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Re: [APML] OT: New M106 Composite
Hi Wei-Hao,
Actually there is an advantage to F9. For high res CCD imaging most people
will apply deconvolution. Deconvolution will work best when the image is
oversampled. Optimally the oversampling (according to Stan Moore) should
be between 3X to 4X seeing. When I did the F9 exposures the seeing was
about 2" and my sampling is about 0.5" /pixel with the ST10XME. This comes
out to be about 4X oversampling. The Nyquist sampling theory is outdated.
I can also tell you from visual examination of the data that the F9 data is
really
superior to the F6 images in regards to resolved detail in the galaxy.
Rob Gendler
email: robgendler@att.net
Web Site: http://www.robgendlerastropics.com
----- Original Message -----
From: "Wei-Hao Wang" <wang@IfA.Hawaii.Edu>
To: <astro-photo@seds.org>
Sent: Wednesday, April 21, 2004 6:35 PM
Subject: Re: [APML] OT: New M106 Composite
> Great image, Rob!
>
> One thing I'm wondering is if it's really necessary to use F9 to
> obtain the details. I believe that your F6 has the same image
> details as F9 (and a wider field), unless the seeing is subarcsec.
>
> At F6, your focal length is about 1.9m. With 1".5 seeing (I assume),
> the FWHM of an unsaturated star on the focal plane is 14 um. The
> diffraction of the telescope at F6 will add another 4 um to this FWHM.
> So the FWHM of stars is at least 18 um, corresponding to 2.6 pixels
> on ST10. In other words, at F6, with 1".5 seeing, you already reach
> Nyquist sampling. Increasing the focal length will make you
> over-sample the stars (and therefore all the details in the image)
> without actually increasing the resolution. This is not true only
> when the seeing is less than 1". In this case, F9 will give you
> a higher resolution.
>
> Cheers,
>
> Wei-Hao
>
>
> ______________________________________________________________________
> Wei-Hao Wang :)
>
> Institute for Astronomy at University of Hawaii
>
> Address: Phone: 808-956-9867
> 2680 Woodlawn Drive Personal Website:
> Honolulu, HI 96822 http://www.ifa.hawaii.edu/~wang
> ______________________________________________________________________
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