[Smolk]

This is probably a setting I've got wrong, but I cannot solve it:

When my K-3 III is in Av-mode with an M-lens (in this case, the Pentax-M 2/85mm, but I've tried other M-lenses as well),

- in Live view I get the shutter and aperture info and a good exposure: f11 1/250 for example.
- In the viewfinder shutter says AUTO and the exposure is wrong (underexposed) and it selects f11 1/4000 (!).

What is going wrong here? It should not make a difference whether I'm in LV or VF I would have thought?
(FYI: the camera has the settings for M-lenses applied.)

[kypfer]

Presumably the aperture ring on the lens is actually set to f/11?
What ISO is the camera set to?
You haven't got any +/- compensation dialled in, have you?
The K-3iii has so many configurable variables it wouldn't surprise me if it "remembered" a different compensation or ISO setting for both l/v and v/f!
I've just tried briefly with an M 28mm f/2.8 on my K-3iii and got good exposures in both v/f and l/v shooting out of the window at ISO 400 at f/8, slight shutter speed variation, but the clouds are scudding past, so struggling a bit to guess what might be wrong at your end.

[Fogel70]

It sounds like a slow aperture on the lens, so it does not fully stop down before the metering is done right before exposure in VF mode.
But I believe the aperture is always stopped down in LV mode, so then it is not affected by a slow aperture.

[Smolk]

Yes, the aperture setting was set to f11, ISO 1000.
That VF and LV differ is what baffles me, apart from the fact that I usually shoot with the VF and that doesn't really work.
(I should perhaps add that in M-setting I get no info about metering, under- or over-exposure, as I would expect. Have used film cameras for the last months mostly so my memory is a bit foggy, but I believe I used to get that info.)

---------- Post added 02-08-2022 at 02:51 PM ----------

It sounds like a slow aperture on the lens, so it does not fully stop down before the metering is done right before exposure in VF mode.
But I believe the aperture is always stopped down in LV mode, so then it is not affected by a slow aperture.

Not sure what you mean by slow aperture but:

- it happens with any M-lens or K-lens that I mount so it is independent of the lens
- there still is an info difference: LV displays shutter speed in Av-mode, VF displays AUTO in Av-mode.

---------- Post added 02-08-2022 at 02:57 PM ----------

I just put an A-lens on the A-position, and that works as it should: no difference between LV and VF views or exposures.
In M-mode, it also displays over- or underexposure.
Perhaps I'm misunderstanding the M- and K-lens functionality, but the difference between LV and VF remains strange.

[UncleVanya]

I don’t have a k3iii, but the thing that may be happening is that the camera has to be wide open for viewfinder use and stopped down to meter. The k3iii max a mode that stops down and meters as it takes the shot. This mode might display that way. The older cameras required pressing the green button in order to meter an m series lens. A lenses communicate their wide open aperture and can be shot without stopping down to meter first. The lens still stops down at the time of exposure but only to capture the image not to meter.

[Fogel70]

In VF mode the aperture is kept fully open (for maximizing light in the VF) until exposure. So the aperture has to stop down in just a few milliseconds just before exposure. If the aperture is slow/sticky on a K/M-series lens it takes longer than that and the metering is done on a wider aperture than used for the exposure, which lead to an underexposed image. As the aperture is held wide open before exposure in VF, the camera can not tell what shutter speed will be used beforehand.

In LV mode the aperture is always stopped down to the selected aperture, which is why you can see shutter speed. And the aperture do not have to be stopped down further before exposure.

K/M-series are very old lenses so they often suffer from slow/sticky apertures, and they may need CLA ("Clean, Lubricate, Adjust"). Many of them may not have been serviced for decades.

On A-series (and later) lenses with aperture on a-position the camera can calculate the exposure from wide open aperture as it know wide open f-number of the lens and how much the lens has been stopped down from that.
On K/M-series lenses the camera has to stop down aperture and make a metering right before exposure, as it do not have any info from the lens.

This is a limitation of the crippled K-mount used on DSLRs, in combination with K/M-series lenses. And I think it becomes even more critical with the new functionality on K3 III for K/M-series lenses.

