extremez
member
Reged: 03/10/07
Posts: 99
Loc: South Glens Falls, NY
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I plan on purchasing the Stiletto deluxe for imaging with the C8(working on getting a smaller refractor and guiding setup, but funds are limited at the moment)
My question is while i have my XT piggybacked on my C8 with my regular lenses, what aids or utilities can I use for focusing, aside from plugging into a monitor and shoot,focus,shoot,focus etc...? I've been taking some images and the stars look bloated with blue halos. I'm guessing my focus isn't on.
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I'm a newbie and loving it!!
C8-SGT XLT w/ CG-5 mount
William Optics ZenithStar 80
Orion ShortTube 80(guide scope)
Canon Rebel XT unmodded/XSI unmodded
Orion Starshoot Autoguider
Philips SPC900NC webcam
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FoxK
Carpal Tunnel
Reged: 11/07/07
Posts: 2662
Loc: Cape Cod, MA
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A "hartmann" mask works well....especially on scopes with a big aperture.
http://www.astropix.com/HTML/I_ASTROP/FOCUS/METHODS.HTM
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Orion 80mm ED Apo Refractor
8" Classic Dob (used as Newtonian on CG5 mount)
Meade 70-AZ-A 70mm Guider using PHD
LS60TCaK/B600/C
CG-5 Advanced GT Mount
Nikon D40x with T-Adaptors
Philips SPC900NC(1/4"ccd)& Quickcam 9000(1/3"CMOS)
Imaging Source DMK 21AU04.AS
- click for cloud prediction for Plymouth, MA. area
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extremez
member
Reged: 03/10/07
Posts: 99
Loc: South Glens Falls, NY
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i won't be using the telescope as the lens. I'll be using my 17-55mm Tamron or Canon 70-300mm. unless there's such a thing as a mini hartmann for dslr lenses. I'm assuming something like dslrfocus or images plus might work. is this right? or even a right angle magnifying viewfinder?
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I'm a newbie and loving it!!
C8-SGT XLT w/ CG-5 mount
William Optics ZenithStar 80
Orion ShortTube 80(guide scope)
Canon Rebel XT unmodded/XSI unmodded
Orion Starshoot Autoguider
Philips SPC900NC webcam
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adrenalynn
member
Reged: 11/01/07
Posts: 25
Loc: Folsom, CA, USA
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You can certainly make a Hartmann mask for a DSLR lens. I use a home-made one on my Tamron 500mm all the time.
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NexStar 5
Original Orion 10" Dob
Canon 20D [unmodified], piggyback and prime focus
Canon A630 (afocal / through-the-EP)
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FoxK
Carpal Tunnel
Reged: 11/07/07
Posts: 2662
Loc: Cape Cod, MA
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Try the cheap alternatives first...I wonder if you can make a mini hartmann lol..i don't see why it wouldn't work....keep in mind that you'd have to find a pretty bright object, but Mars is handy for that these days.
I've heard good things regarding DSLR focus, though its widely used in telescope imagery with a DSLR...good luck and clr skies
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Orion 80mm ED Apo Refractor
8" Classic Dob (used as Newtonian on CG5 mount)
Meade 70-AZ-A 70mm Guider using PHD
LS60TCaK/B600/C
CG-5 Advanced GT Mount
Nikon D40x with T-Adaptors
Philips SPC900NC(1/4"ccd)& Quickcam 9000(1/3"CMOS)
Imaging Source DMK 21AU04.AS
- click for cloud prediction for Plymouth, MA. area
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jgraham
Postmaster
Reged: 12/02/04
Posts: 6764
Loc: Dayton, Ohio
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When using my 17-55 I set the focus on a distant street light using the auto-focus, then swtich to manual to keep it from changing. With my 70-300 I found I can set the focus at 300mm using auto-focus and a bright star (I used Mars last night), then switch to manual and shorten the focal length up to 100mm for wide field imaging. Another thing I'm set up to try is I set the focus of my 17-55 at 55mm on a distant antenna in daylight and marked the barrel of the lens. In theory I might be able to reset the focus using the mark at night. We'll see, I haven't had a chance to test it yet as I've been experimenting with my 70-300 for the past couple of nights.
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-John
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Homebuilt scopes from 4.25-16.5"
Meade LXD75-N6/SN6/SC8, DSX-90, ETX-60BB, ETX-125PE, DS-2130
Orion StarBlast, BinoViewers, Coronado PST
Rebel XT/XTi, DSI Pro (I, II, & III), DSI, LPI, Electronic Eyepiece, Phillips SPC900NC
Tasco 60mm Refractors
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RobTaylor
sage
Reged: 08/22/04
Posts: 447
Loc: Salt Lake, UT
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I've had a lot of luck just setting the lens on the infinity mark and using manual focus. As long as you have a little f/stop like 2.8 to 4.5 to play with you should be pretty good. I use a simple rubber band to deal with lens creep on one lens I have the tends to shift when I point it up.
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Bob Taylor
Orion 80ED & SVP EQ
8" Reflector & Atlas GoTo
16" f/4.45 Dob
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rockace521
sage
Reged: 09/21/06
Posts: 298
Loc: Waco, TX
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Quote:
I've had a lot of luck just setting the lens on the infinity mark and using manual focus. As long as you have a little f/stop like 2.8 to 4.5 to play with you should be pretty good. I use a simple rubber band to deal with lens creep on one lens I have the tends to shift when I point it up.
Ditto that. It may take a couple or 3 tries to get it good and sharp, just zoom all the way in (if possible) on the image to see how sharp your target is. Some lenses have their focus just past infinity, but start out in the neighborhood of infinity and work from there, you'll be good.
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Joel
8" Celestron SCT
SV80S
Atlas EQ-G
40D/Modded 20D/DSI Pro
no pictures to speak of...
