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How to use/meter Manual & M42 Lenses on all Pentax DSLRs (K-1, K-3, K-5, K-30, etc)
Posted By: Adam, 08-12-2010, 04:24 AM

Many Pentax DSLR owners want to use M42 screwmount (Takumar) lenses, or M or K manual lenses, on their cameras because of the low cost and relatively high image quality of these lenses.


If you're wondering whether or not these lenses can be used with Pentax DSLRs (or the K-01), then the answer is yes! Pentax as well as third-party manual and screwmount lenses can easily be mounted on any Pentax DSLR (such as the K-50, K-500, K-30, K-5 series, K-r, K-x, K-7, K10D, K100D, K200D, *ist D, etc.) Just follow this guide!



Modern Pentax DSLRs use the Pentax "K-mount", which employs a bayonet and therefore differs significantly from the M42 screw mount. The older manual M and K (SMC Pentax-M, SMC Pentax) lenses actually use the bayonet, so they will not need an adapter - you can skip straight to the lower portion of this article (starting at "Important!") for information on how to meter with those lenses. Screwmount lenses usually have "Takumar" in their names, and in order to mount screwmount lenses on your k-mount body, you'll need a Pentax k to m42 adapter. Pictured above is the genuine Pentax adapter, which is ideally the one you want to get. Unfortunately, it has been discontinued and can only be purchased second-hand. However, similar third-party adapters are also available. Caution: Many third-party adapters, such as this one, have a protruding flange which will prevent you from focusing all the way to infinity. If you want to buy a third-party adapter (they're generally cheaper), make sure that they don't have this flange. Here's an example of a good third-party adapter.

Once you have your adapter, the next step is to install it on your camera (it can easily be put on and removed on-the-fly). Check out the m42 to k adapter manual. After you've installed the adapter, you'll want to mount the lens. This is done by screwing it into the camera until the lens feels firmly attached. The focusing window and lens ring should line up with the camera just like any other lens. Now that your lens is mounted, let's talk about how to take photos with it.

Important! The hard part is to get the camera to actually fire when a manual lens is mounted. In order to accomplish this, enter your camera's custom function menu, select the "Using Aperture Ring" setting (usually at the end of the menu, #21 on the K-7, #27 on the K-5, #27 on the K-3, #26 on the K-1), and set it to 2 (allowed). Once you do this, the shutter will at least fire, as it wouldn't have with this setting disabled (you would simply have seen an F-- indication on the top LCD/info screen). The setting description should read: 'Shutter will release when aperture ring is not set to the "A" position' when "allowed" is selected. Also note that the mount on the lens must be conductive for electrical current so that it shorts the electrical contacts on the camera body. All Pentax manufactured lenses have a conductive mount, but some third party lenses do not in which case the area of the mount touching the contacts must be sanded down.

K-30, K-50, K-500, K-70, K-S1, K-S2 and K-01 users: make sure you also set your green button "action in M/TAv Mode" to Tv SHIFT. This is found under the button customization menu (page 3 of the main menu) on the K-01 or as a custom function on the K-30, K-50 and K-500. On the K-S2 and K-70, look under the e-dial programming sub-menu under button customization in the record menu.

Finally, ensure that auto ISO is disabled.

Now, let's discuss metering. Since manual lenses don't feed aperture data to the camera, the only way for the camera to check how much light is being passed through the lens is to measure the light while the lens is stopped down. Follow this procedure to properly meter with a screwmount, M, or K lens:

___0. Ensure that the "Using Aperture Ring" custom function is set to "2 (allowed)" (K-30/50/500/01 users must also ensure that the green button is configured to Tv Shift in M/TAv Mode) as described above
  1. Set your camera to M mode using the mode dial (your camera won't fire in other modes*)
  2. Compose and focus your image.
  3. Using the aperture ring (the ring at the very back of your lens; it will have numbers such as 2.8, 4, 5.6, 8 written on it), select your desired aperture setting. Note that the smaller the aperture number is, the more light passes through the lens, and the blurrier the out of focus areas of your photograph will be (and vice-versa).
  4. [Screwmount lenses only] Switch the diaphragm clutch on your lens to "Manual" (you can leave it on Auto when composing and focusing if you don't want a dark viewfinder).
  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.
All that's left now is for you to press the shutter release button to take your photo. Congratulations- you've now learned how to use M42 and M & K manual lenses with Pentax DSLRs!

