Re: [APML] Res, Info and [The End of Tech Pan???]

[Aplanatic@aol.com]

Hi Matt,

> I use medium format PPF (e.g. at 875mm f.l.).  
> I think I understand why that gets better 
> resolution over 35mm PPF (e.g. at 438mm f.l.).
> But why does that improve my SNR over 35mm 
> PPF (e.g. at 438mm f.l.)?

What variables would you like to keep constant when discussing SNR?

Here are some of the possibilities:

Image scale in arcseconds/pixel
Aperture
Focal length
Exposure time ("Sky Fog Limit")

In the end, if the detector is linear then, at the same image scale, the SNR depends only on the aperture and the exposure time.  In your example, the SNR should be close to the same.  However, if you expose each image to the same background density ("Sky fog limit") then, again at the same image scale, the downsized medium format image would have a higher SNR.

Dave Rowe


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