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Roy Salisbury
sage
Reged: 05/26/09
Posts: 228
Loc: Las Vegas, NV
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I have noticed, and been semi-educated on the vignetting issues of using a focal reducer with my DSLR. I was using the standard Celestron F/6.3 at the time. I still use us for some things, but not as much as I did before.
I got to wondering, with the different FR's available (0.5, 0.63, 0.8, ect), what is the maximum FR that I "might" be able to use (in theory).
I need to get one for my AT66ED to flatten out the field a bit and have heard great things about the William Optics 0.8x version II (even if it is one of the most elusive things to find). Would this FR work ok on my CPC as well?
Roy
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Scope: Main - Celestron CPC 800 / Guide - AT66ED
Cameras: Canon EOS 500D DSLR / Orion Starshoot Autoguider / NexImage Webcam
EP's: Baader Hyperion 5mm, 8-24mm Zoom / Celestron 6, 9, 15, 32, 40, 2x Barlow, F6.3 Focal Reducer
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borix
super member
Reged: 04/24/07
Posts: 106
Loc: The Netherlands
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Here I go again plugging my topic. :-)
I tried the WO 0.8 type II reducer with a C9.25 and had (in my view) good results.
I still only used it one night (with the result posted) and I recon I am still a beginner. I hope more experienced users will also try it out and post their thoughts.
See here for my topic.
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Roy Salisbury
sage
Reged: 05/26/09
Posts: 228
Loc: Las Vegas, NV
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OK.. I read your thread. Not entirely the same question I was asking, but its close. I'm wondering what the max FR could be applied to a full frame DSLR so that no distorting happens (elongated stars on the edges and corners).
It looks like, from your images, that at least the filed stays flat in the .8x FR vs the .63x one. The color distortion can be semi-fixed with flats and post processing, but the flat field is what I am mainly looking for.
Roy
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Scope: Main - Celestron CPC 800 / Guide - AT66ED
Cameras: Canon EOS 500D DSLR / Orion Starshoot Autoguider / NexImage Webcam
EP's: Baader Hyperion 5mm, 8-24mm Zoom / Celestron 6, 9, 15, 32, 40, 2x Barlow, F6.3 Focal Reducer
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borix
super member
Reged: 04/24/07
Posts: 106
Loc: The Netherlands
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I do not know what max FR you can use with a full frame DSLR. I just tried to give some information about my experiences with the WO 0.8 FR and a SCT. If it works or not you have to decide for yourself - personally I will definitively use it again (when I get the chance).
Hope others will chime in to answer your question. 
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David Rosenthal
Carpal Tunnel
Reged: 06/23/06
Posts: 1645
Loc: NJ
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I use a William Optics 0.8X FR/FF with my Meade 8 in SCT and am quite pleased with the results. I have been using it for a copuple of years now with my DSLR and have not gone back to the 0.63 unless I want a wider capture.
The 0.8 vignetts much less than the 0.63 does. I tried the 0.33 with a DSLR for a laugh and it vignetted the field more than 50%
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David Rosenthal | Midland Park, NJ
My Image Gallery
http://www.EastCoastAstro.com
Atlas EQ-G EQMOD USBDIR [Self-Hypertuned]
8" Meade SCT | Borg 76ED | Takahashi FS-60C
Self Modded 400D | SX MX716 | DSI Pro | SPC900NC
Series 5000 26mm, Hyperion 17mm, TV 11mm Plossl
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Roy Salisbury
sage
Reged: 05/26/09
Posts: 228
Loc: Las Vegas, NV
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Ok.. two in favor of the WO .8x .. Now I just have to actually find one for sale someplace. These things are hard to find in stock anywhere .. and William Optics no longer sells them on there web site.
Roy
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Scope: Main - Celestron CPC 800 / Guide - AT66ED
Cameras: Canon EOS 500D DSLR / Orion Starshoot Autoguider / NexImage Webcam
EP's: Baader Hyperion 5mm, 8-24mm Zoom / Celestron 6, 9, 15, 32, 40, 2x Barlow, F6.3 Focal Reducer
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Miikka Sikkila
member
Reged: 04/22/09
Posts: 23
Loc: Finland
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Roy!
I use the Celestrons f/6,3 reducer and I'm quite happy with it. It works well with my 450D and 1000D cameras. Getting the f-ratio down will help your tracking with longer exposures. Comparing the CPC's native f/10 to the reducer f-lenght, the differences are dramatic. Also the FOV will allow you to shoot some wider filed photos. Don't know if you can use another, say 0,5x reducer, but you could try this.
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Every morning when the sun goes up, she brings me coffee in my favourite cup!
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Roy Salisbury
sage
Reged: 05/26/09
Posts: 228
Loc: Las Vegas, NV
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I'm starting to find some of the necessary information to answer my initial question so I thought I would update the thread.
First, I finally got a WO .08x FR off AstroMart (arrives today). Hopefully that will help out on my AT66ED.
