What would be your recommendations for using a guide scope and ZWO ASI120MM with 9.25 EDGE HD. I do understand that an OAG is best used with long focal but I'm not ready for it as it seems pretty complicated. All new equipment little experience in astrophotography and I need to practice for some time.
Guide scope
The reducer for the EDGE does not correct, the EDGE is already corrected, it onle reduce and it is expensive https://www.highpointscientific.com/celestron-7x-focal-reducer-for-8-edge-hd
Hi Bernard,
The problem is EdgeHD 9.5 has huge focal length so you would need something like 500mm to guide it (at least). Maybe you could escape with as little as 300mm depending on the pixel size of your main camera, what exposure length you are aiming for and how good is your tracking when unguided, but most likely not. It does not have to be an apo, this is the good news. Even a cheap 80mm f/5 achromat should work well enough as a guidescope. But I don't think it would be more practical than a OAG. In fact this is probably the main reason people prefer OAGs with large SCTs and no so much the mirror flop thing.
The problem is EdgeHD 9.5 has huge focal length so you would need something like 500mm to guide it (at least). Maybe you could escape with as little as 300mm depending on the pixel size of your main camera, what exposure length you are aiming for and how good is your tracking when unguided, but most likely not. It does not have to be an apo, this is the good news. Even a cheap 80mm f/5 achromat should work well enough as a guidescope. But I don't think it would be more practical than a OAG. In fact this is probably the main reason people prefer OAGs with large SCTs and no so much the mirror flop thing.
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Hi Dkamen,
I just received a ZWO ASI224MC which I will use for planetary and the
ZWO ASI 120 for guiding. I will definitely consider other cameras, at least one more.
Do you (or anybody else) have any advice on a choice of OAG that will work best with the EDGE?
The learning curve is going to be steep. Can't wait to move my gear outside.
Clear skies! Ben.
I just received a ZWO ASI224MC which I will use for planetary and the
ZWO ASI 120 for guiding. I will definitely consider other cameras, at least one more.
Do you (or anybody else) have any advice on a choice of OAG that will work best with the EDGE?
The learning curve is going to be steep. Can't wait to move my gear outside.
Clear skies! Ben.
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Hi Bernard,
I was in a similar situation and decided to go with the OAG. I did not completely feel comfortable with that because of the concerns you can read about that it is difficult to find guide stars in the neighborhood of your target. To somehow fix this you need to find an OAG with a large prism and a suitable guiding camera with the right sensor size/resolution.
Furthermore the aspect of focusing the guide scope is important.
On the other hand the main argument pro OAG is that you have no differential flexure as with any guide scope.
Taking all this into consideration I decided to go for the Omegon OAG with micro focuser. I bought it here https://www.astroshop.de/off-axis-guider/omegon-off-axis-guider-off-axis-guider-mit-microfokus/p,49752
I have to admit that I have not yet tried it since I am still struggling right now with basic guiding and getting my mount working properly. I am using a different setup with an old 300mm Zeiss lens and an Orion guide scope in parallel.
Hope you find this useful
Cheers
Gernot
I was in a similar situation and decided to go with the OAG. I did not completely feel comfortable with that because of the concerns you can read about that it is difficult to find guide stars in the neighborhood of your target. To somehow fix this you need to find an OAG with a large prism and a suitable guiding camera with the right sensor size/resolution.
Furthermore the aspect of focusing the guide scope is important.
On the other hand the main argument pro OAG is that you have no differential flexure as with any guide scope.
Taking all this into consideration I decided to go for the Omegon OAG with micro focuser. I bought it here https://www.astroshop.de/off-axis-guider/omegon-off-axis-guider-off-axis-guider-mit-microfokus/p,49752
I have to admit that I have not yet tried it since I am still struggling right now with basic guiding and getting my mount working properly. I am using a different setup with an old 300mm Zeiss lens and an Orion guide scope in parallel.
Hope you find this useful
Cheers
Gernot
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I too am looking for a guide scope - my issue is my eyes cannot focus on red and the laser red focus on the Orion does not work well for me- so I have all may iphone apps and software in daytime mode. Having said that I was looking for a guide scope and even called Orion trying to figure out how to get my AT-AZ mount to work with it. Orion told me it could not be done because there was no port on my mount to guide the AZ mount. Second, the Orion 50mm with guiding camera works for focal lengths under 1500 mm. It has been around for such a long time that the scope and camera are supported well by the software and apps and the newer Orion 60mm with guiding camera is also well liked. My Dobsonian is 1650mm and hence my call to inquire about the possibilities. Orion told me about a Poncet Mount that raises the latitude angle of my base to match my location pointing one axis at north and then my mount could opperate like and EQ mount. Interesting idea but I think I have so much light in my rig that I am going to go the EAA route of short exposures over time in live traking and simply buy the 60mm scope to align my targets without first using an eyepiece before zooming in with my ZWO camera. Let us know what you decide. Dr. H. in Milwaukee.
Bernard,
I use a Celestron OAG with my 9.25 Edge HD. I use a ZWO ASI 174MM mini as a guide camera. The guide camera is super sensitive and it covers the entire OAG window field. Finding guide stars is never a problem, and I can even guide on stars down to 12 magnitude or lower.
The use of an OAG is not complicated and it solved my problem of subframe shift due to mirror shift as the mount tracks a target. Also, the OAG provides a convenient way to rotate the camera for composition and to find guide stars. I put a marker tape on the center of the OAG so that I can set the rotation for an imaging session or return to that position for imaging the same target over multiple nights. The Celestron OAG has a helical focuser, so it is easy to make the guide camera focus parfocal with the imaging camera. The hard part was getting the spacer combination correct to get the proper backfocus. I ended up using a 1 1/2" SCT spacer connected to the scope or the 0.7x focal reducer and connecting the OAG to that spacer. My OAG work like a charm.
Mark W
I use a Celestron OAG with my 9.25 Edge HD. I use a ZWO ASI 174MM mini as a guide camera. The guide camera is super sensitive and it covers the entire OAG window field. Finding guide stars is never a problem, and I can even guide on stars down to 12 magnitude or lower.
The use of an OAG is not complicated and it solved my problem of subframe shift due to mirror shift as the mount tracks a target. Also, the OAG provides a convenient way to rotate the camera for composition and to find guide stars. I put a marker tape on the center of the OAG so that I can set the rotation for an imaging session or return to that position for imaging the same target over multiple nights. The Celestron OAG has a helical focuser, so it is easy to make the guide camera focus parfocal with the imaging camera. The hard part was getting the spacer combination correct to get the proper backfocus. I ended up using a 1 1/2" SCT spacer connected to the scope or the 0.7x focal reducer and connecting the OAG to that spacer. My OAG work like a charm.
Mark W
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Nice replies all, 9.25 EDGE, EQ6-R PRO, ASI174mm for guiding, ASI224mc
waiting for Celestron OAG and sooner than later 0.7x reducer.
. Clear skies and milder temperatures are slowly creeping back.
Clear skies all. Thanks to all for the very helpful replies.
Ben.
waiting for Celestron OAG and sooner than later 0.7x reducer.
. Clear skies and milder temperatures are slowly creeping back.
Clear skies all. Thanks to all for the very helpful replies.
Ben.
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