[Eruditass]

For an example.

With your M42 attached to your Kx (aperture not important) and you have a very different scene with shadows and brighter bits, your shutter button is depressed half way, moving your camera from the shadow areas to the bright parts the shutter speed does not change from 1/125?

As mentioned above, it changes the ISO to keep the shutter locked at 1/125. The final exposure is the same. In extreme conditions when it goes to ISO 100 and there is still too much light, it finally changes the shutter from 1/125. The same happens when the light is too dark and it has reached 12800.

[Mike Cash]

Do you have your ISO set to auto, by any chance? If so, switch to a set ISO and see if that solves the problem.

[Eruditass]

That defeats the purpose of Av mode...

It will just assign a shutter speed based on light. I want it to assign a shutter speed based on the FL I am using, using ISO to get there. Then when it gets there, it can lower the ISO if more light comes.

If I could assign the e-dial or +/- + e-dial to ISO it would be slightly better than M mode.

[ovim]

Just tested my K200D on auto-ISO with a M42 lens and it seems to try to go for 1/90 regardless of the focal length.

[Lowell Goudge]

Auto ISO mode does some wild things and you should probably turn it OFF

the camera does not know aperture with M42 lenses and will set auto ISO to come to some pre-programmed line.

It does the same in flash photography, taking ISO up toi get exposure when you don't want it.

turn off auto ISO mode when using manual lenses.

they are manual for a reason

[Steve Beswick]

I think the OP might be thinking of "hyper Av", or whatever it's called.

[kuuan]

I do not get why setting ISO should mean defeating Av mode?

Me too I'd recommend setting ISO manually ( anytime anyway ) and Av mode should be OK..just about..I am curious how the K-x will measure, the old *istD/Ds were known to measure better than the later K cameras which needed a dial in a exp. comp.. Also exposure very likely will not be perfect, if you run a test with a lens taking sample shots at all apertures you will find that at some f stops exposure will be perfect, in others off to the + or -

[Lowell Goudge]

the old *istD/Ds were known to measure better than the later K cameras which needed a dial in a exp. comp..

I would agree with that, especially K10 and K20

Also exposure very likely will not be perfect, if you run a test with a lens taking sample shots at all apertures you will find that at some f stops exposure will be perfect, in others off to the + or -

very sound advise, I test each of my lenses, not just the old ones, against a block wall and plot grey scale vs aperture, even new lenses are not perfect.

[Eruditass]

Of course the camera does not know the aperture - it only knows the light going in. I've said this several times earlier. When choosing shutter speed and ISO, a camera does not need to know about the aperture! It only needs to know how much light is coming in, or what fraction will be coming in (this is how lenses that transmit aperture work, btw).

It doesn't need to attempt a pre-programmed line (by this I mean how Av works on A+ lenses, increasing the shutter and ISO in a specific pattern), all it needs to do is try to get to a certain shutter for a known focal length. I guess this would make it too easy to use manual lenses and asking too much.

I suppose I was harsh in saying it defeats the purpose of Av mode, it just makes it a marginal improvement over using Pentax-M lenses, where I was misled to believe there was a greater difference.

[Eruditass]

Just tested my K200D on auto-ISO with a M42 lens and it seems to try to go for 1/90 regardless of the focal length.

Thanks! A real response! So Av mode is dumb and sets shutter to a completely arbitrary value. A shame, as it could easily pick a value related to the FL.

[Lowell Goudge]

Of course the camera does not know the aperture - it only knows the light going in. I've said this several times earlier. When choosing shutter speed and ISO, a camera does not need to know about the aperture! It only needs to know how much light is coming in, or what fraction will be coming in (this is how lenses that transmit aperture work, btw).

It doesn't need to attempt a pre-programmed line (by this I mean how Av works on A+ lenses, increasing the shutter and ISO in a specific pattern), all it needs to do is try to get to a certain shutter for a known focal length. I guess this would make it too easy to use manual lenses and asking too much.

I suppose I was harsh in saying it defeats the purpose of Av mode, it just makes it a marginal improvement over using Pentax-M lenses, where I was misled to believe there was a greater difference.

I will be the first to admit there must be something I am missing. why with manual lens do you want to have auto ISO,

I will admig I just tried on my K10D and to a limit it does stick on one shutter speed, until that is, you go outside the range of metering for that shutter, , but just turn auto ISO off and the shutter behaves normally when you turn the aperture ring changing shutter as you change aperture.

I agree, in some ways it might have been interesting if it set shutter speed based on focal lenght for manual lenses in the auto iso mode, but then again why would you want auto iso for a manual lens?

[Lowell Goudge]

as another thought just narrow down the auto ISO range a little. it sounds like you have it covering the entire range at present

[Eruditass]

Out of curiosity, which value does your shutter stick on? Is it like my K-x (1/125), the K20D (1/90), or some new random number?

As mentioned, it would pretty much make M42 lenses automatic, except to change the aperture you rotate the ring.

You said it'd be interesting if it did set the shutter speed based on focal length, then ask why would you want to do that?

If I narrow down the auto ISO, all it will do is make it so in bad light it will lower the shutter speed earlier. Might as well choose manual ISO so I know what it is doing.

Auto ISO with manual aperture lenses is worthless unless you have a lens with a FL that the random shutter speed that the camera picks is worthwhile. So it's ok with my 135/2.8 if I hold it well, and will be OK with my 85mm. My 28mm I'd rather use manual ISO to get a lower ISO and slower shutter speed, and same to some extent with a 50mm.

My 200mm may be stretching it, and mirror lenses need not apply to auto ISO.

It would be sweet if the K-x would change the ISO with the e-dial directly, but I don't think it can. However it is an improvement at least over the K2000, since I can change it with the e-dial when I push the right d-pad button.

[kuuan]

...So Av mode is dumb and sets shutter to a completely arbitrary value...

with selected aperture the camera in auto ISO and Av mode tries to get the shutter speed right and changes the ISO to achieve that. Actually this is what I would want the camera to do, can't see why this is a flaw.

If I do not want the ISO to change but the shutter speed, well, then better to fix the ISO and have the shutter speed will change..

[KungPOW]

Thanks! A real response! So Av mode is dumb and sets shutter to a completely arbitrary value. A shame, as it could easily pick a value related to the FL.

Just want to point out that the previous respnces were also "real". It was you who negleted to tell us that you had the camera on Auto ISO. Good foe Mike to figure that out.

And yes, in auto ISO, my camera wants to stay at 1/100 regardless of the input lens length.

So, turn off auto ISO.

And M42 lenses do work better then M lenses in AV mode. M lenses only work wide open.