The big thing that I noticed was that the focal reducers a very dependent on the distance from the lens to the imaging chip (the back of the FR to the front of the DSLR chip). The Celestron .63x is configured for 106mm and the WO .08x is set for 56mm. I found graph on the web that showed (for the .63) a scale of the focal reduction based on the distance to the chip. Basically, the shorter the distance, the less reduction.
I also found a formula that has been helpful:
(1 - (CCD-FR distance [mm] / FR focal length [mm]).
The FR focal length for the .63x is 285mm, and the .08x is 260mm.
Now, I have not been able to get exact numbers for the camera but from what I have read it is somewhere between 46 and 56 mm from the chip to the front of the camera housing. My T-Ring adds another 10mm. I'm going to go with the larger number (56mm) so that gives me 66mm that I can't do anything about. That means I need another 40mm for the T-Adapter. Guess what, my T-Adapter was 53mm .. for a total of 119mm ...
(1 - (119 / 285) = 0.58
So instead of a 0.63x reduction, I was actually doing a 0.58x reduction. Way too much it seems for my DSLR and scope (elongated stars and lots of vignetting). I have since replaced the T-Adapter with a 40mm adapter so I get the right distance. I'm going to try a few shots with that and see how it turns out. I'm also going to try getting a very short SCT-to-T-Ring adapter (about .8mm). Using that I should change the reduction down to about 0.8x.. I want to see if that removes the vignetting.
What I really need to know from one of the DSLR experts is what is the exact distance from the sensor to the front of the housing (46 to 56 is to much of a gap).
Also, can someone tell me how to calculate the actual imaging area that a FR may produce given a CPC800 and relate that to a DSLR sensor.
Thanks!
Roy
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Scope: Main - Celestron CPC 800 / Guide - AT66ED
Cameras: Canon EOS 500D DSLR / Orion Starshoot Autoguider / NexImage Webcam
EP's: Baader Hyperion 5mm, 8-24mm Zoom / Celestron 6, 9, 15, 32, 40, 2x Barlow, F6.3 Focal Reducer
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quantumac
sage
Reged: 12/17/07
Posts: 387
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Check out this "Focal Reducer Calculator". You can determine your optimal imager placement.
http://timosastro.1g.fi/tools/focalreducer.html
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Scope: Meade 10" LX200R
Guide/Planetary Camera: Imaging Source DBK41AF02.AS
DSO Camera: QHY8
Guide Hardware: Celestron OAG, Shoestring Astronomy GPUSB
Software: Mac OS X, Starry Night Pro, Nebulosity, PHD Guiding, PixInsight, Astro IIDC. No Windows anything.
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mclewis1
Thread Killer
Reged: 02/25/06
Posts: 3946
Loc: New Brunswick, Canada
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Canon DSLR sensor to the front of a T-ring is supposed to be 55-56mm so with the Celestron T-Adapter (50mm) you should get something around 106mm which is the maximum for the F6.3 reducer. Some folks run the reducer with a shorter T-Adapter (using an SCT - T thread adapter and some shorter T thread extensions) for a total of 85-90mm which means something in the .8x range of reduction.
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Mark
C11, C6, APM/TMB115, and AT80ED - Tandem mount CGE and CG-5A, WO EZ-Touch and AT Voyager
25x100s and 8x56s, T-Mount Light, Mark 1 eyeballs - Modded 350D, DSI-P, SPC900, Mallincam
Just because you can doesn't necessarily mean that you should
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Roy Salisbury
sage
Reged: 05/26/09
Posts: 228
Loc: Las Vegas, NV
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Quote:
Canon DSLR sensor to the front of a T-ring is supposed to be 55-56mm
Ok.. perhaps this is why I see both the 46 to 56 numbers... one is without the t-Ting, and one is with (because its 10mm).
Quote:
Some folks run the reducer with a shorter T-Adapter (using an SCT - T thread adapter and some shorter T thread extensions) for a total of 85-90mm which means something in the .8x range of reduction.
Yea.. That is what I am going to try and do.. Get a shorter distance between the FR and the sensor and see whats up. Then start increasing in small increments and see where the best spot is.
Roy
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Scope: Main - Celestron CPC 800 / Guide - AT66ED
Cameras: Canon EOS 500D DSLR / Orion Starshoot Autoguider / NexImage Webcam
EP's: Baader Hyperion 5mm, 8-24mm Zoom / Celestron 6, 9, 15, 32, 40, 2x Barlow, F6.3 Focal Reducer
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Roy Salisbury
sage
Reged: 05/26/09
Posts: 228
Loc: Las Vegas, NV
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Quote:
Check out this "Focal Reducer Calculator". You can determine your optimal imager placement.
http://timosastro.1g.fi/tools/focalreducer.html
I have seen this as well.. and not until just a minute ago did I notice that it has a "Width of the unvignetted field (imaging circle)" calculation as well. I'll have to look at it more closely.
Roy
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Scope: Main - Celestron CPC 800 / Guide - AT66ED
Cameras: Canon EOS 500D DSLR / Orion Starshoot Autoguider / NexImage Webcam
EP's: Baader Hyperion 5mm, 8-24mm Zoom / Celestron 6, 9, 15, 32, 40, 2x Barlow, F6.3 Focal Reducer
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