From: Alan Friedman <alan@greatarrow.com>

Date: September 6, 2005 4:42:42 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: Old Aristarchus VS Stretched Aristarchus Comparion

Hi Bob -

As Milton mentioned, the maximum exposure on the DMK21BF04 is 30 seconds. I did three streams of 30 second frames totaling about 90 frames or 45 minutes of exposure for luminance. I used all except two of the frames. I had taken the time to polar align my 1200 mount quite well - there was a slight drift but the image stayed almost stationery on the chip over the hour of image collection. Unfortunately the 10" mak at 9.8 (with reducer) was two dim for the RGB images (I don't think I can bin the chips for greater sensitivity on this camera?) so I used a low resolution capture for color with the A/P traveler at about 1/5 the focal length of the mak. This made for a lot of color tweaking in Photoshop.

Glad you enjoyed the image. The frames were surprisingly low in noise - I had some hot pixels (and of course forgot to collect a dark frame) and very slight amp glow - both of which were easy to handle in Photoshop. 

best,

Alan

On Sep 6, 2005, at 6:35 PM, bobtek4860 wrote:

Alan,

I really enjoyed your picture of M57.  I'm curious about the data collection you did for the 

shot.  How many frames, exposure time, etc.

Bob

--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@g...> wrote:

> Hi Milton -

> 

> Nice comparison of two processing values. Overall I prefer the first 

> rather than the stretched due to the artifacts introduced in the dark

> regions in the stretched version (perhaps from the sharpening). It is 

> true that curve based adjustment offers a lot more powerful control 

> than a linear adjustment. In the same way an unsharp mask applied to 

> the entire image is less powerful than sharpening applied using 

> selection tools (ie in Photoshop) as some areas of the image are blown 

> out with a sharpening level that is perfect for another area.

> 

> I've uploaded a couple of new images to the files area - an aristarchus

> regions at similar focal length to Milton's but at a different sun 

> angle, an image of the crater moretus and southern highlands region at 

> 7.5 meter focal length, and (in the DSO folder) a just completed webcam 

> image of M57 taken this past weekend at the Black Forest Star Party. 

> I've always wanted to try a deep sky target with my webcam and 

> AstroIIDC - this one came out better than I thought it would.

> 

> Looking forward to meeting some of you in Chicago this week,

> 

> best,

> Alan

> 

> 

> On Sep 6, 2005, at 3:34 PM, Milton Aupperle wrote:

> 

> > Hi Folks;

> >

> >  I was testing out the new image processing module over the weekend in

> >  the Astro IIDC beta version for DSO's and thought it might be

> >  interesting to see what one can do with it with lunar images,

> >  especially along the terminator where contrast can be extreme.

> >

> >  Compare the original "Aristarchus_050420_MJA.jpg" to the new

> >  streteched version "Aristarchus_050420_MJA_Stretched.jpg" in the Lunar

> >  File section. A lot of hidden detail is now visible, especially the 

> > rills.

> >

> >  Using linear level adjustments to bring out the dark areas usually

> >  wipes out the bright areas. But using the Log based curves can solve

> >  this pretty easily.

> >

> >  I may have over sharpened it a little bit in Astro IIDC 2.1, but this

> >  doesn't increase the noise level at all.

> >

> >  TTYL..

> >

> >  Milton Aupperle

> >

> >

> >

> >

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