From: Milton Aupperle <milton@outcastsoft.com>
Date: June 15, 2006 1:01:23 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Monochrome Unibrain results
Hi Jim;
How was your seeing and what was your effective focal length? Also it would be nice if you indicated in the image what your parameters were (i.e location ,name, date, exposure times, aperture, actual focal length, effective focal length, seeing, camera model etc.) too.
I rarely go over 3 meters focal length (2x barlow making it F/25 with a MAK 127 mm scope) unless seeing is exceptional. Also once your over about 3 times what your resolving power is per pixel, your not really capturing any more detail, just spreading it out over a larger area and increasing exposure time.
Besides adding more glass / barlows to increase the focal length, you can also do the same thing by varying the distance between the CCD and the Barlow too.
For example, I have a set of extender rings (8 mm , 28 mm, 38 m lengths - when all attached 144 mm total) that I place between the camera M42 screw mount and the 1.25" male end I attach to the scope. If I add a 28 mm ring I can increase the magnification by about 60% and with all of them on, I can go well over 500%.
And this applies for focal reducers too. If you increase the distance between the Focal Reducer and the CCD you further decrease the magnification. With the MOOG Focal reducer, a 38 mm extender ring decrease the actual focal length from 1512 mm to 533 mm effective focal length. Without the extender ring, I only get 756 mm effective focal length.
However their are limits to this, as you may not have enough in or out travel distance on your focuser to use all the extender rings. And with the MOOG Focal reducer, I start getting some image brightness differences (i.e. darker on the outside, bright on the center) which requires flat field correction to fix it.
On a side note, in case any of you were wondering if Peltier cooling a camera makes a difference reducing image noise for short exposure Planetary, Lunar, Solar imaging, the answer is no it doesn't. Last weekend I ran a series of test to see if it made any difference between subsequent frames with a Flea Camera in 8 bit modes (I did not measure 16 bit). Their was virtually no difference between subsequent frames whether the camera was running uncooled at 34°C or cooled to 9°C at maximum gains (1023). The average variance per pixel between subsequent frames was +/- 4 to 6 out of 256 at exposure times from 16 ms to as slow as 133 ms per frame.
TTYL..
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
Calgary Alberta Canada T2R0N5
1-(403)-229-9456
milton@outcastsoft.com
www.outcastsoft.com
On 13-Jun-06, at 8:01 PM, jimchung2338 wrote:
I recently got a monochrome Unibrain to try and maximize my chances of finding a star to
guide on in my quest to image M51. It is siginificantly more sensitive than my color Unibrain
and being monochrome has a higher resolution.
I was able to double stack a TV 5x Powermate on top of an Orion 2x barlow through my
76mm refractor and still have enough light to image Jupiter. I think at this level the lack of
sharpness is limited by the small aperture optics - roughly equivalent to 450x magnification.
http://groups.yahoo.com/group/Astro_IIDC/files/Planetary/jupitertv5x2xirjune12.jpg