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Zone focus test


eudemian
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A recent thread about zone focusing set me thinking, so I set up a test to try to understand what was going on so I could get to grips with the concept.

 

I set the camera on a tripod and set a series of objects at varying distances from the camera, ie at 1 mtr and quarter meter intervals up to 3.5 meters.

 

I then shot a series of incremental apertures at each specific distance indicated on the lens zone focus. I then repeated the test for various distances going through each aperture 11 to 1.4 for each selected distance. I then repeated the test with two other lenses.

 

I noticed the following strange exposure problem. I had the same ISO selected for all the above shots, all set on Auto WB and Autoexposure mode on the dial.

 

I got several consecutive series of shots with the same time for exposure which of course meant some of the shots were overexposed. This happened with all three lenses and at varying apertures, surely this indicates something is amiss?

I would explain it thus, in each series of aperture changes at a specific distance setting I would get a series of three or four shots with the same time for exposure, this is surely incorrect.

 

I probably wouldn't have noticed this in ordinary shooting (yes this is a strange way to use the camera but I was trying to learn how the zone focus changes with different apertures and distances)

 

I hope this post isn't too boring, and that I have described the setup and problem clearly enough. I should mention that I have just received the camera back with its new shutter.

 

Any advice, (hopefully pertinent) on what this means, or have I got it completely wrong?

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While the shutter when on auto increases or decreases its speed (actually, the delay between the first and the second curtain - the running speed is the same) steplessly, the finder and EXIF readout is changed by steps, each increasing or decreasing by a factor of 1.4 so that two steps make a factor of 2. Do the consecutive exposures look different? Check the histograms. They should be (nearly) identical.

 

If one exposure is made at a little less than a quarter-stop short of, say 1/60th, and the next at a little less than a quarter-stop short of 1/90th, then both may be registered at 1/60th though the two are actually very nearly one stop apart. There are always small inaccuracies in shutters or aperture mechanisms e.g., which are simply negligible in terms of the actual photographic result but which in this digital all-or-nothing age can pop up and confuse us. Just remember that the camera works at a level of accuracy which is far greater than that of any readout.

 

The old man from the Analog Age

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Thanks Lars, that is very informative.

 

First each histogram is different, becomes more squashed up and the photo is obviously getting more and more blown out.

 

The shutter speed is registered as the same in each of the three photographs yet each is shot at a different aperture, ie from f5.6, 4 and 2.8.

 

I am not sure what this means exactly but I have my suspicions. Can you think of a reasonable explanation for this?

 

Again many thanks for your response

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Now you are getting specific. No, three exposures made at 2.8, 4 and 5.6 respectively, and at correspondingly different speeds, should definitely not be registered at the same shutter speed. If that is the case, there's something fishy.

 

Now if you set your shutter to manual speeds, and make, say, one exposure at 2.8 and 1/125th, and one at 5.6 and 1/30th, then the two exposure histograms should look practically identical, because the two exposures should be identical. The exposure E is the product of the time of exposure (governed by shutter speed) and intensity of illumination (regulated by the aperture). Reduce one by half and double the other, and the product will be the same. This is at least what happens with my M8 (and has happened with every camera I have owned during the last half-century). If this is not the case, and the aperture mechanism of the lens is working properly, which you can check by eyeball, then there's something wrong with the shutter.

 

The result should be the same on auto, but then you can't of course check the actual shutter speed except by the monitor readout or the EXIF data, which are suspect.

 

The old man from the Age of 1/25th

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Well that confirms my suspicions Lars.

 

This is a new shutter upgrade, I had a prolonged exposure on day one which I wrote off as a quirk, but this series of test has revealed a problem and I will have to send it back.

 

Boy am I peed off.

 

There are mistakes, human error, cock ups but Leica quality and workmanship seems to be an amalgam of these faults and more,I only hope it will not become a distant, fading memory. Makes me wonder why I pay large amounts of money for faulty repairs and prolonged waiting (over three months for a repair). Or is it a subtle ploy to get me to invest in a M8.2 so I can have a backup?. As you can see I am a typical Leica loyalist, I hate the poor turnarounds, faulty repairs yet I still want to invest in the system, it is illogical isn't it?

 

Thanks for the input.

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By any chance did you have your finger on the shutter release when you changed apertures, or have a cable release and your finger on that at the same time.

If you don't fully release the shutter button and then half press then fire you may be locking the exposure. To lock the exposure all you need to do is depress the shutter release button to a little past the first stop.

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My goodness I will have to take back my critical comments.

 

I can't be sure but I may have kept my finger on the release button as I changed aperture. I was doing a series of test shots going through the different apertures and I may have locked the exposure as you suggest. Normally, of course I would not use the camera like this but I was doing a controlled experiment so I may have let my finger dwell longer on the shutter release as I scrolled through the various apertures.I will experiment further, this does seem like a plausible way to explain my results.

 

If this is the explanation then I feel foolish, or is it a case of learning on the job?

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Another possibility is if you did release the shutter release but then pressed all the way to fire the camera will use the older/original meter reading. You have to do a slight press to let the meter take a reading then fire.

 

That used to happen on my camera, once the meter had passivated the next shot would use the final meter reading unless the meter was re-activated first. I haven't noticed it so much recently, and although I used to be able to reproduce it at will - I couldn't just now when I tried. Could be a firmware fix, or possibly a mechanical change in the shutter release due to usage.

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