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Can Meade f/3.3 Focal Reducer fully illuminate QHY8?

KMLee

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Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« on: September 25, 2007, 11:33:11 AM »
Hello, can Meade f/3.3 Focal Reducer fully illuminate QHY8?

MMys

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #1 on: September 25, 2007, 03:42:08 PM »
No, it can't. Maximu perfect field with Meade SCTs is about 45mm, if you reduce it by 0.33 factor, you obtain field about 15mm in diameter, it is not for qhy8.

I think so 0.63x reducer is very tight for qhy8.
Vixen VC200L V.I.S.A.C., homemade Newton 185/610+Paracorr, Borg 77ED refractor,  optionally with EDF4 reducer, Modified EQ6 mount, Modified EOS 300D, QHY8 ccd camera, MII G2-8300 mono CCD camera, TVGuider.

KMLee

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #2 on: September 26, 2007, 10:39:10 AM »
What about a Optec NextGEN WideField 0.33X Telecompressor Lens? Is it the matter of factor or the size of the reducer?

MMys

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #3 on: September 27, 2007, 08:02:47 AM »
It will matter on field diameter before reduction and on factor. Reduccer size have influence only in case of vignetting (if reducer is less than original field diameter) In this case, there is slight wignenation, but main influence have factor 0,33x. You should have perfect field 84mm in diameter before reduction, to cover APS field after 0,33x reduction.
Vixen VC200L V.I.S.A.C., homemade Newton 185/610+Paracorr, Borg 77ED refractor,  optionally with EDF4 reducer, Modified EQ6 mount, Modified EOS 300D, QHY8 ccd camera, MII G2-8300 mono CCD camera, TVGuider.

KMLee

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #4 on: September 27, 2007, 08:30:02 AM »
It will matter on field diameter before reduction and on factor. Reduccer size have influence only in case of vignetting (if reducer is less than original field diameter) In this case, there is slight wignenation, but main influence have factor 0,33x. You should have perfect field 84mm in diameter before reduction, to cover APS field after 0,33x reduction.
So, the size of the reducer has to be at least slight larger than the CCD field size. And, the field at the back cell times the factor of the reducer has to be larger than the CCD size so that the field of the CCD will be fully illuminated?

I think the largest size of the common visual back of the SCT can be up to 51.8mm with Pete Peterson's Eyeopener II.

MMys

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #5 on: October 03, 2007, 07:25:31 AM »
yes, you are right. Thus QHY8 can not be fully illuminated. My friend tried this once with 10" SCT and 0,33x reducer on Canon 350D DSLR (APS-C size - same as QHY8) and he obtain about 15mm correct circle, around which level very fast falls into totally black image.
 
Vixen VC200L V.I.S.A.C., homemade Newton 185/610+Paracorr, Borg 77ED refractor,  optionally with EDF4 reducer, Modified EQ6 mount, Modified EOS 300D, QHY8 ccd camera, MII G2-8300 mono CCD camera, TVGuider.

KMLee

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #6 on: October 03, 2007, 10:23:25 AM »
yes, you are right. Thus QHY8 can not be fully illuminated. My friend tried this once with 10" SCT and 0,33x reducer on Canon 350D DSLR (APS-C size - same as QHY8) and he obtain about 15mm correct circle, around which level very fast falls into totally black image.
 
I see. What about 0.5x telecompressor?

Gama

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #7 on: October 05, 2007, 03:35:02 AM »
I use the Lumicon Giant reducer on my RCX400, and it works pretty good. It is a .6 reducer from memory.
It should better in a longer F ratio.

Theo.

KMLee

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #8 on: October 05, 2007, 06:23:46 AM »
I use the Lumicon Giant reducer on my RCX400, and it works pretty good. It is a .6 reducer from memory.
It should better in a longer F ratio.

Theo.

Thanks a lot for the reply!

KMLee

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #9 on: October 21, 2007, 09:32:57 AM »
Just found out that no focal reducer will work with QHY8. Even the Optec 0.7X focal reducer can only illuminate 18.5mm diagonally at best.

MMys

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #10 on: October 23, 2007, 01:47:30 PM »
Just found out that no focal reducer will work with QHY8. Even the Optec 0.7X focal reducer can only illuminate 18.5mm diagonally at best.

And what about 0,63 Meade reducer for SCT ? My friend was using it on fullframe film SLR, and there was vignetation only at corners. I looked at these images, and I think so APS-C must fit into illuminated are. There will be some slight vignetation, but not so high and will be corrected by using of flat field.
Vixen VC200L V.I.S.A.C., homemade Newton 185/610+Paracorr, Borg 77ED refractor,  optionally with EDF4 reducer, Modified EQ6 mount, Modified EOS 300D, QHY8 ccd camera, MII G2-8300 mono CCD camera, TVGuider.

KMLee

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #11 on: October 25, 2007, 07:51:14 AM »
Just found out that no focal reducer will work with QHY8. Even the Optec 0.7X focal reducer can only illuminate 18.5mm diagonally at best.

And what about 0,63 Meade reducer for SCT ? My friend was using it on fullframe film SLR, and there was vignetation only at corners. I looked at these images, and I think so APS-C must fit into illuminated are. There will be some slight vignetation, but not so high and will be corrected by using of flat field.
Hmm.. I can't seem to get the figure of the 0.63 Meade FF. Do you know its largest illumination field?

MMys

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #12 on: October 25, 2007, 04:12:19 PM »
You can measure it here:  http://foto.astronomy.cz/other/Xh_LX200_f63.jpg
it is image taken with 8" Meade LX200  SCT (f/10) with Meade 0.63x reducer on full frame film SLR.
Shadow and lack of stars in left lower corner is caused by Off-Axis guider mirror.

I think so APS sensor must fit into reasonable illuminated field with slight vignetation only.
Vixen VC200L V.I.S.A.C., homemade Newton 185/610+Paracorr, Borg 77ED refractor,  optionally with EDF4 reducer, Modified EQ6 mount, Modified EOS 300D, QHY8 ccd camera, MII G2-8300 mono CCD camera, TVGuider.

KMLee

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #13 on: October 26, 2007, 09:54:06 AM »
You can measure it here:  http://foto.astronomy.cz/other/Xh_LX200_f63.jpg
it is image taken with 8" Meade LX200  SCT (f/10) with Meade 0.63x reducer on full frame film SLR.
Shadow and lack of stars in left lower corner is caused by Off-Axis guider mirror.

I think so APS sensor must fit into reasonable illuminated field with slight vignetation only.
MMys, thanks for providing the fact. Could you let me know the algorithm? I haven't learnt any of this yet. :)

MMys

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Re: Can Meade f/3.3 Focal Reducer fully illuminate QHY8?
« Reply #14 on: October 26, 2007, 01:06:25 PM »
What algorithm do you mean  ???

Size of SLR film field is 24x36mm, and APS field approx. 24x16mm. You can print image (or display it on screen) in some suitable scale and measure field size without vignetation and aberations. Or you can draw rectangle 1.6 times proportionally smaller into image by any graphic editor, and check if  image is acceptable in this box.

I could make it quickly, but I'm not at home and I have nothing for doing it, and I have not acces for upload it to WEB server.

Try it yourself, or wait until Monday  ;)


Vixen VC200L V.I.S.A.C., homemade Newton 185/610+Paracorr, Borg 77ED refractor,  optionally with EDF4 reducer, Modified EQ6 mount, Modified EOS 300D, QHY8 ccd camera, MII G2-8300 mono CCD camera, TVGuider.