hagerman@nermal.DEC (05/29/84)
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
ron@brl-vgr.ARPA (Ron Natalie <ron>) (05/30/84)
So go find yourself an old Canon Pelix. -Ron
ddb@mrvax.DEC (DAVID DYER-BENNET MRO1-2/L14 DTN 231-4076) (06/04/84)
...brl-vgr-ron suggests to someone (I just stuck my head in) that he go find an old Canon Pelix to avoid slr vibration. He could also get the version of the new Canon F-1 with the 14 fps motor drive, which also uses a partially-silvered stationary mirror (but is probably much more expensive than an old Pelix). Or he could get an old Leica M2 or M3, or an old or new M4. There would still be some shutter vibration, but it shouldn't be any worse than in a Pelix. Also, rangefinder focusing is a BIG win in dim light. Of course there are other tradeoffs (lens cost, limited range of lenses supported with viewfinder frames, etc.). -- David Dyer-Bennet -- ...decwrl!rhea!mrvax!ddb
nxs@fluke.UUCP (Bruce Golub) (06/04/84)
I agree with the assesment in the Lieca publication; all this take about mirror slap-back and focal plane blur is really nonsense. So is this affliction for tripods. Don't get me wrong, tripods are required in some cases but, for speeds beyond 1/60th of a second they are getting in the way. Taking a tip from marksman: take a deep slow breath, hold it, squeeze (press firmly with a consistant force) the shutter as you start to hold your breath, resume breating. As for using a medium aperature for clarity, never heard of that until I started reading this group. Does someone have a logical (i.e. the physics of why this is). Sounds to me like someone is going off on a mislead tangent. Also,in selecting a film for maximum sharpness I selected Ilfords (although any manufacturer produces a simular type of film and developer, almost) FP4, a slow-medium speed (asa 125) fine grain film, developed in Ilfords Microfine, High energy developer, that allows the film speed of FP4 to be increased to ASA 200 with a loss of sharpness (you may actually go as high as 320, but you're losing the fine grain). In addition, I use the Microfine developer in a diluted solution ( 1 : 1 ), which the manufacturer claims (and I also concur) increases the accutance of the film. As for the camera and equipment end of it, I would recomend that you use good-quality (at least the manufacturers lens, as apposed to bargain brands) lens, with a fixed focal lenth (sorry zoom lovers, they are great but have their limitations). Wide angle lenses (for what I know) are not less sharp then normal or telephoto types. It may appear that way because objects are smaller in relation to the film size and hence require significantly more enlargement to be the same size as an object taken through a normal lens. well what do I know anyway, Bruce Golub John-boy Mfg. etc.
drraymond@watdaisy.UUCP (Darrell Raymond) (06/06/84)
Remember that the Leica publication will be talking about Leicas, which are a little different from other cameras. Leica reflexes have no shock absorbing pad for the mirror, because they don't need one; the mirror is stopped in its cycle and then returned to rest. So while it is true that Leicas don't suffer mirror 'slap', this may not be true in general. Medium apertures have been recommended principally as a trade-off between the tendency of lenses to be at their poorest when fully open and diffraction effects at smaller apertures. Thanks to computers lenses are much more consistent, so that stopping down one or two stops from full aperture is sufficient.
berry@zinfandel.UUCP (06/10/84)
#R:decwrl:-69700:zinfandel:10200010:000:523 zinfandel!berry Jun 6 14:54:00 1984 If you write to Questar (find an ad in any Scientific American) they will tell you how to get your Nikon modified to lock up the mirror before the shutter goes off. This is not automatic, though -- you have to lock the mirror up, trigger the shutter, and then release the mirror. This is OK for long exposures on a tripod (or hanging off the back end of a Questar) but terrible for 'normal' shooting. You pays yer money and ya takes yer cherce. Berry Kercheval Zehntel Inc. (ihnp4!zehntel!zinfandel!berry) (415)932-6900