From: Alan Friedman <alan@greatarrow.com>

Date: June 15, 2006 1:48:54 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Monochrome Unibrain results

Hi Milton -

A good summary.

I recently spent a night imaging Jupiter with my 6" scope - something I had not done in many years. I chose a focal length of about 3 meters (next time I would increase this slightly) which gave similar exposures values to my 10" at 7 meters - my normal set-up for Jupiter. I was surprised how much detail was recorded and how well the image handled being upscaled in Photoshop. When I finished combining the RGB I will share it with the group.

I also found that selection, alignment and stacking in AstroIIDC at this image scale (I used the planetary mode for stacking) was much more dependable than at the larger image scale I usually use. This is probably due to smoother signal, higher contrast features and reduced movement from atmospheric distortion in the individual frames at the shorter focal length. It is really a pleasure to let Astro IIDC do all the work.

I will be interested to see if detail is recorded on Ganymede at the shorter focal length. Capturing this and certain other features (such as recording the location of the Encke division on saturn) have seemed to need a long focal length - but maybe not...

best -

Alan

On Jun 15, 2006, at 3:01 PM, Milton Aupperle wrote:

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

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