Re: [ATM] Diagonal Size

["Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>]

>
> http://www.digital-flight.com/thebigeye/Obstruction/obstruction%20test.htm
>

Something on this page bugs me. In the graphs under the first two pictures,
the whole intensity profile is said to be shifted due to underexposure. The
next conclusion is that image contrast is down because the profile is also
compressed.
In my view this could however be equally well be caused by the
underexposure. If this is the case, the whole reasoning on this page fails.

I would expect that the larger obstruction would leave the large high and
low intensity areas mostly unchanged. The high frequency intensity changes
would however be smoothed,or smeared out, causing loss of detail. This is
something you cannot read from an intensity stat such as shown on the linked
page.

Low frequency contrast, or call it background illumination, would crank up
the low intensity parts, which cover most of the area when watching stars,
and this would be noticeable in an intensity stat. This effects decreases
seeing low intensity objects, but is not really caused by a large
obstruction as such.

Any comments?

Arjan te Marvelde

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