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SCT Adaptors

gary1968

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gary1968

gary1968

Posted
Posted

Howdy,

I contated Ian King the other day for advice on what adaptors I would need to fit my 1000d onto my SCT.

Now, he advised that I needed a SCT > T thread adaptor and a Variable T Extender Tube. He said that I would be better with the variable tube so that I could 'fine tune' the distance between my F6.3 reducer and the camera chip.

After recieving the adaptors I am a bit bit confused. I understand how they go together but I cant figure out what the adjustment is for. When I am looking at the images what am I looking for? How do I know that the extender needs adjusted?

The weather is carp here now so I cant play around with it so thought I'd ask here....... :)

Any help appriciated.

Gary

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martin_h

martin_h

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The extenders enable you to get focus...If you imagine the distance between the back of the SCT through the diagonal and EP to your eye....that is what you are compensating for...there might not be enough focus travel if you mount the camera directly to the back of the tube...I use a QHY8 on my SCT with a reducer as well and I need about 50mm of 'extention' to get focus.

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brianb

brianb

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If you reduce the distance between the focal reducer and the camera sensor below the design amount, you will get less reduction. With more distance, you will get more reduction - but will probably run into vignetting and/or be unable to achieve focus. IIRC the design distance for the standard 0.63x reducer is 110mm from the back face to the focal plane. The camera will use about 43mm of that, so you want approx. 67mm of tube (including the T adapter) between the reducer and the camera.

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Psychobilly

Psychobilly

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... The camera will use about 43mm of that, so you want approx. 67mm of tube (including the T adapter) between the reducer and the camera.

Which is about 55mm in front of the T-Adaptor... Which IIRC is the lenght of all the adaptors Stacked together...

Meade used to use a single piece 55mm long adaptor with the f6.3 and a variable adaptor kit with the f3.3...

As well as varying the reduction you may also notice some differences to the shapes of the stars around the egdes of the image and in particular in the corners...

Peter...

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gary1968

gary1968

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Thanks guys.... :)

So, if I am understanding this right, I need to get the completed adaptor assembly to 67mm in length to get the best from the reducer / camera combination, is that right?......

Gary

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Psychobilly

Psychobilly

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yes... and no...

the t threraded part up until the point it srews into the EOS t adaptor needs to be 55mm which I think means that if its the Meade Variable T adaptor screwing all the bits together...

The distance from the front falnge of the ESo T mount top the sensor will be 55mm so you will end up wih the required 110mm

T adaptors vary in thickness for the different lens mounts so taht the diusatnce from their front flange to the FP is always 55mm allowign common optics to be used witha range of different camera.. go to remember this predates all the "Electrickery" that goes on between a camera and a lens these days...

Peter..

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gary1968

gary1968

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I aint seen the Meade variable jobby, mine is a Baadder Planetarium variable exender.

I might have the idea now Peter, bare with me mate, :) , the variable extender needs to be 55mm long. Then I screw on the SCT>T-ring adaptor to the front end and then the EOS T-ring onto the other. Allowing the assembled adaptor to be fitted to the sct and the camera to that.

Is that right?

Gary

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gary1968

gary1968

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yep and no... lol

After fitting the SCT-T adaptor to the variable t adaptor the distance from the front flange of it to the shoulder on the rear most t-thread should be 55mm...

Peter...

:), :eek: , is that the whole assembly less the EOS T-ring then?

Sorry for all the questions Peter I just wanna make sure I have this right in my head......... :(

Gary

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michael.h.f.wilkinson

michael.h.f.wilkinson

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Actually, because the T-mount specs include the distance from the flange to the image plane, you should be able to use the standard, fixed T mount adapter attached directly to the focal reducer. This works on the Celestron I have. On 35mm film it does cause vignetting, but on an APS-C format sensor it should be OK. A variable adapter does give you a bit more choice in magnification.

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  • 3 months later...
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Hi michael.h.f.wilkinson

Last night I tried just that, with my Celstron 5SE with a f6.3 focal reducer with t-adapter and Olympus OM (film)adapter and olympus om to 4/3 (dslr) adapter!! result got to bed at 2am with not a star imaged, I have ordered adapters that bypass the t-adapter by screwing staight onto the focal reducer to shorten the distance between the DSLR sensor and the focal reducer but what Im hearing on this site so to speak, is that this focal length needs to be incresed to 110mm which contridicts what the celestron sites says. :icon_scratch: Please can you help??:)

Please can anybody help:confused:

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