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Thread started 21 May 2006 (Sunday) 17:24
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Astrophotography Question - please help!

 
rwh
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May 25, 2006 08:04 |  #16

split the two sections of the meade t adapter and try it using the short end only with your camera and no eyepiece. I can focus my etx105 like that but as you say it will not focus using the full length of the adapter.
if you want to try eyepiece projection you will need to purchase one of the scopetronix (or similar)adapters designed to hold an eyepiece.
try a few pictures of the moon and planets using the prime focus method and see how you get on like that, getting good pictures is harder than you may think.




  
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sam ­ bailey
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May 25, 2006 11:53 |  #17

I didn't realize you have the Matsutov, I have the 125 version and I use the exact same setup you have-----identical. Note: The adapter is not designed to use an eyepiece.

Here is your solution (I think I'm certain on this one). The adapter is actually 2 pieces. The tube can be unscrewed. It is hard to see where the threaded joint is, but it is somewhere around the middle. If I recall correctly, I had to do that on mind in order to obtain focus at the camera. I know I am using a "shortened" adapter and I get great focus and pictures. There is no reason you can't also. You have top notch equipment and you will be successful. Let us know how it goes. If we need to talk on the phone also we'll do it.




  
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sam ­ bailey
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May 25, 2006 11:56 |  #18

I didn't see rwh's post. Seems like with your pictures the solution became obvious.




  
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Mathiau
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Aug 09, 2006 18:43 |  #19

so much great info here!


Currently Dreaming about what gear to own in the near future
The trouble with life is theres no background music
WARNING - post on images for critique and other items asking for feedback are simply my personal input and thoughts based on my own experiences and preferences.

  
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ByteTheBullet
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Aug 09, 2006 20:35 as a reply to  @ Mathiau's post |  #20

Not to interrupt here, I was looking into connecting my buddies ETX 60.

Are you trying to mount the camera like in this picture?

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See the last product on this link http://www.scopetronix​.com/trings.htm (external link)

Of course, you will not get the magnification from the eyepiece with this method.

ETA:
You might also want to check out the focus extender from that same site...http://www.scopetronix​.com/focusers.htm (external link)

btw, I am not affiliated with that site in any way.

ByteTheBullet (-:



  
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kfong
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Aug 09, 2006 23:00 as a reply to  @ post 1546650 |  #21

Strange, I have exactly the same setup and I have no problem focusing far objects when doing prime focus. fyi my setup has the following dimension : the distance from the camera EOS mount to the sensor is 44.0 mm, and the t-adapter adds another 10.8mm. The ETX90 photo port T adapter with the extension piece is 36.9mm ( from the flat surface of ETX to the T-thread flat).

Ken

Sun Devil wrote:
First of all, thanks to both Sam Bailey and RWH - there's a few cold beers waiting for either of you if you ever happen to pass through Del Rio, TX!

Ok, here's a few pictures of my setup:

- Canon EOS 20D connects to an EOS T-Ring to a Meade T-Adapter to the Photo Port on the Meade EXT 90.
- When I've used an eyepiece, I've just inserted it into the T-Adapter

I'm looking forward to your comments,
Sun Devil




  
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Adrena1in
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Aug 31, 2007 14:02 as a reply to  @ kfong's post |  #22

Sorry to resurrect an old thread, but I'm having the exact same problem and don't really undestand the solution, so can someone spell it out in "Numpty" language!? :oops:

Okay, so I've got a 400D and a Skywatcher Skyhawk 114M scope. The scope comes with 10mm, "Super 25" Wide angle and 2x Barlow Lenses. I purchased a Celestron T-Ring adapter for the camera, and received in the post today a Celestron T-Adapter. The T-ring and adapter screw together, and the camera fits nicely to the scope.

But the focus range in Prime mode is dire...perhaps 2 to 4 metres focal distance over the entire range of the eye-piece.

What was that about holding a piece of paper over the end of the scope, with no eye-pieces, to determine the focal distance? A piece of paper isn't in focus even when touching the end of my scope! I have to feed something right into the scope to get it in focus! (And even THEN it doesn't appear to focus sharply!)

I wonder if there's something wrong with my scope!? I've used it with the eyepieces for celestial viewing, and have been very happy with it so far, but I dearly want to be able to take astrophotos.

If I connect the 2x Barlow lens I think this is going to work. Earlier in the day, when testing my new adapter, I was trying to focus on the trees outside my window. Couldn't at all with no lens, (they're only a few metres away!), but with the Barlow I could focus on them, and past, so I'm hoping that's at least going to let me focus on the moon or something later, (if these clouds clear).

Any suggestions appreciated.

Thanks,
Tim.


Canon EOS 450D, Sigma 18-200mm, Canon 50mm f/2.5 Macro, 2x TC, Revelation 12" f/5 Dobsonian, Mintron PD2285-EX webcam.

  
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JackProton
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Aug 31, 2007 14:53 |  #23

You're doing prime focus with an eyepiece to T-ring adapter? You may not have enough travel on your focuser for that. In this case, there are a few possible solutions: use a barlow, get a low-profile prime focus adapter, install a new focuser with more travel, adjust the primary mirror to move it forward towards the focuser (this will require re-collimating your scope which can be pretty frustrating if you're doing it for the first time).




  
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Adrena1in
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Sep 01, 2007 03:41 |  #24

JackProton wrote in post #3835535 (external link)
You're doing prime focus with an eyepiece to T-ring adapter?

