[m42man]

what do you mean with variable (max) aperture?
I don't understand the meaning of max.

A zoom has variable focal length, and aperture changes with most zooms when changing the focal length,
so that is clear.
But what about (max)?

Possibly again a question of language!

Well, using Av mode with an afflicted K30/50/70 etc. means that the camera meters with the lens wide open, and you have to perform the calculation for the exposure at the set aperture - and that means that you need to know the wide-open (i.e. max) aperture of the lens, because the exposure at set aperture is calculated relative to the wide-open aperture.

Since many (most) zooms have a variable wide-open aperture, you're never certain what the wide-open f-number is. So you're stuffed, and you probably just resort to using the green button and M mode...

---------- Post added 5th Aug 2022 at 09:06 PM ----------

Your answer is very confusing. The simple fact is that a camera body, like my K30, is usable with a aperture-ring equipped lens. The aperture set may require a slower shutter speed and/or higher ISO setting than the user would prefer, but that has always been the case. The only difference is that the body cannot set the aperture - back to the old days before ‘KA’ lenses.

If your K-30 has a good solenoid, then if you operate in Av mode with a lens whose aperture ring is set to a value (i.e. not "A"), the camera will refuse to stop down, and will take the shot with the lens at wide-open - so, regardless of the aperture set by the ring. You'll get a correctly exposed photo, but always with a wide-open lens.

But if you try that with a K-30 that has a failed solenoid, the camera will stop down in Av mode - but will still expose as if the lens was wide-open. That's why you need to compensate (by the number of stops relative to wide-open) if you want correct exposure.

Does your K-30 have a failed solenoid?

[reh321]

If your K-30 has a good solenoid, then if you operate in Av mode with a lens whose aperture ring is set to a value (i.e. not "A"), the camera will refuse to stop down, and will take the shot with the lens at wide-open - so, regardless of the aperture set by the ring. You'll get a correctly exposed photo, but always with a wide-open lens.

But if you try that with a K-30 that has a failed solenoid, the camera will stop down in Av mode - but will still expose as if the lens was wide-open. That's why you need to compensate (by the number of stops relative to wide-open) if you want correct exposure.

Does your K-30 have a failed solenoid?

My K-30 hasn’t had a working solenoid since 2018.

I have used it with film lenses since then, typically in ‘M’ mode setting the aperture at the lens.

Typically, I use it indoors with an ‘auto’ flash, which measures the light received by the flash.
My ‘FA’ lens is technically “Pentax-FA 1:3.2-4.5 28-105mm IF & AL”.
In practical terms, there is little difference between F/3.2 and F/4.5.
I typically use it near the bottom end and use it out of experience.
Sometimes, I don’t get exposure exactly right, but close enough for gimp to ‘fix’ JPEG files.
Outdoors, I use aperture values like F/8, still in ‘M’ mode, so the ‘bottom’ of the aperture scale has no relevance.

Sometimes I manually focus a M42-mount or true K- mount prime lens, but this discussion has no meaning then.

[m42man]

Yes, the above only applies to K-mount lenses with aperture rings.