A77 versus Full frame

[Chris Malcolm]

I found what I first thought was mirror vibration was an annoying problem with my A550 with a Sony 500mm reflex lens -- whose light weight and short length would magnify vibration rotation effects compared to a physically heavier and longer refractor lens of the same focal length. As I reduced shutter speed it first showed up as a vertically displaced ghost image, a shift of several pixels. As shutter speed dropped that turned into a vertical smear, when then gradually broadened out horizontally. But I was puzzled by the speed at which it showed up -- anything less than 1/300th. That was a lot higher speed than folk suggested was the critical mirror slap vibration speed.

But it's the right kind of speed for shutter slap vibration. So I would say that either there's negligible mirror slap vibration in my A550, or else it's so dominated by the shutter slap vibration problem as to be irrelevant -- with the short & light 500mm reflex lens.

[Greg Beetham]

One of the differences/advances with the A700 shutter was its short cycle time so I guess you can’t have gain without some pain. The A500, A550, A560 and A580 all had 1/160sec shutters (the fastest speed with the shutter fully open) whereas the A700 had a shutter that maxed out at 1/250sec which is quite fast for a focal plane shutter, one wonders if the extra speed also meant a shorter life span, but whatever, it’s quite possible that HF shutter vibrations were more difficult to control as the cycle time became shorter.
One would have to say that using an 800mm lens (1200mm equiv) for general photography isn’t an every day occurrence; it would probably be of benefit to shooters on the more extreme wildlife end of the scale to have a high frequency vibration free camera for maximum image clarity.
Barry I don’t think MLU is of much use in a wildlife situation where you only have moments to shoot most of the time (specially where birds are concerned), but even if you do have time to get it all organized we can clearly see that the electronic shutter is a great asset for sharpness, without that I would be very surprised if your or my KM5D could shoot as cleanly as the A77 examples using an 800mm (1200mm equiv lens) no matter what methods were employed.
I’ve often thought that it would be great if there were a set of leaf shutter primes for the A-mount, the FP shutter is already open all the time now anyway for LV feed and I think many leaf shutter designs exist now that can close down to a pre-set f-stop and then open up again without having to fully close first. There were lots of other designs where the shutter was separate to the iris, some with the iris in front and some behind.
But as far as I know the sensor has to be ‘switched over’ from continuous output to a kind of stack dump still taking mode before a still shot can be taken so the leaf shutter wouldn’t be any kind of operational obstruction one would think, the only limitation with them was they were always rather slow (even if offering full range flash sync) and maxed out at around 1/500sec, but I think there has been improvements in that as well now Mamiya has leaf shutters that are very high speed apparently, also some compacts have very high performing leaf shutters from what I’ve been reading. One area where the FP shutter might still be superior though is with consecutive shots, I don’t know if leaf shutters are amenable to many shots per second (action type shooting), they used too be mainly for landscapes and studio type applications, but they sure are quiet and there is almost no vibration (that I was ever aware of with my leaf shutter lenses).
Greg

Ps Magnar I have a friend who is modifying his 16” for photography and he is using some kind of video camera (web cam derivative I think, I don’t think it has any moving parts), I have had a preliminary look now he has the tracking a bit better sorted and the images of Jupiter were very good I thought, the great red spot seems to be making a comeback of sorts, after fading quite a bit.

[David Kilpatrick]

Greg - a faster transit time (not necessary a faster overall cycle) actually has specific benefits. The main one apart from the flash sync is that a wider focal plane slot (gap) is used for a given shutter speed. This means that slight lack of parallelism or perfect finish to the focal plane leading and trailing curtain edges has less effect on evenness of exposure, and that small acceleration differences also don't have much effect.

With AS/SSS, a faster transit time and wider exposure gap also mean more physical lines of the sensor are involved for any given motion correcting shake, and small distortions of the image are less likely.

The disadvantage is as you suggest. Higher energy needs to be stored before releasing the shutter, all parts are under more strain, and vibration tends to increase.

When Praktica introduced the world's first laminar metal shutter of the modern type, in the Praktica L, I was at photokina. They had a demonstration unit with a bare shutter, and one connected to the lever wind. They invited us to try to cock the shutter by any means directly - it was impossible. The amount of force required would have broken your nail (or finger). The lever wind had a progressive gear, which started applying little force and then passsed through a resistance point. This was the stage when the shutter was cocked.

That shutter could slice carrots or celery - they demonstrated!

David

[Greg Beetham]

Yes David, that was interesting with the slightly wider slit per shutter speed increment beyond sync with a fast cycle time, stands to reason though. I was only looking at the maximum speed where the shutter was still fully open, (no leading or trailing edges) too me that is the shortest cycle time (starting from rest and returning to rest) that that particular shutter design can achieve, if there were any trailing edges using flash with low ambient fill then one would run a great risk of having the usual black bar across the edge of the photo, the shutter edge in transit being frozen by the flash. As Sony claim that the A700 has a maximum sync of 1/250sec I assumed that the shutter would also be fully open (at some point) in that elapsed time, otherwise it wouldn’t BE a sync speed….correct?

I see that one must turn SSS off when using that high sync speed though (1/200sec max with it on 1/250sec with it off) that might be to do with the transit speed of the SSS system itself perhaps but that opens up another thought, what happens when narrower slits are used if the SSS is going left at the beginning and stops and goes right during the transit? That’s why I think SSS doesn’t work beyond a certain magnification limit, if you magnify a subject with a telephoto lens say 15X or 20X you also magnify the wobbles and vibrations by that much too, and worse the SPEED of the wobbles and vibrations are also magnified by that much as well.

I have my suspicions though the A700’s cycle time is changed down to 1/200sec (for the sake of longevity) when setting narrower slit transits (1/500sec through 1/4000sec) to achieve the usual FP fake high shutter speeds beyond cycle time.
That Praktica shutter was fascinating (leaf shutter?) one wouldn’t want to accidentally get ones finger in it while demonstrating or trying too cock it…
Greg