From: Milton Aupperle <milton@outcastsoft.com>

Date: March 27, 2012 2:45:46 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Venus True/False

Hi Alan;

On 27-Mar-12, at 1:29 PM, Alan Friedman wrote:

Thanks for the feedback, Milton. I did experiment with 2x2 binning and it does help with the exposure, but the stacked results were not as good as 1x1. I didn't try 16 bit capture mode. The detail is so minimal, it seemed that 256 gradations were enough. I do use 16bit most of the time for solar imaging where there is huge dynamic range to capture.

Try 16 bit next time, especially with darker images like the one you showed. That 8 bit image only has a range of 20 to 73 (out of 255 shades). So you only have 53 gray tones to work with in 8 bit. If it had been 16 bit, you would have had at least 13,568 gray shades - and that's before stacking. You likely would not need as many frames either to remove the noise.

Also 2x2 binning in 16 bit likely will produce better results, as it has more shades to work with.

Your suggestion to image Venus in daytime is right on the money. The seeing with 2 hours or so of sunset is some of the best of the day.. It's amazing how it falls off almost immediately after sunset.

Great. If it ever clears up here, I'll give it a try.

TTYL..

Milton Aupperle

best,

Alan

< /div>

On Mar 27, 2012, at 2:09 PM, Milton Aupperle wrote:

Hi Alan;

Thanks for the details.

That is quite a noisy image, but with a bit of processing, you can see

all the features you show in your stacked image.

Are you shooting in 8 bit or 16 bit? 16 will give better gradations.

Since Venus doesn't have fine (< 2 pixel width) details, you might

want to experiment using Mono 2x2 binning, which will give you roughly

4 times increase in brightness. So you could reduce the Brightness

(Gain) and / or increase the frame rate too.

Also the software binning does not reduce image size, so the image

scale remains the same.

HTH..

Milton Aupperle

On 27-Mar-12, at 11:36 AM, Alan Friedman wrote:

> Thanks Milton,

> The bright regions represent the highest albedo in the cloud tops...

> though beyond this I don't know. I did find that the cloud rotation

> is quite fast... obvious movement is seen in 30 minutes. As you've

> guessed, the data is shot at high gain and is quite noisy. One has

> to take as many frames as possible in a short time span. I used both

> 33ms and 66ms shutter settings. 33 required maximum brightness and

> the frames were still quite dim. 66 could be used with the

> brightness slider setting down to 640, though the resulting frames

> were softer. Here is a single frame from one of the 33ms streams:

> http://www.avertedimagination.com/images/33_1.jpg

> best,

> Alan

> On Mar 27, 2012, at 1:19 PM, Milton Aupperle wrote:

Milton J. Aupperle

President

ASC - Aupperle Services and Contracting

Mac Software (Drivers, Components and Application) Specialist

#1106 - 428 Chaparral Ravine View SE.

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1-(403)-453-1624

milton@outcastsoft.com