In my experience, the best way to focus is to use LiveView, zoom the
screen in on a star, and use manual focus. Correct focus is never at the
lens' infinity setting. :-)
Jostein
Den 04.12.2016 22.50, skrev Larry Colen:
Igor PDML-StR wrote:
Larry,
I haven't done much of astro-photography, so, I am just
curious: why focusing at infinity wouldn't work in this case
(i.e. turning the focusing ring to the end of the range)?
Is it just because the particular lens(es) are not designed or
manufactured well for infinity focus? (E.g. they have "beyond infinity"
focus at the end of the wring range.)
Exactly. I've been told that "to infinity and beyond" is necessary for
autofocus, although that doesn't seem true for my FA77. I suspect that
it's just a lot less expensive to guarantee that a camera will focus
past infinity than to carefully calibrate to go exactly to infinity. I
wonder how much sample variation there is in registration distance
between the mount and the sensor, as that would also affect the
"infinity focus point".
Igor
Larry Colen Sun, 04 Dec 2016 11:49:18 -0800 wrote:
Jostein wrote:
Your results are on par with what I've got from single exposures with
the Sigma 500/4.5. Proper focusing seems to be the limiting factor
rather than actual MTF resolution.
Yes, focusing was a real challenge. If I remember to bring my green
laser, I can aim that at a distant point and have something to focus on.
I probably should have tried focusing on Sirius, it was a lot brighter.
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