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2020BC
scholastic sledgehammer
Reged: 08/03/05
Posts: 900
Loc: Australia
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Without using live-view or autofocus the easiest way to get a good focus with SLR lenses is to do this (click here)
If you're using the standard lenses that came with the Canon XT you'll definitely get star bloat because those lenses aren't the best for astrophotography. Stopping them down to f4 or lower helps but only a bit. You'll always get blue halos around stars with those lenses.
Strongly suggest that you purchase the Canon 50mm f1.8 EF II ($US 90) and stop it down to f/4. That little lens will let you do stuff like this (click here) Most of my widefields have been taken using this focusing technique. I use a magnifying glass to check that my focus marks are aligned and it takes all of a couple of minutes to get good focus. A bit of blutac completes the job to hold focus for the whole night 
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There's no hiding the decline...
EQ-6 SN8; Baader MPCC Coma Corrector
Orion 80ED; WO x0.8 Field Flattener
Mintron 62V1P-Ex; & 13V1C Video & DMK 21AU04.AS
Canon Digital Rebel 350D DSLR (50mm f1.8 & 200mm f2.8L USM II) and a bunch of other stuff.
Visit My Website
Edited by 2020BC (01/06/08 02:55 AM)
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Rat8bug
Pooh-Bah
Reged: 01/07/05
Posts: 1472
Loc: Michigan
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I have found that an angle finder works quite well, focusing on a brighter star....
http://www.barrie-tao.com/d70finder.html
Ciao....Barry
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Nikon D40/D50/D70 DSLR
WO 105mm Triplet APO
WO Zenithstar 66SD APO (Black 'n Blue)
WO 8 x 45mm APO Bino
UO 20 x 80mm Bino
Vixen 80SS Refractor
Orion 127mm Apex Maksutov
Vixen GP-DX with Skysensor 2000
SBIG STV and e-finder
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extremez
member
Reged: 03/10/07
Posts: 99
Loc: South Glens Falls, NY
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Bob and Joel - I've tried that but both lenses go beyond infinty and bringing them back and achieving focus seems difficult for me. It turns into a constant back,forward,back,etc...
2020BC - I'm using the same lens you have 75-300. I misquoted the FL above. do you image with that lens and experience the same halos?
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I'm a newbie and loving it!!
C8-SGT XLT w/ CG-5 mount
William Optics ZenithStar 80
Orion ShortTube 80(guide scope)
Canon Rebel XT unmodded/XSI unmodded
Orion Starshoot Autoguider
Philips SPC900NC webcam
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extremez
member
Reged: 03/10/07
Posts: 99
Loc: South Glens Falls, NY
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Check these out. I'll see how they do on my next session.
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2101593/page/0/view/collapsed/sb/5/o/all/fpart/1
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I'm a newbie and loving it!!
C8-SGT XLT w/ CG-5 mount
William Optics ZenithStar 80
Orion ShortTube 80(guide scope)
Canon Rebel XT unmodded/XSI unmodded
Orion Starshoot Autoguider
Philips SPC900NC webcam
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jgraham
Postmaster
Reged: 12/02/04
Posts: 6764
Loc: Dayton, Ohio
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I'm going to have to give the little focusing mask a try. I've been using an old trick we used to use in the days of 35mm SLR photography; when using a zoom lens we'd set the focus with the lens set at its maximum focal length, then shorten it up, that way you were sure you had the best focus. This has worked well for me using my EF 75-300 focussing on a bright star at 300mm using autofocus, switching to manual focus to keep if from changing, then shortening the focal length up to 100mm (or so). Still, I'd like to try the mask at 300mm to see how well is works.
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-John
================================================
Homebuilt scopes from 4.25-16.5"
Meade LXD75-N6/SN6/SC8, DSX-90, ETX-60BB, ETX-125PE, DS-2130
Orion StarBlast, BinoViewers, Coronado PST
Rebel XT/XTi, DSI Pro (I, II, & III), DSI, LPI, Electronic Eyepiece, Phillips SPC900NC
Tasco 60mm Refractors
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PGW Steve
professor emeritus
Reged: 10/03/06
Posts: 632
Loc: Winnipeg, Canada
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None of my Canon lenses are parafocal in that I can change the focal length without the focus going bad. If I change the FL, I have to refocus. With the 40D this is no longer a problem with live view.
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A-P 1200GTO - On the list for a Mach1GTO
14" LX200R OTA
FSQ106ED Tak .75 reducer +1.6 extender
WO Megrez 80mm 600mm triplet APO
WO ZenithStar 66 Triplet ED APO
EQ 6 PRO, HEQ-5 PRO
Astrotrac TT320, Manfrotto 475&488
DSI PRO II W/filters, Orion SSAG
Hutech 40D and Unmodded EOS 40D
16-35mm f2.8L II, 24-70mm f2.8L,70-200mm f2.8L IS 300mmf4.L, 400mmf5.6L
31T5,22T4,13E,9T6,8E,5T6,3.5T6
5’X8’ Wells Cargo trailer to haul it in!!!
Edited by PGW Steve (01/06/08 10:08 PM)
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RobTaylor
sage
Reged: 08/22/04
Posts: 447
Loc: Salt Lake, UT
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On some lenses the infinity mark is not exactly infinity, it may be slightly before or slightly after. All lenses will go past infinifty to provide a saftey margin for the mechanics. Try a long focus in daylight at a high contrast target well off in the distance so you know exactly where infinity is on that lens, the Moon is another good target to see where inifinity is for a given lens. I also recommend something like f/4 rather than f/2.8. But in general starting with the infinity mark and f/4 is good starting point.
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Bob Taylor
Orion 80ED & SVP EQ
8" Reflector & Atlas GoTo
16" f/4.45 Dob
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