hight of static part of focuser from top of mounting plate: 2.4cm
camera at prime focus:
Distance top of static part of focuser to top of moving part: 4.4cm
==> 6.8 cm from mounting plate to focal point
(40mm K. eye piece focusing same object:
Distance top of static part of focuser to top of moving part: 3.3cm
why was this measurement necessary?)
the image quality was really poor. washed out, blurry, dark.
I hope that was caused by high humidity, warmer tube than outside air and my awkward acrobatics on the back seat of the car ...
will have to repeat test on stars with scope properly mounted and cooled.
but view through 40mm K was good.
the FOV was much bigger through the eyepiece, too. ... must keep that in mind that the camera produces such a tiny field!
the 1st photo was taken with same settings as the prime focal one: ISO 200, 1/250secs - it shows the object on the distant hill at the horizon.
2nd photo: prime focus
3rd: prime focus cropped and lightened
a T-minus adaptor, as Daniel has suggested, is supposed to be "an inch shorter" than usual t-ring-t-adapter solutions. that's how far the specification re length goes ...
I hope that this one part does not require a t-ring but screws directly into the lens mount and fits into focuser barrel?... I hope. daniel? did you buy this part?
it's a 2" solution; my current rack&pinion focuser is 1.25".
now I need to find a 2" focuser "low profile" which is within the 6.8cm range of the focal point and still allows for the "1 inch shorter than usual t-minus-adaptor".
Silv,
What you need is someone standing next to you that has been through all this.
If you get 100% stuck, contact me via PM, and somehow we can meet up. Failing that, try Andrew Buckingham at the Auckland StarDome, I'm sure he will be able to assist. He also is likely to have some of the bits you may need.
Once you get it working you will realize how simple it really is. I successfully used a Nex5 on my scopes, now use a Fuji, same principle though.
Gary
What you need is someone standing next to you that has been through all this.
I wouldn't want to be that someone standing next to me ...
And I wouldn't want to put that kind of load onto one single person's shoulders, either.
I am a complete noob in ALL aspects; optics, mechanics, using tools, DSLR photography, astronomy ... did I miss anything?
I get impatient now and feel the pressure... because very soon, I will have to start looking for a new job and then go to work all day. I won't have the time nor the energy, anymore, to fiddle and figure and find out about things - like I did for the past 3 months.
Maybe, I will take you up on the offer, some day. And maybe, I will contact Andrew. Thank you!
(I was hoping for star parties but they were all canceled since I joined the club. )
Ah well. It was fun up to now. Really good fun!
Gotta see to it that the dollar flow changes direction.
the prime focus image is washed out by haze and stray light getting in all over the place, but it doesn't look too bad at all considering how you took it. (stray light was the reason for suggesting that you image from inside a darkened room). Try enlarging the same portion of your first image and see how much better the scope is.
from your measurements, the image plane is a fair way out from the tube and you have 2cm to play with in the existing focuser. If it is only a 1.25 focuser, you will need to get a 2inch Crayford, and it looks like you probably have enough back focus to use a standard one without moving the mirror. I don't have my scopes where I am, so can't measure one up, but maybe someone else can help. The adapter that Daniel suggested looks ideal. Most of it will slide into a 2 inch focuser tube and only about the top 8mm of it (the knurled ring and the bit with the white dot) will be visible between the focuser and camera. You probably have more than 8mm of focus adjustment available, so this should work fine.
"why was this measurement necessary?" only needed if you had been unable to get to focus.
Suggest that you take Gary up on his very generous offer or see if someone from the club can help. Someone with experience could size up the situation in a few minutes and save you hours of frustration and potentially unsuitable purchases.
anyway, congrats on getting some images - your system works.
anyway, congrats on getting some images - your system works.
when motivation is low, little sentences like this open the brain by brightening the mood
it looks as if tomorrow night there will be a cloud break - the dry kind. I will measure prime focus, again, on stars.
The focuser tube height will vary with the distance to the object to be focused on... hmm. only now, your test requirement of a few km distance makes click.
Re the tiny field of view on the tiny camera chip:
I noticed that by moving the camera on the focuser barrel, I got different parts of the whole image that was visible through the eye piece.
is there a device that would allow the camera position to be adjusted while mounted in prime focus? I mean, without having to move the whole telescope? or will the FOV be bigger once the camera is properly mounted?
if such a device exists, it must be somehow determined by the focuser model it will sit in. or rather, the focuser model will be determined by that device and the focal point of the t-mounted cam.
Hm, ... it works with glass. I can't afford good glass at this stage.
It might be possible to get a device which can move the camera while mounted.
