 'bright' (light), will DSS 'darken' them so I get a black sky? - Sorry for the stupid question.) If it is quite 'bright' - what should I be adjusting then? For example, I am going to do f/2.0 on a f/1.4 lens at 1600 ISO at 10 seconds. That's going to result in a bright image - right? In my head, I'm thinking "That isn't right!" - but it is, as DSS adjusts it?
2. Also, does the fact that I have a 'bright' object, like Mars mean that the camera is less able to pick up the stars around it? Would I have gotten better results if I hadn't chosen mars?
3. What ISO is best for my particular situation? From what I was reading, some are doing anything up to 12,000+ and claiming it doesn't matter, while others go for 400-800, or 1200. I'm thinking I should go 1600.
4. Is the best focus actually just short of infinity, or infinity?

Next up will be the Southern Cross with modifications applied.

Edit

Ok, several (e.g.16/32) 'dark shots'. Good for one night.
Hi Jethro,

As I was in your spot not long ago and from the responses here, I'm not sure if it was clear why you would want to do some of the things noted above and the trade offs etc.

Focus to Infinity. Use your camera's live view on a bright star and zoom in as far as possible to focus. This should result in the best focus. If the moon is up or a street light is visible at a distance (more than 50 mtrs type thing) you can use the Auto focus to focus on it.
Just remember to switch back to manual focus when you go to take your images. (Nothing worse than setting focus, switching to you target to have the camera sit there and try to refocus because you left it on AF).


With star trailing, I thought someone mentioned the "Rule of 500" previously. But given you use an APS-C size sensor you will need to multiply the lens FL by the crop factor (it's 1.6 with Canon sensors).

So your 35mm lens is now "effectively" a 56mm lens. Divide 500 by this 56mm and you get how many seconds you can expose for before getting trailing. (about 8-9 secs). Its not a hard and fast rule but will get you in the ball park for exposure times.

Next point is stopping down the aperture. This is generally done to get better star shapes at the edge of the frame. When the lens is "wide open" (Low F Number) you will get star trailing towards the corners of the frame. Stopping the aperture down can reduce or eliminate this. It comes with the trade off however, that you will not collect as much light and you will need to up your iso or expose longer to compensate.


ISO settings is a bit of a trial and error thing. You should be able to do some google searches around what ISO works best for your camera. I found a page just the other day that mentioned 800 iso on my Canon 1200D was best. I'll try and find the link again.
Generally 800 - 1600 ISO is the sweet spot I think. When I was doing static exposures I would go up to 6400 iso. It brings in alot of additional noise, but with stacking and dark frames you can negate this to some degree. Its a learning curve, so try different iso's and then process them and see what works for your camera and location.

I found that link to ISO for different Camera's - http://dslr-astrophotography.com/iso...-sony-cameras/


As for your questions about your images looking very "Bright" or white. You want to expose the image for long enough that the histogram is right around 50%. (Google how to bring up the histogram on your camera if you don't know how. It's quite helpful).
If its too low, up the exposure time or ISO or open the aperture up. If its "over -exposed" (Your image looks very white or histogram above 70%) drop the exposure time, ISO or close the aperture a bit. Experiment here till your around the 40-60% mark on your histogram. (Your images could just look very bright due to light pollution or sky glow. In this case your best to head out to a dark site, unless your pretty handy with photoshop, this will make post processing much more difficult).


And the more frames you can stack the better. It will result in a cleaner final image. So try for at least 15-20 frames for both light and dark. (Others may be able to correct me here but 20-30 dark frames will generally be enough even if you do more then that of the light frames).

And always shoot in RAW and turn off Noise reduction in your camera.


Alot of these point's were probably already covered, but from the way your asked your questions I got the feeling you may not of understood some of it. (I felt the same way when doing my research starting out). Hopefully this clarified things a bit and gave you a few more pointers.
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  #25  
Old 01-11-2018, 10:33 AM
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Quote:
Originally Posted by Jasp05 View Post
... So your 35mm lens is now "effectively" a 56mm lens. ...
Jasp, there is no such thing as "effective FL" - 35mm FL lens will always be 35mm FL, regardless of sensor size.
Only the FOV of the camera is smaller.
This misconception was started by "artist"-photographers who had no knowledge about optics, and we should try to root it out - it doesn't help understanding the technology at all, and after all, AP is in essence techical photography...
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  #26  
Old 01-11-2018, 11:21 AM
Jasp05 (Aaron)
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Quote:
Originally Posted by bojan View Post
Jasp, there is no such thing as "effective FL" - 35mm FL lens will always be 35mm FL, regardless of sensor size.
Only the FOV of the camera is smaller.
This misconception was started by "artist"-photographers who had no knowledge about optics, and we should try to root it out - it doesn't help understanding the technology at all, and after all, AP is in essence techical photography...
I understand it may not be "technically" correct Bojan. But for a beginner it is probably the simplest way to understand the concept of how crop sensors affect field of view through a given Focal length lens.

