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Old 06-09-2020, 05:26 PM
Nightingale
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OAG for SCT- yea or nay?

I am in a little bit of a conundrum.. i currently have a 60mm f/4 guidescope with a barlow attached to it for my meade 12inch.. tracking around the celestial equator is excellent but otherwise it is a little bit of a hit and miss.. would a bigger and better guidescope help? Or should i go for an OAG?... if you think OAG is the best option, how much of a problem would it be finding a guide star with these gadgets?
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Old 06-09-2020, 05:44 PM
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My first foray into astrophotography was with a Meade 8 inch F10 SCT on a NEQ6Pro. I used a ZWO OAG with ASI120MM-S, home made motor focuser driving a WO crayford focuser. After a bit of tuning in regard to the positioning of the OAG mirror. This was to optimise the star light in but avoiding creating an obstruction to the main camera and of course getting it parfocal with the main camera. I never had any problem getting guide stars and guiding was better than using a guide scope.
The scope itself was not designed for photography so results were limited in that respect but it was fun to make do with what I had on hand.
I still use OAG but in a refractor set up.
Mike
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Old 06-09-2020, 08:30 PM
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Merlin66 (Ken)
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+1 for an OAG on a 12" SCT @ f10
I use it all the time for spectroscopy.
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Old 07-09-2020, 01:09 PM
Nightingale
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Spartacus - your 8 inch, i assume will capture a bigger area of the sky.. i am just worried that my 12 inch will not have enough starts in the periphery.. i might bite the bullet and get a Zwo OAG for trials.. just don't like all the hassle that comes with an OAG..
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Old 07-09-2020, 02:22 PM
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multiweb (Marc)
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Quote:
Originally Posted by Nightingale View Post
Spartacus - your 8 inch, i assume will capture a bigger area of the sky.. i am just worried that my 12 inch will not have enough starts in the periphery.. i might bite the bullet and get a Zwo OAG for trials.. just don't like all the hassle that comes with an OAG..
Once you go OAG you'll never go back. The benefits far outweigh everything else. Your 12" is a light bucket. You will find a guide star. Even a faint one.
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Old 07-09-2020, 03:14 PM
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Yep Marc is correct. Your FOV at F10 would be the same as mine but you would have 12 inches worth of photons crammed down to your camera. So you would have an advantage over my set up. Although the OAG takes a small proportion of those photons you would have ample to get a guide star.
I even experimented with solving from the OAG image and was able to do this more often than not. So this just shows that there are plenty of guide stars to play with.

Technically it is not difficult and as you are already using ZWO cameras the ZWO OAG is designed to make it easy to get the correct back focus.
Once you have got it parfocal with your main camera it is a breeze .
The other advantage is that you don't have to bother with having the extraweight of a guide scope. The really short FL ones will be a real struggle. Flex can also create issues with guiding that you just don't get with OAG.

Hope this helps to reassure

Mike
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Old 07-09-2020, 03:25 PM
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Mike, et al,
If the prism in the OAG is set correctly it will not interfere with the photons going to the main camera.
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Old 07-09-2020, 03:47 PM
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Yes of course you are right otherwise it would cause a shadow on the sensor.

Mike
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