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Thread: m4/3rds AF lenses

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    Question m4/3rds AF lenses

    The m4/3rds lenses stay with their iris at the chosen position (say, f/11). While trying to make a photo, for the AF to function effectively, they open wide. After AF is achieved or the shutter is tripped, they close down to the aperture and a picture is taken (even in full manual mode this happens with the system lenses from Pana and Oly)

    All auto reflex cameras (SLRs and DSLRs) keep the diaphram fully open and it stops down only when the picture is about to be captured.

    The aperture scenario:

    M4/3rds:

    Closed-open-closed

    Auto reflex SLR:

    Open-closed

    Why must this delay happen? Shouldn't Pana and Oly change this?

    Thoughts?
    Last edited by Vivek; 18th October 2009 at 13:26.

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    Re: m4/3rds AF lenses

    I'm not so sure about your description, but isn't the iris also part of the shutter -- they don't have a focal plane shutter.
    Sláinte

    Robert.

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    Re: m4/3rds AF lenses

    Robert, The iris isn't part of the shutter and they (m4/3rds cams) do have a focal plane shutter (remove lens from your E-P1, set the cam to operate without a lens attached and trip the shutter. You will see the focal plane shutter).

    The shutter stays open to allow for liveview.

    It closes and opens when a shot is taken (SLR: shutter stays closed and it opens when a shot is taken).

    While I understand the need for the shutter to be open (for live view), I can not understand the lens diaphram operation of the G lenses.

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    Re: m4/3rds AF lenses

    Perhaps it has to do with metering? i.e. iris wide open for focussing, iris stopped down for metering? A reflex SLR can plainly do wide open metering, but it meters from a cell in the viewfinder, AFAIK, and the sensor is not exposed to light. Small sensor cameras usually only have a couple of apertures, and with non-interchangeable lenses may be more likely to have lens shutters, so are a slightly different set of circumstances. This may be a technical issue of live-view cameras, that hasn't been solved, yet?

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    Re: m4/3rds AF lenses

    Metering works just fine with manual lenses at wide open or stopped down apertures.

    I can see one solution to this problem: AF lenses with a real aperture ring that can be controlled on the lens itself.

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    Re: m4/3rds AF lenses

    One of the advantages of this format is that you can see, in realtime, the exact depth of field you'll get on your LCD or EVF. On an SLR, one used to have to press a button to get this, a very dim image of it, too.

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    Re: m4/3rds AF lenses

    "Metering works just fine with manual lenses at wide open or stopped down apertures."

    Yes - it meters using the actual aperture on the lens; my suggestion was that with the AF lenses the cameras want to do the same thing - meter at actual aperture, rather than meter at full aperture and compensate for the known difference.

    @mabelsound - if the cameras could, or would, focus and meter at full aperture, then one might well want a stop-down/depth-of-field preview button, as some SLR's have, to close the aperture, but then they could use gaining on the electronic display to avoid having a dim image - as I believe that they do with manual lenses now.

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    Re: m4/3rds AF lenses

    According to DPReview m4/3rds cameras including the new GF-1 got the worst shutter lag than Dslar cameras out there. I think M8 has the least shutter lag in mirrorless cameras.

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    Re: m4/3rds AF lenses

    I don't know what DPReview is talking about there. I can detect no shutter lag at all. Are they including AF time? The GF1 is very responsive, as far as I can tell, every bit as responsive as my M7 or R-D1.

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    Re: m4/3rds AF lenses

    GF1 behaves the same way as an SLR. Open before the shot, then closed to take the shot, then open again after the shot. Only if you have depth of field preview set does it do the closed/open/closed approach.

    Greg

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    Re: m4/3rds AF lenses

    The GF1 has a button to show depth of field: it closes the aperture in live view. AFAIK the aperture is only closed for the photo itself.
    The shutter has to be opened for live view ofcourse. That is the main difference to a SLR in this aspect.
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    Re: m4/3rds AF lenses

    Quote Originally Posted by Vivek View Post
    Robert, The iris isn't part of the shutter and they (m4/3rds cams) do have a focal plane shutter (remove lens from your E-P1, set the cam to operate without a lens attached and trip the shutter. You will see the focal plane shutter).
    You're quite right, sorry for the confusion.
    Sláinte

    Robert.

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    Re: m4/3rds AF lenses

    Quote Originally Posted by Greg Seitz View Post
    GF1 behaves the same way as an SLR. Open before the shot, then closed to take the shot, then open again after the shot. Only if you have depth of field preview set does it do the closed/open/closed approach.

    Greg
    You're right--I had been using legacy lenses this week and was thinking of that behavior.

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    Re: m4/3rds AF lenses

    Quote Originally Posted by Greg Seitz View Post
    GF1 behaves the same way as an SLR. Open before the shot, then closed to take the shot, then open again after the shot. Only if you have depth of field preview set does it do the closed/open/closed approach.

    Greg
    Thanks, Greg. That is a good thing.

    I am sure the live view DSLRs like the current Nikon cams (D90, D5000, D300s, D3s) or Pentax Kx would behave this way as well.

    I was puzzled with the way it works on the G1 (or is there a setting that would avoid that?).

    Robert, No problems. It isn't exactly a focal plane shutter either. It is located about ~1cm away from the sensor plane!

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    Re: m4/3rds AF lenses

    Quote Originally Posted by cdnguyen View Post
    According to DPReview m4/3rds cameras including the new GF-1 got the worst shutter lag than Dslar cameras out there. I think M8 has the least shutter lag in mirrorless cameras.
    This came up some time ago in a thread about the G1. Shutter lag for these cameras is in the same ballpark as similarly priced DSLRs.

    According to Imaging Resource, the G1 has a shutter lag of 0.077s and the Nikon D80 is 0.083. The GF1 is listed is 0.072. This is pre-focused, which is the comparison that counts as it eliminates autofocus differences.

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    Re: m4/3rds AF lenses

    Quote Originally Posted by Vivek View Post
    The m4/3rds lenses stay with their iris at the chosen position (say, f/11). While trying to make a photo, for the AF to function effectively, they open wide. After AF is achieved or the shutter is tripped, they close down to the aperture and a picture is taken (even in full manual mode this happens with the system lenses from Pana and Oly)

    All auto reflex cameras (SLRs and DSLRs) keep the diaphram fully open and it stops down only when the picture is about to be captured.

    The aperture scenario:

    M4/3rds:

    Closed-open-closed

    Auto reflex SLR:

    Open-closed

    Why must this delay happen? Shouldn't Pana and Oly change this?

    Thoughts?
    I don't believe the G1 does this. Mine definitely has the lens wide open, then when I start the the picture taking sequence and start pressing on the button the AF gets locked and the exposure is shown in the viewfinder before the shot is taken. I guess the camera might possibly tweak the exposure after the diaphragm is closed down, but I don't know. I might be able to test it.

    Then as I press further, the diaphragm stops down and the shutter closes, the sensor is purged (that's why the shutter has to close first), the shutter opens and takes the picture, the shutter closes and the sensor is read, the shutter opens while the diaphragm opens up again and the system is recocked. I'm not sure of the exact sequence of some of these items but that is essentially what happens, and that is of course why the shutter delay is somewhat higher than a good SLR or even moreso a Leica M.

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