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Old 29-01-2009, 08:54 AM
keppar (Graham)
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focus Ceestron c8

HI all
Having trouble focusing with a Celestron SCT C8, dslr, filter and a focal reducer i,m not sure if I need more travel (longer adapter tubes) or ths camera needs to be closer to scope. Any thoughts ?
Thanks Kepp
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Old 29-01-2009, 09:10 AM
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Hey there Kepp

Sounds like the distance between the rear of the reducers back lens and the cameras focal plane is too great. I had a similar problem on my C8 until I found a t-threaded adapter that was a lot shorter than the standard ones sold by Meade and Celestron. I ended up using the barrel off of a 2" GSO SCT diagonal, which breaks down into a tube and thread just the right length. Call Mike at Bintel in Sydney - he's got a box full of these barrels on the shelf.
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Old 29-01-2009, 11:31 AM
keppar (Graham)
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Thanks Here is a photo of setup
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Old 29-01-2009, 11:48 AM
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Here are a couple of mine - including the actual adapter. You can judge by the length what is required on a C8.
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Old 29-01-2009, 01:38 PM
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Hi Kepp,

You shouldn't have any problems focusing with that setup. I used to have my setup in the same orientation as yours minus the skylight filter.

What type of focal reducer are you using. F/6.3 or F/3.3?

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Old 29-01-2009, 02:08 PM
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Hi Kepp,

You shouldn't have any problems focusing with that setup. I used to have my setup in the same orientation as yours minus the skylight filter.

What type of focal reducer are you using. F/6.3 or F/3.3?

It also matters what type of camera you use Matty. The distance from the bayonet to the actual sensor plane (denoted by the circle with a line through it stamped on top of your body) differs between models and brands. My 350D is 49-odd mm whilst my Nikon's is only 41mm. My 350d won't work on my f6.3 reducer (which I suspect is what Keppar has) unless I use the shorter tube, whereas my Nikon's fine.
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Old 29-01-2009, 02:09 PM
keppar (Graham)
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Matt 6.3 .I thought I read somewhere that it is critical to have the correct distance from the focal reducer to the camera chip
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Old 29-01-2009, 02:10 PM
keppar (Graham)
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Gents I have a canon 40d
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Old 29-01-2009, 02:12 PM
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Kepp - what's that distance I spoke of on your camera - from the bayonet facing to the sensor plane mark?
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Old 29-01-2009, 02:14 PM
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Quote:
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It also matters what type of camera you use Matty. The distance from the bayonet to the actual sensor plane (denoted by the circle with a line through it stamped on top of your body) differs between models and brands. My 350D is 49-odd mm whilst my Nikon's is only 41mm. My 350d won't work on my f6.3 reducer (which I suspect is what Keppar has) unless I use the shorter tube, whereas my Nikon's fine.
Ah... I see. You learn something new everyday.

Thanks Chris.
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Old 29-01-2009, 02:17 PM
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Ah... I see. You learn something new everyday.
What's the 450's distance Matty?
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Old 29-01-2009, 02:24 PM
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What's the 450's distance Matty?
Approx 45mm.

I also just measured the distance from the sensor to the focal reducer as well. Which is 210mm. Might help?

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Old 29-01-2009, 02:34 PM
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What marker did you use on the casing of the reducer? Distance (I believe) is usually measured to the rear of the rear lens surface - which you can't see when it's all screwed in place.
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Old 29-01-2009, 02:53 PM
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I measured to the rear of the reducer (facing to the sensor). The line where it connects to the next adapter.

If that makes sense?

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Old 30-01-2009, 08:22 AM
keppar (Graham)
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Chris Mine measures 47mm
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Old 30-01-2009, 09:04 AM
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Chris Mine measures 47mm
OK - so 2mm shorter than the 350D. Your tube must be only a smidgen too long then. Did you give Bintel a buzz and ask about the tubes they have?
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Old 30-01-2009, 05:38 PM
keppar (Graham)
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Yea they are sending one that is only 20mm long the one I have now is approx 50 mm
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Old 30-01-2009, 06:16 PM
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While we are on the subject of distances. What is the ideal distance from the FR to the DSLR sensor?

I remember reading about it but don't recall.

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Old 30-01-2009, 08:57 PM
keppar (Graham)
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Matt dont quote me but I believe it was between 50 -75 mm
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