Re: [APML] Reducing Coma

[Roland Roberts <roland@astrofoto.org>]

>>>>> "Bobby" == Bobby Middleton <bobm@koyote.com> writes:

    >> Roland Roberts wrote:
    >> > I was just hoping someone could chime in with personal
    >> > experience or a knowledge of optics that said "yes, it
    >> > does/sometimes helps."

    Bobby> It will definately help. It's a matter of the geometry of
    Bobby> the light cone.

Great!  I think next week I'll take the first good night and try
shooting a roll of Fuji Press 1600 to test the lens at different
stops.  I shot a test roll last month and the film seems to do well
enough with exposures out to about 5-minutes (which is as long as I
tried for my lens test).  It's grainy, but I don't really care for
lens testing.

    >> Perhaps some of the much more knowlegable will weigh in here,

    Bobby> Just because a lens is expensive doesn't mean that it will
    Bobby> be a good astro lens but you can pretty much bet that if
    Bobby> it's cheap it WON'T be a good astro lens.  The exception to
    Bobby> this are the 50mm lenses. They're not too expensive anyway
    Bobby> and some Nikon and Canon lenses 50mm lenses are considered
    Bobby> good.  Check the archives; there's lots of lens talk in
    Bobby> there.  I know Nikons pretty well; the 50mm f/1.4 is good;
    Bobby> so is the older 105mm f/2.5. The 180mm f/2.8 is good but
    Bobby> will cost $250+ used.  Vignetting plus spherical and
    Bobby> chromatic abberation are the key issues.

I've been pleasantly surprised with all of my Pentax K-mount lenses in
that once stopped down two stops they seem to work quite well.  And
none of them have show lateral chromatic aberration, unlike my older
screw-mount lenses.

I've wondered if it is worth money in the long run to buy Nikon or
Canon equipment; Nikon seems to have a good reputation for nice glass
and some fast lenses.  

roland
-- 
		       PGP Key ID: 66 BC 3B CD
Roland B. Roberts, PhD                             RL Enterprises
roland@rlenter.com                     76-15 113th Street, Apt 3B
roland@astrofoto.org                       Forest Hills, NY 11375

--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>