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08-21-2012, 05:30 PM   #1
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Does Stop Down Metering Apply

Does the concept of "stop down metering" apply when shooting with a lens that communicates electronically with the camera body? Or is this only a technique applicable to only when shooting with manual lenses that do not communicate with the camera body.

08-21-2012, 05:33 PM   #2
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It is only useful with lenses lacking the A contacts, since the body can work out what the light level will be when the aperture closes to take the shot, it just has to know the maximum aperture of the lens.
08-21-2012, 06:44 PM   #3
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QuoteOriginally posted by elliott Quote
It is only useful with lenses lacking the A contacts, since the body can work out what the light level will be when the aperture closes to take the shot, it just has to know the maximum aperture of the lens.
Actually it can be used with any lens when the camera's in M mode. Set the aperture (whether through the camera's dial or the aperture ring) and it will set the proper shutter speed for the exposure.
08-21-2012, 06:58 PM   #4
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QuoteOriginally posted by DSims Quote
Actually it can be used with any lens when the camera's in M mode. Set the aperture (whether through the camera's dial or the aperture ring) and it will set the proper shutter speed for the exposure.
At least on my K100D, it won't stop down the lens when pressing the AE-L button (green button on newer bodies) if I have an A lens mounted with the aperture ring in the A position. Manual exposure lenses or A lenses with the ring not in A mode will be stopped down when the button is pressed. It still sets the shutter speed, but it sets it with the aperture still wide open. I have to pull the DOF preview to stop down an A lens.

08-21-2012, 07:21 PM   #5
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QuoteOriginally posted by elliott Quote
At least on my K100D, it won't stop down the lens when pressing the AE-L button (green button on newer bodies) if I have an A lens mounted with the aperture ring in the A position.
It works on my K-5 and K200D. I haven't had my K100D Super for a while, so I can't compare.
08-21-2012, 07:29 PM   #6
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QuoteOriginally posted by DSims Quote
It works on my K-5 and K200D. I haven't had my K100D Super for a while, so I can't compare.
But is there a reason to utilize the technique if you are shooting with a lens that communicates electronically with the camera body?
08-21-2012, 08:22 PM   #7
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The only reason I can think of, is to preview the depth of field at the same time. My experience with my K-5 is that it stop-down metering seems to be less accurate than letting the camera meter the traditional (non-stop-down) way. I think there might have been some previous threads about the accuracy/inaccuracy of stop-down metering.
08-21-2012, 08:59 PM   #8
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QuoteOriginally posted by CMG Quote
But is there a reason to utilize the technique if you are shooting with a lens that communicates electronically with the camera body?
Yes, sometimes you want to be in M mode to prevent the exposure from changing on you automatically, or for some other reason. This allows you to quickly re-set the the exposure when your scene changes. With the aperture ring in the A position you may not hear a physical stop down, but the exposure will be adjusted and the effect will be the same.

08-21-2012, 09:16 PM   #9
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QuoteOriginally posted by DSims Quote
With the aperture ring in the A position you may not hear a physical stop down, but the exposure will be adjusted and the effect will be the same.
That is what I said earlier, with an A lens it is not stopping the lens down, you don't hear the actuator moving the aperture lever, you don't see the viewfinder darken. It is not stop down metering with an A lens, it is open aperture metering. Stop down metering is inherently inaccurate, since the focus screen in modern cameras is not linear, so at smaller apertures the exposure is thrown off, it makes more sense to leave the aperture open and then calculate it.
08-21-2012, 09:24 PM   #10
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QuoteOriginally posted by elliott Quote
That is what I said earlier, with an A lens it is not stopping the lens down, you don't hear the actuator moving the aperture lever, you don't see the viewfinder darken. It is not stop down metering with an A lens, it is open aperture metering.
OK, sorry about the miscommunication. My point is that the technique of using the green button (or whatever button applies on his camera model) is still useful, and the technique is identical whether the lens is actually "stopping down" physically or not. As Tanzer suggested, perhaps it is more accurate when it doesn't have to actually stop-down - I don't know.
08-21-2012, 09:40 PM   #11
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QuoteOriginally posted by elliott Quote
That is what I said earlier, with an A lens it is not stopping the lens down, you don't hear the actuator moving the aperture lever, you don't see the viewfinder darken. It is not stop down metering with an A lens, it is open aperture metering. Stop down metering is inherently inaccurate, since the focus screen in modern cameras is not linear, so at smaller apertures the exposure is thrown off, it makes more sense to leave the aperture open and then calculate it.
Good info! Thanks.
08-22-2012, 01:00 AM   #12
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also with old PKA zooms without constant F number, like my Sigma 35-70mm 2.8-4.0.
It has just a single contact and camera body has no way of knowing what focal length was chosen, so at wide end is OK to use all auto metering modes but at tele is better to use Green Button and stop down metering, otherwise camera will use 2.8 instead of 4.0 to do exposure calculations.
08-22-2012, 04:41 AM   #13
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QuoteOriginally posted by i_trax Quote
also with old PKA zooms without constant F number, like my Sigma 35-70mm 2.8-4.0.
It has just a single contact and camera body has no way of knowing what focal length was chosen, so at wide end is OK to use all auto metering modes but at tele is better to use Green Button and stop down metering, otherwise camera will use 2.8 instead of 4.0 to do exposure calculations.
I don't think this is true, based on some time I had with a PKA zoom (Quantaray f/2.8-4.0). The camera just thinks it got darker outside (or maybe inserted a ND filter) when you zoom to tele, and it recalculates the shutter and/or aperture from there. It doesn't need to know that the "f/2.8" is actually f/4.0, it just tries to stop down the lens by whatever number of stops from where it is when wide open.

