That is the only modern lens that I own, and I love it! It's sharp, fast for a zoom, and has all the modern electronic connections to make it jump thorugh all the hoops it's supposed to. The rest of my lenses are old dinosaurs. Reallty good, sharp dinosaurs, but dinosaurs nontheless.

A Lexar Write Accelerated card certanly makes a difference on my D, it's the fastest card I have and it makes a big difference in continuous mode.

Well, I tried testing the DOF preview in Av and M. It seems when the shutter fires, the apature closes down in any mode. But you are right, in Av the DOF preview doesn't stop down the lens whereas in M it does! I still can't figure out how I've been getting my correct exposures, since if the lens doesn't stop down with DOF preview in Apeture priority, how can I be getting correct exposures at differrent apetures with the correswponding differnt shutter speeds???

Nearest I can figure, maybe the camera is making an instantanious measurement as you make the exposure? Otherwise, I can't explain why if I shoot at a small apeture in Av I get a longer shutter speed than wide open, but the image is still properly exposed!

A mystery has been comitted. But you are correct, the lens does not shut down with DOF preview in Av but the diaphram does shut down when the shutter fires. This is all very mysterious!

I heard once that the LX measured exposure during the time the shutter was actually closed. Could this technology somehow be linked to the sensor itself? I think further research is defenitely in order here.

But you are correct that the DOF preview doesn't close the diaphram in Av, but firing he shutter does. Now I'm really puzzled!!

Here's the problem; you haven't pulled the ring to DOF preview, so the camera has no idea what the lens is set to. That's the critical step, and that's why we think we're talking about the same thing but we're not!
What's missing from your description is the step where you pull the power switch to DOF preview while the camera is in Av mode. That step tells the camera what the lens is set to, if you forget that step the camera has no idea what is on the front of it.

So, by using the DOF preview, you get corrrect exposures. I repeated the test with a third party lens, an ancient K mount Vivitar 135mm f/2.8 Close Focus (great lens). If the DOF preview is pressed to tell the camera what the lens is set to then the camera assumes the apeture is whatever it was when you pressed the DOF preview. If the light changes, the camera knows what it measured as far as light, and adjusts the shutter speed accordingly.

If the meter shuts off, and you don't press the DOF preview again, the camera is clueless and will probably not give you a proper exposure.

Now, I have tried what you describe and gotten the results you describe. So pulling the DOF preview in Av mode is the thing that makes the difference. As long as you don't touch the apeture ring while the meter is on, you can just swing from a light scene to a dark scene and the camera will give you correct exposure. I use this and it works.

There's some other thing in all this that's causing us to disagree about what are apparently two diffeent sets of conditions!

Actually, I modified my post to include the test you suggested. The same apature yielded different shutter speeds, and all exposures were correct.

I don't know about the different times the lens stops down. Try this:

Put the camera on Av and Manual Focus.

Put in an M lens.

Set the apature to f/22.

Take your initial reading.

Before the meter shuts off, fire the shutter and look at the lens. It stops down during the exposure.

Take several exposures in different lighting conditions before the meter shuts off. Check the shutter speeds and histograms on your exposures.

The shutter speeds will be different, and all images will be exposed correctly (according to the center-weigted meter).

This means the lens is stopped down during the exposure, not necessarily befiore or after.

I will use this on a third M lens later on today.

This should show you that the lens is stopping down to whatever it's set to when the exposure is taken. Only the shutter speed changes, because the camera can't change the lens apeture. It is what it is.

That's the idea of apeture-preferred exposure, you set the apeture and the camera's meter adjusts the shutter speed.

Again, check your firmware version. If you hold the Menu button down while turning on the power, you'll get the version number of the firmware displayed on the LCD. If it's not 1.12, go get the update and try all this again!

Thanks for the tip! Great idea!

No., they are not at the same shutter speed.


You didn't read the post (nobody reads post number....oh, wait,that's on the Adobe forum!).


