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SnaggS
member
Reged: 12/12/06
Posts: 64
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I have a Sky 90 and p2Z on order. For photo gear I have a FM3a and Tachihara 4x5 view camera.
* How big is the light cone on my Sky 90? Can I do medium format with it (I've got rolls of E100G in the fridge).
* I know that Tak make all sorts of accesories for imaging. Field flatener, something else to rotate the camera, flip mirrors etc. I just don't know what I need.
First thing I've already ordered is a piggy back mount for the tripod so I can start doing some widefield.
Daniel.
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ZachK
professor emeritus
Reged: 08/21/05
Posts: 667
Loc: Israel
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First of all read Suk's wide field article! also I have some notes over on my blog http://israeliskies.blogspot.com/
Right now the biggest question I have re Large format is which film to use. At some point I will buy boxes of the most probable brands and head to the negev to test them.
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Zach Kessin
Yesha Israel
Meade ETX 127 Mak-Cass
15x70 Celestron Skymaster Binoculars
Sinar F 4x5 view camera
Rolliflex Camera 80mm F2.8
Pentax K-1000 Camera 35,50 and 60--300mm zoom
3 kids, Large cat, small dog
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ZachK
professor emeritus
Reged: 08/21/05
Posts: 667
Loc: Israel
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Oh if you want a 4x5 ronchi grateing that you can put over your ground glass for focusing I have one. I haven't actually tried it yet.
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Zach Kessin
Yesha Israel
Meade ETX 127 Mak-Cass
15x70 Celestron Skymaster Binoculars
Sinar F 4x5 view camera
Rolliflex Camera 80mm F2.8
Pentax K-1000 Camera 35,50 and 60--300mm zoom
3 kids, Large cat, small dog
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SnaggS
member
Reged: 12/12/06
Posts: 64
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Just a question, wouldn't the stars just be at infinity focus? Wouldn't you just focus at something in the far distance while its light and use that?
Daniel.
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Takahashi Sky 90 on P2Z
Edmunds 4mm Ortho, 8mm RKE, 12mm RKE
Televue 24mm Panoptic
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ZachK
professor emeritus
Reged: 08/21/05
Posts: 667
Loc: Israel
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Yes the stars by definition are at infinity, but getting perfect focus can be a trick. And the ground glass can be kind of dim and hard to focus on. A larger lens helps (i have a 300mm F4.5 on order). The Ronchi grating (or a hartman mask/knife edge etc) uses an optical trick to get a perfect focus.
You can also just go out and take a loupe and play with the focus until you get a star as small as possible.
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Zach Kessin
Yesha Israel
Meade ETX 127 Mak-Cass
15x70 Celestron Skymaster Binoculars
Sinar F 4x5 view camera
Rolliflex Camera 80mm F2.8
Pentax K-1000 Camera 35,50 and 60--300mm zoom
3 kids, Large cat, small dog
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SnaggS
member
Reged: 12/12/06
Posts: 64
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I see in the Sky 90 system charts that it shows the Mamiya M645 as a option. I take it then that this won't vignette on the Sky 90?
Daniel.
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Takahashi Sky 90 on P2Z
Edmunds 4mm Ortho, 8mm RKE, 12mm RKE
Televue 24mm Panoptic
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ClownFish
Post Laureate
Reged: 04/26/05
Posts: 5600
Loc: Islamabad, Pakistan
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One thing about focus - precise focusing on an object with your own eyes, especially in daylight, is extremely difficult. Your eyes will refocus an out-of-focus image making you think you have found the perfect focus spot, when in reality you are not. On a daylight image, you can get away with a very tiny amount of mis-focus and not see much of a difference. Stars however, are not as forgiving. You can spot an out-of-focus star very easy, and if you enlarge the photo, you will notice the loss of details in extended objects too.
CF
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Learn all about POLAR ALIGNMENT with my Drift Method Tutorial and simulator!! Or visit my Foreign Service Blog!
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SnaggS
member
Reged: 12/12/06
Posts: 64
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Here is a question. If I mount my Mamiya 645 on the back of the scope. Do I still need a Ronchi grating to focus? Where do I get one and where do I put it 
Daniel.
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Takahashi Sky 90 on P2Z
Edmunds 4mm Ortho, 8mm RKE, 12mm RKE
Televue 24mm Panoptic
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