[vonBaloney]

I've tried the whole deal with not mounting them all the way and it scares the hell out of me.

Not for telephotos or heavy lenses, but a 28 or slim 50, works ok...

[aleonx3]

Yes, it can be done by removing the aperture lever, and the process is reversible (as long as you retain the aperture mechanism part for future restoration). Depending on the lens, some are easier than others. The removal of aperture lever in k-mount allows the lens to open and close aperture when mounted on the camera, therefore, one can use Av mode as in stop-down metering. Otherwise, one can only use the k-mount lens in M mode.

There is one slight disadvantage, however, if you plan to shoot at smaller aperture (f8 or higher), then the viewfinder gets very dark and not easy to focus. A way to get around that would be to turn it wide-open first to focus and then once focus is obtained, then turn the aperture ring to the desired aperture (eg. f8). With the eyes kept on the viewfinder, I usually just count the number of clicks to get the desired aperture (effect). This is what I usually do using m42 lens without A/M switch.

[Lowell Goudge]

Should this work, in theory? What does one lose, besides open aperture metering? I think it'd be worth the trade-off to be able to use K and M lenses in AV mode, instead of using the Green button. Has anybody done this?

My own view it it is an absolute waste of time and risks doing permanent damage to the lens.

Shoot manual, use the green button. You don.t need to meter between each shot. When I shot film, I would meter on a paved surface , tree trunk etc, as a poor substitute for a grey card. You have a histogram on your camera. Meter on a neutral lit subject, check the histogram, adjust if necessary to centre the peak of the histogram and then shoot until the light changes.

Then you gain tremendously with open aperture focusing.

[stevebrot]

Has anybody done this?

Mostly Canon FF shooters.

The biggest pro is IMO real time metering if you are going to be shooting in a scene with a lot of lighting changes, plus realtime view of the actual DOF.

The biggest negative is loss of the automatic diaphragm actuation. Real time metering is highly overrated and the rapidly changing light scenario relatively rare*, IMHO. Meter once and shoot away until the lighting itself changes. Compare these flows:

Manual/Preset diaphragm, emasculated K-mount and M42 (Av mode):

• Manually open aperture
• Frame and focus
• Manually stop down aperture to desired DOF or shutter speed
• Make exposure
• Repeat sequence

Auto diaphragm actuation, K-mount (M mode):

• Select aperture using aperture ring
• Press green button
• Frame, focus, exposure
• Repeat last step

The second flow is analogous to how things work with stop-down meter cameras such as the Spotmatic. Automatic diaphragm actuation is a huge advantage. Without such, SLR shooting for many subjects is sort of a joke and often enough the saddest part is that the photographer will often forget to do that manual stop-down and/or miss the shot as a result.

For example...Below is a photo taken with a Pentax SV in a difficult lighting situation. The exposure settings were based on an incident reading from a hand-held meter with the Timberline Lodge in Oregon as the subject. I was walking around to the back side of the building looking for interesting angles when I saw a snowboarder coming rapidly down the trail to my left. All I had to do was bring camera to eye, focus, and take the shot. If the M/A switch had been on the "M" side, I would have missed either focus or the action.



For those that are interested, the exposure settings were originally used for the photo linked below:

https://flic.kr/p/88FYwm


Steve

* The most common error is to mistake light vs. dark subjects as requiring different exposure even though both have the same illumination.

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Last edited by stevebrot; 08-14-2015 at 10:46 AM.

[narual]

Wouldn't a piece of tape covering up all the pins give you the same result? Seems like whenever I put a lens on that has a non-conductive backing, it treats it like an M42

[Lowell Goudge]

Wouldn't a piece of tape covering up all the pins give you the same result? Seems like whenever I put a lens on that has a non-conductive backing, it treats it like an M42

Depends on the body. K10 and earlier this would have no impact.

Later bodies wouldn't trip the shutter unless the pins are there. But neither would up give you the effect you want.

[marcusBMG]

I'm with Lowell on this, I'm hardly using the green button any more these days (but it's good that its there). With my "K" 28mm* I use Av to get a handle on the light wide open, chimp to check. Then I just use the speed dial to change the shutter to match the aperture in M. One stop for every two clicks on the aperture ring. Bracket as necessary.
The fact is "green buttoning" isn't any more accurate (see Lowell's graph) so you're chimping and tweaking the exposure anyway using it.

*slightly more complicated with this lens because it starts at f3.5, first two clicks covers more than one stop.

[pathdoc]

One stop for every two clicks on the aperture ring.

I've come across a few lenses for which there were no intermediate clicks past f/11, but these are either 3rd party non-A K mount or M42. On that basis, it pays to know your individual lens. But given that, and provided the light stays steady, your method sounds pretty good.

first two clicks covers more than one stop.

I always thought 3.5 to 4 was half a stop. The next click should be the half-stop between 4 and 5.6, yes? So how can it be more than one? Or is the thing marked as 3.5 then 5.6 with the stop in between being the midway point rather than f/4.0?

[marcusBMG]

I always thought 3.5 to 4 was half a stop. The next click should be the half-stop between 4 and 5.6, yes? So how can it be more than one? Or is the thing marked as 3.5 then 5.6 with the stop in between being the midway point rather than f/4.0?

You had me scurrying to check the lens ... 2 clicks from f3.5 to f5.6 nuff said.

[wtlwdwgn]

One of the reasons I like the Taks is the A/M switch so I can focus at max aperture and then stop down with a flick of the switch. I've never figured out how to use the green button. Of course I could be a little dense.

[jkomp316]

I do this to ALL of my K and M lenses. Run it in AV mode, adjust +/-EV accordingly, then fire away. Doesn't bother me at all. Its all about catching the shot.

[gofour3]

ou had me scurrying to check the lens ... 2 clicks from f3.5 to f5.6 nuff said.

I always thought 3.5 to 4 was half a stop. The next click should be the half-stop between 4 and 5.6, yes? So how can it be more than one? Or is the thing marked as 3.5 then 5.6 with the stop in between being the midway point rather than f/4.0?

The click stop between f3.5 and f5.6 is f4.8. This is true for all Pentax lenses with a maximum aperture of f3.5.

Phil.

[Fat Albert]

I do this to ALL of my K and M lenses. Run it in AV mode, adjust +/-EV accordingly, then fire away. Doesn't bother me at all. Its all about catching the shot.

Excuse me while I grab my popcorn...this should be good!

[ScooterMaxi Jim]

Maybe it's due to the fact that I never really owned a film camera, but if I was having to deal with changing light or subject, I probably wouldn't pick a manual lens. Also, I'm a back-button-AF'er, so I'm used to being required to hit a button before releasing the shutter. I would just hit a different button.

I feel like I'm coming off condescending, and I'm really not intending to.

I'm with you on this - even having shot film for much longer than digital. It isn't as if you can't adjust the exposure after the test shot, and it isn't as though minor under-exposure is going to ruin a shot with the newer sensors (assuming shooting in RAW). If you think about it, Green Button metering is Av already - you have set the aperture and the camera decides on the shutter speed.

If I have a jewel of a manual lens, even altering it temporarily feels like I'm violating a trust. Just not worth the thought of it.

[Fat Albert]

If you think about it, Green Button metering is Av already - you have set the aperture and the camera decides on the shutter speed.

If I have a jewel of a manual lens, even altering it temporarily feels like I'm violating a trust. Just not worth the thought of it.

You have to set aperture AND ISO.

It's a lens, not a sacred covenant. If I can modify it without hurting it, I'll do so without losing any sleep over it. YMMV