Brian Swale wrote:
>>Manuel Viet wrote:
>>
>>>Le samedi 30 Juillet 2005 13:19, Brian Swale a écrit :
>>>
>>>>I think that for OMs, vibration has been the unsolved bugbear. Mostly
>>>>unsolved - and for me it would still be unsolved were it not for the tests
>>>>done and put on the 'net by Gary Reece; and for the information so freely
>>>>given in this group - all of which has made a huge difference to my
>>>>enjoyment
>>>>of photography.
>>>>
>>>>
>>>Could someone please expand a bit on that topic ? A while ago, I've been
>>>responsible for a wet lab activity in a college, and we had a Pentax K1000
>>>for
>>>15 students, so I generaly let them use my own OM-1 as well to speed up the
>>>turnover a bit. Clearly, while pentax pictures were "good enough", OM pics
>>>were always a bit sharper.
>>>
The issue depends on how the camera is used. Hand held, there is
generally no appreciable difference. Shutter speeds are relatively fast
and/or sharpness suffers equally in either camera from too slow a
shutter speed, and the hands damp vibration.
The issue is really only with tripod, etc. held shots. Here, the verious
machanical movements of miror, aperture stop down mechanism, curtain
releases and first curtain landing can all set up sympathetic vibrations
in the body, lens, body/lens connection and all the parts and connection
of the tripod and head. That is why Oly always said in their
instructions for lenses over 50mm, "...to prevent camera shake: When
using a tripod, hold the camera steady with both hands and press the
shutter release with the ball of finger, not with the cable release."
>>>So I'm wondering under which circumstances that vibration "bug" would show ;
>>>maybe on landscape pictures, tripod mounted, long
>>>exposures ?
>>>
It seems to depend a lot on the lens. You can tell which ones, mostly
modest teles and zooms, by looking at the detail of Gary's tests.
>>>But then, why would so many astrophotographers give an arm and a leg to get
>>>an OM today ? I'm confused.
>>>
I suppose it depends a lot on the exposure length. If you are making a
two hour exposure, the camera can jump up and down an inch for less than
a second, then settle down and the exposure won't be affected. If you
are making a two second exposure, it can make a considerable difference.
Honestly, if they are using OM-1 bodies and getting good results, the
mirror lock-up probably doesn't much matter. But it feels so techie to
push the little lever before the exposure and release it after.... If
mechanical vibration from the mirror and aperture operation makes a big
difference, onw should use a Nikon F/F2, where mirror LU and aperture
pre closing are available mechanically. Astrophotographers do prefer
mechanical cameras for the simple reason that the mechanical Bulb
operation doesn't wear out a battery.
>>-------------------------------------------------------------
>>
>>I think most of what is known on the subject of OM vibration emanates
>>from Gary Reese's extensive lens testing here:
>><http://members.aol.com/olympusom/lenstests/default.htm>
>>
>>Gary eventually realized that vibration with certain bodies and lenses
>>was signfificantly impacting performance. In fact, many lenses, when
>>retested using methods to reduce body induced vibration, showed much
>>better performance than the initial testing. This probably happens with
>>many other brands of camera bodies as well but you won't find it
>>documented as you do here.
>>
>>
>
>I'm pretty sure that Gary wrote in the last 12 - 18 months, that if he were to
>contemplate doing this marathon set of tests again, he'd eliminate the
>shutter / aperture / mirror effects by setting the gear up, closing out all
>light,
>and illuminating the target with flash.
>
>That way the "lens alone" would be tested; but one could say this would be
>a little academic since in use, the lens has to be attached to a camera body.
>However, I for one would like to see the results from testing some lenses this
>way versus attached to an OM body, so one would know the goal to aim for.
>
>
All very well, but I'm glad he did it the way he did, because it
revealed a great deal of data of which we would be ignorant and which is
of great practical value in using the equipment.
Moose
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