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01-13-2010, 05:07 AM   #1
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accuracy of K-x metering manual / M42 lenses?

*
  • please anybody tell me your experience how the K-x meters when using old manual, specially M42 lenses, in Av mode and / or M mode pressing green button
    ( is there any green button on the K-x, or which is the equivalent? )

additional information appreciated:
have you changed the focus screen of your K-x to a split focus screen?
if so, how easy / difficult was it?
had that changed how the camera meters M42 lenses?
same informations regarding K-7 appreciated as well.

I am still using a *istDs which is doing a fine job metering M42 lenses in Av mode. Reports say that all the later K models, until release of K-7 and K-x, had needed a dial in of 1.5 exposure correction resp. that replacing their focus screen with that of the *istD/Ds would elevate the correctness of measuring to the level of the *istD/Ds

thank you

01-13-2010, 06:23 AM   #2
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I have posted several times the performance of the K10D, and *istD and lastly with my K7, using my 50mm F1.4. Not with any M42 lenses. I could do that, and also add the characteristics, but here is the graph of performance for my 3 bodies.



The test for an M42 lens would be to focus on a block wall using average metering (anything but spot will default to average) and then measure the grey scale value for each aperture click.

My experiencewith *istD and K10D on M42 lenses is that they under expose by a stop

If you perform the test, I would suggest the following approach. Do the test once with no exposure compensation to show the errors, and then repeat it with an exposure compensation that gives you an average, over all F Stops of a grey scale of 120. Note with contrast and saturation neutral, each stop around normal exposure of 120 is 45 greyscale/.
01-16-2010, 05:11 PM   #3
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thank you Lowell, very interesting graph indeed!
I went ahead and ordered a K-x, I shall come back to report about it's performance metering old lenses, above all M42 lenses in Av mode

Last edited by kuuan; 01-16-2010 at 05:36 PM.
01-22-2010, 11:33 AM   #4
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the K-x arrived yesterday, my first impression for using manual / M42 lenses:

accuracy of automatic exposure in Av mode using a M42 f1.4/50mm S-M-C Takumar:



overexposed at f1.4,
hardly any more @f2 and spot on all through f11
f16 underexposed
- very positively impressed!!

Focusing seems to be easier than on my *istDs, at least compared to before I had installed a split focus screen on the *ist even though on paper the viewfinder on the K-x should be inferior
catch focus seems very accurate, even usable @f1.4(!)?

01-22-2010, 11:55 AM   #5
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My only comment on the histograms is that they are much harder than you think to develop a conclusion. when I do my shots, it is a block wall because then 100% of the histogram is within about +/- 10% of the center This makes it easy to measure accurately the metering.

with an image, containing as your's does, components over the entire histogram, you can't really measure accurately how it would meter a single color and intensity.

I appreciate subjects are much more interesting than a block wall, but to have other than qualitative results, you need a consistantly lit uniform subject.
01-22-2010, 12:04 PM   #6
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thank you for your comment Lowell, this makes sense.
the picture these histograms were taken off btw. is the pic showing the Konica camera
I may redo the test, resp. will find how the K-x does while using it soon enough anyway ;-)
01-22-2010, 12:33 PM   #7
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QuoteOriginally posted by kuuan Quote
thank you for your comment Lowell, this makes sense.
the picture these histograms were taken off btw. is the pic showing the Konica camera
I may redo the test, resp. will find how the K-x does while using it soon enough anyway ;-)
what I do, as I stated is use a block wall or paved road. anything that is essentyally 1 color and uniformly lit.

then i use my photo editor to measure the grey scale value. In PSP X2 which I use, you can either measure the entire screen, or a sleection., I select the central 10%, although you could also use this method to look at the vignetting as a function of f stop by also plotting corner greysale vs f stop and comparing with center.
01-22-2010, 01:01 PM   #8
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I use a wall in the house or a grey card. I'm familiar with where either of these should fall on the histogram.

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