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02-08-2012, 01:39 AM   #1
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KM light meter compared with k100d

Just got a KM camera and before i put a film through it I first checked the light meter against the meter in my k100d.

It seems that the KM's meter is consistently overexposing by one stop compared with the modern k100d. Is this a normal experience when using old film cameras? I know i can compensate with the ASA speed dial anyway. I could just run a test film through it and do some bracketing to fully test out the exposure i get. Any suggestions?

My question is should i expect that the metering for film to be different than digital? I wouldn't have thought so, but I wanted to see if others are having issues with their old film camera's metering.

02-08-2012, 02:06 AM   #2
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If both meters are accurate they should agree. Overexposing one stop on negative film isn't that big a deal. I would just shoot a roll of something cheap and see how it turns out. If you write down your settings for each shot you can see which combination of settings gave you good results or problems once the film is developed.

Keep in mind the KM uses a centre weighted meter, which may be different than what you have your K100d set to.
02-08-2012, 06:54 AM   #3
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Depending on lens that's mounted, I find the K100D tends to favor underexposure. This is also scene dependent, with the matrix metering. You should try the K100D in center weighted metering mode, to compare apples to apples.
02-08-2012, 10:43 AM   #4
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And you may have already done this, but make sure ISO speeds match in both cameras.

02-08-2012, 01:45 PM   #5
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I had the cameras set up to be as equal as possible. So ISO and centre weighted meter was set on the k100d in order to match the KM. The lenses were different though. The combination of shutter and f/stop are not the same on both cameras as well, which made things harder. The k100d offers a half or third of a stop in between the shutter speeds allowed on the KM. It took some hunting around for scenes which gave an equal setting or else I just made the necessary calculation to compare.

I'm going to run a film through the camera and keep note of the settings and maybe take some shots with the digital just to have another comparison. From then onwards everything should be fine.

How much exposure latitude can film handle anyway? I am guessing that the development stage is set as a constant (unless the film is meant to be pushed). So is the compensation of the exposure made at the printing/scanning stage in a similar way to a RAW digital image? How do different films cope with non-perfect exposure i.e. negative colour, slide or B&W etc.?
02-08-2012, 02:29 PM   #6
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Exposure latitude depends on the film - often it will be mentioned in the manufacturer's data sheet. For C41 films compensation would usually be done by adjusting your printing, while with traditional black and white you can adjust both printing and development.

Ilford claims that you can get printable negative from XP2 exposed anywhere from 50 to 800 ISO and processed as standard C41 film. C41 colour film and traditional black and white film often have relatively wide exposure latitude, while slide film generally has less latitude.
02-08-2012, 07:23 PM   #7
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To match up exposures perfectly, it would be preferable to use an evenly lit gray card to fill most of the scene. Using the same lens should keep everything matched up as close as possible.

I conducted a few film tests for latitude with the following films. Determined optimum exposure shutter/aperture via gray card then vary the shutter speed so many stops under and over this reference point. Scan auto exposure on with no color, levels or post process shadows/highlights adjustments.

Larger vesion Fuji 100 -> http://www.fototime.com/5662A1CA253B2E0/orig.jpg

Larger version Kodak BW400CN Exposure -> http://www.fototime.com/0A2BFD8BCB1F695/orig.jpg

Larger version Kodak Portra 400 -> http://www.fototime.com/B1379B2FE749C83/orig.jpg
02-09-2012, 02:04 AM   #8
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Wow, thanks LesDMess. It really shows that I could live with an accuracy of +/- one stop either side of optimum. The Fuji 100 seems to me to perform very well as does the BW. Does the kodak portra 400 vary more due to the higher speed? Do lower speed films have more margin for error? Would portra 160 give more latitude if light conditions allow its use over the 400?

02-09-2012, 06:03 AM   #9
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Of course you have to qualify each film and I certainly have not done that although I am trying . . . ;-)

Knowing I can overexpose by a lot, I came upon this scene that metered at 1/60 & f16 but I wanted to shoot at 1/4 or 1/2 so I knew Kodak Ektar 100 can handle it and it did without using ND filters.




Or when you have a scene with excessive contrast, you have a lot of latitude to "equalize" the scene.

02-09-2012, 10:02 AM   #10
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Just goes to show that film has way more dynamic range than digital, even RAW. This is one reason I am trying film. I can get amazing results very cheaply compared to a full frame DSLR. But I also like the way each film has its own personality straight out of the camera, whereas with digital this means sitting at a computer and digitally processing each shot.

Did you have to tinker with the waterfall image? It looks amazing considering the exposure settings. Seems like i don't really need to worry too much about hitting the exposure perfectly every time. I only have experience with digital and it really needs to be close. I have heard that the digital sensor's response is closest to slide film, where the latitude for correct exposure is quite small.
02-10-2012, 11:44 AM   #11
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You mentioned you were using different lenses on each camera. I've done similar comparisons with new film bodies vs my digital (or even other film bodies) and I've found that if you have different lenses on each camera you can end up with difference in meter readings. I use the same lens on both cameras that way it removes the lens as the variable. Different lenses can have different light transmission characteristics based on the quality of the optics and lens coating, the difference between a cheap lens and a high quality lens can easily add up to a full stop.
02-10-2012, 05:23 PM   #12
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The Pentax KM SLR exposure meter is at most mildly center-weighted.
Doubtless your DSLR takes a more center-weighted reading in any mode.

Further an accurate comparison would require use of lenses
with identical field of view (i.e. focal length) on both cameras.

Chris

Last edited by ChrisPlatt; 02-11-2012 at 07:56 PM.
02-18-2012, 12:22 PM   #13
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It has been a while, but I had some time to play around today. In my original post I said that the KM over-exposed. What I really meant to say was that the light meter was suggesting that the settings would over-expose. i.e. that the needle is higher than the mid-point. I was thinking of it a bit backwards.

Since I last posted I have bought a P30t for a really good price. This camera is amazing - large, clear viewfinder with a diagonal split focus screen. Very quick to focus and nice and easy to use in Av or manual. I wish my k100d had a good split focus screen. Using this after using only DSLRs was a revelation. Anyway, back to light meter issues.

I was able to put the P30t in the mix with the k100d super and the KM. All three cameras were tested with the same lens. I used the A 50 f1.7 as this is compatible with the k100d.

Most of the time the k100d and P30t agreed, but the KM definitely sets the needle about 1 stop above the middle. Inside the house, under lights things go all over the place. I thing that the k100d and P30t were close enough though.

I have managed to convince myself that the KM is suggesting over-exposure by 1 stop. I have gathered from this post and some research that it is better to ever expose than to under expose film. With this in mind I will run a test film through the KM with the ISO speed compensated down one stop.
02-18-2012, 05:35 PM   #14
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One stop consistent underexposed is not too bad and is a matter of adjustment. It is also not an uncommon behavior of cameras of that age. Alternately, you can just set the ISO/ASA one stop lower speed.


Steve
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