I don't claim to be an expert and was just passing on information that I'd picked up over my first 12 months in this hobby. Apologies if I have misled anyone..
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  #27  
Old 01-11-2018, 11:30 AM
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Originally Posted by Jasp05 View Post
I understand it may not be "technically" correct Bojan. But for a beginner it is probably the simplest way to understand the concept of how crop sensors affect field of view through a given Focal length lens...
I can't agree with this... we can't feed beginners with misconceptions from the very start.
Cropped sensor is smaller and that is why the FOV is smaller .. not because "efective" FL is longer.
We had a discussion here on IIS, there was one begginer who after some time calculateed his camera scale (pixel size in arcsec) wrongly and was confused with results when he went to plate solving website - results did no match his figures....

Last edited by bojan; 01-11-2018 at 11:52 AM.
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  #28  
Old 03-11-2018, 09:42 PM
Jethro777 (Jethro)
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Well, after a few further adjustments, here is a new attempt.
Naturally, I just pointed it at the stars and shot. Next time, I am going to try and point it at something specific.

Settings are now 1200 ISO, 2.8 (Samyang 35mm f/1.4), 10 seconds.
Took 17 Darks, 31 Lights.
I also removed the UV filter I had on front for day photography. Colours seem more vivid than my last attempt. I'm more optimistic.
DSS appears to have a setting to correct for 'bright' pictures. Awesome. Now I will collect more light!!

I can locate the large Magellanic cloud with an app, I wonder if I could expect to see that if I point correctly?

There doesn't seem to be much 'straight up', does there?

Much of what I am trying to see is so close to the horizon that it is obscured by trees and houses / palm trees.

I have the 100mm lens also, I wonder if that would make a difference - maybe for the Magellanic cloud...

Thank you for the many helpful posts. I do read them all carefully.

Next attempt:

1. More ISO!!
2. Point the camera at something specific.
3. Take the dark shots at the end of the session rather than at the start.

QUESTION - what I see via a single raw shot is far... more detailed than the DSS result. This makes me suspect I'm not using DSS correctly, and that is where my issues lie.

Would someone be so kind as to look at my RAW and see how I am REALLY doing with my image capture?

LINK : https://drive.google.com/open?id=1oi...c-djFGIvPKWRKo

PIC EXPLANATION

1. Processed finished pic from DSS after processing (Whole frame)
2. Section from single RAW file captured (f/2.8, ISO 1200, 10 seconds)
3. What DSS did with it - same section
4. Section of the sky shown from sky mapping program

I have put up a close up of a raw - the dss conversion at the end, and a pic of the section of the sky it's taken from so you can recognize it.

What do you think?

As far as the star tracker - steady progress there.
I have bought a nice Velbon SGB3 which is built like a tank.
I've secured two wood boards, not solid pine, sadly, but will probably do the trick.
Cheap laser pointer ordered as well as various bits and pieces.
Attached Thumbnails
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Click for full-size image (Small-Series-4-As-Shot-RAW.jpg)
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Click for full-size image (Small-Series-4-Post-DSS.jpg)
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Click for full-size image (IMG_2218.PNG)
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Last edited by Jethro777; 04-11-2018 at 07:26 AM.
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  #29  
Old 04-11-2018, 06:55 AM
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Hmm.. not quite like that.
Full frame lens used with APS sensor will collect exactly the same amout of light, ...
YES, the lens will collect exactly the same amout of light, BUT it is incapable of delivering all of that light to the smaller APSc sensor (without further optics & a necessarily different flange distance).

The APSc sensor can only "see" a rectangle of 23.5mm x 15.7mm within the circa 43.2mm Full-frame image circle being cast by the Full-frame lens at the focal plane (based on an APSc sensor size of 23.5mm x 15.7mm).
The APSc image sensor therefore sees 25.2% of the area of the circa 43.2mm image circle cast by the Full-frame lens.

The Full-frame sensor on the other hand "sees" a rectangle of 36mm x 24mm within the circa 43.2mm Full-frame image circle being cast by the Full-frame lens at the focal plane (based on a Full-frame sensor size of 36mm x 24mm).
The Full-frame image sensor therefore sees 58.9% of the area of the circa 43.2mm image circle cast by the Full-frame lens.

