[yophie]

Just bought an adorable 'pancake' 1:2.8 40mm pentax-m lens and was so excited to try it out - I have a pentax k-r but when I attached it, no option to change the aperture or shutter speed was available on AF or M on any setting. Why is this happening and what can I do to fix it?!

[jatrax]

It is an 'M' series lens, so no electronic contacts. All manual and you need to use the aperture ring to set aperture and stop down metering to set exposure.

See here: https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/110658-u...x-dslrs-f.html

[Na Horuk]

I have a pentax k-r but when I attached it, no option to change the aperture or shutter speed was available on AF or M on any setting. Why is this happening and what can I do to fix it?!

It is an M series lens, so it cannot be recognized. This lens is what, 30 years old? It was literally made before AF (Autofocus) was invented, before even camera-controlled aperture was around. Looong before digital cameras were invented.

Anyway, switch to M mode, set a static ISO number (not a range), select the aperture on the aperture ring, press green button, wait for the camera to stop down aperture, meter and adjust shutter speed, now press shutter and bam! Photo! The green button (metering) is not necessary, you can just do it by hand if you know what shutter speed is needed, but it is a good shortcut. Of course, you have to set focus using the focusing ring on the lens.
You might have to go into Menu, towards the back of the options, and Enable the Aperture ring use before the camera will let you take photos. And you might have to change shutter priority (not focus confirm priority) if you run into any problems. The camera focus confirm still works and can help you to an extent (little hexagon in viewfinder)

Also, you can read about Catch in focus (aka focus trapping) if you want something similar to AF.
Have fun with your new old lens It has a nice character to it and it is very compact

[stevebrot]

This...

You might have to go into Menu, towards the back of the options, and Enable the Aperture ring use.

Steve

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Last edited by stevebrot; 04-25-2016 at 04:23 PM.

[Blacknight659]

Na Horuk said it best.

You can us Manual mode. Set your ISO manually, Set the aperture on your lens to what ever you like, press the Green button. The camera will Stop down the lens, take a meter reading, and set the shutter speed for the scene.

EASY!

Luck for us Pentax users this is a viable feature. I have a M 50 1.7 and love it. This is only a minor inconvenience to use legendary glass.

Enjoy your lens, I have been looking for one so if you ever get tired of it let me know.

[Na Horuk]

The other thing you can do is switch to Av mode (or any mode other than B and M; they all default to Av with a manual lens, just look at the icon in the LCD screen), choose an ISO range (like 100-1600), and take photos directly - but the camera will never stop down the lens in Av mode. in some cases this is useful, but often lenses are not perfect at their widest aperture. The 40mm at f2.8 might not be perfect, but it has interesting bokeh at mid-close range

Finally, A series and newer lenses (those with A on aperture ring), will let you use P mode and others normally. If the lens has A on aperture ring, then it can communicate the aperture to the camera, so you can select aperture on camera. M series is the last series without this feature. Modern DA lenses often don't even have an aperture ring at all, they are locked in A.
The series after A, labelled F, is the first with AF and everything. Just so you know if you want to buy any more legacy lenses, so you know how much automation they have.
Third party glass is more complicated. But generally you want to look for the label AF if you want autofocus, and a little button and letter A on the aperture ring if you want auto-aperture (or a complete lack of aperture ring, it is equivalent)