I could then take several partial images of the whole sky covered by the secondary as seen through an eye piece - and stitch the images together, later on.
the chip is actually a fairly big one as chips go.
as you slide the camera around you will get images from different parts of the focal plane produced by the mirror. Only the central bit is really good and you want to firmly fix your camera so that bit stays on your chip. When you collimate your scope you are positioning the primary mirror so that it puts the best bit of the image plane on the centre of the chip.
One of the reasons for using a scope is that it will give you high magnification so you can see fine detail (it also captures lots of light). Forget about focal reducers and image stitching for now - your combination will provide a good field of view for years worth of imaging.
You will probably not get any useful results on stars by holding the camera against the focuser - they are hard to focus on without a very steady setup and you will need to use exposure times of seconds rather than 1/250. Could try it on the moon though - you might be lucky and get a wobble free image and you can also measure the actual height of the focal plane. You should see the whole of the moon.
then you need to wait until you get a better focuser and a camera adapter before you can try serious imaging. Therin lies a whole new set of challenges.
I wouldn't want to be that someone standing next to me ...
And I wouldn't want to put that kind of load onto one single person's shoulders, either.
I am a complete noob in ALL aspects; optics, mechanics, using tools, DSLR photography, astronomy ... did I miss anything?
I get impatient now and feel the pressure... because very soon, I will have to start looking for a new job and then go to work all day. I won't have the time nor the energy, anymore, to fiddle and figure and find out about things - like I did for the past 3 months.
And I am not there, yet. Simply not there, yet.
Sorry for the rant.
Hahahaha , we've all gone through that phase at one stage or another Silv. It's all part of the big learning curve. Half the fun is solving the problems and learning the lessons I reckon. One of the reasons I love it anyway, I NEED a challenge to keep me focussed.
Hang in there and it will all come together. I can post a few pix of my prime setup and the components if it helps. You do need manual control.
I set mine for BULB and use a remote timer cable as the max is 30 secs without. Also means I don't have to touch anything to start the exposure.
good test!
I felt and saw what happens with a bad focuser.
the words "feather" and "touch" were on the tip of my tongue ...
I also found that I will greatly benefit from a pure visual observation phase. I haven't done that at all, yet. Only for star aligning - and apart from that I captured piggy back photos.
But it will help me find my way around with the smaller field of view in the mounted camera.
With a better focuser, focusing itself will be easy in 4x zoom of the live view display.
I am really happy. Yay! Thank you all and thank you Shiraz!
the star images tonight were all wobbly in the same pattern. I assume that was caused by the shutter on the ingeniously stable rubber band mount.
they also showed some coned and some circled shadows which are not to be explained by that wobble.
that could be just the normal "coning" effect I read about but it could also be something else.
I read Shira'z thread about a DIY additional collimation tool and checked my super duper collimation using a small flash light and a baker's syringe - there's lots of room for improvement, too.
wow, that is impressive progress... well done, nice image
The wobble is possibly due to small tracking errors in the mount - what exposure time did you use? The cone+circle shapes are due to coma which becomes progressively worse away from the central sweet spot. Looks like the sweet spot is not quite central in the camera field of view, so collimation is a bit off or the camera is not central in the field of view.
the DIY collimation tool is a good addition to standard collimation techniques because it quickly shows you if anything is way out of alignment - sometimes collimation can proceed even with major misalignment and your system will never really work properly. Don't try to use it as an alternative to standard techniques though - it doesn't tell you everything.
my alignment was hm ... quick and dirty? - so I had to make do with 15 seconds ISO1600. 20 seconds were already streaky.
the small tracking errors causing the wobble - like mechanical stops or something? uuuaaaahhhh!
No, no, I don't think that was the cause. On all images the stars all have 1 jitter in them. You know. Like as if you had touched the camera slightly. Such a regular mechanical error would be weird. You'd say so too would you see the jitter. I feel it's the shutter clicking while the camera is in that kind of floating rubber band mount.
Yeah, "coma" - that's the word.
No, I won't be "using" your DIY tool for real collimation. But it definitely showed me that the mirrors are completely off
Come on, let's have a beer or some other fizzy drink!
The wobble is possibly due to small tracking errors in the mount
this nags at me.
how to find out if it's just the camera shutter or the mount?
if it is the mount, the jiggle should happen multiple times in longer exposures - especially well visible in star trails. (he he he, it's good to be good in inaccurate alignment!)
if it is the shutter the jig will only happen once in any image.
I think I'll do the test again with that rubber band mount.
if it turns out that it is the mount/motor - how would I fix that if not by buying a new mount?
if it is the motor/mount then prime focal photos - even with a proper adapter and focuser - would certainly always show this error? or would the proper focuser and t-connection smoothen the jig - as I hope it would if the shutter were the culprit.
why go prime focal, at all, and invest money in a focuser and t-connection prior to having a proper mount?
yup. next clear night it's another prime focus test. I so hope it's only the shutter...
