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Autoguiding with a camera lens

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I have a 200mm f2.8 camera lens (72mm aperture) that I would like to use with a SPC900 to autoguide. My scope is a 10" f4.3 reflector with a focal length of 1092mm.

1. Is this possible?

2. Would I need to use a barlow to increase the magnification/focal length? If so, what power barlow?

3. I plan to use a UV/IR filter on the front of the lens, would it be better to use one between webcam and lens?

4. If it is possible to use the webcam would I need to LX mod it as it would be tricky to mount the lens in guide rings?

5. Does anyone have any recommendations for adapters to mount a canon EOS lens to a webcam?

Edited by angusb1
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1. People do use this type of camera lens/webcam combination for guiding, can't say whether you specifics will work though.

2. Not necessarily, infact it would reduce your field of view which might make getting a guide start in the frame more difficult.

3. I'd think using a common 1.25" filter on the webcam rather than a larger one on the lens would be cheaper, though I'm assuming the webcam has a 1.25" threaded nose piece on it.

4. My 9x50 finder guider is 50mm aperture with a focal length of about 200mm and it works fine with my SPC900 webcam.

5. Google for Moog adaptors.

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1. Yes...

2. Probably not....

3. Either...

4. It's a short focal length fast lens so try pointing it at the night sky and see what happens... see if you can see stars using PHD...

5. You can make a cheap adaptor to try it using a 35mm film canister and an old rear lens cap...


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1. Yes but...see 2.

2. A 200mm fl I find is problematic for guiding longer fl scopes >1500mm; you could add a x2 barlow or a x2 camera extender


4. A Lx mod is probably required to get good guide stars. Think about selling the webcam ( or keep it for planetary/ lunar/ solar imaging) and go for a QHY5

5. I made my own from a camera extension tube and a 1.25" extension tube....PM me or you can buy the ready made ones from Mogg.


Edited by Merlin66
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Thanks for the replies everyone. I've gone for the rear lens cap and 35mm film canister to make an adaptor and I'll just see if PHD can find anything.

If it works make something more permenant...

Does the lens you are using have a manual aperture ring...

If not you might have to use some tricks to get the aperture to open up

1 Turn camera on and select the aperture setting you want (the minimum in this case)

2 Hold down the depth of field preview button

3 While holding down the button remove the lens. This way the lens iris will stay where it last was.


Edited by Psychobilly
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Cheers Peter, it hasn't arrived from ebay yet :D but I think it has no manual adjustment for aperture. I was going to try setting the aperture wide open with the lens on my 30D then removing it and putting it on the webcam. I think if there is no electrical signal to the lens it will stay at whatever it was last set to. Do you think this will work?

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Thats how to do it...

Although the lens is probaly wide open by default ... you only need to do this if you want to close it down... at least the canon lenses I have just checked are all wide open by deafult...

Edited by Psychobilly
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