Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1330
Loc: Kiev, Ukraine
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Actually you don't need to illuminate 100% of DSLR chip. Some vignetting is OK and can be corrected with flat fields.
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fetoma
Pooh-Bah
Reged: 09/26/06
Posts: 1300
Loc: NW Ohio
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Dennis, what do you think the minimum 100% illumination dimension would be accceptable then with good flats?
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Frank in NW Ohio
Vixen CF VC200L and R200SS
Meade SN-10
Celestron 9.25" and 6" SCT's
Meade 8" f/6.3 SCT
Intes-Micro M73
Stellarvue 80/480 LOMO Triplet
William Optics FLT-110 w/TEC Lens
Starlight Instruments 12.5" RC
Takahashi FS-60C
Celestron CGE
FLI ML8300 w/CFW-2-7
Canon T1i
www.jerseydevilastronomy.com
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Moggi1964
Postmaster
Reged: 11/07/05
Posts: 3062
Loc: Madison. NJ. USA
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Maybe another Rosin candidate?
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Morris
WO110 w/TEC lens
WO80EDII and 66SD
Astrosystems Telekit 10" with F/6 JC Wilkinson mirror
Seymor Rosin F/4.5 Astrograph in the making
Criterion RV6 - July 1974
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fetoma
Pooh-Bah
Reged: 09/26/06
Posts: 1300
Loc: NW Ohio
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Morris,
The mirror is Parabolic.
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Frank in NW Ohio
Vixen CF VC200L and R200SS
Meade SN-10
Celestron 9.25" and 6" SCT's
Meade 8" f/6.3 SCT
Intes-Micro M73
Stellarvue 80/480 LOMO Triplet
William Optics FLT-110 w/TEC Lens
Starlight Instruments 12.5" RC
Takahashi FS-60C
Celestron CGE
FLI ML8300 w/CFW-2-7
Canon T1i
www.jerseydevilastronomy.com
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Moggi1964
Postmaster
Reged: 11/07/05
Posts: 3062
Loc: Madison. NJ. USA
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Actually, looking at it a Brit might describe it as:
"partly bolloxed" 
I get your drift though.
It's going to be a great system that it ends up being hooked to. Can't wait to see it take shape Frank.
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Morris
WO110 w/TEC lens
WO80EDII and 66SD
Astrosystems Telekit 10" with F/6 JC Wilkinson mirror
Seymor Rosin F/4.5 Astrograph in the making
Criterion RV6 - July 1974
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1330
Loc: Kiev, Ukraine
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Given DSLR size of 22.5x15vv I would say that 10mm fully illuminated circle is more than enough. It will fall off after that but not that dramatically. 15mm would be better, but it will require larger secondary mirror, low profile focuser, etc. Everything depends on your buget. If you can afford Clements focuser, 3" corrector, etc. than it's probably the way to go. If no, than pick GSO Low Profile focuser, MPCC or Paracorr and have fun
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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I would prefer a minimum of a 20mm image circle. This would not require that much of a larger secondary, and a stock Feathertouch 2" could still be used. ANYTHING one can do to reduce the need for flats is a good thing. Most imagers will tell you that a correctly illuminated FOV should mean you need flats only for correction of dust and dirt.
JMO's
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1330
Loc: Kiev, Ukraine
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I would say that too Still flats are required.
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1330
Loc: Kiev, Ukraine
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All I want to say is that try to get field as much as possible without radical measures (like 3" focuser) and everything will be good.
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fetoma
Pooh-Bah
Reged: 09/26/06
Posts: 1300
Loc: NW Ohio
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OK Bobby, I know you've done lots of imaging with the Canon DSLR and you say the minimum image circle has to be 20mm, so what would the optimum image circle be?
Dennis, what do you mean by "fall off"? Anything over a 15mm image circle, which is the width of the chip, is going to be lost anyway, correct?
I would need an image circle of 27mm to cover the chip diagonally, so that would be alot of wasted area not even covered by the chip, correct?
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Frank in NW Ohio
Vixen CF VC200L and R200SS
Meade SN-10
Celestron 9.25" and 6" SCT's
Meade 8" f/6.3 SCT
Intes-Micro M73
Stellarvue 80/480 LOMO Triplet
William Optics FLT-110 w/TEC Lens
Starlight Instruments 12.5" RC
Takahashi FS-60C
Celestron CGE
FLI ML8300 w/CFW-2-7
Canon T1i
www.jerseydevilastronomy.com
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1330
Loc: Kiev, Ukraine
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It there was about illumination, which is not clear from the context. Sorry. I meant that illumination will drop after the fully illuminated circle. I wonder if anyone can calculate how much you loose on the border of the chip with 10mm, 15mm, 20mm full illuminated circle.
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