Steps of 0.1mm would work. Add one and recheck with a focus test shot. Check all 4 corners of the image. Then repeat until the elongated stars are round. The image takes on a definite sharper overall look when you get it right.
Yes the lens is worth it. If you plan on using a medium format camera you may need the Pentax 300mm 67 F4 EDIF lens instead. I tried my 645 lens on a FLI Proline 16803 and it gave poor stars in the corners so I used a smaller camera - FLI Microline 16200 APSh sensor and stars were good in the corners.
One of the better results:
https://pbase.com/gregbradley/image/167787458/large
Greg.
Quote:
Originally Posted by Astrofriend
Hi Greg,
Thanks for long detailed answer.
It's more the camera hanging on the lens. The camera is atached with an adapter to the lens. Each has some play, and even the lens have a play. Three different places, but I have a spring that press the camera against the lens to help get rid of the play. But even so there is a tilt.
You can see here:
http://www.astrofriend.eu/astronomy/...645-300ed.html
I will try to put in something on one side of the bayonet to find out how much shims I need, maybe steps of 0.1 mm, or ? But I can also 3D-Print something that hold it together with correct angle and have it adjustable.
I think the lens is good enough to spend that time on it. Or wath do you say ?
My plan is to buy a mirrorless medium format camera in the future. Then there isn't so much optics to choose from.
Lars |