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Celestron C8 F6/3 reducer corrector and ? for FF DSLR ?

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Hi chaps, I've just picked up a bargain C8 for 360 quid. I'd like to use it for imaging so as a minimum I need a SCT to canon adapter. But I want to purchase an  f6.3 reducer/flattener too.

After hunting through the forums it would seem that latest consensus is that the antares one is identical to the celestron, but 85 quid. And in stock somewhere.. so I planned to get that.

Either way, I have an SCT to camera issue. And since with the flattener it needs about 50mm extension to reach focus (105-110mm) than means a reasonably amount of a tube that would, if I got the celestron adapter be standard t/42mm size... which seems to me not a great idea for a FF DSLR.

I'd have though ideally you want to got SCT to canon direct, or SCT to 48mm to canon ?

So though the celestron and others offer this:



I'm gonna get vignetting surely ? why reduce SCT 2" down to 42mm ??

I'd have though a canon 48mm like https://www.firstlightoptics.com/adapters/ts-ultra-short-adapter-from-m48-to-canon-eos-ef-only-1-mm-length.html

would be prefered, with a 48mm tube and a 48mm to SCT ?

Basically a bit confused - what are folk using out there ?

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Wait for a pro-answer, but what I remember from my own c8/reducer/dslr setup, some Celestron reducers dont require the 105-110 backfocus, its mentioned in the description of that reducer.  And the eventually needed extension could be useful filled with an oag.  Mine was 35 mm thick, and a normal thickness eos t-ring made me reach the required backfocus with some small extension rings. 

Edited by Robindonne
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On 25/06/2021 at 17:01, Anubis1311 said:

Where did you pick up your C8? I’ve been looking for ages and can’t find one anywhere near as cheap as that?! Was it is good condition or did you have to clean it up?

ebay. it has one 5mm long then scratch on front glass, but mint other than that. yeh, not sure why it was so cheap, but having used it now I can tell you it works a treat - i posted my M27 image in beginning imaging last week from it.

Definately got a bargain for sure.

I've a 48mm to SCT ordered which should let me use filters and my 48mm t-ring and DSLR, though I expect to use it mainly with my ASI224 for planetary.

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The t ring will give you the required backfocus..never see any vignette issues with my 100d.. what canon are you using? A quick search says this from Celestron ....


With the f/6.3 Reducer/Corrector and an 8" OTA you will have no problem with an APS size CCD sensor (13.6mm off axis). Vignetting occurs gradually as you move off-axis with all SCTs (with or without a reducer corrector, slightly more so with the reducer). With the reducer, your field will be ~ 30% vignetted at 13.6 mm off axis (0.6 degrees). That amount of vignetting is manageable with post processing - you'll never see it in the final image with proper flat field subtraction.

At f/10, your Rebel will see only 0.38 degrees off axis at 13.6mm, and vignetting will be about 17%.

I did this a few years ago c8 reducer and 100d, at the time I was ecstatic.  . This year its time for a revisit



Edited by newbie alert
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It's a 6d, so Full frame. I posted on another thread some results - but with a 42mm t-ring considerable vignetting, and through .67 reducer, terrible. Hence, the 48mm t-ring and attempt to keep it at min 48mm all the way through.

But yet, no probs with 1200d aps-c job.

still waiting on SCT-48mm to arrive from germany so can't confirm if there is an improvement or not yet.

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I wouldn't expect the SCT reducer to work well with a full frame sensor. Better to use an APS-C sensor instead, like a Canon 80D, from what I know.




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