Posts Made By: Jim Thommes

Jason,
Nice cluster. Your comments are interseting in that this one is one my list this year for a "revisit". I think I will try it at about 1600 mm.

Eric,
The image is nice. I agree with Jason on the smoothing - but that really only comes out on my monitor at high gamma. The Ha exposures really seem to highlight the star forming.

It does appear on my monitor as if the red is strong. Possibly the saturation may be a bit high as well.

Brian,
Looks pretty good. I'm not sure what there is to be unhappy about (except maybe you wanted to get color too 8) ).

Seriously though, background looks good, stars look good, Good resolution - Nice image.

Brian,
Great resolution - super image.

I tend to agree with Maurice - on my monitor the image seems biased a bit toward magenta. It made me wonder if you did the color exposures on different nights and if the conditions may have been variable. Also, your total time on green was low, but I assume you average (or median, or sigma combine) - in which case fewer subs are not variation of signal scale - just more or less noise. Now if you did a summing combine, there could be trouble.

Thanks for the comments folks!

Jason,
Congrats on the M13 shot. You had many challenges to confront - you did and as a result, produced your M13 image.

Floyd,
A really nice Image. M106 is one ov my favorites. You captured it (and all its friends) well.

I like your second image - I think it has better appeal than the first.

Hi Charles,
I'm here and I have scanned this thread a bit. Some answers are well provided. Here is my 2 cents worth...

I believe the best image comes from the recommended. In the case of the 0.63 x designs I belive that distance is 85 mm. These reducer focal lengths are about 230 mm. You could actually check this by holding your reducer in one hand and a ruler in the other over a flat matte surface on a moon lit night. Move the reducer up and down until you see the moon focus on the flat surface - use the ruler to measure the distance from the reducer to the surface.

The reduction you get when you use a reducer is:

reduction = 1 - (D / FL)

D is the distance to the focal plane, FL is the reducer's focal length.

So 1 - (85 / 230) = .63

What makes this distance optimal is the flatness correction at different wavelengths. My opinion is you will get best shaped stars at this distance. When you stray from this distance, you degrad from the optimum. My observation is that this degradation is gradual as you shorten the distance and more extreme as you lengthen the distance. Thus your f/7.8 may not be too discernable from the f/6.3. However, take it to f/5.0 or so and I think you will start to see bloated stars and poor shaped edge stars.

Tyler,
Yup, I like #2 much better - nice image.

Dietmar,
Nice image. This one is my target for my next session - I hope I can even get close to your image.

I have noticed too that while I have some clear nights in my part of the word, the seeing and wind seem to have gotten worse.