Telescope Reviews: Finder scope as a poor man's guide scope?

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Anonymous
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Finder scope as a poor man's guide scope? new

#47178 - 01/29/04 10:01 AM

There is another thread in one of the other forums asking about a small aperture, short focal length finder scope being used as a guide scope with an auto-guider attached.

Is there any reason why I would not be able to do the same with my 50mm Antares finder? I believe the focal length is around 220-230mm as measured. I don't really know exactly what it is.

Are there any disadvantages to doing this? Any advantages besides money and weight saving?

I can interchange EP's on this finder if I have to with it's 1.25" diagonal. I'm not really sure if an autoguider uses an EP because I'm not familiar with them so any comments or suggestions would be appreciated.

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jrcrilly
Refractor wienie again

Reged: 04/30/03
Posts: 22461
Loc: NE Ohio

Re: Finder scope as a poor man's guide scope? new

[Re: ]
#47189 - 01/29/04 10:37 AM

Hi, Schultze.

One rule of thumb used by folks with autoguiders is that the focal length of the guidescope should be at least half the focal length of the imaging scope - and preferably more. This is because the image scale of the guidescope should be sufficiently similar to that of the imaging scope to permit the guidescope to see errors that would appear in the image.

The autoguiders I've seen all fit into a 1.25" eyepiece holder so you wouldn't have any mechanical issues.

--------------------
John C
Urban Observatory
Tele Vue Pronto
A&M/Astreya 76mm F/6 APO
TMB/LOMO 80mm F/7.5 APO
Tak FSQ-106N F/5 APO
Meade 152ED F/9 "APO"
152mm F/10 achromat
Tak CN-212 8" F/12 classical Cass/ F/4 Newt
Teeter 20" F/3.8 truss Newt w/ServoCat
LXD750, EM-200, CI-700
ST-10XME

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Suk Lee
Post Laureate

Reged: 10/07/03
Posts: 4315
Loc: Pleasanton, CA

Re: Finder scope as a poor man's guide scope? new

[Re: jrcrilly]
#47226 - 01/29/04 11:49 AM

Quote:

the focal length of the guidescope should be at least half the focal length of the imaging scope - and preferably more

Schultze, John:

The one exception I know of to this fine rule is that if you're using an STV, you can get away with a 100mm focal length guiding up to around 1500mm of main scope (their e-Finder). The STV has a pretty sophisticated algorithm that interpolates the centroid - they claim within something like 1/10 of a pixel.

Unlike the ST4, which definitely wanted a long focal length guidescope, the STV is OK with a short scope if it creates a small bright guidestar. I particularly like the STV with my Megrez80 with a 0.33x Meade reducer.

Cheers,
Suk

--------------------
http://www.siliconvalleyskies.com

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Anonymous
Unregistered

Re: Finder scope as a poor man's guide scope? [Re: Suk Lee]
#47261 - 01/29/04 01:16 PM

Thanks for the answers guys.

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