Given equal flange distances, on an APSc and Full-frame camera, as is typical for Sony, Nikon, etc.. and not considering the use of reducers, etc on say mirrorless cameras, then The ratio of those two percentages, 2.33:1 indicates that the Full-frame image sensor receives 2.33 times more total light than the APSc image sensor, or put another way the APSc sensor receives 42.9% of the light received by the full-frame sensor. It should be noted however: that the light per unit area (of sensor), and hence the exposure, on both sensors will/can be the same, BUT the Total light delivered to the sensor, if you could count the number of photons delivered to the sensor, will NOT be.

Quote:
Originally Posted by bojan View Post
Hmm.. not quite like that.
... , and it will still be 35mm FL...
YES of course, in this example it is physically ALWAYS a 35mm focal length lens, it's just that it behaves differently on a APSc sized sensor compared to the Full-frame sensor for which it was designed.

Best
JA

Last edited by JA; 04-11-2018 at 02:36 PM. Reason: reformat
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  #30  
Old 04-11-2018, 07:31 AM
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Jethro,
Have you looked at CCDCalc?
http://www.newastro.com/book_new/camera_app.html
This allows you to enter the lens and camera parameters and shows the image size using various astronomical objects as a guide.....
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  #31  
Old 04-11-2018, 03:56 PM
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Quote:
There doesn't seem to be much 'straight up', does there?
That's true. But that magically changes over the course of the seasons and a single night, too.
Quote:
Much of what I am trying to see is so close to the horizon that it is obscured by trees and houses / palm trees.
But those objects will be higher in the sky either later at night or in winter. Have a look at your astronomy app how that changes. Following the 600 rule, you are right to avoid those low targets.
Quote:
I have the 100mm lens also, I wonder if that would make a difference - maybe for the Magellanic cloud...
a huge difference. Also in terms of shorter exposures before stars are trailing. LMC and SMC are totally cool objects in the Southern Hemisphere Sky. 2 galaxies, hanging there like cloud puffs, so big? You got to take photos and investigate them!

Quote:
Next attempt:

1. More ISO!!
2. Point the camera at something specific.
3. Take the dark shots at the end of the session rather than at the start.

Except for the higher ISO. Taken from a city, high ISO digital photos do contain more light because the computer inside the camera thinks it's meaningful light and amplifies it.
But it isn't, really. It's just streetlights. Better not to be amplified. But when the camera computer did amplify it and saved it into the ARW-file, you have a hard time later to get rid of the unwanted light.
At 10 secs exposure you don't "waste" much time when playing around. So test your theory of higher ISO against the reality. Take a set of lights (and darks afterwards, yes!) of a piece of sky and let DSS to its thing with that set. Take another set of lights with ISO 1250 of the same piece of sky like in your test shots here (and a set of darks with the same ISO afterwards, yes!) and compare the result.

Quote:
QUESTION - what I see via a single raw shot is far... more detailed than the DSS result. This makes me suspect I'm not using DSS correctly, and that is where my issues lie.
a) Your raw-file is almost perfect in terms of star trailing. 1 second less would have been great, I think. The stars are oval shaped, drooping down.
b) The stars aren't quite in focus. Is the lens capable of that at f/2? It might gain in sharpness at f/4, actually.
DSS discards blurry stars - and that's in your case most of the visible light dots. DSS also counts the stars and you get the option at the very end of the settings process to tell DSS to reduce the amount of stars to some value. Maybe you did that. I think it's a DSS default setting to reduce the amount of stars. But I'm not too sure. But in any case: blurry stars are being left out. You have a lot of them. Because the lens wasn't focussed precisely enough.



Quote:
As far as the star tracker - steady progress there.
great project !

Last edited by silv; 04-11-2018 at 04:07 PM.
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  #32  
Old 04-11-2018, 06:54 PM
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Amazingly helpful post Annette.

Thank you so much for taking the trouble to make such detailed observations and pinpointing some of the issues so clearly for me.

Much appreciated!

Let's see what I can do with it.
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Old 04-11-2018, 07:10 PM
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Old 05-11-2018, 01:05 PM
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Hate to disillusion you but there is no such thing a budget astrophotography you may start out not spending much but there is always, always that bit more kit that you'll need. It will more than likely stay in a draw unused after purchase but at the time you really need it!
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Old 09-11-2018, 06:06 AM
Jethro777 (Jethro)
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New Lens and Image of Orion's Belt

Well,

I applied a lot of advice here (Thank you very much!), and I had some issues with star trailing (I got a bit greedy and went for a higher exposure than I could afford, lol).
I also got some tips on post auto-tiff (DSS) photoshop adjustment - just curves and levels, and black/white point adjustment that was very helpful.

