Metering with manual lenses--exasperated!

donutley · 10-12-2008, 03:41 PM

Here's my challenge: I recently bought a manual lenses badged by Sears--a very nice light 135/2.8 from the 80s, I believe. It's a fun little lens that I am hoping to get a lot of use from, but this is the first time I've used a manual lens (I have an A series zoom and some DA lenses). I'm using them on a K10D body.

I've done all that I know to do (from the research I've done on this forum)--set the custom menu to allow the aperture ring on the lens to be used, set the camera to M, set for center-weighted metering, used the green button to step down meter. All works great at 2.8--great exposure. I shift to 4.0--same thing. I move to 5.6--the correct shutter settings seems to register in the viewfinder, but it overexposes just a tad compared to the previous shots.

Then when I go to f8, it completely blows out the highlights--very overexposed.

Is there a reason for this that I'm unaware of? Do I have to step down meter only at the largest aperture (2.8)? Your help will be greatly appreciated.

Don Utley

*Mike Cash* · 10-12-2008, 03:50 PM

That's something that the K10D seems to have a reputation for doing. One of the reasons I was never interested in buying one.

*Canada_Rockies* · 10-12-2008, 04:13 PM

There is an alternate solution to your troubles. The lens may have a sticky aperture. If you have very sensitive fingertips, set the aperture to f/22 with the lens off the camera, and gently move the stop down lever. You should feel an absolutely even move, with no sudden increases in tension. The tension will increase slowly as you compress the return spring, but there should be no jumps.

Try an alternative metering method, the one I use. Set our lens to the preferred aperture, then with your depth of field set to optical (through the lens, neither LCD nor Live View) and meter by pulling the on/off switch to the dof setting and use the over/under scale to set your exposure.

That said, I find that only settings between f/8 and f/11 are accurate with my M 400/5.6. As these are the most useful apertures with the lens, it does not bother me too much. If it is outside that range, I apply corrective exposure settings on the scale.

donutley · 10-12-2008, 04:32 PM

Great! I checked the aperture as you suggested--and it seems fine. I then tried your alternative method of metering and it works great. Thanks, Albert. This is a life-saver!!

pschlute · 10-12-2008, 04:43 PM

The progressive overexposure as you stop down is well documented with the K10D. I wont go into the reasons here, you can do a search if you want to find out.

One fix is to fit a new focus screen, ones from the DS or an LL80 will solve your problem.

Or you can press the green button to meter with the aperture wide open and then stop down to your required aperture and adjust the shutter speed by the same number of stops.

This has nothing to do with sticky aperture blades, and using the DOF preview button to meter will give you the same overexposure problems.

Lowell Goudge · 10-12-2008, 06:02 PM

it all comes down to the focusing screen

See the following

http://www.pentaxforums.com/forums/241716-post69.html

this also causes the K10D to over expose when using teleconverters with pass through contacts, because it needs to know the real apature to meter correctly.

Pentax is aware of it but the official response I got was they did not have enough credible complaints to act on it before they finished all sopftware for the K10D and finished production.

jgredline · 10-12-2008, 07:52 PM

Sorry that i missed this, but can one point me to the complete thread on the focusing screens and split screen threads.
Thanks.

clee01l · 10-12-2008, 08:22 PM

You might buy a standalone light meter and go full manual

*Stratman* · 10-12-2008, 08:35 PM

Originally Posted by Mike Cash

That's something that the K10D seems to have a reputation for doing. One of the reasons I was never interested in buying one.

Mike, how does the K20 do with manual k mount lenses with the green button? My K110 is pretty accurate with them, but the K10 is a pain in the #$% with the green button.

*Mike Cash* · 10-12-2008, 08:49 PM

Originally Posted by Stratman

Mike, how does the K20 do with manual k mount lenses with the green button? My K110 is pretty accurate with them, but the K10 is a pain in the #$% with the green button.

I haven't even tried it that way. Works great with M42s, though. I have no reason to put an M-series K-mount on my K20D, but I keep them around for my film ME.

*Stratman* · 10-12-2008, 08:51 PM

Hmmm, does it meter pretty accurately with the M42s in AV mode? or do you use the green button for those?

*Canada_Rockies* · 10-12-2008, 10:21 PM

Originally Posted by Stratman

Hmmm, does it meter pretty accurately with the M42s in AV mode? or do you use the green button for those?

M42 lenses meter stopped down, so the error does not occur. My system for solving the problem is to use only those apertures for which I know the exposure is correctly metered. I have an M macro and an M 400, and I do not have the cash to replace them with A or later lenses, so I have had to figure out which apertures work and which don't. I am still calibrating the M 100 macro, because I often want to use an aperture much smaller than is accurate, and need to know how far off the metering is and which way so I can correct for it. In the mean time I know that both my M's meter closely at f/8, and use the meter once, shoot many times system. Sunny 16 is a bear to use with a macro - I don't even try - but works like a gem on the 400.

dlacouture · 10-13-2008, 02:16 AM

Unfortunately, no, m42s also suffer from the same problem : underexposure above f/5.6, overexposure below f/8...

I'll try the LL60 in a little while, just to see how it handles things...

For those interested, I tried a split-screen from jinfinance (chinese vendor on ebay), and it shows the same behavior as the original screen, but with a slight +2/3ev overexposure (which is not so bad as it sort of solves my problem of -1ev underexposure with my fast manual lenses)...

RiceHigh · 10-13-2008, 05:23 AM

RiceHigh's Pentax Blog: When the Focusing Screen Lies (for Focusing and Metering)

Of course it is a known problem for many Pentax users, not an officially admitted one.

Solution? Yes, replace an older DS screen to it and quite some users reported it works! But why newer stuff from Pentax have more problems remain a mystery to most of us!

Originally Posted by donutley

Here's my challenge: I recently bought a manual lenses badged by Sears--a very nice light 135/2.8 from the 80s, I believe. It's a fun little lens that I am hoping to get a lot of use from, but this is the first time I've used a manual lens (I have an A series zoom and some DA lenses). I'm using them on a K10D body.

I've done all that I know to do (from the research I've done on this forum)--set the custom menu to allow the aperture ring on the lens to be used, set the camera to M, set for center-weighted metering, used the green button to step down meter. All works great at 2.8--great exposure. I shift to 4.0--same thing. I move to 5.6--the correct shutter settings seems to register in the viewfinder, but it overexposes just a tad compared to the previous shots. Then when I go to f8, it completely blows out the highlights--very overexposed. Is there a reason for this that I'm unaware of? Do I have to step down meter only at the largest aperture (2.8)? Your help will be greatly appreciated.

Don Utley

stevebrot · 10-13-2008, 10:10 AM

As noted above, the K10D (and K20D for that matter) have well-documented metering issues with M-42 and non-A K-mount lenses. I have heard all sorts of reasoning on this matter as to causes. The focus screen has been singled out, but there have been posts that indicate no improvement with replacement screen. Pentax has been pretty mum about workarounds.

Here are my observations as the owner of a K10D and a few non-A lenses:

There is no general bias to apply to exposure
The pattern varies according to lens. Some overexpose at larger apertures, others at smaller
Most will meter correctly at f/5.6-f/8.0

My general approach is to either

Meter at f/5.6 and manually calculate shutter speed for the desired aperture.

-- OR --

Do the green button at the desired aperture and chimp the histogram to determine the best shutter speed.

Steve

BTW...The accuracy at f/5.6 noted above is a generality. My Zenitar 16/2.8 with green-button overexposes 2-3 stops regardless of aperture.