And for me, oddly, stop-down metering made things worse. I am learning that this is probably because of the non-linear focusing screen's EV response that some others have described. The wide-open metering on the Quantaray always worked right.
08-22-2012, 05:05 AM - 1 Like   #14
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QuoteOriginally posted by i_trax Quote
also with old PKA zooms without constant F number, like my Sigma 35-70mm 2.8-4.0.
It has just a single contact and camera body has no way of knowing what focal length was chosen, so at wide end is OK to use all auto metering modes but at tele is better to use Green Button and stop down metering, otherwise camera will use 2.8 instead of 4.0 to do exposure calculations.
QuoteOriginally posted by Tanzer Quote
I don't think this is true, based on some time I had with a PKA zoom (Quantaray f/2.8-4.0). The camera just thinks it got darker outside (or maybe inserted a ND filter) when you zoom to tele, and it recalculates the shutter and/or aperture from there. It doesn't need to know that the "f/2.8" is actually f/4.0, it just tries to stop down the lens by whatever number of stops from where it is when wide open.

And for me, oddly, stop-down metering made things worse. I am learning that this is probably because of the non-linear focusing screen's EV response that some others have described. The wide-open metering on the Quantaray always worked right.
There are truths and half truths in what is being discussed here.

The stopped down metering, / green button etc, was initially introduced in the film era. My PZ-1 had it for example. The function at that time, was a single button push to return you to what the metering considered "correct" exposure. on the PZ-1 the only difference was that we had an uncrippled K mount, so the camera knew how many stops down from wide open the lens was.

Now, come to the DSLR era and no aperture coupling. With manual aperture lenses, the camera stops down to meter, with A lenses it reads the scene wide open and sets the settings accordingly (just like my PZ-1 did)

The real issue with DSLRs is the non-linear performance of the focusing screen at different apertures. There have been a ton of debates over the years about this, and i have even taken the time to test this on several cameras

the latest iteration of my tests with the help of other forum members is attached here



the issue with variable aperture lenses is that some even in MF days had solutions to report the correct aperture through the 5 aperture contacts. sigma for example had a sliding switch that as you zoomed (2 ring zoom) it reconfigured the contacts. others as suggested just assumed that the day got darker, and with the limited range zooms in the MF days, if you were off nominal aperture by +/- 1 stop there was no issue, but with the K10D and later DSLRs this could lead to big errors, same with adding a TC that fed lens data straight through. 1 2x TC om my sigma 70-200/2.8 caused a 1.3 stop over exposure on the K10D (it was obvious why when looking at the chart) and it also plays hell with P-TTL flash, which absolutely MUST know the true open aperture to get things right.
08-22-2012, 09:25 PM   #15
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I didn't realize that some KA lenses could vary the aperture contacts (i.e., other than through to the seventh contact on KAF lenses), but that sure sounds reasonable. However, the Quantaray f/2.8-4.0 that I mentioned did not support this. It always showed "f2.8" in the viewfinder and exif regardless of zoom setting. And yet the exposures were always correct, when metering in "A" mode, and I didn't notice any +/- 1EV errors. I'm not sure I understand all of the data you are presenting Lowell - is what I am describing consistent with your expectation, or are you saying that the shots were actually off by up to 1EV and I just didn't notice?

I never got around to testing P-TTL flash with the lens since I returned the lens to my buddy before I had a flash.
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