From: "Tim" <tjp314@pacbell.net>

Date: October 21, 2005 3:36:26 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: some thoughts on sampling

Alan:

This is very useful.  When you posted your inital post about this a couple days ago (?), I 

had a flash of "aha!" when I remembered a similar experiment I did about 5 years ago with 

my Jaegers 6" f/10 and Starlight Xpress HX516 on Jupiter.  First, I had to find the best 

wavelength to maximize contrast.  For Jupiter, a green filter gave me the best results by 

far.  I had limited options at the time in the way of barlow projections - I had a Televue 

2.5x and a cheap Meade 3x (one of those with about a 6" extension tube that I picked up 

new at RTMC for ten bucks!).  As I recall, the image scales through both worked out about 

the same - 1/3" per pixel.  I tried a few eyepiece projection options to vary that scale, but 

1/3" per pixel on Jupiter produced by far the sharpest results using Maxim's deconvolution 

filters on stacks of about a half dozen frames.  

I remember many years ago marveling that folks like Don Parker were imaging at 1/4" per 

pixel, and in some cases (particularly  in the past 5 years or so), people were imaging at 

up to 1/10" per pixel.  

Anyway, after your post about this, I did the math on my latest stuff and realized that I was 

shooting at less than 1/8" per pixel.  Like you, I think that's pushing it for the poor seeing 

I've had mostly of late, so I'm going to try to drop down closer to 1/4" and see how that 

works (I'm also thinking of breaking out the Jaegers on the NJP, as I recently mounted a 

dovetail plate on it so I can do that!).

But it's amazing that I'd forgotten to try different values.  Probably because the Flea is so 

much more sensitive than the Aplux or ToUcam, I thought I could keep working at that 

scale.  

It didn't even occur to me that was my problem after trying all the processing software I'm 

familiar with - Registax, Keith's IS, Lynkeos, and of course Astro IIDC.  Results for all of 

these were pretty similar, though Keith's and Astro IIDC produced noticeably best results.  

And for Registax, since I'm processing video's through Virtual PC, I have to first crop them 

to 320x240 with AstroYacker and convert them to AVI with Quicktime Pro before I can run 

Registax.  

best,

-Tim Parker

--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@g...> wrote:

I thought I would post this note I sent in response to a question that 

came up at a recent presentation on my set-up for planetary imaging. - 

Alan

At the meeting last week, Dennis asked a question which I didn't have

 an accurate answer for - what is the sampling ratio of my planetary

 set-up. For you non-ccders, this is a measure of the physical

 resolution of the set-up expressed in the number of pixels used to

 cover a one arc second slice of the subject.

 I had a chance (rather a need, the seeing was poor each time I went

 out) this week to try out a few different settings and measure the

 results. Mars was just a shade under 20 arc seconds in diameter so the

 math was easy!

 My usual set-up uses the 10" f14.6 scope with a Baader FFC (a fancy

 flourite barlow) followed by a filterwheel and camera, which yields

 about f48. I've had some good luck on good nights with this set-up for

 saturn and jupiter. At this setting mars is recorded with 250 pixels -

 .08"/pixel (or, 12.5 pixels/arc second)

 For the Oct 19 mars dust image I used an old A/P 2X barlow in front of

 the filter wheel yielding about f29, or .13"/pixel (or 7.5 pixels/arc

 second).

 For the mars image from this morning I used a 1.5" extension between

 the barlow and the filterwheel bringing the system to f34, or

 .11"/pixel (or 8.75 pixels/arc second).

 My initial impressions - f48 is probably too much magnification for the

 usual 4-6/10 seeing around here. Comparing the f29 and f48 streams I

 found I could get a tiny bit more detail if I selected and aligned the

 f48 frames by hand. But I might also be able to achieve this if I took

 that time on the f29 frames. As it was, I was able to get good auto

 stacking results at f29 and complete the entire LRGB image in about an

 hour.

 Remember that the albedo detail on mars is low contrast - the moon

 would be a different story. On almost any decent night the longer

 effective focal length would capture additional detail on the moon. But

 on mars, the f29 was just about as good - with much easier focusing

 because of the higher contrast image. I was also able to completely

 select, align and stack using automated software because of the

 predictable character of the sharp images at the lower magnification

 (the big images are softer and can fool the software into a poor

 selection of the best frames.)

 Overall - I think f34 is a good compromise and probably about perfect

 for all but the best nights in WNY.

 This is a long ramble - I hope some of you find it useful.

 cheers-

 Alan