The SMC P-M 50mm F1.4 is my first prime lens for my K100D. I bought it from a second hand camera shop at Pasar Baru for quite a cheap price. It wasn’t in mint condition, and didn’t come with front and back lens cap. But still very usable and produces quite sharp pictures.

Anyway, unlike the “A” lens, the “M” doesn’t come with “Auto” setting for aperture. On an “A” (and above, except the DA and DA*) lens, Auto setting lets you set the aperture value from the camera body, instead of the aperture ring. This means, with an “M” lens, the only way to set the aperture value, is through the aperture ring on the lens.

On a plus side, since K100D Shake Reduction function is onboard of the camera body, this means any lens, including my old “M” lens will have shake reduction feature.

To use my SMC P-M 50mm F1.4 (or any SMC-M lenses) on K100D, I have to do several steps:

1. Setup SR function
Unlike newer lenses, the SMC P-M 50mm F1.4 doesn’t provide focus length and aperture info needed for the SR function to work, so you have to manually input them. When I mount the lens to my K100D and turn my camera on, it automatically ask you to input the focus length infos. You can change the value by entering the “Rec. Mode” menu via the “MENU” button, and change the “Shake Reduction” value.

2. Allow the use of aperture ring
Go to the “Custom Setting” menu via “MENU” button, change the “Using aperture ring” value to “2 Permitted”. This setting will allow you to set aperture by using the aperture ring on the lens.

3. Change the AE-L button function
Go to the “Custom Setting” menu via “MENU” button, change the “AE-L bttn on M expsr” value to “2 Tv Shift”. This setting will let the camera to shift shutter speed when the “AE-L” button is pressed on manual mode.

4. Switch to Manual Mode
To put the camera into Manual Mode, turn the dial to point to “M”. Manual Mode will let you set the aperture value via the aperture ring on the lens. You can shoot in “Av” mode, but it will only work with the aperture open wide.

5. Switch to manual focus
Actually, you can shoot in “AF” but only if the focus is confirmed. Switching to “MF” will let you shoot anytime.

6. Select the correct ISO
On Manual Mode, Auto-ISO doesn’t work, so you need to setup the ISO value manually.

When you have followed above steps, you are ready to shoot with your SMC P-M lens, here are the steps:

1. Set aperture value via the aperture ring
2. Frame your shot
3. Focus with the lens focus ring
4. Press the shutter halfway to confirm focus (optional)
5. Press the AE-L button to get shutter speed
6. Shoot

As a side note, DOF on a F1.4 lens is pretty tight, the lens is best used when stopped down. You don’t have to press the AE-L button every time you shoot, and you can always manually set the shutter speed, if you want.

Here’s a sample shot from the M 50mm:

This one is taken with the M 50mm and a Metz 32-Z1 flash unit.


dubesor pointed me to a discussion on dpreview on similar topic by Sean Nelson. One of the step that I stated was to switch the focusing method from AF to MF, since on AF, you can only shoot when the focus is confirmed by the camera. From my experience, getting focus confirmation on this lens is kinda hard, and even when the focus is confirmed, you usually are required to make small adjustment, hence throwing the focus confirmation off, and leave you unable to shoot.

But if you’re confident enough with the focus confirmation, shooting in AF can help you focus in some way. First you manually focus as best as you can, press “AE-L” to meter, and then fully press the shutter. It won’t rightly shoot, since you don’t have the focus confirmation yet. Then you adjust the focus by moving the camera slowly toward or away from the object. As soon as the camera detect the focus confirmation, it’ll automatically take the shot.

There are some major drawbacks with this method. One, there will be camera shake, since the shot is taken while you move the camera. Luckily, with K100D, you’ll have SR function virtually on all of your lens. The second, is that you will not be able to compose your shot. While using the M lens, instead of 11 focus point, You’ll only have a single focus point, which is right in the middle. Since the focus confirmation only works on the focus point, you need to put the object of the photo right in the middle of the frame of your shot. So recomposing your shot is required, if you want to use the focus confirmation function, and put the focus object other than in the middle of the frame of your shot. With the first method (using MF instead of AF), when the focus is confirmed by the body, you can lock the focus by keep half-pressing the shutter button, and proceed to recompose the frame. Or if you don’t need focus confirmation, you can immediately start focusing after composing the shot. But when shooting in AF, you need to fully press the shutter, eliminating focus lock function, and the resulting the shot taken as soon as the focus is confirmed.

By ikhsan

13 thoughts on “SMC Pentax-M 50mm F1.4 on Pentax K100D”
  1. Hi dubesor,

    Thank you for the comment. I also learned new tricks based on link that you’ve provided.
    I think exposure bracketing on M with old glass is kind of impossible without the camera changing the shutter speed, since the aperture is set directly on the lens, and the camera has no way to alter them.

  2. Thx a lot ^^
    my K100D is my first Reflex ever and i just get the exact same SMC 50m as my only lens.I was desapointed to see the “af “message until i found this saved my day 😉

    (I had another lens, in fact, but a stereoscopic one from loreo…^^)

  3. Yes I m using the loreo lens on a K100D,it s quite a narrow lens (the final frame is only 7,5×10 because there s 2 views on the pic).And you need a viewer (cheap) to see the stetro effect once printed.I ll send you some shoots when i m happy with it (i m new to reflex as i say ^^)
    (ps: could i mail you about questions on the smc 50 ? i can t seem to have aperture ring detected by the k100d..But i m having fun with it anyway)

  4. well, I’m a newbie also to SLR 😀 But ask anyway. Some of my local mailing list buddy might be able to answer your question. You can send me e-mail to

    Technically an SMC-M lens can’t “speak” to DSLR body since it has no contact to point (the one that look like a couple small golden ball on the back of your kit lens), thus your body won’t show aperture value on the upper lcd. the only way to know whether the body “detect” the current aperture of your lens is when you meter with the AE-L button. When you have done all of the six steps above, set the aperture value to a value (let say 1.4), then press AE-L button. Note the aperture value given by the camera. Next, change the aperture value again with the aperture ring (let say 2.8), and press AE-L to meter again. If the the camera give a different result than before, than the body is able to “recognize” the aperture that you set with the ring. But due to the limitation that I mentioned above, the body won’t record the aperture value on the exif tag of the image taken with an SMC-M lens

  5. Thank you for the tips. I was shooting for two months in Av mode with wide open aperture on M lenses. And the DOF was sometimes too narrow.

  6. Nice read. Some time ago I bought the 1.7 version of this lens. Never paid much attention to brand or specs of a lens, but the quality of the Pentax SMC lenses convinced me otherwise. The pictures of the Nuvi on my blog are all made with this lens.

  7. I recently dropped this lens on the kitchen floor and I can no longer focus it…go figure.

    I currently have it all in pieces, but cannot figure out how to pop the center piece back into place.

    Any idears?

  8. thankyou so much. i have a beautiful pentax m 1.7 50mm lens and couldn’t figure out how to make it work on my ist d dslr. now i’m taking beautiful bokeh shots. Thankyou!!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.