Will be a getting an older model Celestron C9.25 SCT to expand my options, but I have so far only used a refractor so I have some question on what best to do. I will use a CEM70 as mount. Mostly I will use it for planetary and lunar captures, for this I have a ASI462MC and the ADC. Have some barlow options with this as well but that's for a later stage. For planetary and Lunar how necessary is an auto guider? or can the firecapture guiding do this on its own? I understand that for DSO work the reducer will be necessary as will the OAG. But i see a lot of reference to adding external focusers to SCT's.How essential is this and what experiences do people have with this?Am thinking of adding the Celestron OAG with an ASI174MM Mini for the guiding and will use my ASI183MM for capture (suboptimal I know but end of year budget only goes so far) Thanks for any input its much appreciated before I invest in a lot of new toys
C9.25 SCT external Focuser?
I have a newer EdgeHD 9.25 and use the Pegasus Focus Cube Zero on it. It works great and was the last automation piece to add so I can completely image from inside the house. I originally had the Celestron Motor Focuser installed but didn't like it as it was prone to come loose (which is kind of scary).
I've seen others add a completely separate moonlight type focuser directly in the image train and lock down the main mirror focuser. To me, that seemed more trouble than benefit.
Hope this helps.
Kevin
I've seen others add a completely separate moonlight type focuser directly in the image train and lock down the main mirror focuser. To me, that seemed more trouble than benefit.
Hope this helps.
Kevin
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For planetary work you don't need any guiding as long as the mount is reasonably polar aligned. And don't need any external focuser although an external crayford would be recommended for DSO work. In my experience with SCTs once you accomodated the intial flop and the scope is still well collimated (in focus) you won't need much fiddling with the focuser anyway, that is for reasonably well built SCT and planetary imaging. But then nothing prevents you spending as much as the entire scope on a fancy electronic motorised focuser…
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+1 for no guiding. You are working at such a long focal length for planetary that guiding would be more of a nuisance than a help as it adjusts itself. I use the Celestron motorized focuser on my 9.25 (I am in the exact same situation as you as I only use it for planetary) and having the ability to focus from my computer at the table without my hands on it is very valuable!
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The issue with a SCT is mirror shift. This is cause by the mirror moving on the baffle tube to focus and causing an angular shif in the mirror. Not mirror flop. Mirror flop is caused by the weight of the mirror causing a lateral movement as the scope moves in RA.
I have three Celestron SCTs. And owned 3 others in the pass. My 9.25 ANF C11 is the older carbon fiber models. I have a newer Edge 8. I also have two Maksotov that focus like a SCT.
SO, I am familiar with them. Mirror shift will vary from scope to scope. Some better than others. Replacing the stars are focused with the Starlight Feather Touch helps some, but if you add a Crawford focused, you don,t need both. Unless, you don,t want to use the Crawford for visual, and would like 1 to 10 reduction.
Guiding will not be neccassary for planetary. You will be using such fast exposures, that guiding would not be able to keep up anyway, and guiding correction my actually cause problems. The whole session will only be 2 to 3 min total.
Depending on the size of the chip, the planet may move off the screen as focus causes the mirror to shift. Your composition will certainly change. From center to one side. All of that is increased with a Barlow.
Having a separate Crawford focused will eliminate these issues. I used a older used Starlight Feather Touch 2".
To lower the F ratio for DSO , I would highly recommend Starzona's SCT reducer. I have the older f7.5 version and it works extremely well. Very easy to insert into the 2" focuser.
Also I recommend the dew shield with built in heater element. It is difficult to impossible for a heater to exchange heat thru a dew shield. And do not wrap in around the tube. That will only create tube currents in the tube. Which will destroy your optical resolution. You want to bring that heat to the corrector plate.
The centering of the corrector plate is another issue. Celestron does a good job with this on the Edge units, because of the internal flattened. But they don't do it well with the standard models. That is because the spherical primary and secondary will collimate fairly well even if the secondary is not well centered on the optical axis. But, a better centered secondary is advatagist for imaging. Check out Starzona's site as to how to do this. It is crucial for Fastar/Hyperstar imaging.
I hope this helps.
Lynn K.
I have three Celestron SCTs. And owned 3 others in the pass. My 9.25 ANF C11 is the older carbon fiber models. I have a newer Edge 8. I also have two Maksotov that focus like a SCT.
SO, I am familiar with them. Mirror shift will vary from scope to scope. Some better than others. Replacing the stars are focused with the Starlight Feather Touch helps some, but if you add a Crawford focused, you don,t need both. Unless, you don,t want to use the Crawford for visual, and would like 1 to 10 reduction.
Guiding will not be neccassary for planetary. You will be using such fast exposures, that guiding would not be able to keep up anyway, and guiding correction my actually cause problems. The whole session will only be 2 to 3 min total.
Depending on the size of the chip, the planet may move off the screen as focus causes the mirror to shift. Your composition will certainly change. From center to one side. All of that is increased with a Barlow.
Having a separate Crawford focused will eliminate these issues. I used a older used Starlight Feather Touch 2".
To lower the F ratio for DSO , I would highly recommend Starzona's SCT reducer. I have the older f7.5 version and it works extremely well. Very easy to insert into the 2" focuser.
Also I recommend the dew shield with built in heater element. It is difficult to impossible for a heater to exchange heat thru a dew shield. And do not wrap in around the tube. That will only create tube currents in the tube. Which will destroy your optical resolution. You want to bring that heat to the corrector plate.
The centering of the corrector plate is another issue. Celestron does a good job with this on the Edge units, because of the internal flattened. But they don't do it well with the standard models. That is because the spherical primary and secondary will collimate fairly well even if the secondary is not well centered on the optical axis. But, a better centered secondary is advatagist for imaging. Check out Starzona's site as to how to do this. It is crucial for Fastar/Hyperstar imaging.
I hope this helps.
Lynn K.
Thanks for the answers. So for planetary it’s easy enough. I’ll probably go with an EAF as I love that one on my refractor.
leave the DSO work to my refractor for the moment should be a bit easier on the wallet until I can afford a good camera to match the C9.25
leave the DSO work to my refractor for the moment should be a bit easier on the wallet until I can afford a good camera to match the C9.25