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From: hagerman@nermal.DEC
Newsgroups: net.rec.photo
Subject: vibration in slr cameras
Message-ID: <697@decwrl.UUCP>
Date: Mon, 28-May-84 17:03:01 EDT
Article-I.D.: decwrl.697
Posted: Mon May 28 17:03:01 1984
Date-Received: Fri, 1-Jun-84 01:08:17 EDT
Organization: DEC Engineering Network
Lines: 46

x
The original question was about mirror 'flop' in 35mm slr cameras.
Paraphrases of two articles on the subject follow.

From Alfred Blaker's 'Field Photography':

With a focal plane shutter, under extreme cases, a smearing in the
direction of the shutter travel can be observed.  For the Nikon F the
worst speed is 1/15 second.
A streaked or distinct double image can be observed due to motion
caused by vibration set up by the mirror travel.  Note that this is
a separate effect from the above.  For the Nikon F the worst speed is
again 1/15 second.
The two effects are distinct and it is possible to reduce one without
affecting the other.  Most metal tripods are not sturdy enough to
eliminate the problem--they are likely to resonate with the vibrations.

Two methods of reducing the problem are suggested.  First, one can
mount the camera loosely on a tripod and use his own hands to absorb
the vibrations.  Second, two sand- or bean-bags are used, one between
the tripod and the camera with the second draped over the camera.
The camera is not fastened to the tripod but rather sitting
on the bag which is sitting on the tripod.

From 'Leica Fotographie' (a hobbyist magazine distributed by E. Leitz
and with a heavy Leica emphasis), 2/1981, 'How Serious is Mirror Slap',
by H.W.Staubach:

"The people who nourish this reputation [i.e. that slr cameras are
deficient because of mirror 'slap'] are principally recruited from
the ranks of rangefinder fanatics."
A thesis by Martin Bantel of Stuttgart University concludes that
tripods do not solve the problem, and that on a tripod the lack of
image sharpness is in proportion to shutter speed as
1/2:1/30:1/500 = 5:10:2.  This is because for very long exposures
the time of vibration is only a small fraction of the total
exposure time, while at very short exposures only a fraction of
the total vibration amplitude is recorded on the film.  Bantel
concludes that the shutter speeds 1/8, 1/15, and 1/30 should be
avoided.  The camera tested was not mentioned.

Both authors agree that for hand-held photography, camera motion
is by far the biggest problem.  Blaker recommends the use of 1/250
or 1/500 second.

- D. Hagerman