An autofocus Trioplan 180mm


Link Posted 22/11/2022 - 01:20
I have been remounting old lenses to M42 screw mount for a while and, by necessity, they must be used in manual or AV mode. Each lens usually needs some additional extension tubes between the mount and the camera body to account for its particular focal length. I have known for a long time that in order to make (e.g.) Jessop auto extension tubes work you need to scratch some of the black paint off the rear flange so that the pins on the camera body are shorted out but that only permits a Pentax camera to control the aperture of its own, native 'A' series lenses and so is of no use for my M42 conversions.

However, enter the 'F' series x1.7 Auto Focus adapter! I realised that if I exchanged one of the M42 extension tubes for a 'K' mount equivalent then the narrow mounting flange of the M42 tube (which isn't wide enough to cover the pins on the camera body) is swapped for the far wider flange of the K tube (which does cover the camera's pins). Scratch off the paint from this tube and you short out the pins on the AF adapter - which promptly goes to work the moment you half press the shutter release.

K1 with F series AF adapter fitted, followed by a K mount tube with an M42 > K adapter to engage the next (M42) tube, then a focusing helicoid and, finally, the converted shutter and lens assembly (in this case, with a gorgeous 105mm Trioplan fitted in it). The resulting focal length is just shy of 180mm.

The rear of the K mount extension tube showing the bare metal that shorts out the pins of the AF adapter.

The AF adapter is not supposed to work with an aperture smaller than f4.5 but this one goes down to F7.1 before it refuses to play. I have always had super pictures from this lens, even hand focusing but auto focus nails it with just that extra bit of accuracy. I am delighted with my bit of tinkering !I was intending to go out with it today but it hammered down with rain so you will have to make do with some indoor shots .....

This about 3cm long. I found it in the gutter !

This was posed on the end of a skewer (cloned out) in front of the mouth of a black plastic waste bin and lit by off camera low powered flash from the side. Using a bin like this produces a really profound black. Crop or clone out the edges of the bin and it's quite effective.

These are the last of our tomatoes from the garden and about to be made into soup.

A very close up, almost macro shot

And the rain that didn't stop all day long.

And not a hint of bubble bokeh anywhere (although it can indeed produce it).
Both the *istDS and the K5 are incurably addicted to old glass

My page on Photocrowd - link


Link Posted 22/11/2022 - 07:44
Quite ingenious.

My Flickr page


Link Posted 22/11/2022 - 09:39
Love these kind of threads, so interesting and informative.
Be well, stay safe.


Link Posted 22/11/2022 - 11:56
What them others said
And, so cool walking around with this lens on your camera


Link Posted 22/11/2022 - 14:49
Bravo for lateral thinking!

And the results are great!

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