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02-21-2009, 11:34 AM   #1
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Metering issues with MF lenses

I've been trying to compare my MF lens normal primes: M50 1.4, M50 2.0, and M40 2.8.

I've been using the stop down method with my k200d: set camera to "manual", set aperture, press green button to let camera meter and for camera to set shutter speed.
I noticed that with my M50 1.4 that the it exposes fine @ full open, however once I start stopping down to smaller apertures, the shots tend to be overexposed. Not sure yet if it's a consistent overexposure. I'd post some 'controlled shots' but my camera's original lithium batteries have finally died so I can't do so.

It seems I don't get this with the M40. Haven't quite noticed it with M50 since I've been taking test shots mainly wide open. Do I have sticky aperture blades on my M50 1.4 or something? Once I get some more batteries (another post .... as my rechargeables don't seem to work on the camera, works on the flash though)

Of course it could all be due to the dude behind the lens

02-21-2009, 11:50 AM   #2
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This is one of the known "problems" with these and other manuals. When you change aperture, you have to change EV compensation too. Positive or negative is dependent on the lens you've got.... Just a matter of experience and of knowing your lenses, I guess. You could also check my reply in this thread.

Succes!
02-21-2009, 11:55 AM   #3
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This is a known issue, at least with the K10D. I think all Pentax DSLRs after the *ist series have this problem. The problem is related to the incompatibility between the focusing screen and the old lenses. What makes it difficult to deal with is that the extend of the problem varies with each lens.

There are two options:

1. Meter at full aperture of the lens when it is most accurate (least inaccurate), then adjust the aperture and the shutter speed accordingly.

2. If possible, replace the focusing screen with the one for the *ist series (e.g. LL-60).

I've heard that some after-market focusing screens (with split image) can also fix this problem. But there is no concrete data on this.
02-21-2009, 01:29 PM   #4
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QuoteOriginally posted by PentHassyKon Quote
I've been trying to compare my MF lens normal primes: M50 1.4, M50 2.0, and M40 2.8.

I've been using the stop down method with my k200d: set camera to "manual", set aperture, press green button to let camera meter and for camera to set shutter speed.
I noticed that with my M50 1.4 that the it exposes fine @ full open, however once I start stopping down to smaller apertures, the shots tend to be overexposed. Not sure yet if it's a consistent overexposure. I'd post some 'controlled shots' but my camera's original lithium batteries have finally died so I can't do so.

It seems I don't get this with the M40. Haven't quite noticed it with M50 since I've been taking test shots mainly wide open. Do I have sticky aperture blades on my M50 1.4 or something? Once I get some more batteries (another post .... as my rechargeables don't seem to work on the camera, works on the flash though)

Of course it could all be due to the dude behind the lens
Sticky aperture blades would cause overexposure. With a couple of M50 lenses, you can compare them without dealing with the possible issue of metering errors. Off the camera, set them to f22 and flick the aperture lever. The aperture should snap open and closed. On camera, you can use one lens to measure and set the exposure, take a photo, then swap lenses and take a second photo at the same settings. The exposures should be nearly identical, not more than 1/3 stop difference.

You should also be able to meter wide open, then with a constant light source, a tripod and in M mode, close up one stop on the aperture ring and go down one stop on shutter speed (don't re-meter, just take the photo). All these exposures should come out very close to each other.

02-21-2009, 02:20 PM   #5
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The "known" issue really applies only to the K10D and K20D, which share the same focus screen. The K100D and K200D do not normally exhibit any real problems here. I've done a test with my M135/3.5, doing a Green button exposure after each click of the aperture ring, and the resulting exposures match as perfectly as can be - within a quarter of a stop of each other as measured in PP. The fact that some of the OP's lenses don't exhibit this does suggest perhaps sticky aperture blades - or perhaps the mechanism that sets the aperture just isn't that accurate. how big discrepancy are we talking about?
02-21-2009, 03:01 PM   #6
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I noticed a big improve in metering with M lenses in M mode and M42 lenses in Av mode with my K-m. Before on my K10D I had to change the EV compensation everytime I change aperture setting on M42 lenses. Now on the K-m I don't have to do this anymore, the metering is spot on. But I noticed that with some of the M42 lenses I have to permanently dial some +EV but it is spot on for any aperture settings of this lens. And the Metering using the green button in M mode with M lenses is always spot on.
02-21-2009, 05:03 PM   #7
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QuoteOriginally posted by Marc Sabatella Quote
The "known" issue really applies only to the K10D and K20D, which share the same focus screen. <snip>
OK, this explains why I was having so much trouble trying to use my M50 1.7 on my K10D. Back to learning about this and testing it.
Brian
02-21-2009, 10:40 PM   #8
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Original Poster
QuoteOriginally posted by SOldBear Quote
This is a known issue, at least with the K10D. I think all Pentax DSLRs after the *ist series have this problem. The problem is related to the incompatibility between the focusing screen and the old lenses. What makes it difficult to deal with is that the extend of the problem varies with each lens.

There are two options:

1. Meter at full aperture of the lens when it is most accurate (least inaccurate), then adjust the aperture and the shutter speed accordingly.

