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02-01-2014, 04:57 PM   #1
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Using K Mount Manual Lens on K-30, K-50?

Hello Everyone,

I am new to the forums and also new to K-50. Recently acquired a K-50 and mounted an SMC Takumar to it via m42 adapter, I noticed that manual mode metering only works in Liveview and not through viewfinder. I wonder if that is the same case with K mount manual lens such as K or M or A primes. Does anyone know if will camera meter in viewfinder mode using green button with K mount manual lens? Any insight would be appreciated.

02-01-2014, 05:05 PM   #2
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Have you checked out this guide? ---> https://www.pentaxforums.com/forums/58-pentax-beginners-corner-q/110658-using...x-dslrs-f.html
02-01-2014, 05:08 PM - 2 Likes   #3
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Hi,
What you are seeing is the same with what I saw when playing with my friend's new K-50.
  • Green button metering using the optical viewfinder sensors fails in M-mode when using lenses having a non-conductive base such as your SMC Takumar
  • Green button metering in M-mode works fine for Liveview* with all non-A contact lenses
  • Green button metering works fine for the optical viewfinder with all K-mount lenses
  • A-series and newer work in all modes/views when the aperture ring is on the A setting
You might want to consider using Av mode with your M42 lenses. While the manual suggests that the metering may not be reliable in that mode, I did a quick test and exposures seemed to be reasonable and comparable to those done in Liveview.


Steve

* Metering in Liveview is based on the measured response from the camera's image sensor. Viewfinder metering, on the other hand, uses the SPD sensors in the prism housing that meter off the image projected on the focus screen. The two systems differ in how they work with lenses lacking support for body-controlled aperture ("A" contacts).

Last edited by stevebrot; 02-01-2014 at 05:34 PM.
02-01-2014, 05:15 PM   #4
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Go to Menu and Enable aperture ring at the very end.
The link that was posted is also a great reference.

With m42 lenses, its best to switch camera to Av mode and it will meter continuously. you can even use Auto-ISO. Keep the aperture on the lens wide open when you focus, and then twist it down to the aperture that you want. Now the camera will automatically choose the shutter speed and ISO and you can take a well-exposed shot.
M mode is also your friend. There you need green button to meter. Keep in mind that you don't have to meter. If you pay attention, you will develop a consciousness of what aperture, shutter, and ISO you want for your shot.

Edit: With K and M lenses, the camera doesn't know the aperture, but it can at least close the aperture. This means you can press green button and the camera will stop down the lens (to the aperture you selected on the lens' ring) and then adjust the shutter speed. But you can't select the aperture on the camera, it will say F--. With A lenses you get basically full aperture-automation and access to Av mode and everything. A lenses are basically DA without the AF and focal length info.

02-01-2014, 09:53 PM - 1 Like   #5
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I used Av mode for everything - manual and auto lenses. Manual lenses with a switch to toggle Auto and Manual aperture modes are golden. Preset your aperture to whatever you want. Toggle the lens into Auto mode. Focus wide open. Flick the lens switch to manual for stopping down. Take the shot.

You do have to learn the quirks of the exposure response for different amounts of actual light hitting the system. It's not linear. You may find yourself adding +1/3 for f/5.6 and taking away -2/3 at f/11.
02-02-2014, 12:54 AM   #6
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QuoteOriginally posted by Julie Quote


That guide is not correct for a screw mount lens on a K50.
Metering with the VF in Manual mode does not work.
02-03-2014, 02:05 PM   #7
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Thanks for your replies everyone!
02-03-2014, 02:07 PM   #8
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QuoteOriginally posted by 6BQ5 Quote
I used Av mode for everything - manual and auto lenses. Manual lenses with a switch to toggle Auto and Manual aperture modes are golden. Preset your aperture to whatever you want. Toggle the lens into Auto mode. Focus wide open. Flick the lens switch to manual for stopping down. Take the shot.

You do have to learn the quirks of the exposure response for different amounts of actual light hitting the system. It's not linear. You may find yourself adding +1/3 for f/5.6 and taking away -2/3 at f/11.
I definitely agree on the non linearity of the system. Do you find that AV tends to underexpose at larger apertures?


