From: Alan Friedman <alan@greatarrow.com>

Date: August 27, 2009 1:33:31 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] gain vs frame rate [1 Attachment]

Hi Willie,

There are so many trade offs in imaging... use more selected frames to get better signal vs. less selected frames to maximize the sharpness of the data... Many of these cancel each other out, meaning that you can get the same results with both techniques. A complication is the seeing, which comes in many different flavors - some of which can be juggled by the software quite well while others others provide a real challenge to stacking and processing routines.

On gain settings, I am very often working at levels above 900 in Astro IIDC. The DMK mono camera noise is quite manageable at these levels in my opinion. It really depends on the seeing and the subject whether it makes sense to drop to a lower frame rate and slower shutter setting to improve the signal in the individual frames. 

best,

Alan

On Aug 27, 2009, at 2:56 PM, Willie Strickland wrote:

[Attachment(s) from Willie Strickland included below] 

Generally speaking, would it be better to go with lower gain and
settle for lower frame rate? I have been trying to get the highest
frame rate that I can and then adjusting the gain as needed.

For each filter, I increase the gain until I start to get saturated
pixels and then back it off 50 or so units. Then I click the Calc Avg
Sharpness button, then I capture 600-800 frames. I often grab 2 or 3
movies with each filter and always recalculate the average sharpness
just before capturing.

As to the Sharpness value, is 2 better than 5 or vice versa? I
thought maybe the smaller the sharpness value, the better the focus
and the smaller the range, the better the seeing. But looking back at
the movies, I am not sure. I just reread the pages that discuss
sharpness and didnt find a specific definition of sharpness value.

The example below is Jupiter with my DMK21AF04 on the .6m scope. I
usually do not get any moons in the frame unless they are quite close.

Willie Strickland
cwskas@earthlink.net

On Aug 20, 2009, at 10:09 AM, milton_aupperle wrote:

> Your STD96 value is higher than I mention, but you also have a much
> higher sharpness value range than I typically see (I'm used to 1 or
> 2, your getting 5), so you can expect higher STD. You likely had
> Jupiter filling the image?
>
> Your Brightness / Gains were fairly high (608 out of about 1024), so
> you likely need 100 to 300 frames to suppress the pixel noise,
> depending on how much sharpening you plan on doing after stacking.