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10-30-2008, 01:41 AM   #1
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To KatzEyes or FocusingScreen owners...

Hello!

I'm currently trying to determine which screens are actually working well with the K10, metering-wise. Sorry if you feel this thread is a re-run of my previous thread, but I think this will really help a lot of people...

It's now a rather well known fact that the factory screen is not linear (meaning that it will underexpose above f/4 and overexpose below f/5.6), thus not really adapted to PK or M42 lenses.

Could you do this quick experiment with your 3rd party focus screen and post your results here? This would be really great! (The whole process take about 30s)

- set the body to 100iso, MF, and daylight WB
- use a constant light source (I stuck my lens against a blank laptop screen!)
- physically select an aperture on the lens, push green button, and shoot.

At the end of your aperture range, in playback mode, thumbnail display, check that the exposure is constant from one pic to the other. If this is the case, then the screen has a linear response.

Thanks for your time!

10-30-2008, 01:42 AM   #2
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And I'll post my own tests here :

- Factory screen :
> NOT LINEAR!
> underexposure above f/4
> overexposure under f/5.6

- Chinese split-screen (from K1000 focus screen) :
> NOT LINEAR!
> underexposure above f/4
> overexposure under f/5.6

- *ist LL-60 screen :
> LINEAR!
> constant -2/3Ev underexposure
10-30-2008, 04:41 AM   #3
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first of all, I think you have got it wrong with respect to metering.

below F4 the screen causes under exposure and above 5.6 over exposure.

if you are going to post results, DO IT PROPERLY not with vauge expressions of exposure but with data, Use a uniform surface, block wall paved road etc. use green button metering in manual, and record F stop for each exposure, Measure grey scale in a photo editor, and post grey scale vs apature.
see the post below.

https://www.pentaxforums.com/forums/241716-post69.html
10-30-2008, 05:11 AM   #4
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Lowell, we said exactly the same thing, it all depends on what "above" means for you... In my case, I'm talking about actual aperture dimensions, so "above f/4" means f/2.8, f/2, and so on... In yours, "Above" refers to the numerical value of the aperture...
Maybe this is not the standard terminology, I'll change it if needed.

Now, there is no need to actually read a grey scale in a photo editor... Just compare theorical and actual speeds and this will give you the exact Ev difference at a given aperture. Not vague, but precise and easy. Granted, this is by supposing that shutter speeds and apertures are acurate...
Having tried the gray scale approach myself, I even found this method more precise, as noise can really mess with the gray patch readings...
My charts were really close to yours now I see it again, by the way.

Okay, my fault, I was rather vague in the first post...
So, for those interested in this experiments, please post an Aperture/speed array of your results. I'll do the maths myself so you won't lose too much time on this!

Thanks again!

10-30-2008, 06:15 AM   #5
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So is some of this to determine how the chinese version will compare to the Katz Eye?

Sorry, I want spit screen but don't want to fork out $100 so I am keeping an eye on the data and opinions of such.
10-30-2008, 06:47 AM   #6
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QuoteOriginally posted by OrenMc Quote
So is some of this to determine how the chinese version will compare to the Katz Eye?

Sorry, I want spit screen but don't want to fork out $100 so I am keeping an eye on the data and opinions of such.
That is the idea. I am in the same boat, I know (as I have measured it carefully) the K10D has issues with manual lens metering and the standard focusing screen. I also don't want to spend unnecessairly on the split image screen at this point, without having some good data on how it preforms. Although many people have made statements or offered general impressions, I would love, just once, to see real data. In camera tests tell you nothing about whether the lens is slightly off on f stop, or whether the results are being distorted by the camera's EV adjustments not matching the lenses 1/2 stop apature detents, or whether you are just on the threshold of a metering step, i.e. either up or down by the next 1/3 or 1/2 stop increment.
10-30-2008, 08:33 AM   #7
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I have the katz eye on my K20D, and on my K10D before that. My Pentax DSLR's have never metered perfectly, with factory screens or with the Katz Eye's. Sometimes it overexposed, sometimes under. I've always just taken a few test shots, chimped the histo, adjusted the EV, and forgot about it. Simple & easy.

You guys must be bored.
10-30-2008, 09:22 AM   #8
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Not a case of being bored as it is a case of needing more reliable metering with non A lenses, of which I have 8.

Presently, I rely on the *istD metering with these lenses, but would like to do more with them at higher resolution. I don't always have time to shoot, check histogram and shoot again when shooting wildlife.

With A lenses I agree, errors are usually consistent with each lens, and yes, you can take a test shot, set EV comp and forget about it, which is what I do with a TC on my Sigma 70-200 F2.8, but when you have an error that is variable due to selected F stop on a manual apature lens, you can't do that.

