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Hi,
I answere you all here.
I have not try to use this lens or any other with external aperture in astronomy. But I have done that with old CRT projectors with positive results. I have done these late test at full aperture, earlier test at f/4 I see lot of "star rays" around brigth stars because of the aperture. With an external aperture this rays will be reduced.
My Sigma APO has better sharpness and also have motorfocus built in. Now when I have been used with the motorfocus and remote control from the smartphone I miss that when using the Pentax 67 lens.
I hope in future to have a sensor in full frame + size, then these Pentax medium format lenses will shine. But already now can I see the very low vignetting on a full frame sensor as a positive thing. And as you say, monochrome images and even better narrow band reduce the chromatic problem.
But for the moment I see this it as an interesting experiment. I will do more test later with this lens.
The Pentax 67 ED 300 lens I have read a lot positive thing about. Maybe I found a 300/400 mm ED f/4 lens in future.
Greg, nice photos you had with your 300 mm lens!
Lars
Last edited by Astrofriend; 04-11-2018 at 11:07 AM.
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