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Minor Surgery to fit a Pentax K mount lens to a Canon Full Frame camera

There are an abundance of top quality older Pentax K mount lenses available second hand. These lenses were made in the 1970s though the 1980s and, with an adapter, these work very well on Canons APS-C cameras (550D, 60D, 7D etc.). But they won’t fit on the full frame models (5DII, 5DIII, 6D etc.) Well, they fit, but when you go to take a photo the mirror smashes into the back of the lens in a most unhealthy way.

Fortunately, with a little minor surgery this can be corrected. After the surgery, the lens will loose some of its function if you decide you want to mount it on a Pentax camera –

M series lenses  – the lever is used to keep the aperture open until you click the shutter. If you use the lens on a modern Pentax camera you need to use manual exposure and meter when using the Depth of Field preview button. This is a real hassle. If you do the surgery as I describe the aperture will close or open as you move the aperture ring, and you can use Aperture priority automatic exposure. The viewfinder will get darker as you stop down, but I think this is better than having to muck about with the DoF button.

A series lenses – The lens will work well on a modern Pentax camera and will interface with the cameras electronics. The surgery will work as I have described, but this will significantly devalue the lens to anyone who wants so use it on a Pentax camera.

Therefore I’d only recommend doing this to an M series lens. How do you know if it is an M series lens? On the A series there is a green A (for Automatic) setting next to 22 on the aperture ring. The M series don’t have this setting.

Here we can see the problem – it is the aperture lever and guard that we need to remove.


Step one is to remove the five screws retaining the base plate of the lens.


Step two is to pull the base plate off the rear of the lens. I’ve indicated the guard and lever that we are going to remove. With the base plate removed you can actually remove the aperture ring and more – but unless you want a tricky job of figuring out how to put it back together I’d strongly advise leaving everything else just where it is.


Step three is to cut the lever. Since this is hidden inside the lens we don’t need to be too fussy about the quality of the finish, and since we don’t want filings inside the lens, I’d recommend this somewhat barbaric method. Grab it with a pair of needle nose pliers and bend it back and forth until it snaps off. It looks ugly, but we won’t see it when were finished.


Step four is to remove the guard. On later models this is hard plastic, and can be easily removed with a sharp knife. You could file or sand the edge to get it smooth, but I think you are more likely to introduce filings into the mechanism, so I prefer to just cut it down and leave it a little rough.

On older models this is brass. You will need to use a cutter (side cutters or a pincer) to get it as close as you can, and then file the edge to get it smooth, and then make sure you have blown out all the filings.

Step five – reassemble the lens. There is only one position the five screw holes will match up, so this is quite easy. You can see where the guard used to be.



Step six – fit suitable adaptor. Here I’ve used a ‘chipped’ model. With a non-chipped model the camera has no information that a lens is attached and will register the aperture of the lens as 00. The chip tells the camera that a 50mm 1.4 lens is attached (even though this is actually a 135mm f/2.5), and that’s what shows up in the EXIF data. Because the camera knows a lens is attached the focus confirmation works the camera doesn’t focus automatically, but it will indicate when you have correct focus.


In the end you have a great lens at an affordable price. In this case I paid $NZ70 for the lens and $NZ60 for the adaptor.


DSLR vs. iPhone

The other evening I went down to the new cycleway near my house, in the hope the at the city council might have built a nicely photogenic object near my home. As it turns out the cycleway is not as photogenic as I’d hoped – it might be better in fog or rain though. The lights in the distance are quite distracting. You don’t really notice them when you are there, since these are on the other side of the harbour, but they stick out in the photos.

I took a few shots, and I’ve posted the best one here. It’s not a great shot. The lens flare detracts from it, and the lights in the background also remove the atmosphere. But, apart from the lens flare, it is clear and sharp. It was shot with a Pentax K-5 on a tripod, using a Sigma 10-20mm lens.

But on the way home I thought I’d give my iPhone a shot at the same scene. This is an iPhone 4S with a Schneider wide-angle lens, and uses Hipstamatic. The iPhone really is not a great device for shooting in poor light, yet the results here are not too bad. It’s not sharp, but it is atmospheric. Since I used the randomise function on the iPhone (see the post below on serendipity) I had no idea what the shot would turn out like. I took eight shots – four were complete rubbish, and the remainder each had something to recommend them.

With the shot from the Pentax shot you can see the distracting background. I was thinking that some fog or rain might add the atmosphere I felt I needed for the shot I imagined, yet the unusual, LoFi exposure of the iPhone has provided me with a similar effect to the fog.

Conclusion – you can’t expect an iPhone to compete with a serious camera in terms of getting a detailed sharp image, but sometimes you can get an interesting atmospheric shot, a shot where the low quality can enhance the emotional impact. And, of course, the best camera is the one you have with you.