K10D Stop down metering exposure problem

You can either have a digital preview, as you seem to be using, where the camera displays an image on screen, but doesn't record it to the card, or you can have Optical preview, when the camera simply closes the lens down to the selected aperture - just like traditional 'Depth of Field Preview'. This is what John's refering to. The options are in a custom setting somewhere (I don't have the K10D so can't tell you where).

Dan

you don't need to hold the lever during the exposure, only while metering.

I use it this way:

1. centre subject in frame
2. flick DOF preview with finger, check exposure is correct and take the opportunity to check the DOF as well while you're at it
3. adjust shutter speed/aperture as needed
4. release DOF preview switch, compose and shoot


It's literally exactly the same as using a Spotmatic series, just that the meter on/off switch is now the DOF preview lever.

The more things change, the more they stay the same.

correct



again correct, you understand perfectly (or at least we are both wrong the same way lol)

yes, but this only happens when the camera is operating an A series lens.
The camera is able to tell that the lens is not in A setting because the contacts don't engage (if you look at the back of an A series lens and move the aperture ring into/out of A, you will notice that one of the contacts moves in and out as you do so), or else everything is shorted if it's an M series or earlier lens.

unless an A series lens is detected, the actuator moves the whole way down (or doesn't move at all if the camera is in Av mode).


the camera only needs this information if it is trying to set the aperture itself or use multi segment metering. All it actually needs for stopped down centre weighted or spot metering is a light reading. For open aperture metering it would need a relative aperture value, but in stop down mode the light falling on the meter is exactly what will fall on the sensor and no other information is (should be) needed.

It's a dreadfully awkward thing to do IMHO. Which is why I use A series or later lenses on the DSLRs.

I don't see the point in struggling when the right kit for the job is readily available.

Ok, a quick empirical check of the green button/DOF preview lever gives the following results:

With:

- Camera in Manual
- A series lens but not in A (ie using aperture ring...)

... the DOF preview lever stops the lens down but does not set the shutter speed. You get an exposure readout (x stops over or under) while you hold it stopped down and you can alter the shutter speed manually until it reads "correct".

... the green button stops the lens down, AND sets the shutter speed to whatever it thinks is correct.

I could detect no difference between:

a) the shutter speed selected by the camera using the green button
b) the shutter speed selected manually, adjusting while stopped down until the readout indicates correct.

Conclusions:

1. As a means of quickly setting the shutter speed the camera thinks is correct given an aperture selected on the lens using the aperture ring, the green button is clearly superior.

2. As a means of getting a correct exposure with a non-A lens, it is no different from using the DOF preview lever.

Did the camera give the correct exposure in both instances?

I didn't check this. I was testing only the difference, if any, between the metering with green button vs DOF preview.

Given that it's given the wrong exposure with green-button stop-down in much of my other testing, I would speculate that since it's the same with DOF preview, it's just as wrong, if you get my drift.

I've got some numbers describing what I did, which I need to write down properly.. I'll post them when I get the chance.

only in the same way as Av mode is "clearly superior" to M mode


Don't get me wrong, I use the green button probably more often than DOF preview. The green button method is faster and on my *istDL2 it's more or less allways what I use. On my K10D where I know that the exposure will be off a bit the more I stop down I tend to use DOF preview and set my exposure accordingly. I'm slowly getting a feel for what will work out well.

given unlimited cash, I couldn't agree more. If I had the money all my M series and equivalent glass would be out the window tomorrow to be replaced by nice shiney new lenses. Saddly this is not an option for me, so I am slowly learning the ideosyncrasies of the K10D's meter.

It's really no different than learning to guess if it was a 1 stop evening or a 2 stop evening with my KR5 (always underexposed in low light), it's just not something one expects to have to do with a new DSLR. Especially not when the previous version worked fine.

I think on the whole I'm just going to use my M series and earlier lenses on the *istDL2.

???

I'm not suggesting Av is superior to M for a moment. Horses for courses.

I thought I was being specific - if your objective is to pick an aperture on a pre-A lens, and set the shutter speed for "correct" exposure, the green button is quicker, and hence superior to the DOF lever method, which only gives an exposure readout - you have to then choose the exposure and set it yourself.

The thing is, as you don't get better (as in 'more correct') exposure information by using DOF preview, I suspect it's quicker to press the green button, and then dial in whatever compensation is needed to offset its error.

I haven't worked out any rules about such compensation yet, and I doubt if I will. As John says, it's all just such a faff that I'm using my A- and later lenses more and more. If I have to use either of my M lenses, it'll be for something specific, almost certainly on a tripod, where trial and error will be perfectly adequate to get the exposure right.

Depending on the lens, there is an active market on eBay for M and K series optics. Even more so when the lens is one of the rarer ones. A 20mm f4 will always do well, a 50mm f2 will sell but for a low price.

Many of the more mundane A lenses sell for quite low prices - a 35-70mm f4 went recebtly for about £35 and it looked spotless.

In this way, at little expense if any, I have switched to A series only for my manual focus lenses.

After hearing that the exposure errors with the K10D might have to do with the grip, I tested it with an old M 200/4 lens with and with and without the grip.

