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12-11-2013, 05:38 PM   #1
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Using M lenses without pressing the green button?

I recently bought my K-30 and I am falling in love with it specially with manual lenses. The green button is a great feature on Pentax cameras and it helps a lot. Most of the time the metering done by the green button is just fine and it does not need any modification. So, I just wonder if it is possible to ask the camera to do an auto metering without pressing the green button whenever I press the shutter button? For instance using one of user defined modes U1 or U2?

12-11-2013, 05:51 PM   #2
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I don't think what you are asking is possible.

You can also meter by pressing the +/- button, I think. Av mode meters continuously, but always shoots wide open. It also allows auto ISO. Its great for preset lenses, where you stop down by hand.

Keep in mind that you don't have to meter before every shot, you can just take photos or adjust by feeling.

There are some hacks that allow you to use some more modes with your manual lenses, but I am not quite sure on the details. I think you need to hack the camera mount and short some contacts or something. I think there are some threads or blog posts about this.

Another great Pentax feature is catch in focus (focus trapping). Many threads on this, and it can give you some AF-like functionality with old manual lenses.
12-11-2013, 06:58 PM   #3
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QuoteOriginally posted by Na Horuk Quote
I don't think what you are asking is possible.

You can also meter by pressing the +/- button, I think.
Your first statement is, as far as I've been able to determine, correct. I just tried using the +/- button, and it does not stop down a manual lens to take a meter reading.

With some Pentax DSLR models, where the DOF preview is available as a 3rd position for the on/off switch, the meter is active during DOF preview, allowing you to scan and meter various parts of a scene. Very useful if you have spot metering enabled.

The K30 does not offer DOF preview in this way. You can configure the Fx button to be a DOF preview button. Unfortunately, when you activate DOF preview using this button, the meter is not enabled. So a handy feature of my old K200D isn't supported by my brand new K30.

This has been discussed several times in the K30/K50 section of the forum.
12-11-2013, 06:59 PM   #4
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Short answer is nope.

The camera is not capable of doing a pre-exposure metering to emulate Av mode.

As for hacks, there is nothing you can do that will allow your non-A contact lenses to support modes other than M. The contacts are only have the story. The other half is an aperture actuator that is calibrated to deliver a given opening size for a given travel of the actuator lever.

That being said, you may want to consider that metering before every shot is often not needed. Unless the light or subject changes, your original reading and settings will likely be just fine. That approach worked well in the days before exposure automation and works just as well today.


Steve

12-11-2013, 07:29 PM   #5
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And since you don't meter every shot, shoot in RAW, and fix the exposure in post. I find that as long as I'm within 2 stops or so of the "correct" exposure, I can correct the RAW with no noticeable ill effects.
12-11-2013, 07:30 PM   #6
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Thank you guys for the answers. Nice tips in the replies.

So, what I understand is that it's not possible. But it seems to be a firmware limitation, not a physical limitation. Isn't there anything like Canon's Magic Lantern for Pentax cameras?
12-11-2013, 11:03 PM   #7
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QuoteOriginally posted by galaxytab Quote
Thank you guys for the answers. Nice tips in the replies.

So, what I understand is that it's not possible. But it seems to be a firmware limitation, not a physical limitation. Isn't there anything like Canon's Magic Lantern for Pentax cameras?
I'm afraid it is a physical limitation: Pentax DSLRs use what's known as a "crippled" lens mount, meaning that there is no coupling of aperture ring position to the camera body. So, the camera has no means of knowing the working aperture, and therefore can't calculate the correct exposure when metering from the wide open lens.
12-12-2013, 01:48 AM   #8
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I have a few M lenses I cut the aperture lever off. This lets me run Av mode and stop down the aperture ring on the lens. Depending on the body it auto meters very well without having to fiddle with the green button.

12-12-2013, 03:22 AM   #9
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QuoteOriginally posted by jkomp316 Quote
I have a few M lenses I cut the aperture lever off. This lets me run Av mode and stop down the aperture ring on the lens. Depending on the body it auto meters very well without having to fiddle with the green button.
Could you please explain more about cutting the aperture lever or link to the procedure.
12-12-2013, 04:36 AM   #10
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You take the back off, detach the aperture feeler, but don't, just sell it and get an old takumar, it will give you the same result witg out cocking up a lens
12-12-2013, 04:49 AM   #11
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QuoteOriginally posted by tromboads Quote
You take the back off, detach the aperture feeler, but don't, just sell it and get an old takumar, it will give you the same result witg out cocking up a lens
Could someone explain to me what the functionality of that little metal piece is? What's the downside of removing it?
12-12-2013, 05:33 AM   #12
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That's the aperture control ya dofus the camera has a lever that keeps pressure on it (thus keeping it open) until the shutter is fired.

Take the lens of your camera, now set your f stop to say 22. Now manually close the leaver. Notice it opens up the aperture?

When mounted to the camera there is pressure on that leaver until the shutter is fired.

If this is all new to you, just sell it and buy some m42 glass which has a preset aperture
if you hate the little green button so much. Better yet, just get a modern automatic lens I suppose.
12-12-2013, 05:56 AM   #13
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QuoteOriginally posted by m42man Quote
I'm afraid it is a physical limitation: Pentax DSLRs use what's known as a "crippled" lens mount, meaning that there is no coupling of aperture ring position to the camera body. So, the camera has no means of knowing the working aperture, and therefore can't calculate the correct exposure when metering from the wide open lens.
You are correct - getting full metering is restricted by the crippled lens mount. However, if the meter was active during DOF preview, as it is with other Pentax DSLR models, you'd have a bit more flexibility than is offered with the Green button. I can't imagine that there is any physical limitation that prevented Pentax from keeping the meter active during DOF preview - my guess is that they're trying to make using old glass less attractive.

As to removing the aperture control lever, if I understand correctly, this will turn your M series lens into a Stop-Down metering lens. To my mind, this is a step backwards, as you'll end up with a very dim image in your viewfinder if you stop down at all. It will certainly work, but if you stop down at all, focusing is going to be more difficult.

YMMV
12-12-2013, 10:59 AM   #14
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QuoteOriginally posted by galaxytab Quote
Isn't there anything like Canon's Magic Lantern for Pentax cameras?
Nope...


Steve
12-12-2013, 11:02 AM   #15
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QuoteOriginally posted by jkomp316 Quote
Depending on the body it auto meters very well without having to fiddle with the green button.
Except that the metering is not very reliable at apertures wider than about f/4. That is the major difference between Av and M mode when using manual aperture lenses with the newer bodies. With older bodies such as my K10D, stop-down metering sucks regardless of mode. Pentax fixed the problem with the K-7 for M-mode, but not Av (for obvious reasons, if you think about it).


Steve
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