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12-05-2010, 03:25 AM - 1 Like   #16
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It's still not good, similar to K7.
The margin of deviation is about 2 EV values.

lens 1: A50/1.2
lens 2: Voigt 58/1.4

a) K5 and lens in A-mode
b) K5 in M-mode, lens controls aperture

lens set to infinity, shooting white screen, measuring in PS the grey value (y-axis).

Result:

A50/1.2

x-axis: f1.2 1.4 2.0 2.8 4.0 5.6 8.0 11 16 22


Voigt 58/1.4

x-axis: f1.4 2.0 2.8 4.0 5.6 8.0 11 16


Last edited by blende8; 12-05-2010 at 11:15 AM.
12-05-2010, 06:25 AM   #17
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Thanks. Results are intereting but one question. Did you measure whole scene or center 10% for greyscale? The reason i ask is i want to take vignetting, which is common wide open out of the equation.
Also note if all settings are neutral 45 greyscale is 1 EV
12-05-2010, 07:18 AM   #18
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I measured the center 50x50 pixels.
12-05-2010, 07:46 AM   #19
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Hi;

I have read a lot of posts about the metering on these cameras, mostly around stop down
for M lenses and AV for M42s.
With my KX what I believe is the real problem is the firmware should set the metering with or without the Contacts Shorted Out !
All of my lenses that contact, meter the same as manual stop down, no need to add + 1.7 EV. The M lenses could work in AV if the cam would stop down meter with the half press on the shutter as it should with AL- lock, otherwise just disengage the aperture lever on the lens and it will be as good as the M42s. Have converted 2 OM and 1 Nikon to work as well.

I would like to thank ALL of you for the invaluable info on this Forum that has helped me since the purchase of my Pentax. ( You could tape a beer can with a hole in it on these things and still get a good picture ! )

12-05-2010, 10:11 AM   #20
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QuoteOriginally posted by blende8 Quote
I measured the center 50x50 pixels.
Two more questions, maybe three
Was the paper the cull frame?
Spot or cw/ matrix metering?
How do these lenses perform on any other bodies you have?
12-05-2010, 11:03 AM - 2 Likes   #21
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QuoteOriginally posted by Lowell Goudge Quote
Was the paper the cull frame?
Spot or cw/ matrix metering?
How do these lenses perform on any other bodies you have?
- full frame
- matrix
- On the K20 the effect is similar, but stronger:



I had the K7 for a day for testing and I think the K7 is similar to the K5.

Last edited by blende8; 12-05-2010 at 11:13 AM.
12-05-2010, 11:44 AM   #22
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Thanks for these blende8, very helpful (+rep to you).

I wonder whether the results would be different for center-weighted than matrix (thinking of all my M-lenses and M42 lenses for which I don't get matrix). Would be an interesting experiment.
12-05-2010, 11:51 AM   #23
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QuoteOriginally posted by macTak Quote
Thanks for these blende8, very helpful (+rep to you).

I wonder whether the results would be different for center-weighted than matrix (thinking of all my M-lenses and M42 lenses for which I don't get matrix). Would be an interesting experiment.
It should not matter because there is no change in illuminatiOn this is why the test wants a full frame uniform surface

Note with this test if you look at the corner exposure you will also be able to measure vignetting

12-05-2010, 05:47 PM - 1 Like   #24
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I have taken Bende8's data and plotted it on my chart.

Sorry for the messy appearance, but this shows the basic results

It is quite interesting, in that it shows the K20D exposure to be very close to the same as K10D, with the K5D much improved.

Bende8, one thing I see with the A50/1.2 is that it appears the aperture control is inaccurate at F22,

The 58mm seems to have a couple of different issues, but appears to meter similar to the A50 in manual mode. In automatic it appears the aperture mechanism is no where near as linear and accurate as the A50.

Overall, I would say the K5 meters almost as good as the *istD, with only a slight dip at large apertures, and does meter better than the K7D.

The K20D test really validates the method, as it has long been suspected the K10D and K20D share metering issues, here, with 2 different cameras and testers and lenses, we come up with almost identical test results between an A50/1.2 in manual, and a K50/1.4 and K20 vs K10.
Attached Images
 

Last edited by Lowell Goudge; 12-05-2010 at 05:55 PM.
12-06-2010, 01:25 AM   #25
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Thank you Lowell, for plotting these together!

QuoteOriginally posted by Lowell Goudge Quote
Bende8, one thing I see with the A50/1.2 is that it appears the aperture control is inaccurate at F22,
Yes, it's interesting.
If I had more time I would measure all my lenses this way and perhaps with some other targets, too.
You learn something about their metering characteristics and can estimate the accuracy and possible problems.

And you see the spots on the sensor at f22.
12-06-2010, 01:44 AM   #26
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QuoteOriginally posted by blende8 Quote
Thank you Lowell, for plotting these together!

If I had more time I would measure all my lenses this way and perhaps with some other targets, too.
You learn something about their metering characteristics and can estimate the accuracy and possible problems.

You can skip measuring all lenses if you do it direct on the camera.
The K10D and K20D (don't own newer camera's) apply a measurement correction as function of the full open aperture as reported by the lens contacts.

Using a constant lightsource, and setting the camera to use the same aperture, and changing the contacts so the lens detects different open apertures, the camera used correction curve can be determined.
This avoids the extra inaccuracy of the lens.
12-06-2010, 02:59 AM   #27
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QuoteOriginally posted by glasbak Quote
You can skip measuring all lenses if you do it direct on the camera.
You get the correction curve of the camera, right.
But it appears that the lenses nevertheless all operate slightly different, perhaps due to slight variances in the aperture size, coupler position etc.

But seriously, do you really want to know all these aberrations, divergences and non-linearities of your lenses?
12-06-2010, 04:59 AM   #28
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QuoteOriginally posted by blende8 Quote
You get the correction curve of the camera, right.
But it appears that the lenses nevertheless all operate slightly different, perhaps due to slight variances in the aperture size, coupler position etc.

But seriously, do you really want to know all these aberrations, divergences and non-linearities of your lenses?
The biggest reason, I think, to map the performance of your lenses is to understand how each lens performs. If you really rely on the metering to be correct, it is useful to know when it will fail. Bende8's A50/1.2 is a great example. In a mode metering is spot on until F22 then it is about half a stop out I would want to know that

As to the time to do all the lenses start one lens per day
12-06-2010, 06:30 AM   #29
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QuoteOriginally posted by glasbak Quote
You can skip measuring all lenses if you do it direct on the camera.
The K10D and K20D (don't own newer camera's) apply a measurement correction as function of the full open aperture as reported by the lens contacts.

Using a constant lightsource, and setting the camera to use the same aperture, and changing the contacts so the lens detects different open apertures, the camera used correction curve can be determined.
This avoids the extra inaccuracy of the lens.
Measuring lenses directly is nothing to do with the camera function, but the lens function.

Note the exposure error of the voight 58mmF1.4, and the unexplained error in the A50F1.2. I would think any photographer would like to know how each of his lenses metered in advance of using them.

I am very far behind in testing all of my lenses, but plan to get back at it. Considering I have changed out the focusing screen in my *istD and K10D, and have added a K7D to my camera list, this is a lot of tests considering 30+ lenses and a few teleconverter combinations that I really do use frequently
12-07-2010, 05:59 AM   #30
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Just a shameless bump to the top and a request to move this to the K5 forum as it seems it should be there
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