Re: [APML] new galaxy shots

["Bobby Middleton" <bobm@koyote.com>]

Thanks to all who made comments on my new pics. I will respond to the many
questions from different list members below so look all the way through if
you asked me a question on these:

>From: Jeff Ball
> I am curious whether or not you picked up any visual
> differences in the two hypered films, 5 hour vs. 9 hour?  Did you notice
> any one film outperforming the other?

It's a little early to tell. I've only done a couple of nights with the 5
hour hyper and some of those are trailed due to the st-4 glitch so I really
didn't inspect those closely. I did have a bit of green color shift on the 2
earlier M-101 shots that were hypered 9 hours but they were also taken with
a crescent moon up low so that might be the reason for that. It was not
present on the 2 shots of m-101 hypered 5 hours but no moon either. With the
9 hour hyper times I often noticed a big cyan cast on a lot of shots done
last fall; haven't seen this with the 5 hour shots yet but again it's too
early to draw sound conclusions.

> From Pete Mumbower
> I am curious as to who made the primary mirror in the 12.5" ?

Pete it's a Jerry Wilkinson primary according to Tony Hallas who owned the
scope before me.

> From Mike Smith:
> I did notice a difference in color between M83 and the other two images.
> The HII regions in M101 are washed out and there is a cyan cast to the
> arms, while in M83 the HII regions are redder and the arms are have a
> magenta cast. I don't want to start another discussion on what constitutes
> true color in astronomical objects which can be difficult enough to
define,
> let alone reproduce, but I thought I would mention it.
> Also, are these full frame images?

Your diagnosis is quite correct and I have also noted these color shifts.
Don't know exactly where to point the finger.  The M-83 negs had a good
green color shift which I removed with photoshop. I get this green color
shift on southern low-horizon objects very often. Quite possibly the color
casts you see are a result of inconsistant color correction in processing on
my part. I sure don't have all that figured out yet if one can even figure
it all out anyway.

M-83 and M-104 are almost full frame; perhaps 10-15% cropped out. M-101 is
not; the 2 pairs of images were done 2 N-S and the other 2 E-W, so it's
close to only 1/2 frame after compositing the 2 sets.

Bobby Middleton
http://www.koyote.com/users/bobm/word.htm


--  APML Archives at <http://www.system.missouri.edu/apml/>  ---
                Unsubscribe at <majordomo@seds.org>