From: Milton Aupperle <milton@outcastsoft.com>
Date: April 22, 2010 2:31:55 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Flea 3 question about compatibility with AstroIIDC and gain considerations.
On 22-Apr-10, at 12:04 PM, doodlebun wrote:
In the past week a ground swell of excitement is building for the new PGR Flea3 camera.
Anthony Wesley (Bird) is singing the praises of this camera but he doesn't use Astro IIDC. He brought up a gain issue that I would like to hear some expert commentary by Milton before I spend $500+ for this camera. Straight from the horses mouth...
Ok, I've heard back from PGR about something I noticed on the Flea3, I didn't want to say too much before checking with them in case this interesting behaviour was going to somehow "go away" in future, but they seem happy enough with it.
The Flea3 officially supports gain values from -2db to 24db, *but* this can be easily bypassed and gain values up to 33.2db are possible. The image is amazingly bright at 33.2db and the background noise is still very low. This is a killer feature of the camera, but you need software that will know how to access this extra gain or else you'll see a limit of 24db.
Coriander under Linux supports the over-gain values as-is, and for Windows users I've emailed Torsten about adding support into Firecapture for it.
The way to access the exctra gain is very easy really - the camera control registers have two ways to set the gain, either a slider value from 0 to 762 that is mapped onto gain values between -2db and 24db, or using the "absolute value" registers where you write the actual gain value requested as a floating point number.
We don't currently support Absolute Gain registers in Astro IIDC. And each model has a different gain ranges too (my Grasshopper has gains from 64 to 746, my Flea has gains from 200 to 1023).
Also, we do check the expected range of all absolute registers and stick to those min max limits, so if the official upper limit is 24 db, then that's as far as it goes. I will not send out of spec values to camera registers.
In the second case, using the absolute value register for gain its possible to input values up to 33.2 and the camera responds accordingly :-)
I have a really hard time believing that having extra gain is a good thing. I'd also like to see how they "quantify" noise levels versus gain too. Is this some eyeballed guess or do they do multiple runs and correlate the results? Noise is the measure of randomness and all gain does is amplify that noise. So I don't see how increasing the gain above range limits is likely to be "magical".
I recently did a gain versus noise measurements on my Grasshopper (this takes the better part of a day to measure the curves and noise characteristics, I only measured noise up to mid point of gain range). Frankly the noise levels go up Astronomically once your above 350 gain (min gain is 64, Max gain is 746). At a gain value of 746 max, the brightness is amplified by 43.00 times over what the brightness is at 64 gain, but the noise is terrible and you need hundreds of frames stacked to compensate for this.
For DSO imaging, I have my Grasshopper gains at 251 which results in a 2.71 times increase i brightness and about a 2.5 times increase in noise level over what I get at 64. Going higher drastically increases the noise level unacceptably, so that I need to shoot more frames which increases the total exposure time and night time up here is rapidly decreasing (doesn't get dark here now until almost 10:30 pm).
Lastly, I don't know if Astro IIDC 4.05.04 or earlier will recognize a Flea 3 camera or not. It depends on what the internal model number is and PGR doesn't tell me anymore what those numbers are until after the camera is shipping and they finally get around to document them in their camera manuals. I have removed this checking in Astro IIDC 4.06. A1 so I don't have to wait for them to do it anymore. However I can't guarantee all their cameras work - some models are not IIDC Compliant - so that's on your head now.
HTH..
Milton Aupperle