RE: [APML] Celestron/Epoch 8" Schmidt 35mm Illumination

["Loke Tan" <tan@cox.net>]

Chris,

 The image I shot was near zenith  and the sky at mag 6.5. Yes, a sky
gradient can cause this, though I doubt to this degree. Your points are well
taken but this is about the best controlled conditions I can do. The
non-linear response of the film makes the results not reflect actual light
profile of the optics though it does not effect symmetry. Using a CCD would
show the actual light dropoff of the optics.

Loke




> -----Original Message-----
> From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]On
> Behalf Of Chris Schur
> Sent: Friday, November 01, 2002 6:44 AM
> To: astro-photo@seds.org
> Subject: RE: [APML] Celestron/Epoch 8" Schmidt 35mm Illumination
>
>
> Loke, maybe you need to shoot a flat field to see the proper
> vignette.  You
> may be measureing a sky gradient, or a reflection off of the rather
> unbaffled tube end.  A more controlled enviornment is needed.
>
> Chris Schur
>
> -----Original Message-----
> From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]On
> Behalf Of Loke Tan
> Sent: Friday, November 01, 2002 5:04 AM
> To: Astro-Photo@Seds.Org
> Subject: [APML] Celestron/Epoch 8" Schmidt 35mm Illumination
>
>
>
> FYI, since we were discussing the illumination of the Tak E210, I
> thought I
> would post some data I have on my 8" Schmidt camera. The light drop-off is
> approximately 13% on the left edge and 9% on the right.
>
> http://starryscapes.com/tmp/m87_R_illum.jpg
>
> I do not understand why it is asymmetrical as the Schmidt should be
> exceptionally well centered and collimated. The jpg is a raw scan with no
> levels or curves applied.
>
> Loke
>
>
>
>
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