From: Milton Aupperle <milton@outcastsoft.com>
Date: January 22, 2010 2:53:38 PM MST
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Re: 12 bits vs 60 fps, which is better?
Hi Dave;
On 22-Jan-10, at 2:08 PM, doodlebun wrote:
Thanks for your thoughts Milton. I thought the only available frame rates are 30 and 60 fps because thats all that shows in the drop down menu under standard 8 bit. I do see the Format 7 modes in the drop down menu but I am clueless as to how to use it properly. The modes as I understand it will capture at a user defined ROI at intermediate rates that will be selectable in the fps field of Astro IIDC. The use of ROI is tempting but I need the image to stay in the restricted area which can be tough depending on conditions.
Format 7 is a mess for what frame rates are supported. It's based on packet sizes and the packet sizes usually changes for each ROI size used. We would need to use a completely different interface to fully make use of it and it would raise a tonne of support questions and be confusing as all hell to support.
This results in having really odd frame rates like 53.6674567 one time, then decrease ROI by say 8 pixels and it may jump to 69.4567 fps when you next look at the frame rate. And it varies by manufacturer, camera model and CCD in it too (well also firmware load too, when they change the Micro Controller / CPU / FPGA code).
So we shoe horn Format 7 into the existing range of FPS and make it as close as possible to the expected. So if you select say 60 fps for Camera Frame rate for FMT7 cameras, the delivered frame rates is somewhere between > 30 and <= 60 fps, usually as close to 60 as possible.
The only special case in FMT 7 is the maximum frame rate when your at 240 fps. When you select that we use the maximum packet size the camera supports, so the camera runs flat out.
Please note this ONLY applies to cameras using a FMT7 mode. In the non FMT7 modes, the frame rate will be accurately reflected in what FPS you select for a camera Frame Rate, assuming the manufacturer doesn't lie to us about what the camera can or can't do.
Under conditions of average seeing and a bright planet wouldn't you give more importance to getting up to 60 fps without having to resort to the Format 7 modes?
Usually yes.
Some nights, exposure time will not eliminate turbulence. I was shooting the full moon at 0.05 ms exposures and still getting significant turbulence between individual frames at 1384x1036 sizes.
Now some thoughts on your Flea2. When you 2x2 bin, you essentially have pixels that are 9 microns square vs my 7.4 microns square with no binning on my Dragonfly2. Wouldn't the Flea2 configured that way make a far more sensitive planetary camera than the Dragonfly2 or the Skynx for that matter?
Yes it would be more sensitive, by the square of the pixels size. So 9*9 (81)÷ 7.4*7.4 (54.76) is 1.48 times. And you would not lose the resolution that traditional binning does either, either as my software binning in Astro IIDC uses forward sum binning (something I developed myself) which bins the pixels but preserves the size.
That is what I did for my Saturn shot form last year:
http://www.outcastsoft.com/AstroImages/Saturn20090502MJA.jpg
And you can bin your Dragonfly2 any time you want to.
HTH..
Milton Aupperle
Dave
Dave
--- In Astro_IIDC@yahoogroups.com, Milton Aupperle <milton@...> wrote:
Hi doodlebun;
Actually, have you tried any of the FMT7 modes for it? I have a Flea2
(FL2-08S2C) 1024x768 here and if I run it at 516x388 in 16 bit with a
FireWire 400 cable I can capture at 53 fps delivered to disk.
According to the tech specs for the 640x480 DragonFly2, at 640x240
size you should be able to run as high as 50 fps in 16 bit. Cropping
it using ROI (see pages 27 and 28 of the Astro IIDC Manual) may help
too.
Over all I would agree with what your saying, especially when your
being forced to under expose to achieve better frame rates and then
stretching the image.
If you have really good seeing, you likely can tease a bit more subtle
information from Mars for 12 bit rather than 8 bit.
HTH..
Milton Aupperle
On 22-Jan-10, at 12:13 PM, doodlebun wrote:
I have recently graduated from a DMK21AF04 to a DragonFly2 camera.
I've been photographing Mars in two different monochromatic modes...
30 fps @ 12 bits and 60 fps at 8 bits. You cannot capture at 60fps
at 12 bits as we all know. I captured 1500 frames and took the best
400. Astro IIDC processed the movie and I compared the two RGB
images. Not a hell of lot of difference. With Mars we have a bright
planet that can be captured (with a C14 @ f/25)) at 60 fps @ 8 bits
with a minimum of noise yet a wide histogram that contains at least
200 of the 256 available levels of grey. Naturally the 30 fps
capture was even somewhat brighter at the same noise level.
So my question is this: Should one even bother using 12 bits on
bright objects that don't require much histogram stretching? It
would seem to me that if you captured a dim image (say Saturn, right
now) 12 bits would be more appropriate. If a Saturn image was
captured at only 10% as bright as maximum (i.e. the image had only
26 levels of grey in it, then when you stretched the 8 bit image the
banding could ruin the image. But if you captured the dim image at
12 bits, then you have effectively captured 400 out of 4096 grey
levels. This should yield a much better looking image when stretched
should it not?
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