#1  
Old 01-08-2007, 03:02 PM
Roof
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Not able to focus using Camera on scope

Dear All,


Recently i bought a Skywatcher Refractor telescope D70xF900mm, I must admit just for fun. We talked to the guy in the store and we wanted something for day and night viewing. Then one night we discovered saturn (Fantastic), We were very excited. Problem was saturn was very small. More money then sense we thought a bit bigger scope, Bigger saturn, So we went to a different store and bought a skywatcher Reflector 130x1000mm, A bit dissapointed when Saturn wasn't as big as the moon, The guy in the store told me that that was never going to happen but it should look a bit better, Which is true. Nevermind i'm still having fun, I don't watch television as much.

As my other hobby is a bit of photography, You guessed right, My camera had to go on my telescope. Went to the store and bought a little tube and a t-ring.

I though to myself let's try the moon first and see what happens, Big dissapointment i could not get the focus on the moon. As i'm very very new to all of this and a bit unknowing i would like to ask the following.

The first time i didn't use any eyepiece (no focus possible) I tried no tube, half a tube, full length tube i could not get the moon in focus. Used a 20 mm eyepiece and i just can't get it focussed.

My own answer is get a 40mm eyepiece or another one of these tubes and i should be right. Is this going to solve my little problem ??

Camera that i have is a pentax k100d.

I have search the net and nobody seem to have this problem, Is it me that does something wrong.

I'm still very excited about this whole skywatching bussiness.

Thanks so much for any help.

Roof.
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  #2  
Old 01-08-2007, 03:16 PM
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Outbackmanyep
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G'Day!
Im guessing that back focus is the problem, you could try using the afocal method, which is imaging through the eyepiece, separate & independant of attaching it to the scope.....try the moon tonight, focus on the moon as you normally would visually then hold your camera to the eyepiece, try not to rest it on the scope as vibration and bumping will blur the image, maybe zoom in a little if you can to help fill the field of view on the camera, its a little tricky but it should be a start.
A lot of newtonian reflectors have trouble with being able to focus using a camera.
There are a couple of ways of avoiding it but essentially a Schmidt-Cassegrain or Maksutov catadioptric telescopes were built with photography in mind.....
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Old 01-08-2007, 04:02 PM
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iceman (Mike)
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Hi Roof, welcome to IIS.

There's a few discussions here on IIS about similar problems focusing a DSLR on a newtonian at prime focus. It usually can't be done without moving the mirror up the tube. The problem is usually in-focus.

So, you can either do that, or use afocal methods. ie: put an eyepiece in, and use the lens on the camera, and shove the 2 together
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Old 01-08-2007, 06:40 PM
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Hi Roof

We have a Skywatcher 200 x 1000mm f5 Newtonian Reflector which was originally fitted with a rack & pinion focuser, the same as your scope.
In order to reach focus with our Pentax ist DL, (which is similar to your K100D ) we purchased a Lumicon Low Profile 2" Adaptor.

This adaptor when fitted on to your T-Ring will allow your camera to fit close in to your focuser giving you the extra in travel to achieve focus.

The only problem is that in order to use this adapter you will need to make a spacer as the inside diameter of your focuser is larger than the diameter of the adaptor.
I made a spacer using plastic water pipe with a 52mm inside diameter.
If you want to persue this avenue I can make a spacer for you - gratis off course.

The Low Profile Adapter can be purchased from My Astro Shop per this link http:www.myastroshop.com.au/products/details.asp?id=MAS-266

Page one of our web page, listed below shows some of the images taken with this set up.

Hope this helps

David

Last edited by Tamtarn; 01-08-2007 at 07:31 PM.
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  #5  
Old 01-08-2007, 07:30 PM
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StarLane
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I have the same problem with my 10inch F5 reflector, I can not achieve focus using the prime focus method, not enough inward focus travel.
To fix this:
1. Move the mirror up the tube, requires the drilling of new holes to hold the mirror cell - messy.
2. Buy a low profile focuser, this my help depending on how far IN the focal plan is.
3. Shoot using the afocal method as others have suggested, hold the camera with lens up to the eyepiece.
4. Shoot using the eyepiece projection method, attach the SLR camera body (with no lens) directly onto the eyepiece. Only some eyepieces have a thread on top to enable this. An adapter is also required in addition to a T-ring. I use this method to bring my SLR to focus. I use Baader Hyperion and Pentax XW eyepieces for this.
Hope this helps.
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Old 01-08-2007, 08:29 PM
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Hi Paul

I agree moving the mirror up is not a job I would look forward to.

Eyepiece projection works well as you can confirm.

Hand held afocal can be done but results vary.

Our 12" Dob won't come to focus with the camera unless we fit a Low Profile Focuser, because it has a 1500mm focal length.
Your 10" Dob has the same problem as it has a 1250mm focal length.

Roof's scope has a 1000mm focal length with a rack and pinion focuser and that is why it will come to focus with a low profile adaptor.

I first used a low profile adaptor for imaging and now use a low profile focuser and they both work on a 1000mm scope.
The low profile focuser is a 10:1 and is great , but I don't think roof would want to go down that path just yet.

David

Last edited by Tamtarn; 01-08-2007 at 08:49 PM.
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  #7  
Old 01-08-2007, 08:36 PM
Hagar (Doug)
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I had a similar problem with a 10" Dob I ended up cutting 50mm off the bottom of the telescope and refixing the mirror cell. The only crunch was to reach focus with an EP I had to buy a 50mm EP extender from Bintel. It now works fine for a DSLR and an EP.

Good luck

Doug
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  #8  
Old 02-08-2007, 01:46 PM
Roof
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Quote:
Originally Posted by Tamtarn View Post
Hi Roof


I made a spacer using plastic water pipe with a 52mm inside diameter.
If you want to persue this avenue I can make a spacer for you - gratis off course.



David
Thanks David for the offer, But i'm not really sure what i should do, I really thought that it was something really simple to fix but it seems to me a lot harder than it is. As i am very new to all of this i think i should give it all a bit of a think.

And then to everyone else thanks for the help and the support, I think i might leave this matter for a little while.

Maybe i should learn to walk first before i can run.

Thanks so much.

Roof.
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Old 03-08-2007, 12:25 PM
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ving (David)
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Quote:
Originally Posted by iceman View Post
Hi Roof, welcome to IIS.

There's a few discussions here on IIS about similar problems focusing a DSLR on a newtonian at prime focus. It usually can't be done without moving the mirror up the tube. The problem is usually in-focus.

So, you can either do that, or use afocal methods. ie: put an eyepiece in, and use the lens on the camera, and shove the 2 together
he probably takes the diagonal out of the Refractor first mike.
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  #10  
Old 03-08-2007, 12:29 PM
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iceman (Mike)
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It's a reflector?
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  #11  
Old 03-08-2007, 01:09 PM
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ving (David)
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just proves that one has to read the posts properly hey... i'll just hide now

lol
no wonder i was confused...

reflector, yup the mirror needs to be moved up to get focus in most cases... as stated
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  #12  
Old 26-09-2007, 06:22 AM
Roof
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Thank you all again for your advice, I haven't been to this website for a while sort of busy with a lot of other things.

I still find it very frustrating that big company's can't take in consideration when designing a scope that people would like to put camera's on it.

I honestly don't want to cut,unscrew or do anything to that scope, It didn't cost the world but still.

As i have been reading a lot of websites and your advice, I am going to relax about this camera stuff and just watch and learn.

I think i left it a bit late to thank you all, But i am very grateful for all your advice.... Thanks so much...

Roof
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