It seems the grip doesn't make much of a difference. With this particular lens, it was:

f/4 good. slightly dark (histogram towards left
f/5.6 - f/16 good, histogram in middle.
f/22-f/32 slight overexposure but mostly highlights. Recoverable in RAW.

I tried with the grip turned off but still attached to the camera. I tested without the grip. Some of the more extreme shots at f/22 or f/32 were perhaps slightly less overexposed, but fully recoverable in Adobe Camera RAW.

I tested with and without the shake reduction. Did not seem to make much of a difference.
It was an ordinary street scene in a city, not extreme dynamic range. With the lens wide open, the exposures were always withing range, but leaned towards the left. The default in ACR was a touch dark, easy enough to fix.

f/5.6 to f/16 the histogram was more spread out (?!?!) but the photos were well exposed.

Only at the two smallest apertures, f/22 and f/32, were there any blown highlights. And those scenes were recoverable in Camera RAW.
Oddly, the first exposure of each series (after turning the camera on and off) was completely blown out. I had to press the green button a second time, and after that it continued to work fine. Strange.

This was a test with one lens, on a tripod. So now you know you can probably shoot with the M 200/4 lens in RAW (I used DNG) and get good results.

Perhaps later in the week I'll test some other old M lenses.

This is the scene I tested:

http://www.gartenphotography.com/private/test/test_image.jpg

Here's the flag at 100%, no sharpening applied:

http://www.gartenphotography.com/private/test/flag.jpg


Here's a corner at 100%., again no sharpening:

http://www.gartenphotography.com/private/test/corner.jpg

Obviously, this is a pretty decent lens. I'm glad it works as well as it does with the K10D.

Oh dear - I wish I had read this site properly a couple of weeks ago......

After waiting a long time for Pentax to bring out a digital camera even half as good as the LX I was delighted to see the recent very positive reviews of the K10D in Amateur Photographer & What Digital Camera. Here at last was a digital SLR worthy of the Pentax name offering 10 MP and the option of using my old M series lenses. Digital need no longer mean Extachrome and a slide scanner!

No mention in the press of the "known issue" of exposure problems with M series lenses. Oh yes, Pentax mentioned "restrictions", but these were described in terms of limiting the full functionality - ie a manual lens is clearly never going to be able to work in full program mode or autofocus. And of course, with the previous experience of ist DS users singing the praises of the easy use of M lenses who would have thought that there would be a problem?

All well & good until you read the instruction manual..and its tales of "exposure error" - what exactly does this mean I thought. And of course, it means exactly what ChrisA has described. In my case, accurate exposure (measured against performance with the "digital" lens and against my lightmeter and against my LX) is acheived at f5.6 and f8 with wild underexposure in low light conditions occuring at f16 and f22.

The result is EXACTLY the same whether you use the green button or use DOF preview and manual adjustment - the fact is that the lightmeter is off.

So - 30 years after I was the proud owner of my first SLR, a Praktica with stop down TTL metering, I find that Pentax have managed to produce a camera on which the lightmeter does not work in the most basic of modes. Quite simply; it is unable to measure accurately the amount of light coming through the hole!

It is not a matter of "changing technology" and incompatability with older lenses - the fact is that M lenses were compatible in this mode with the *istD series cameras and there is no real reason why they should not be able to work on the K10D. This camera has clearly been released onto the market before this issue was resolved (otherwise why acknowledge the fault in the manual) in the hope that either very few people will notice OR that we will put up with it.

Question is what are people doing about it? I am now very tempted to send the camera back from whence it came and shoot off a stiff letter to the MD of Pentax in Japan, suggesting that he take a long hard look at an LX, MX, ME super, Spotmatic or even an old Praktica or Zenith and find out how they managed to acheive this minor miracle 40 years ago!

Is it just a few of us (in which case they should replace ours with one that works) or does everyone really have this issue and just not care about it?
I have grown rather attached to my M series 15mm f3.5 rectilinear, 20mm f4, 200mm f2.5 and 300mm M* f4 lenses...amongst others, and may just revert back to the LX, Ektachrome & the slide scanner!

I think this is to a large extent a moot point in that there is full compatibilty from the A series onwards. That dates back over 25 years, give or take, and I don't think we could really grumble too much at that. It's much better than Canon, perhaps on a par with Nikon and vastly better than Olympus. Olympus offer an OM adapter that has lots of restrictions as to which apertures can even be used.

Like it or not, the future is with the new digital lenses and the backwards comaptibility is just a bonus.

The irony is that go back even further and it gets better again - the screw thread lenses are, in my opinion, actually easier to use on digital than the K and M series ones.

I am enjoying the K10D very much and using it with lenses it is designed for.

As stated in my test, if you turn off the grip (no need to remove it), you can obtain acceptable results with at least one M series lens. More to be tested later.

If you aren't interested in shooting RAW, then you shouldn't be playing with older M and K lenses. jpeg is for snapshots, RAW is for serious photography.

I'm sure I'll get flamed for this opinion, however that's my experience. I have over 35 years' experience in professional photography, and I think I might have learned a thing or two over the years.