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Off axis Guider question

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4 replies to this topic

#1
skye at night

skye at night

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and relevent to use of OA with Adaptive optics also...

Just wondering how these systems cope in finding a suitable bright guide star as presumably the guide star has to be close to the area being imaged and may be an issue on a faint nebula etc...

thanks

steve
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#2
Merlin66

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The pick off prism is large enough to usually give a choice of guide stars.
As the prism is close to the edge of the field it doesn't matter what the target is - faint galaxy, DSO etc it looks at the nearby area.
(Sometimes it is useful to have a OAG where the prism can rotate around the edge of the field to give more options.)
http://stargazerslou...irst-light.html
If you page down on this link you'll see examples of the guide FOV and the stars picked up by the guide camera

Can't comment on AO - never tried it.


Ken

Edited by Merlin66, 25 January 2010 - 02:58 PM.

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#3
skye at night

skye at night

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thanks,

did not realise that they could be 'adjusted'

steve
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#4
Merlin66

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On the Celestron OAG the prism can be moved in and out of the FOV as well as rotating about 120 degrees.
"Astronomical Spectroscopy-The Final Frontier" -to boldly go where few amateurs have gone before.

C11, NEQ6pro, DMK41AF04, ATik314L+, 1000D modded, SM60DS/BF15, 102mmPST, Spectra-L200 and other Spectroscope(s).
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes -How to use them" - Springer
http://tech.groups.y...l_spectroscopy/

#5
astronomer2002

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I have used these a lot over the years and finding a suitable guide star is often a problem. Most OAG setups allow the prism to be moved in/out but beware of causing shaddowing/vignetting on the imaging chip. Using the SX AO unit the problem is similar and you usually have to compromise on the composition of the image. Most objects do have stars of 12th mag near to them and these are perfectly adequate for electronic guiding purposes. If you can just about see it with the image stretched to max then you can guide on it. Of course, you have to watch that the seeing doesn't deteriorate during the exposure if you're guiding on the edge!




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