*Screwmount lenses may also be used in Av mode since they are always stopped down to the aperture you will be shooting at (unlike M&K lenses, which are stopped down only when the shutter is released or when you meter as described above).

Note: if your aperture ring has an "A" on it, instead of doing stop-down metering as per this guide, you'll want to set the ring to "A" and use the camera's scrollweel to adjust the aperture via Av mode.

Click here if you found this article helpful!

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Last edited by Ole; 02-12-2011 at 11:46 AM.
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08-10-2014, 10:23 AM   #211
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Thank you Not A Number and Adam for the explanations. When I tried using the M lenses in Av mode they seemed to work okay but I had them wide open.

08-10-2014, 10:27 AM   #212
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Av mode can be used but the lens will always be wide open.
08-13-2014, 02:58 AM   #213
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QuoteOriginally posted by Not a Number Quote
Av mode can be used but the lens will always be wide open.
A good trick is to unmount the M lens 7-9 mm from its locked position. this frees up the aperture lever and allows the lens to respond to the aperture ring. I drill a small hole at this point so the body's locking pin can engage the lens. The lens sits there quite securely.
08-21-2014, 07:22 AM   #214
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Hey ppl heres a new one....im using a K-50 and i love shooting my manual lenses but i just got a SMC Pentax-M 40-80mm 1:2.8-4.0 and when i shoot as always and trying to use the green button it takes a picture but the camera says "this file cant be shown". and after gours and hous reading in this forum i just have to ask for some assistans.....
everything is set as told and when usung m42 lenses the green button does its stuff (altogh everything is almost pitch black due to faulty shutter setting aka the green button)
i dont realy care about that but now this lense takes a picture the cant be seen whats up with that??

Stay safe //Matt,Sweden

08-21-2014, 08:01 AM   #215
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Do you have the camera set for Aperture in #2? This is a requirement to be able to use the green button. Also, you do not need the green button when using M42 lenses.
08-21-2014, 09:48 AM   #216
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Typical settings for all models are (actual verbiage in menu may be different): enable use of aperture ring, green button to Tv shift in Manual and Tav mode, DOF preview to optical, ISO not set to auto.. On the high-end models with non-A lenses operating the DOF preview will stop-down and meter through the lens displaying the exposure bars which can be adjusted by the aperture ring and edial (for shutter speed).
08-21-2014, 10:47 AM   #217
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my K-50 is set up properly and when i use a m42 the green button does what it is suppose to but now when i put on my Pentax-M 40-80 micro and push the green button it takes a picture but the camera can show the file..... and i havent touched anything in settings...
08-21-2014, 10:57 AM   #218
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It sounds like it is doing a DOF digital preview. Check your customizations for green button and DOF preview. I'm not familiar with the K-50 menus. Is the image getting saved to to card? If not then it is doing the DOF preview to digital.

08-21-2014, 11:45 AM   #219
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cant find anything about DOF in the meny but green is set to TVshift and apature ring permitted aka setting 2, and like i said what confuses me is that with a m42 green button does its job(not good but still..) and when i change to my Pentax-M zoom 40-80 macro and not tuching anything besides turning the camera off and on then all of a sudden green button does that DOF digi preview but the sound of it....
08-21-2014, 01:44 PM   #220
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When using a K-mount lens without a-mode you have to put the camera in M-mode and set the aperture on the aperture ring. You measure light by pushing the green button. It stops down the aperture and measures light. It does not expose a picture but it does set the correct shutter speed. You then have to push the shutter button to make an exposure. The green button is just for measuring. Specific instructions for the K-50 you can find here: Using Older Lenses on the PENTAX K-50 | Ricoh Imaging Support
08-21-2014, 03:01 PM   #221
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QuoteOriginally posted by D1N0 Quote
When using a K-mount lens without a-mode you have to put the camera in M-mode and set the aperture on the aperture ring. You measure light by pushing the green button. It stops down the aperture and measures light. It does not expose a picture but it does set the correct shutter speed. You then have to push the shutter button to make an exposure. The green button is just for measuring. Specific instructions for the K-50 you can find here: Using Older Lenses on the PENTAX K-50 | Ricoh Imaging Support
Ahh ok that makes sence, but why doesnt it do that when a m42 is on it?
when i use the green button then it just changes my shutter and nothing more...
08-21-2014, 03:17 PM   #222
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m42 lenses do not have an aperture lever that will work on a dslr. You put them in manual mode. (there is a auto/manual lever on the lens, when there is not the lens has to be adapted for digital) In manual mode the aperture will always close when you stop down. The viewfinder will become darker. You can use them even in P-mode. The camera will automatically switch to Av. In my experience you have to adjust exposure manually on m42 lenses because measurement is of about a stop too dark wide open to a stop to bright about F8. A question of experience. Under exposure is usually no problem when you shout raw because of the dynamic range of the image you can adjust it in post processing.
08-21-2014, 03:56 PM   #223
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so when shooting with a m42 i best leave our dear green button alone?
08-21-2014, 04:18 PM   #224
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Always Av mode