Prime focus in that I connect my camera, with the relevant T-ring and T-adapters, directly to the telescope eyepiece...yes. I thought this was the correct method.

I undestand now what was meant by pointing the scope at a light-source and checking the distance of the focussed projected image through the eye-piece. It's a very short focal length, and I simply can't get my camera close enough. Even the Barlow doesn't help...I still can't focus on celestial objects.

I'll investigate those other options you mentioned, thanks.


Canon EOS 450D, Sigma 18-200mm, Canon 50mm f/2.5 Macro, 2x TC, Revelation 12" f/5 Dobsonian, Mintron PD2285-EX webcam.

  
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JackProton
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Sep 01, 2007 04:10 |  #25

If you're using an eyepiece and a T-ring and adapter without a camera lens, that's called "eyepiece projection". Eyepiece projection severely degrades image quality and presents such a dim image that proper focus is extremely difficult to determine and you can easily outstrip the usable magnification of the scope. If this is the method you're trying to use, I would suggest starting out with a very low-power eyepiece such as a 30mm. The image quality is also highly dependant on the quality of the eyepiece - orthoscopic types are supposed to work better for this. This is a very difficult type of imaging and I've seen much better results than I was able to get from folks just pointing a camera with a lens into the scope's eyepiece.

Also consider trying a prime focus adapter that doesn't use an eyepiece at all so that the the scope becomes a simple large telephoto lens. This is much easier to work with.. great for moon shots but Jupiter, Saturn and Mars will appear VERY small.




  
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Adrena1in
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Sep 01, 2007 04:48 |  #26

JackProton wrote in post #3838861 (external link)
Also consider trying a prime focus adapter that doesn't use an eyepiece at all so that the the scope becomes a simple large telephoto lens. This is much easier to work with.. great for moon shots but Jupiter, Saturn and Mars will appear VERY small.

Okay, I've confused matters a bit...I'm not using any lenses at all. By "eyepiece" I meant the focusser on the scope, sorry. I'm connecting my lensless camera to the lensless telescope using (what I thought was) the appropriate adapters.

Here are some images to explain better;

Skywatcher Skyhawk

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No lens in focusser
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Camera body, T-ring and T-adapter
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Camera with adapters
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Camera mounted in focusser
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The problem definitely seems to be that the focal range is way shorter than the distance from the focusser to the camera, and there doesn't seem to be any way to get the camera nearer. I guess a lower profile T-adapter, as you said earlier, might be the solution, or a lens-projection adapter of some sort. (I just don't want to keep forking out £15 to £30 for "bits" if they're still not going to do the job, so that's why I was hoping someone might have had a very similar setup to me and experienced the same problems, and knows the definitive answer.)

Thanks.

Canon EOS 450D, Sigma 18-200mm, Canon 50mm f/2.5 Macro, 2x TC, Revelation 12" f/5 Dobsonian, Mintron PD2285-EX webcam.

  
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WGK
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Sep 01, 2007 07:17 |  #27

Del Rio Texas - I learned to fly airplanes at Laughlin AFB in the 70's. Is the base still used for flight training? Could not think of a better location to do astrphotgraphy. Please post some of your pictures once you work through your adapter issues.




  
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JackProton
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Sep 01, 2007 14:21 |  #28

Sorry for the confusion. Moving the primary mirror forward is your best bet. You'll need a collimation tool though to help align the mirror properly.

If the end of the focuser unscrews - the eyepiece holder part with the set-screw - you could try removing it and seeing if that affords you enough extra travel to focus with the camera and T-adapter. Its difficult to use this way but it'll give you an idea if a low-profile T-adapter can help or not.




  
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puttick
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Sep 01, 2007 15:18 |  #29

Adrena1in - what you are doing is called prime focus photography - you are positioning the camera so that the film plane (in this case, sensor) sits exactly where the image is formed. It seems that when attached to "your" scope, "your" particular adapter is not the right length to be able to produce an image on the sensor, even when you use the full range of movement of the focussing tube.

You can determine exactly how long the adapter needs to be very easily. Set the scope up without an eyepiece, looking at the moon (this is a convenient bright object at infinity), and using a piece of paper held over the focussing tube (N.B. no eyepiece!), move it up and down until you see the moon's image sharply on the paper. That is the distance you need to position the camera's sensor.

Now you should be able to work out how long your adapter needs to be. If it's the too short, you can buy extension tubes (in your case I would assume 1.25" diameter) - if too long, you need a shorter adapter. As jack proton says above, moving the primary mirror may solve the problem but you need to do what I have outlined first to determine the correct position of "prime focus".

Good luck
Nigel


Nigel Puttick
North Yorkshire, UK

  
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Adrena1in
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Sep 01, 2007 16:44 |  #30

Thanks Puttick, I've since understood what has been mentioned here about checking the focal range, and unfortunately, in my case, the range is very small...to the order of about 2cm. Even with the bare camera body held right up against my empty focussing tube it's still not close enough.

A low-profile focussing tube replacement is going to be unrealistically expensive. I've been recommended a mutli-purpose coma corrector, but one of these is going to cost as much as I paid for my scope and tripod put together. I might see about a lens-projection adapter, but really, if I'm going to get serious about astrophotography, I think I need to accept that my current scope simply isn't going to cut it.

Thanks everyone.


Canon EOS 450D, Sigma 18-200mm, Canon 50mm f/2.5 Macro, 2x TC, Revelation 12" f/5 Dobsonian, Mintron PD2285-EX webcam.

  
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Astrophotography Question - please help!
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