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[OM] Fisheye question: was 8mm on eBay

Subject: [OM] Fisheye question: was 8mm on eBay
From: Roger Wesson <roger@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Mon, 08 Oct 2001 18:04:00 +0100
Tom Scales wrote:

...
> It went to a good home and is being used for astrophotography, which seems
> to be a perfect use for it.
> 
> Tom

Hmm. This has got me thinking.  8mm at f/2.8 = 2.9mm absolute aperture. 
For astrophotography purposes this is small.  Now, I've got a 0.42x
adaptor thing that screws onto a 49mm filter thread, giving a circle
frame fisheye when used with a 28mm lens.  It seems to me that, as it's
a 28/2.8 lens, with adaptor it must effectively be a 12/1.2 lens,
because the absolute aperture hasn't been changed, and indeed the
viewfinder image looks brighter to me.  Therefore it seems to me an
adaptor is a better solution than a proper fisheye lens.  Is this right
or have I missed some salient point?

Roger
Not suggesting, of course, that I wouldn't want an 8/2.8!

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