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Celestron C9.25 XLT for AP?


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Been offered a mint C9.25 for a decent price. Wonder how it fairs for AP? I'm mainly interested in galaxies and would be using my QHY268C with it on my EQ6R Pro. Does the 6.3 reducer help coma and field flatness? Are there other reducer/flatteners out there? Any opinions welcome :) I'd be fitting either a EAF or Celestron motor focuser so not worried about not having mirror locks.

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I owned a Celestron C9,25-CGE (XLT),OTA 2350mm once. It can produce decent pictures in the center but when it comes to edges things got worse.
I tried: Meades f/6.3 Focal Reducer/Field Flattener, Celestrons Reducer/Corrector f/6.3 and Starizonas SCT Corrector II - 0.63X Reducer/Coma Corrector


 

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Hmm what happened? Oh I will continue here.
The scope I owned is probably best suited for planetary and observing and it only got F10 so it needs rather much light and a dark site to come to its best.
I have written some about this tube I owned and the reducers on my webpage if you are intersted: http://www.itskane.se/picastro.asp?part=4
This is of course only my own experience as maybe others do not agree upon.

You can as I said get good pictures in the center area. This one is a picture taken with the 9,25 and a Canon 700D Baader mod. and it is of course rather much croped.

pic44.jpg.4ed28e557d07a7639391cbd9bd1cb591.jpg

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4 hours ago, AndyThilo said:

Been offered a mint C9.25 for a decent price. Wonder how it fairs for AP? I'm mainly interested in galaxies and would be using my QHY268C with it on my EQ6R Pro. Does the 6.3 reducer help coma and field flatness? Are there other reducer/flatteners out there? Any opinions welcome :) I'd be fitting either a EAF or Celestron motor focuser so not worried about not having mirror locks.

For planetary imaging it'll be great, for deep sky, not so much. 

I was playing around with my c6 last night to see if l could get a decent image of m51 (at native f10) and the stars looked awful - quite severe coma in all but the very centre of the frame. The galaxy itself looked quite pleasing though. 

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Your chip is APS-c sized, I think, so the flattener should cover it tolerably well. You would still be massively oversampled, though, at about 0.5 arcseconds per pixel. You'd be wanting to software bin down to about half that, since a good EQ6 under guiding cannot be expected to beat 0.5 arcsecs RMS (supporting imaging at twice that, so 1"P/P. There is no point in sampling below that.)

With present technology, and notably highly sensitive cameras like yours with small pixels, an SCT strikes me as being a 'hard work solution' to the DS imaging problem. For some reason they tend to produce big stars, for one thing. My inclination would be to go for a significantly shorter focal length since you'll get the same real resolution of detail out if it, plus a wider field field of view and probably better stars.

I have a 10 inch flat field SCT sitting in a cupboard but since I don't feel it is likely to beat my 1 metre FL refractor I still haven't given it an airing. Maybe I should but my present setup ain't broke...

In a nutshell I think modern cameras may have put long focal lengths out of business for deep sky imaging.

Olly

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Starizona offers a (pricey) reducer/corrector for SCT. Availability is a problem, of course (and you could buy an RC8 for this price, I guess).

You can crop the imx571 image and use the good center part (the C9.25 with the square imx533 is nice for galaxies).

Guiding with an OAG is necessary, if you want good results. Due to f/10, it'll be a little challenging to collect enough photons.

Check at Astrobin for images done with this OTA, to get a feel about its capabilities.

N.F.

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13 hours ago, ollypenrice said:

Your chip is APS-c sized, I think, so the flattener should cover it tolerably well. You would still be massively oversampled, though, at about 0.5 arcseconds per pixel. You'd be wanting to software bin down to about half that, since a good EQ6 under guiding cannot be expected to beat 0.5 arcsecs RMS (supporting imaging at twice that, so 1"P/P. There is no point in sampling below that.)

With present technology, and notably highly sensitive cameras like yours with small pixels, an SCT strikes me as being a 'hard work solution' to the DS imaging problem. For some reason they tend to produce big stars, for one thing. My inclination would be to go for a significantly shorter focal length since you'll get the same real resolution of detail out if it, plus a wider field field of view and probably better stars.

I have a 10 inch flat field SCT sitting in a cupboard but since I don't feel it is likely to beat my 1 metre FL refractor I still haven't given it an airing. Maybe I should but my present setup ain't broke...

In a nutshell I think modern cameras may have put long focal lengths out of business for deep sky imaging.

Olly

Thanks for the honest answer and is rather what I am thinking also. My current 130mm (910mm fl) triplet will probably produce better images even when cropped in. It's just always the desire to  have more optical focal length. And I think you're right, modern CMOS cameras just don't have big enough pixels for long FL dustbins. 

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46 minutes ago, AndyThilo said:

Thanks for the honest answer and is rather what I am thinking also. My current 130mm (910mm fl) triplet will probably produce better images even when cropped in. It's just always the desire to  have more optical focal length. And I think you're right, modern CMOS cameras just don't have big enough pixels for long FL dustbins. 

Interestingly even some daytime photographers, paticularly in sports and wildlife, are expressing reservations about the diminishing pixel sizes at focal lengths of only 600mm or so.

Olly

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