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Manual Metering on Pentax DSLRs with Manual and Automatic Lenses
Posted By: Adam, 05-04-2010, 09:11 AM

No matter what camera you're using, you have to match your chosen aperture to a shutter speed that will provide adequate lighting for your photo. You can do this with an external spot meter, but since all modern cameras are equipped with a light meter, your best bet is to use the camera body.

Open-aperture (a.k.a. when you're looking straight through the lens and don't have to stop the lens down) metering with the K-mount system started with the KM/KX/K1000/K2. On the KM/KX/K1000 cameras, you have to always manually set both the shutter speed and aperture. In most cases, you'd be setting the shutter speed first, so then you'd need to adjust the aperture until the lighting were correct. This is indicated to you by the camera by an analog arrow within the viewfinder. Once the arrow reached the middle (KM/K1000 - on the KX/K2 two needles must be made overlap), you'd be good to shoot!

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Now let's jump to the digital age, or how you'd likely be doing this.



Instead of using the arrow, you'd be using the digital light meter shown in item 10 above. (positioning varies slightly by camera body, K10D's viewfinder shown above). The green bar is centered in the middle is analogous to the K1000's arrow being centered.

Getting this light meter to activate for you might be the trick part. First off, make sure you set your camera to M mode (or, if you want the camera to automatically set the shutter speed for you and not have to worry about anything else, just use Av mode :P). If you're using an auto-aperture lens (A, F, FA, DA, DFA, FA J, DA L lenses), then you can simply adjust shutter speed and aperture on your camera using the scroll wheels. If not (for M, K, and screwmount lenses), then you FIRST have to set the desired aperture using the lens's aperture ring, THEN stop the lens down to meter (by pulling the on/off switch past 'on' so that it stays at the position indicated by the aperture icon and then adjusting the shutter speed so that the light meter is centered OR just hit the green button and the camera will adjust the value automatically). Also, make sure that in the menu, you've allowed the aperture ring to be in a position other than 'A'; this is a custom function.

Hope this help you and others out

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01-02-2016, 09:20 PM   #16
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QuoteOriginally posted by You3andme Quote
Just to reinforce the good advice found on this forum, a M42 screw mount lens (such as my lovely SMC Takumar 50 f1:1.4) works perfectly on my K5 (with an adaptor, of course) in either Av or TAv mode. The apeture control on the lens needs to be set to manual (rather than auto). The camera then meters on the chosen f stop. The advantage of using these modes over the M mode is that auto ISO is available. By the way, my K5 meters far more accurately and consistently than my K-x when using manual lenses.
This is what I'm talking about. Everyone (Pentax/Ricoh website, this forum, other sources) says you need to use the "M" mode when you have a lens mounted via an M-42 adapter. This just doesn't work. The green button (on those cameras so equipped) doesn't work. AV and TAV modes work so well that it's almost easier using old lenses through the M-42 mount than using Pentax-M lenses with K-mount: you choose the aperture on the lens, and the camera automatically chooses the shutter speed. If you want a higher shutter speed to stop action, choose a lower aperture number; if you want a lower shutter speed to blur action, choose a higher aperture number. It's a bit like the old Program mode—you choose one setting and the camera compensates to make sure the shot is exposed properly.

NOTE: In TAV mode, though, you need to limit the ISO range; otherwise, the shutter speed might be all over the place as the camera assigns different sensitivities.

01-02-2016, 09:35 PM   #17
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QuoteOriginally posted by fotograffiti Quote
This is what I'm talking about. Everyone (Pentax/Ricoh website, this forum, other sources) says you need to use the "M" mode when you have a lens mounted via an M-42 adapter. This just doesn't work. The green button (on those cameras so equipped) doesn't work. AV and TAV modes work so well that it's almost easier using old lenses through the M-42 mount than using Pentax-M lenses with K-mount: you choose the aperture on the lens, and the camera automatically chooses the shutter speed. If you want a higher shutter speed to stop action, choose a lower aperture number; if you want a lower shutter speed to blur action, choose a higher aperture number. It's a bit like the old Program mode—you choose one setting and the camera compensates to make sure the shot is exposed properly.

NOTE: In TAV mode, though, you need to limit the ISO range; otherwise, the shutter speed might be all over the place as the camera assigns different sensitivities.
Yes, you can safely use Av mode with M42 lenses, since they have a manual diaphragm (this is clearly stated in our manual lens guide). M mode should also work with any manual lens, however. If it doesn't, check to see that your green button's "action in M/TAv Mode" is set to Tv SHIFT (K-30, K-50, K-S1, K-S2, K-01), or post on the forum for more troubleshooting help.

As you observed, M42 lenses are faster to meter with, but your viewfinder does darken as you stop down, so there's a trade-off.

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01-03-2016, 11:25 AM   #18
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This is where the confusion came in for me, Adam:

5. Measure the light by either pressing the "Green Button", or pushing your power button to DOF preview mode (only available on high-end bodies). Your camera will automatically set the shutter speed for you.

That does not apply to M-42 mount lenses on the K-50 cameras, and probably other models. The green button has no effect.

Still, Pentax forums gives clearer information than the Ricoh site... and yes, stopping down does darken the image in the viewfinder with the M-42 mount lenses. BUT, fortunately one doesn't have to struggle to focus manually in the dimmed light, since the camera indicates proper focus.
01-03-2016, 12:47 PM   #19
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QuoteOriginally posted by fotograffiti Quote
This is where the confusion came in for me, Adam:

5. Measure the light by either pressing the "Green Button", or pushing your power button to DOF preview mode (only available on high-end bodies). Your camera will automatically set the shutter speed for you.

That does not apply to M-42 mount lenses on the K-50 cameras, and probably other models. The green button has no effect.
It does - if you set your green button action for M mode to "Tv shift".

01-05-2016, 12:13 PM   #20
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My K-50 has been set to "TV shift" (by the way, that's under "e-dial programming" on page 4 of the main menu) and still the green button does not work with M-42 mounted lenses. Nothing happens when I push the green button. But there is no need for the green button with M-42 lenses, because (in AV mode) the meter reads the open/closed down aperture and automatically selects the proper shutter speed.
01-06-2016, 03:38 AM   #21
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QuoteOriginally posted by fotograffiti Quote
My K-50 has been set to "TV shift" (by the way, that's under "e-dial programming" on page 4 of the main menu) and still the green button does not work with M-42 mounted lenses. Nothing happens when I push the green button. But there is no need for the green button with M-42 lenses, because (in AV mode) the meter reads the open/closed down aperture and automatically selects the proper shutter speed.
The green button most certainly work that way on the K-5 and K-3 - that is, when the GB is pressed in M mode, the camera will meter the light and set the shutter speed accordingly. The lens will have to be stopped down manually first, of course.

As you say, Av mode is more convenient in most cases. Whether one chooses M mode or Av mode + EV comp when the light meter gets it wrong is a matter of taste.
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