It's made such a difference! I know it sounds silly, but I had no idea there were so many stars behind the stars. So, so satisfying.

I'm told the lens I am using (Minolta 100mm f/2.8) is unusually suited for astrophotography as it is a particular high grade macro lens with a flatter field than usual and is sharp.

Now I REALLY want to get that barn door tracker working.

Camera Settings:

Sony SLT A77 Mirrorless
Minolta 100mm f/2.8
f.2.8 wide open
3.2 second exposure time
ISO 2000

Dark, Bias and Light frames used. Did not use any Flat as I can't make them properly. (What suggestions do you have for making them?)

1x Full 100mm Frame (non cropped)
1 x 100% Small Pic of Nebula to see Detail
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Last edited by Jethro777; 09-11-2018 at 06:30 AM.
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Old 09-11-2018, 06:46 AM
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Quote:
Originally Posted by JA View Post
....... if you could count the number of photons delivered to the sensor, will NOT be.


YES of course, in this example it is physically ALWAYS a 35mm focal length lens, it's just that it behaves differently on a APSc sized sensor compared to the Full-frame sensor for which it was designed.

Best
JA

JA, total number of photons delivered to the sensor (as a whole) is irrelevant for exposure time etc... what is relevant is photon flux per pixel (or flux per mm^2) and that will be the same for the same lens (including f/ number).


ONLY difference with different sensor size will be the field of view.
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Old 09-11-2018, 07:52 AM
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JA/Bojan - I'm getting rather confused. Will this affect how I process / take my images?

I can't change my sensor size, and I think I've worked out my max. exposure time given what I have, right?

Or is the technical discussion probably way beyond me right now?

If so, I would love some more tips from you both on on how to get the most out of what gear I have!
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Old 09-11-2018, 08:06 AM
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Jethro,

Do not worry about processing - this discussion has no relevance to what you are doing...

It is about some definitions that need to be clarified.

The point I am making is the amount of light, collected by lens aperture that reaches the individual pixel is the same regardless of sensor size (of course, assuming the pixel size is the same), and it depends only on lens diameter and FL (F-number).

My cameras (60D, 450D) also have APS sensor and I am using lenses designed for FF (24x36mm sensor size).

Lens performance will always be compromised at the corners of the sensor (film, CCD...), and it will always be better in the centre.

So, smaller sensorr actually means you will not see those imperfections that would appear in corners of the FF sensor (and FF means 24x36mm, and that size comes from Leica-format film, which is considered as some sort od standard (not really relevant today really))


You are already achieving almost maximum with what you have.

Perhaps what you need is to use smaller aperture (higher f-number) to limit CA and coma (that also means longer exposures).
I have very good results with Canon FD 100mm f/2.8 lens, but I had to stop it dowm to f/3.5 ~ f/4 to remove CA (blue/red collars around bright stars).
(see here)




I had best results with 200mm -400mm prime lenses with external aperture mask (made of black paper or some sheet material) placed in front of the lens.

This has the same effect as increasing f-number (F/4 ~ f/5.6) but there are no diffraction steaks (because the aperture is round, not segmented as with internal iris).

Last edited by bojan; 09-11-2018 at 08:23 AM.
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Old 09-11-2018, 08:30 AM
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For flats, I used tracing paper placed to cover the lens and clear blue sky...

Take couple of exposures (histogram should have maximum at ~1/3), DSS will make the master flat, which you can use from then on (just make sure that for actual imaging you use the same camera, same lens, same f-stop).
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Old 09-11-2018, 08:36 AM
Jethro777 (Jethro)
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Quote:
Originally Posted by Merlin66 View Post
Jethro,
Have you looked at CCDCalc?
http://www.newastro.com/book_new/camera_app.html
This allows you to enter the lens and camera parameters and shows the image size using various astronomical objects as a guide.....
Thanks, I will need to give this some more thought. As I am using a 100mm Minolta f/2.8 and a Sony SLT-A77V only, I am not sure how to use it, and to understand exactly what it does for me yet.


Quote:
Originally Posted by bojan View Post
For flats, I used tracing paper placed to cover the lens and clear blue sky...

Take couple of exposures (histogram should have maximum at ~1/3), DSS will make the master flat, which you can use from then on (just make sure that for actual imaging you use the same camera, same lens, same f-stop).
That's helpful. So really, I can make a set of 'master flats' of likely apertures I will use for my lens and reuse them.

Can I do the same for Darks / Bias or do these need to be done on the night?

I was wondering what exactly can be blended together in DSS when it comes to 'Lights'. Not aperture? Not ISO?
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