10-30-2008, 10:12 AM   #9
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QuoteOriginally posted by Lowell Goudge Quote
.....
With A lenses I agree, errors are usually consistent with each lens, and yes, you can take a test shot, set EV comp and forget about it, which is what I do with a TC on my Sigma 70-200 F2.8, but when you have an error that is variable due to selected F stop on a manual apature lens, you can't do that.
With regard to the manual aperture and lens, I still essentially do the EV comp... it's the shutter speed. I typically shoot manual and select an aperture and then a shutter speed to get the exposure as I want. If I chimp the histogram and I need an adjustment, I usually just shift the shutter speed to get the EV I want.
10-30-2008, 01:57 PM   #10
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QuoteOriginally posted by emalvick Quote
With regard to the manual aperture and lens, I still essentially do the EV comp... it's the shutter speed. I typically shoot manual and select an aperture and then a shutter speed to get the exposure as I want. If I chimp the histogram and I need an adjustment, I usually just shift the shutter speed to get the EV I want.
I don't disagree, but it is not as easy or simple as it A should be, or B is on my *istD which meters corretly with pushing the green button on any manual apature lens.

For most cases, it is not an issue, either with lenses stopped down below F8 because you always have to add about 1 1/2 stops, BUT the issue is with a fast lens, where depending on apature at the time, the compensation can be over, under or none, it is a bit of a pain. As I said earlier, my real problem is that when shooting with a long lens, through shadows and constantly changing apature, it becomes rather bothersome. If I am just out walking about, I will meter off the road (18% grey) set things once and be done with it.
10-30-2008, 02:07 PM   #11
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QuoteOriginally posted by Lowell Goudge Quote
I don't disagree, but it is not as easy or simple as it A should be, or B is on my *istD which meters corretly with pushing the green button on any manual apature lens.

For most cases, it is not an issue, either with lenses stopped down below F8 because you always have to add about 1 1/2 stops, BUT the issue is with a fast lens, where depending on apature at the time, the compensation can be over, under or none, it is a bit of a pain. As I said earlier, my real problem is that when shooting with a long lens, through shadows and constantly changing apature, it becomes rather bothersome. If I am just out walking about, I will meter off the road (18% grey) set things once and be done with it.
The constant changes is part of the reason I've gone to almost exclusive manual exposure and I rarely use the green button. I also hate dealing with the constant changing aperture or other items, so for me, I use manual exposure as a kind of aperture priority... i.e. set an aperture then adjust shutter speed to get the exposure I want (accounting for my typical over under exposure compensations).

Of course all of this is because the green button doesn't work as well or consistently as it should. With the K10d being my first dSLR, I guess I should be glad that I haven't had the luxury of how well it could work as you do with the *istD. It would only make me more anxious to have the behavior fixed. As it is, this issue is a minor inconvenience compared to my previous non dSLR cameras or even my old film SLR which had no automatic settings whatsoever (a 1960's vintage Minolta).
10-30-2008, 02:18 PM   #12
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QuoteOriginally posted by emalvick Quote
The constant changes is part of the reason I've gone to almost exclusive manual exposure and I rarely use the green button. I also hate dealing with the constant changing aperture or other items, so for me, I use manual exposure as a kind of aperture priority... i.e. set an aperture then adjust shutter speed to get the exposure I want (accounting for my typical over under exposure compensations).

Of course all of this is because the green button doesn't work as well or consistently as it should. With the K10d being my first dSLR, I guess I should be glad that I haven't had the luxury of how well it could work as you do with the *istD. It would only make me more anxious to have the behavior fixed. As it is, this issue is a minor inconvenience compared to my previous non dSLR cameras or even my old film SLR which had no automatic settings whatsoever (a 1960's vintage Minolta).
welcome to pentax and the 21st century
10-30-2008, 07:57 PM   #13
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I've just installed a split screen from a mob called GadgetInfinity (I think) into my K10D. Haven't used it enough to have any opinion about exposure accuracy (the few pictures I've taken were while experimenting with a Nikon/PK adaptor from the same mob).

However, reading the process to be followed... is this only a worry for 'old' & 'fast' lenses. I only have 16-45 and 50-200's, so I have no aperture rings and I can't go wider than f4 (unless I bolt on a Nikkor)

Nige.
10-30-2008, 08:11 PM   #14
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QuoteOriginally posted by HGMonaro Quote
I've just installed a split screen from a mob called GadgetInfinity (I think) into my K10D. Haven't used it enough to have any opinion about exposure accuracy (the few pictures I've taken were while experimenting with a Nikon/PK adaptor from the same mob).

However, reading the process to be followed... is this only a worry for 'old' & 'fast' lenses. I only have 16-45 and 50-200's, so I have no aperture rings and I can't go wider than f4 (unless I bolt on a Nikkor)

Nige.
a bit off topic, but I would love to know how the nikon to PK adaptor works, and whether it is optically compensated to correct for infinity focus
10-30-2008, 11:59 PM   #15
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At first, this thread was making me worried because I'm thinking about getting the split-screen. But then I realised I could relax. I have the K10D, I know it's capable of so many things, but I rarely step outside of full manual control and never let the camera try to think for me. And worrisome issues like this make me glad I don't. Sometimes I think it's a pity many of us have to overcapitalize on such highly technical pieces of equipment simply to continue with basic photography in the digital environment. Someone please bring out a nuts-and-bolts manual DSLR!!

That's my Friday rant. As you were.
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