Old 12-06-2010, 04:54 AM
astrospotter (Mark)
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How evil is an f/6.3 reducer?

This is a re-post I had on begining astrophotography which may be better in this area as it may be just above a beginner topic perhaps.

I have a williams optics FLT110 f/6.5 APO with the WO 0.8 field flattener. This is collecting photons into a Canon 40d and does this job as well as can be expected. Now I seek broader field of view with same scope.

What sort of evil things will happen to the image if I try to use a Celestron f/6.3 focal reducer between the 40D and the field flattener?

I would expect the image gets warped to some extent but if I don't stitch mosaics is it not warped so badly as to still generate fair results for single frame sized shots?

Does the the reducer re-introduce gobs of chromatic garbage in the corners?

Do the corners become un-usable due to focus?

Does it 'just work' and I am over-analyzing this? (doubt this is the case).

Now if you don't think I am insane just yet, how about the same trick with a Meade f/3.3 focal reducer (it is ok to laugh, I can take it).

Thanks for any knowledgeable replies from anybody who has actually tried this OR knows the direct results of someone who has actually tried this. I know the image will suffer, just don't have a feel for how much yet.

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Old 12-06-2010, 05:16 AM
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riklaunim is offline
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f 3.3 reducer provides only 9mm corrected circle. f 6.3 is designed to iluminate APS-C sensor (DSLR). Optimal distance to sensor is 105 mm. I've seen few images of setup where it is used with a refractor.
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Old 12-06-2010, 08:04 AM
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gbeal is offline
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I haven't tried it, but am looking at it from a different direction to what you are perhaps.
Unless I am mistaken, the reducer/correctors you mention are designed for an SCT style of scope, and as such are not suitable at all for the refractor. Each has it's own set of requirements in a reducer or corrector, and I guess using a SCT unit on a refractor will result in "unusual effects" over the image, and especially at the corners.
My suggestion is to continue with the W/O unit you are currently using, and if you want wider, simply get a shorter focal length scope.
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Old 12-06-2010, 08:52 AM
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[1ponders] (Paul)
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Check the review articles. I did a review on the 6.3s (celestron and meade) on and ED80. Not very impressive at all.

BTW there was at least one batch or 6.3 that are asticmatic. The one I have is unfortunately from that batch. It wasn't used in the ED test though.
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Old 12-06-2010, 03:42 PM
astrospotter (Mark)
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Thanks for inputs

Sounds like it is a no-go. Yes the f/6.3 is made for SCT and that is what I used it for as 11" SCT for a few years because the SCT has a mighty narrow FOV with such high focal length.

Also thanks for input on 80mm actual tests.

Only if there were a reducer meant for this WO f/6.5 scope would it have a nice optical match is my take away (shy of 'just buy a new scope')

Thanks all,
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