Last edited by Relativity; 02-03-2014 at 06:41 PM.
02-03-2014, 07:17 PM   #9
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QuoteOriginally posted by Relativity Quote
I definitely agree on the non linearity of the system. Do you find that AV tends to underexpose at larger apertures?

If you mean larger aperture values, like f/8 to f/11, then yes but only slightly. I usually add +1/3 or +2/3. Maybe there is something about the increased DoF that causes more light to strike perpendicular to the photo sites and that makes the sensing system think there is more light than really is?
07-08-2014, 01:39 PM   #10
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QuoteOriginally posted by stevebrot Quote
What you are seeing is the same with what I saw when playing with my friend's new K-50.
  • Green button metering using the optical viewfinder sensors fails in M-mode when using lenses having a non-conductive base such as your SMC Takumar
  • Green button metering in M-mode works fine for Liveview* with all non-A contact lenses
  • Green button metering works fine for the optical viewfinder with all K-mount lenses
  • A-series and newer work in all modes/views when the aperture ring is on the A setting
* Metering in Liveview is based on the measured response from the camera's image sensor. Viewfinder metering, on the other hand, uses the SPD sensors in the prism housing that meter off the image projected on the focus screen. The two systems differ in how they work with lenses lacking support for body-controlled aperture ("A" contacts).
A few questions about this. I have a K-50 and mine isn't working as I expect it to do with M series lenses. I have an M Series 50mm F/2 that I am using as my main test lens for this. When I use it - pushing the green button while the camera is set on M and I am using the optical viewfinder gives me two issues - first no meter shows up before or after hitting the green button. Second the lens stops down and then immediately reopens. This happens in liveview also.
No metering scale shows up.

The mount of the lens is metal and unpainted and doesn't appear to be odd in that respect. I have an older lens that is an 80-320 zoom that no longer works in A mode and no longer autofocuses which acts like an M lens - it works no better than the real M series lens.
07-08-2014, 03:55 PM   #11
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I think I have this correct. I do it, but I'm not certain I can explain it.

If you think about it, on a manual camera we have an ISO fixed by the film, guess at the proper aperture and shutter speed and then use the meter to 'test' whether these guesses will yield a properly exposed photo. If the meter indicates under- or over-exposure we adjust the aperture or shutter speed accordingly, depending on our priority, until the exposure is adequate (not taking into account pushing or pulling the film).

A digital camera allows all three metrics to float in combination to achieve best exposure, subject to whatever priority you tell the camera you have (using the Mode dial - P, Av, Tv, TAv, plus Auto ISO limits, fixed ISO, etc.).

With a pre-A K-mount lens, in all modes other than full manual one of the two adjustable factors (you set the aperture on the lens) must float for the meter to have any effect on the exposure. You choose the floating metric(s) when you choose your Mode. Even in Manual Mode either the shutter speed or the ISO must float or else the meter function cannot adjust anything. You choose which you will allow the camera to adjust in the Menu Settings for M Mode or by allowing AutoISO with the 4-way controller. If you want to use a K-3 like a digital film camera in M Mode you have to adjust everything yourself - then you shouldn't expect the camera to do anything.

On a flagship camera (K-3) that displays a meter bar, you can manually set all three metrics and 'see' the meter's feedback about your potential exposure, then you can adjust any or all of the metrics and meter again until you are satisfied. Typically I set a maximum ISO and meter using the DoF Lever (not the Green Button) to see the meter and the proposed ISO. Typically I adjust shutter speed using the e-Dial but sometimes I use Exposure Compensation if I want the aperture, Tv and ISO combination I have and still need to adjust the exposure.

I don't know if that helps for a K-50 but I suspect you received incorrect feedback from the Customer Service Rep. Pentax cameras will meter and use all Pentax lenses with varying degrees of limitation and accuracy.
07-08-2014, 04:05 PM   #12
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Oh right, ISO should not be set to AUTO. Otherwise the green button manual metering won't work either.
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