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Author Topic: Mirror Lock-up is a bigger deal than previously thought  (Read 9959 times)
elf
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« Reply #40 on: April 26, 2009, 02:02:19 AM »
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Quote from: Ray
The heavier mirror of the 5D is probably what contributed (in my experiments) to the noticeable image degradation at 1/30th sec on a fairly lightweight travelling tripod (but firmly planted on a tiled floor) compared to the complete lack of image degradation from my 20D on the same tripod at the same shutter speed without MLU being enabled. But I still think it's reasonable to deduce that the unusually noisy mirror-flip (and possibly also shutter) of the 20D probably helps image quality, in the absence of MLU. The lower frequency vibrations are transformed into harmless higher frequencies, which are not good for wildlife shots of course. There's a trade-off.

Such issues really require a lot of time-consuming experimentation under various conditions. I'm all in favour of 'knowing thy equipment', but most of us would rather spend our time just taking photos. It requires a scientific frame of mind to make such careful comparisons to determine at what shutter speeds on a particular camera, on a particular tripod, MLU has the most benefit, if any benifit at all.

Have you tried shooting without using the in-camera shutter to see if it really is the shutter that causes the problem? Shoot in a dark room with a long shutter speed and use room lights to control the exposure time.
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Ray
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« Reply #41 on: April 26, 2009, 04:14:38 AM »
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Quote from: elf
Have you tried shooting without using the in-camera shutter to see if it really is the shutter that causes the problem? Shoot in a dark room with a long shutter speed and use room lights to control the exposure time.

No. I've never done any tests to try and separate mirror slap from shutter vibration. I read years ago that the critical shutter speeds when mirror slap can be a problem are from 2 secs to 1/60th. I've never found a problem outside this range. If the shutter itself also causes a degree of image-degrading vibration, I don't see what can be done about it if it's in the same shutter speed range where mirror slap is also a problem, except use a faster shutter speed.

I was surprised that I couldn't see any difference with the 20D in this range from 2 secs to 1/60th, comparing images with and without MLU enabled. The 5D behaved more typically with the greatest blur at 1/30th without MLU, slightly less at 1/15th and almost none at 1/60th.
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Rob C
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« Reply #42 on: April 26, 2009, 05:27:06 AM »
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Ray, as I think I mentioned before, hard tiles are perhaps worse inducers of vibration than you think. They are totally rigid and incapable of absorbing any vibration and thus dampening it. I think that the same basic notion is at play even when using a strong tripod which fails to have sufficient mass to stop the shakes before they happen. And we havenīt even touched on the kind of feet the tripod may have.

Maybe thatīs the secret behind the old Gitzos which are damn uncomfortable for even healthy people to cart around; perhaps they work better than lighter carbon fibre Gitzos? Who will ever test them, and on which brand of perfect camera? Impossible, of course, all cameras and exposure systems are flawed when movement is required to make that exposure; it is simply a matter of acceptable degree.

Rob C
« Last Edit: April 26, 2009, 05:28:13 AM by Rob C » Logged

Ray
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« Reply #43 on: April 26, 2009, 07:40:20 AM »
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Quote from: Rob C
Ray, as I think I mentioned before, hard tiles are perhaps worse inducers of vibration than you think.

Rob,
But not sufficient to cause any image blur when the 20D, with ultra-light 50/1.8 II, is on the tripod, with or without MLU enabled. One could spend the rest of one's life testing how different cameras behave when attached to different tripods on various surfaces and also when using different lenses which have a different balance and weight. Is it worth the trouble? I just use the 2 sec to 1/60th range as a general guide. I might do some tests with the 50D to see if I can detect any shutter vibration, ie. take a few shots ranging from 2 secs to say 1/200th all with MLU enabled.

All my tripods have rubberised feet by the way.
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