Full continuously variable Apeture priority with M lenses

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!

I don't think you are right, Arthur.

In any mode other than Manual, the camera will not stop the lens down. So although it will expose correctly (by adjusting the shutter speed), it will not give you the aperture you want. Whatever the aperture is set at, the picture will be taken at full aperture.

G

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.

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.

Hi Arthur

I had a strange sense of deja vu when I found this message!

It's always appreciated if a post only appears once in one thread so we don't get too cluttered and confused......Thanks!

Hot pixel removal is standard in Capture One (even the LE version) Saves me a bundle of time processing, especially for ISO1600 and ISO3200 shots
Matt

You've missed the point, Arthur. I agree that the camera sets the correct shutter speed, but it does so for the widest aperture.

Put your lens on f8 and take a shot. Then (with the same light conditions) put it on f1.4 and take a shot. Both will be correctly exposed, and both will be at the same shutter speed (press the Info button to check). That means that both would have used the same aperture, to wit: f1.4 (wide-open).

Try a proper controlled test!

I have to admit I fell into the same trap when I first got my camera. It's still quite a useful feature provided you have a lens that's sharp wide-open, and are happy with a narrow DOF. For portraits, of course, a less-than-sharp lens and a narrow DOF may be just what you want.

G

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.

Thanks for the tip! Great idea!

Try this:

Put the lens on f22.
Select manual mode.
Press the green button.
Note the shutter speed indicated.

Put the lens on f22.
Select Av mode.
Lightly depress the shutter button to activate the meter.
Note the shutter speed indicated.
Now trip the shutter.
Press the Playback button, then the Info button twice.
Note the shutter speed.

If your theory is correct, the shutter speeds should be the same in all three cases. If they are, then you have a very special version of the camera, because neither of mine behave like this.

G

I think I can explain what is happening here.

In any mode other than manual, the camera takes a meter reading and adjusts either the shutter speed or the aperture or both (depending on which mode was selected) to give the correct exposure.

In Av mode, with the lens set on the A setting (which won't apply to M and K lenses), the camera will base the meter reading on the aperture that has been set on the body, and will adjust the shutter speed accordingly.

In Tv mode, it will accept the speed that has been set, and adjust the aperture accordingly.

In Program mode, it will set both (if neither of the wheels has been turned to fix either the aperture or the speed).

If the lens is not on the A setting, the camera has no way to adjust the aperture, and no way to know what aperture is set if the lens lacks contacts (ie: K and M lenses). So in these cases, it takes the reading at full aperture, and DELAYS stopping down the lens until the picture has been taken. That means the picture is taken at full aperture, as with the meter reading.

You can actually see this if you set the lens to f22, and fire the shutter first in Manual mode, then in Av. In Manual mode the lens immediately goes blank apart from the small hole in the middle representing f22. In Av mode the shutter fires, and then the lens closes down much more briefly.

A moment's thought should suffice to convince Arthur that there is no way that the camera can operate in Av mode with the K and M lenses (other than using the lens full-open). It simply doesn't know what aperture has been set on the lens.

G

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!

Arthur Dent wrote: "The same apature yielded different shutter speeds, and all exposures were correct."

If that statement is true, then the light must have been different each time, and if that was so, then you aren't proving anything.

You must carry out these tests with the SAME light.

With the same light, the camera will give you the same shutter speed in Av mode (and correct exposure) regardless of what aperture you set.

Try what I suggested. You will find, when you look at the lens, that it stops down AFTER the shutter has tripped when in Av mode, but BEFORE in Manual.

You are so convinced that you are right that you are refusing to look facts in the face. Sleep on it, and have another go tomorrow with an open mind.

G

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!

Well it has been fun reading this as the day has progressed! Can I add a word or two but my results come from a DS. Sorry, I know it may be putting another unknown in but hopefully it performs very similar to the D in this respect.

When I first tried what Arthur suggested I thought he was on to something but sorry Arthur I now fully agree with George. It is hard because you do get a properly exposed picture so you assume it is taken at the aperture set on the lens but IT IS NOT it is at full aperture and the speed has adjusted accordingly. So yes, it is aperture priority but you have no control over the aperture, it’s fully open.

The way I finally convinced myself was to use low light and a small aperture so that in Av mode, after pulling the DOF ring, then firing the shutter I could hear that the shutter was firing at a speed correct for the fully open lens.

Interestingly, I found that when set to Av and pulling the DOF ring it does not close the iris. It sounds like it does but on looking into the lens it does not. I have just looked through the viewfinder and that does not darken either!!! So it cannot be checking the light anyway or if it is, it is doing it at full aperture.

Hope this helps Arthur,

Dave.