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01-11-2011, 10:45 PM   #1
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Can you use the camera's metering when using a lens like the Super Tak's?

Hi All,
I asked this in the lens section and wanted to post it here as well for additional exposure. I have some Super Takumar lenses I'd like to use on my K20D. How do you meter using older manual lenses?
Thanks,

01-11-2011, 11:48 PM   #2
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I shoot in manual about 99% of the time so this works in manual or aperture priority:
Activating the DOF preview will give you a meter reading, but he green button is generally quicker and will set the shutter to match exposure with whatever you set the aperture to.
01-12-2011, 12:03 AM   #3
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QuoteOriginally posted by johnny9fingers Quote
I have some Super Takumar lenses I'd like to use on my K20D. How do you meter using older manual lenses?
As stated in the post above, you can close down the lens to the aperture you want, then use Av or M (green button) mode.

But K10D and K20D are notorious for incorrect exposure with manual lenses (including pK lenses). To verify, try this: set the lens at the largest aperture, note the shutter speed recommended by the body, then close the lens's aperture one stop at a time, and note the shutter speed. In theory, the shutter speed will be halved each time. But that doesn't happen in reality. IME, the smaller the aperture, the more pronounced the exposure error.

You'll have to learn the character of each lens and adjust the exposure accordingly.
01-12-2011, 08:04 AM   #4
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There are a couple of ways to go about this, depending on your preferences.

I use Av Mode with my M42 lenses, where I focus wide open, and then stop down manyally to shoot. In Avmode, the camera meters off the light coming through the lens and therefore, tracks the change in lighting as you stop down.

The other way is to use M mode, and set the metering either with Green button or using the DOF preview to activate metering, and adjust the aperture and shutter separately.

Some people use Manual mode and the A/M switch on the lens to switch back and forth between wide open and stopped down on the lens. (Kind of like a preset lens and the stop down ring)

It is really your option,

The only thing I would suggest is that you look at your lenses and how each behave on the K20.

The K10and K20 have a reputation for odd metering behavior with manual aperture and M42 lenses including offsets of 1-2 stops as well as inconsistent (to varrying degrees as a function of aperture ) exposure.

I test each lens against a uniformly lit surface (Block wall or paved roadway) and measure the greyscale value of the shot as a fucntion of aperture. This lets me know how to set exposure if I really want it spot on.

01-13-2011, 03:36 PM   #5
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As mentioned, metering on K20D etc is sometimes inconsistent with some manual lenses -- and some are no problem at all. I use too many lenses to bother with rigorously testing each one and recording the results. When I slap-on a different lens, I fire a couple test shots to see what ballpark it's in, and adjust accordingly. And when I shoot, I chimp the results, and adjust again as needed, etc.

I'm sure others have better explanations, but I blame the K20D's default of center-weighted metering when using manual lenses. A workaround is to put a middle-brightness zone in the center of the viewfinder. The output can always be cropped to a desired composition. That's the same approach as using CIF: focus on the center and shoot. Yes, crop, to eliminate any unnecessary elements in the picture. Some purists and dilettantes will insist that you must "get it right in-camera" but those of us who've ever HAD to produce pictures, work otherwise.
01-13-2011, 04:53 PM   #6
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RioRico

The metering issue is divided into two parts

First is the issue with the focusing screen that leads to irratic behavior as a function of F Stop. This has been reasonably documented by myself and others

Second is whether the lens contacts are shorted or not. Insulated mounts lead to a global under exposure of a few stops on some cameras

Knowing how each lens behaves relative to the offset speeds up explsure calibration

Knowing the general performance as a function of aperture let's you adjust on the fly.

Without knowing the two leaves too much to chance if you need one shot without any test exposure
01-14-2011, 03:02 AM   #7
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QuoteOriginally posted by Lowell Goudge Quote
Second is whether the lens contacts are shorted or not. Insulated mounts lead to a global under exposure of a few stops on some cameras
This is curious. I shoot with some screwmount lenses with narrow bases that leave my K20D's contacts completely untouched, and yet get dead-on readings. I just haven't seen any consistency in the factors leading to misreadings.
01-14-2011, 06:33 AM   #8
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QuoteOriginally posted by RioRico Quote
This is curious. I shoot with some screwmount lenses with narrow bases that leave my K20D's contacts completely untouched, and yet get dead-on readings. I just haven't seen any consistency in the factors leading to misreadings.
i will try to define this a little further, with some testing in the future, but here goes.

On my *istD for example, If I use a K50F1.4, metering is almost spot on, wide open, and drifting slightly upward by 1/2 stop as you stop down to minimum aperture.

if I use my super tak 50F1.4 (version 1 but I don't think it matters) I need to add exposure compensation to get wide open metering correct and then it behaves just like the K50.

What I intend to do, is to try the same test on the super Tak, using a flanged adaptor.

My impression is that if all pins are left unconnected, metering has a bias that needs exposure compensation. EDIT update, Tested *istD with SMC TAK 35F2 using flanged and real pentax adaptor. lens equally underexposes in AV mode using both flanged and unflanged adaptors

I have noticed that my K10D is different in this respect, so I plan to do the test on it and my K7 as well

I think there are small differences in how individual cameras, or perhaps camera modes react, with different contact connections.

For example, the K7 will not give focus confirmation if the data pin is not shorted to the lens mount on a manual aperture lens, This was a topic of the forum a while back with vivitar autro extension tubes, which have a black painted/anodized lens mount that insulates the pins. sanding through to base metal corrects this issue on the extension tubes.


Last edited by Lowell Goudge; 01-14-2011 at 07:31 AM.
01-14-2011, 05:52 PM   #9
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On the K10D, my experience is that the metering behavior will vary with aperture - I notice underexposure wide open and overexposure when I stop down (in between, of course there is an aperture setting where the metering is just right - it's usually not an aperture setting I prefer to use ). But at a given aperture, the metering is fairly reliable. So I just learned how much to compensate for each lens at a given aperture.
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