I deliberately chose an apeture that is three stops difffeent from the widest apeture.

Then I tried the test you suggested, take a photo at f/1.4 and then take the same photo (after re-doing the measurement at f/11) at f/11. I got all correct expoxures. At different shutter speeds!

Then, in a bolt of devine inspiration (a in the gods whispering "you idiot, why don't you just watch the lens. DUH!") I looked into the lens as the shutter fired while set to Av (apeture priority}while stopped down th f/8. In a dark area, the camera set a long enough shutter speed for me to see that the blades do, indeed, close down during exposure.



Since both test lenses are so old that they have only one way of closing the diaphram, it makes sense that whatever you set on the apeture ring will be what it shoots at. Remember, the initial reading was taken with the DOF preview engaged, which closes the diaphram. The whole point is that the camera remembers the apeture you tested, and adjusts shutter speed.

This only works if you DO NOT move the apeture ring after your initial reading and you DO NOT let the meter turn of. Once the meter shuts off, you need to pull the control to DOF preview again to let the camera know what you're set to.

So grab an old M or K lens, set it to a small apeture, set the camera to Av (apeture priority), measure the light somewhere, and then look into the lens as you fire the shutter. You will see the blades close while the exposure is taken.

Note that I'm useing firmware version 1.12, this did not work when the camera still had 1.00 and I don't know if it works with other firmware in it. But version 1.12 apparently does allow the lens to shut down.

OK, kids here are the hard results of a controlled test. Firmware version 1.12.

Meter operating time set to 30 seconds, in custom functions.

Format set to RAW

Focus selector set to Manual (it's an M lens, after all)

Mode set to Apeture Priority ("Av").

50mm f/1.4 Pentax-M lens set to F/4 on apeture ring.

Initial reading taken in one light level, camera moved without re-testing while shutter speed varied in viewfinder display.

Subsequent photos taken during the 30 second meter operating period in different lighting levels.

Results:

All frames werre correctly exposed. Shutter speed ranged from 1/2000 to 1/6 second, lens was left at f/4.

This seems to indicate that once the camera knows what the lens is set to, the shutter speed is set accordingly, and the lens closes to the selected apeture.

So you can basically use old non-automatic lenses in apeture priority mode, Pentax has pulled off a slick save and redeemed themselves (partially) in the eyes of professional and enthusiast users.

If you're monitoring these forums, Pentax, put the full KAF mount into the next series of DSLR's.

And put in pixel mapping, it's a big selling point on the Olympus cameras and the strategy works. You could even license the dust removal from Olympus and have the most usable DSLR in the industry!

In case of any doubt, there is an adapter for K mount lenses (and many others) to fit them on the Olympus DSLR's. Olympus was smart when they chose the back focus of the four-thirds system.

Test it. I got an 85mm f/2 M lens to expose properly in a number of different lighting conditions, specifically starting at one illumination and then changing, and exposing without having the camera stop the lens down again. I will re-try the test, but I'm sure it worked. It worked in the field, but since things are going so fast, I didn't really pay attention to where the light was when I took a measurement. I'll report back later after I make another test.

The normal procedure to use K or M lenses on the *st D is either, set the apeture, press the green button, focus, and shoot, or set your apeture, pull the mode ring to DOF preview, let it go, focus and shoot.

This means if the light changes you need to pull the ring or push the button again, to have the camera re-meter the scene. This is done with the camera set to Manual mode.

Set the camera in Apeture Priority mode, and when you pull the ring to DOF the camera sets the shutter speed and as long as you keep your hand on the shutter button (to deep the meter on) the shutter speed changes continuously, as the light changes.

Thus with old non-A lenses (M, K, etc) you get full automatic apeture priority exposure. Pretty slick.

It still doesn't forgive them for leaving out the cam that senses the apeture in the old lenses, but it cetanly is a good save. At least they can think on their feet!