Using K-1 and manual focus Canon FL 55 f 1.2 converted to K mount, no lever. This lens is not auto--I mean you set the aperture, take your light reading, then manually step the lens down to take a photo. Actually, in decent light you can take the reading and focus while already in the selected aperture, saving one step in the shooting process.

However, even when you set the mode dial to M, the display still says Av, and the camera automatically meters for the correct exposure. All this is without using the green button at all. Is that the way it should be operating? I thought I would have to set my aperture, push the green button for correct exposure, and then take the shot. I do not understand why, when the dial is in M mode, the screen continues to show Av mode, and there appears no way that I can set the camera to M mode.

I would like to use M mode in order to make my own shutter speed selections from time to time for creative purposes, but as things are working at present, the camera always selects the shutter speed.

I will appreciate any comments and expertise on this matter. Many thanks.
08-21-2014, 04:49 PM   #225
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QuoteOriginally posted by sourcenemy Quote
so when shooting with a m42 i best leave our dear green button alone?
I downloaded the K50 manual (English). See page 114 on setting Depth of Field preview to the RAW/FX+ button.

Let's review:

What M42 adapter are you using? Is it a genuine Pentax adapter, a 3rd party copy of the Pentax adapter or a 3rd party adapter with a flange? If it is a flanged adapter is it bare metal or painted/coated/anodized (usually black)? This may make a difference as the flangeless adapters or painted flanged adapters do not short the contact pins on the camera body. On some bodies or perhaps firmware versions the green button and DOF preview behaves differently if the contacts are shorted or not.

For manual exposure camera should be set to Manual, aperture ring enabled, ISO anything but AUTO, green button in M or Tav set to Tv shift, DOF preview to optical on the RAW button. Liveview disabled for these examples.

M42 lenses:
Turn on the camera, set to Manual mode. Lens should be wide open - if the lens has manual/auto switch moving the switch so the word "auto" appears will open the iris all the way no matter what the f-stop is set to on the ring. If it is set so the word "man" is visible or the lens doe not have a switch set ring to the largest aperture. Half press the shutter button to turn on the meter, focus confirmation and shake reduction. Compose and focus. Set the f-stop you want to use. If an auto lens slide the switch so "auto" is visible. The lens should now be stopped down. Check composition - note focus confirmation may not work at the point depending on the f-stop. Press the green button - the camera will measure the light coming through the stop-down lens and set the appropriate shutter speed. Adjust the exposure with the edial or aperture ring (this is mostly a matter of experience). Take your exposure.

K-mount lenses - non-A with bare metal mounts:
Turn on the camera, set to Manual mode. Half press the shutter. Focus and compose. Set the f-stop - lens should remain wide open regardless of f-stop setting unless it has been modified or damaged. Press the green button - lens should should stop down briefly, the camera measures the light coming through the stop-down lens and set the appropriate shutter speed. Adjust exposure with either the aperture ring or the shutter speed edial.

So really the only procedural difference between M42 and non-A K mount lenses is that you have to manually stop down M42 lenses.

But as noted before the green button or DOF may behave differently on some bodies depending on if the contacts are shorted or not.

This is entirely up to you at the risk of getting dust on the sensor - try pressing the green button with no lens attached. Does it behave the same as with the M42 lens (assuming non-flanged adapter) or a it does with your K-mount lens? Another way would be to put some non-conducting tape or a slip of paper between the contacts on the lens and camera body mount.

What happens if you use Liveview?
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