2. If possible, replace the focusing screen with the one for the *ist series (e.g. LL-60).

I've heard that some after-market focusing screens (with split image) can also fix this problem. But there is no concrete data on this.
QuoteOriginally posted by Just1MoreDave Quote
Sticky aperture blades would cause overexposure. With a couple of M50 lenses, you can compare them without dealing with the possible issue of metering errors. Off the camera, set them to f22 and flick the aperture lever. The aperture should snap open and closed. On camera, you can use one lens to measure and set the exposure, take a photo, then swap lenses and take a second photo at the same settings. The exposures should be nearly identical, not more than 1/3 stop difference.

You should also be able to meter wide open, then with a constant light source, a tripod and in M mode, close up one stop on the aperture ring and go down one stop on shutter speed (don't re-meter, just take the photo). All these exposures should come out very close to each other.
At 1st reading SOldbear's answer kinda made me think - this no longer sounds like 'stop down' metering. It sounds like I can only meter full open, then adjust my shutter speed depending on how many stops I want to stop down. Too many gyrations for me to make it worthwile. I can't imagine any of you LBA fanatics out there doing this unless it's because all you LBA's shoot wide open all the time.

I checked my lenses off camera-
Looks like I may have the sticky aperture blade symptom. My M50 1.4 aperture blades do open and close but not as quickly as those on my M40.
So, is there a tutorial around so I can help clear this issue up? It seems my Viv S1 28-90 has the same issue. I also have a Viv 28-85 which won't even stop down - always wide open. What causes a slow to close aperture blade - oil, gunk or spring?

02-22-2009, 01:01 AM   #9
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QuoteOriginally posted by PentHassyKon Quote
At 1st reading SOldbear's answer kinda made me think - this no longer sounds like 'stop down' metering. It sounds like I can only meter full open, then adjust my shutter speed depending on how many stops I want to stop down. Too many gyrations for me to make it worthwile. I can't imagine any of you LBA fanatics out there doing this unless it's because all you LBA's shoot wide open all the time.
I have a bunch of old lenses, and because of this problem, didn't use them often until I bought an LL-60 screen. Now that the exposure problem is fixed, I'm using the old lenses more and more.

QuoteQuote:
I checked my lenses off camera-
Looks like I may have the sticky aperture blade symptom. My M50 1.4 aperture blades do open and close but not as quickly as those on my M40.
So, is there a tutorial around so I can help clear this issue up? It seems my Viv S1 28-90 has the same issue. I also have a Viv 28-85 which won't even stop down - always wide open. What causes a slow to close aperture blade - oil, gunk or spring?
The aperture blade problem can have many different causes. But the most common is oil on blades. Please read this thread.

Sooner or later, you'll learn how to perform surgery on lenses.
04-29-2009, 06:06 PM   #10
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LL-60 works!

My LL-60 arrived from Japan in the mail today. I just put it into my K10D and put on the M 400/5.6. My shutter speeds got twice as long every time I changed to a smaller stop. All the way from f/5.6 to f/45. Yaaahooooo!!!!

Thank you everyone who suggested this. It works! Yay!

Did I mention I'm happy?
04-29-2009, 06:13 PM   #11
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QuoteOriginally posted by Canada_Rockies Quote
My LL-60 arrived from Japan in the mail today. I just put it into my K10D and put on the M 400/5.6. My shutter speeds got twice as long every time I changed to a smaller stop. All the way from f/5.6 to f/45. Yaaahooooo!!!!

Thank you everyone who suggested this. It works! Yay!

Did I mention I'm happy?
Way to go, Rockies.

Can you imagine that many times I got slapped on my wrist by suggesting the LL-60 screen to fix the over-exposure problem?
04-29-2009, 06:17 PM   #12
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This is yet another reason why Pentax should stop using a crippled lensmount. If they had the aperture arm in the mount for non-A lenses then everything would be metered wide open and then adjusted accordingly & correctly for smaller apertures. For a company that takes pride in its backward compatibility, using a crippled lensmount is a slap in the face.
04-29-2009, 06:31 PM   #13
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QuoteOriginally posted by SOldBear Quote
Way to go, Rockies.

Can you imagine that many times I got slapped on my wrist by suggesting the LL-60 screen to fix the over-exposure problem?
Yeah, but you were not the only one pushing the LL-60. I'm now a fan as well. Tomorrow I'll be testing it with the DA lenses to see if that metering has gone off at all. If all I have to do is mount a DA lens and add 1/2 stop or something, I'll take it.

BTW - I only have one dust speck in my viewfinder now. I was luckier switching screens this time.
04-29-2009, 07:11 PM   #14
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QuoteOriginally posted by F16 Quote
This is yet another reason why Pentax should stop using a crippled lensmount. If they had the aperture arm in the mount for non-A lenses then everything would be metered wide open and then adjusted accordingly & correctly for smaller apertures. For a company that takes pride in its backward compatibility, using a crippled lensmount is a slap in the face.
Yeah, that and the silly P-TTL.

If they kept TTL, flash metering would be correct (at least in theory) no matter what I attached to the camera body, even a pin hole body cap.

Now getting consistent correct flash exposure with the built-in flash and an M-lens has become next to impossible.
04-29-2009, 07:36 PM   #15
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can I use the LL-60 or LL-80 on the 200?
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