[AZ-Observing] Re: Was Saturday Great or What???
- From: "Keith Schlottman, CPA" <keith@xxxxxxxxxxxxxxxxx>
- To: <az-observing@xxxxxxxxxxxxx>
- Date: Mon, 1 May 2006 16:32:42 -0700
Brian and Dean - I'm enjoying your comments - I sure appreciate the analysis
that you are putting into this image. It can only help me improve future
pictures.
I did have the automatic noise subtraction turned on so I assume that the
majority of hot pixels were subtracted. I'm interested to hear about the
comatic stars in the corners, I hadn't noticed that.
If either of you would like, I would be glad to send you the original .raw
file, which is approximately 7Mb in size. I don't have the skill to
determine how much damage was done to the image by the jpeg compression, but
I'm sure there was some loss of quality.
Keith
-----Original Message-----
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Sent: 05/01/2006 4:11 PM
To: az-observing@xxxxxxxxxxxxx
Subject: [AZ-Observing] Re: Was Saturday Great or What???
Brian-
The 20Da has 6.4 micron pixels, so my math (better check it!) says that
with a 24mm lens, resolution should be 56 arcseconds, about what you said
the image demonstrated... I do not know how jpeg compression works,
though you can see artifacts in Keith's full-scale image. Normally ar
full resolution, with lots of structure, my jpegs can be 2-3 mbytes,
though admittedly I rarely shoot wide field images, so don't know if we
are losing anything. Certainly with smaller files, don't you lose
resolution and magnitude information?
-Dean
>>> the jpeg compression would really kill your resolution and limiting
>>> magnitude.
>
> Does the jpeg compression process bin pixels as well as lopping
> off bits? I noticed that stars in the corners of the image were
> elongated radially (looking fairly comatic), so I assumed the posted
> image was showing the full angular resolution, even if the dynamic
> range was compressed. I guess the more direct question would be:
> how big are the pixels on the chip, so one could derive arcsec/pixel?
> One could then compare that against the delivered image quality.
>
> \Brian
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