[Smolk]

Thanks for this explanation - which sounds right, chimes in with my experiences. And so I tested all my old lenses: just 2 worked fine (SMC Takumar 2.5/135mm, K 3.5/28mm), 5 of them need a service.
On the one hand, if that's what it is, I'm not too disturbed. On the other hand, it's not so easy to find a place where you can have this done for a reasonable price. Even though these are manual lenses so easier to dismantle.

In VF mode the aperture is kept fully open (for maximizing light in the VF) until exposure. So the aperture has to stop down in just a few milliseconds just before exposure. If the aperture is slow/sticky on a K/M-series lens it takes longer than that and the metering is done on a wider aperture than used for the exposure, which lead to an underexposed image. As the aperture is held wide open before exposure in VF, the camera can not tell what shutter speed will be used beforehand.

In LV mode the aperture is always stopped down to the selected aperture, which is why you can see shutter speed. And the aperture do not have to be stopped down further before exposure.

K/M-series are very old lenses so they often suffer from slow/sticky apertures, and they may need CLA ("Clean, Lubricate, Adjust"). Many of them may not have been serviced for decades.

On A-series (and later) lenses with aperture on a-position the camera can calculate the exposure from wide open aperture as it know wide open f-number of the lens and how much the lens has been stopped down from that.
On K/M-series lenses the camera has to stop down aperture and make a metering right before exposure, as it do not have any info from the lens.

This is a limitation of the crippled K-mount used on DSLRs, in combination with K/M-series lenses. And I think it becomes even more critical with the new functionality on K3 III for K/M-series lenses.

[pschlute]

That VF and LV differ is what baffles me, apart from the fact that I usually shoot with the VF and that doesn't really work

You have had good advice on what may be the cause here, but just to add that metering in LV and VF may not always be the same, but they should be very close (which is obviously not happening here).

LV metering is done off the sensor itself. VF metering is done by the light meter which sits between the focus screen and the prism.

When metering using the VF it is important to remember that if your eye is not at the VF, and thus shielding any light from entering, this can fool the meter into giving an underexposed image if you have a strong light source behind you. This goes for modern lenses too.

[Fogel70]

Thanks for this explanation - which sounds right, chimes in with my experiences. And so I tested all my old lenses: just 2 worked fine (SMC Takumar 2.5/135mm, K 3.5/28mm), 5 of them need a service.
On the one hand, if that's what it is, I'm not too disturbed. On the other hand, it's not so easy to find a place where you can have this done for a reasonable price. Even though these are manual lenses so easier to dismantle.

I do not have K3 III, but I believe it is also possible to use these old manual lenses in M-mode with optiical DOF preview (on the power switch) and manually tune in shutter speed after exposure meter.
As you can activate the DOF preview for as long as you like, it should not matter if the aperture is a little slow.

And if using M-mode you do not have to meter before every image.

[Smolk]

I do not have K3 III, but I believe it is also possible to use these old manual lenses in M-mode with optiical DOF preview (on the power switch) and manually tune in shutter speed after exposure meter.
As you can activate the DOF preview for as long as you like, it should not matter if the aperture is a little slow.

And if using M-mode you do not have to meter before every image.

Yes, in M-mode it is possible to activate the DOF-preview, hence get an accurate metering. But the process isn't as fast as on my manual film cameras... and it doesn't help in Av mode.

[pschlute]

Yes, in M-mode it is possible to activate the DOF-preview, hence get an accurate metering. But the process isn't as fast as on my manual film cameras

Although it will work as accurately, you are correct it is not as easy or fast as with older film cameras. This is because the "crippled" K-mount, introduced around the year 2000, did away with a physical coupling that can tell the camera what aperture the lens is set to. It has never been re-introduced. I imagine the designers of the day did not anticipate we would still be using "K" and M series lenses on our cameras.

and it doesn't help in Av mode

Av mode should be working with auto stop-down on the K3 III. Can you do a video looking at the front of the lens that shows how the blades are stopping down in Av mode. It might provide some clues.

[bicycle]

This might be simplistic but it has tripped me up a couple of times when I was new to digital. Check to make sure that the camera isn't remembering a different metering pattern between the two settings (LV vs VF). I have accidentally changed my normal center weighted metering to spot metering. Then my photos came out either too light or dark depending what the spot fell on in the center of the photo. Sadly it took me way more time to figure this out than it should have.

Bob