Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site drusd.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!ihnp4!drutx!drusd!phl
From: phl@drusd.UUCP (LavettePH)
Newsgroups: net.rec.photo
Subject: Re: re: Camera Vibration
Message-ID: <1253@drusd.UUCP>
Date: Tue, 12-Mar-85 10:54:54 EST
Article-I.D.: drusd.1253
Posted: Tue Mar 12 10:54:54 1985
Date-Received: Wed, 13-Mar-85 01:06:33 EST
Organization: AT&T Information Systems Laboratories, Denver
Lines: 42

I'm afraid I confused resolution with brilliance in a previous article.  What
I meant to say was that, all other factors being equal, when you double the
aperature there is a two-fold improvement in resolving power, light gathering
is boosted by a factor of four and the area of the Airy-disc is cut to one
quarter.  This all results in a sixteen-fold gain in image brightness.

This phenomenon is very pronounced in small telescopes and binoculars and can
be easily seen by comparing the images seen through 7X35 and 7X50 binoculars.
Check how well each one defines the small twigs on a dead tree at a hundred
yards and the contrast between the twigs and their background.

Similarly, there is a two-fold increase in brilliance achieved when a 60mm
main lens is substituted for one 50mm in diameter.  A lot of the advantages of
a larger aperature are lost when a compound lens refracting telephoto is used
due to internal reflections between the glass surfaces. Cassegrian and catidiop-
tric lenses perform better in this respect due to their simplicity.

Before you spend too much money why not perform two simple tests?

First, get a resolution test sheet (Librarys usually have them.) and test your
lens to see just what its capabilities are.  It could be out of spec for any
number of reasons.

Second, cover a large reflector with a sheet of foil with small pinholes poked
in it.  Photograph the pinholes from a good distance using your tripod and
cable release or whatever other release method you wish.  B&W negatives are all
you need and the exposure isn't critical.  When you get your negatives, mount
them in slide mounts and project them as large as you can.  Circles will indi-
cate everything is A-OK.  Commas or bars indicate camera movement.  This is a
cheap and dirty way to compare methods or cameras.  It's also a good way to
find out how slow a shutter speed you can hand-hold any lens.  BTW it is the
shape of the image you should be interested in.  Some halo-ing is normal.

I suggest you isolate your problem as much as much as you can before changing
equipment.  The subtle differences caused by small variations in position during
exposure, focus, resolution and contrast are very hard to isolate by looking at
a regular slide or print of a landscape or any other normal photograph.

Now explain to me why a slide that looks razor sharp on a fifty inch screen 
comes out a fuzzy mess on an 8X10 glossy :=)

- Phil