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07-05-2008, 05:20 PM   #31
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QuoteOriginally posted by falconeye Quote
Thanks for the link. I added a comment over there.

This info is both pessimistic and optimistic, though.
Pessimistic, because 0.5mm travel is already enough to gain 4 stops -- for any focal length. I did the math myself.
Optimistic, because much more travel is required since you can't keep the sensor centered BEFORE the shutter is actually pressed. How much isn't known from sources I know. And ignored by the source you mentioned.
why not keep the sensor centered until the shutter is open?

07-05-2008, 06:49 PM   #32
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QuoteOriginally posted by OniFactor Quote
5mm travel is HUGE, Kungpow. here's an article that explains most of the math of how to figure out how much travel you need

Super Steady Shot with Full Frame Sensors
Thanks for the link. Its an interesting read.

It explains how much the sensor needs to move, but it does not say how much it does.

I found this photo of the pentax SR system.

Pentax Introduces 10.2MP Pentax K10D Digital SLR Camera

To me it looks like the cutouts in the sensor frame are about 7.5mm across. This is an estimate. I am assuming that the three open squares are what defines the max sensor travel. To me they look like they are about 1/2 the vertical sensor dimension.

I cannot see the support pins that would go through the holes, so I will guess. 3mm pins would allow 4.5mm of vertical travel (6.36mm diagonal). So if the sensor is allowed to move 2.25mm left/right and up/down (from center), then the minimum image circle needs to be just under 50mm diameter.

Would a typical Pentax lens, for a full frame camera have an image circle of +50mm? I have no idea.

If it does then there is no need to crop the image when using SR and a Full Frame lens.
07-06-2008, 05:34 AM   #33
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QuoteOriginally posted by OniFactor Quote
why not keep the sensor centered until the shutter is open?
The sensor can't accelerate at infinite acceleration. Therefore, it is kept in constant anti-phase motion, starting with the half-press. According to various sources, it needs about 0.5s from half-press to get ready. This time is recorded in the EXIF, actually.

However, the time between half-press and actual shutter release can be large.

In the K20D's Live View, when I rotate the camera by, say, 30, I can see how the Live image crawls for re-center after the rotation is complete. I got the impression that his takes about 2s. If true, the max travel would have to be large enough for a 2s exposure. Also, the Live image moves considerably which means that it must travel by more than, say, 30 pixels (which would translate to only 4 pixels on the Live image).

On the other side, technical progress may bring this time down and make this consideration less a concern with a FF camera.


QuoteOriginally posted by KungPOW Quote
So if the sensor is allowed to move 2.25mm left/right and up/down (from center), then the minimum image circle needs to be just under 50mm diameter.
This 2mm travel distance would be consistent with my argument above.

However, as I said, technical progress for a FF camera may bring this down anywhere between 0.7 and 1.5mm.
07-06-2008, 07:58 PM   #34
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There is also idea that we can see new type of bayonet - hybrid bayonet for AF645, 135 and 67 lenses. The using of 645 lenses at FF can help to use SR without any problem.

07-07-2008, 12:55 AM   #35
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Lots of utterly preposterous claims and ideas in this thread. I'll just wait it out a couple more months.
07-07-2008, 01:41 AM   #36
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QuoteOriginally posted by falconeye Quote
Therefore, it is kept in constant anti-phase motion, starting with the half-press.
You are wrong. With half-press, the only thing that starts working is gyroscopes and collecting information from them. Anti-phase motion starts only when you fully press shutter button. (You can check it by yourself - after shot you can feel and hear the sound of dropped down matrix (at least in K10D/K100D), if you just half-press - nothing happens)
07-07-2008, 01:55 AM   #37
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FF Sensor

Yes i hope that pentax do come out with a Full Frame Sensor...
07-07-2008, 03:27 AM   #38
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QuoteOriginally posted by Zebooka Quote
You are wrong. With half-press, the only thing that starts working is gyroscopes and collecting information from them. Anti-phase motion starts only when you fully press shutter button.
I stand corrected.

Thank You for having pointed out my mistake. It is true, and even simpler to check on a K20D
In Live View, the SR makes a noticeable sound. In shutter half press: no noise.

There are no real gyroscopes to start (it uses angular velocity detectors based on a measurement of the coriolis force enacted on a vibrating piezo element -- it is all in a single semiconductor element per axis, the Murata's ENC-03R http://www.murata.com/catalog/s42e.pdf.

So, I am actually wondering what happens during the 0.5s half press delay until SR gets ready. But you are right, it is NOT the CMOS sensor starting moving.


I found a way to actually measure the travel distance, now

In Live View, put your K20D on a table and turn it quickly by 30 or so. After the movement stops, the Live View will have been pushed to the opposite border and NOW starts crawling, slowly, to the center of the new direction. It takes about 2.5s to do so. The crawling distance is a good quarter of a field in the Live View 4x4 grid. 23.4mm *1/15 = 1.56mm.

So, the travel distance is about 1.5mm, making the required image circle larger by 3mm. This would actually be enough for 5 stops gain... A FF camera may live with <1mm travel distance w/o degradation of the SR performance.


Last edited by falconeye; 07-07-2008 at 03:40 AM.
07-07-2008, 04:27 AM   #39
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Another way but maybe more difficilut to measure:

* Remove the lens
* Look at the mount
* Start a Long pose (e.g. B mode)
* move the camera straght (e.g.) left.
* See how much the sensor moved.

Easy enough.. butyou can only measure the max move possible, that way obviously.

On my K100D, I estimates the (max) sensor move to about half a centimeter (in each direction).

Do not forget that each camera has slightly different SR implementation, so the travel distance/reactivity time is specific to each camera.
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