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Forum: Pentax Medium Format
08-03-2015, 02:01 AM
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There were thin spots in the clouds last night. I set up on the tripod and took some 2 second snaps at f/4 ISO 2500. No stars visible, but there they were in the picture. They look fine except for the slight trailing, so I'm ok I think.
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Forum: Pentax Medium Format
08-01-2015, 11:16 PM
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I don't know. I was told by a vendor that there is an interaction between the lens and a body. In fact I did read in the manual that close focus issues are fixed by adjust 3 mirror screws in the body. My own tests indicate a lack of focus for objects 2m away, for example. Not a big deal. I don't need close focus, only infinity.
Bought the lens on Ebay and seems in near perfect shape. Flat frames look great, after some cleaning.
However if no sharp focus at infinity, it's useless to me. I can get a refund from Ebay, if I do it pretty soon. Of course, this is all academic without stars to test on. Clouds and more clouds.
---------- Post added 08-01-15 at 11:20 PM ----------
I'll be using a Nikon APC sensor. That may help. What f/stop did you find a sharp focus at? I'm reluctant to use the iris, but could cut a mask for it.
---------- Post added 08-01-15 at 11:23 PM ----------
There is a difference between the focus of something "far away" and a point source hundreds of light years away. My capture software will measure FWHM in real time. It only takes a very tiny error to be obvious in an astro photo. Hence my concern.
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Forum: Pentax Medium Format
07-31-2015, 09:51 PM
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I bought the lens with the intent of adapting it to my Nikon D5100 for wide field astro photography. . Seems to be nearly new and clean glass. Adapter is fine, using manual setting. I'll probably shoot at f/4. I have imaging software that will give the FWHM of a star to aid in focus. I realize that the closer than infinity focus requires a matching camera body. Not concerned with that, just infinity. Isn't it true that without a body the lens will default to infinity focus?
It's been cloudy for 3 months and no end in sight, so love to get this worry off my mind so I can keep or return the lens. Is there any way of adjusting the infinity stop a little if needs be? Imaging clouds, focus seems ok, but for those not familiar, FWHM on a star is extremely critical/accurate. -Thanks-Jack
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Forum: Welcomes and Introductions
07-31-2015, 04:49 AM
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Trying to count the galaxies in the Markarian's Chain image I gave up at 20. Of course stage 3 will fix the problems I see in this.
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Forum: Welcomes and Introductions
07-30-2015, 12:51 AM
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I like the KIIs, same sensor as my D5100. I just modified the sensor, removed the anti aliasing, and the color filter. Added a Baader astro conversion filter as the stock color filters eliminate light from the Hydrogen Alpha part of the spectrum which is needed for emission nebulae.
I started last May with astro -stage 1, DSLR on tripod. Milky way shot was one of the first.
Stage 2 added EQmount and GSO scope with auto guiding. Markarian's Chain image was from March, end of Stage 2. Then the skies closed out until maybe October.
Stage 3 in works now adding: plate solving, coma corrector, motor focuser, and the Pentax.
BTW any way I can help, I'm happy to.--Jack
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Forum: Welcomes and Introductions
07-29-2015, 05:32 AM
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Hi, I'm Jack. I live in N.E. Thailand. I've been a hobby photog for50 od years, obviously film mostly. Got a Nikon D5100 almost 2 years back and I love it. I've been doing astro photography about a year now. Warning the hobby will empty your wallet. If it doesn't, you aren't really into it ;-) . I just decided to do some wide field with my DSLR adapted to a Pentax SMC 67 IF 200mm. It won't quite reach focus at infinity, even hard on the stop. Love to find an adjustment for this, as those pesky stars are far.
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