M42 adaptor question

I am thinking of buying a cheap M42 lens for my K-x. Never used any M42 and K mount adaptor, so I was wondering if anyone can help me with a few questions:

1. Can you use stop-down metering with such a combination (i.e. with the green button)?
2. Can I leave the M42 adapter permanently on the lens, i.e. change lenses quickly like any other k mount lens?
3. I read some things about adaptors that have a little spring, and where you need to unscrew the lens first, then remove the adaptor with a tool. Other people were talking about adaptors with a flange that don't need that, which sounds more convenient. Does anyone have first hand info about that?

Thanks in advance for your help!

1. No. The camera doesn't have any mechanical connection to the lens so it can't stop it down. You need to use the lens in (M)anual mode (there's usually an Auto/Manual switch near the aperture ring) and stop it down using the aperture ring itself. A good method for many people is to set the lens to (A)uto, pre-select the aperture, focus with the lens open, set the lens to (M)anual, take a meter reading and then shoot.

2. Yes. But see below.

3. You can remove the springs, they're usually held on by a tiny screw. If you intend leaving the adapter on the lens then this is a must - if you intend leaving it on the camera then leave the spring clip in place to stop it coming off every time you dismount a lens. Adapters with flanges don't allow for infinity focus so avoid them!

Cheers hefty! Hmmm... maybe a silly question but I am not used to non-PK mount lenses at all... what's the technique to take a meter reading if you can't use the green button?

You can use the green button but it won't stop the lens down - you need to do that part for yourself. In other words unless the lens is set (by you) to a manual value, the camera will meter (and shoot) wide open.

I find M42 lenses easiest to use in Av (Aperture Priority) mode as the metering will always be based on whatever the lens is set to at the moment you press the shutter. In that particular respect I find M42 lenses easier to work with than early (K and M series) K-mount lenses.

Many thanks again for that info, hefty. I never realised that M42 lenses work so well in Av mode, which is quite good... my preferred mode anyway, although, as you point out, non-A k mount lenses don't work so well with it.