Playing The Long Game: Outdoor Photography With Telezooms

Achieving focus


Time for an update: I still use film, though. Not vast quantities, but I have a darkroom, and I'm not afraid to use it.

I enjoy every image I take: I hope you'll enjoy looking at them.
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Achieving focus

8 Jun 2020 8:36AM   Views : 438 Unique : 318


I was discussing focussing aids with a friend yesterday, although she didn’t know it…

So I’ve been thinking about the changes in how lenses focus, and the various implications. We’ll start where I did when I was in my teens, with manual focus.

Most of the simplest and cheapest lenses focus by the front part rotating and moving backwards and forwards. It’s mechanically easy to design – just a screw mechanism moving one tube inside another.


There are, I believe, some quality issues with this, so it’s not terribly common. It’s far more usual for a lens to have a much more sophisticated mechanism that allows the whole of the lens to move backwards and forwards, usually without anything other than the focus ring rotating. This may not seem like a very big deal, but with the aperture mechanism in the moving part, the position of the aperture ring and the index line would move around: not great (but it does happen on a few lenses).

Usually, the focus ring was nice and wide, to give a good grip for the fingers, and the movement was nicely damped: no backlash at all, and enough resistance to prevent accidental movement. The feel of a good lens is a wonderful thing: silky and purposeful.


Everything changed with autofocus: as the electric motor doing the work had to work from a battery with limited capacity, the aim was to reduce resistance to a minimum. As for manual focus, it took a back seat, and early AF lenses often had a narrow focus ring. There tended to be a thorough lack of ‘feel’ and bags of backlash.

The whole thing was so iffy that Zeiss stated that it wasn’t possible to make an AF lens that met their standards: that might be why they collaborated with Yashica over the Contax AX, possibly the oddest AF camera ever, in which the whole mirror box, shutter and film were moved backwards and forwards, behind a stately manual focus lens. Fortunately, Zeiss have found a way to make it work now…

Eventually, it became apparent that even with the magic of three AF spots, some people, sometimes, would need to focus manually, and broader focus rings came back in.

And, somewhere along the way, designers discovered that you can, if you’re clever enough, make a lens focus without all this unseemly external movement, by moving a few elements inside the lens relative to each other. Loads of big pluses: less mechanical work to do, so less drain on batteries. No rotating front elements, twisting graduated filters out of true. And – importantly for digital – no tendency to suck air (and dust) into the lens and mirror box as the glass moves away from the sensor.

There’s plenty to say about how – other than AF – we check that things are in focus: but to do that properly, I’ve got to work out how to take a picture through the viewfinders of cameras. Wish me luck: any tips welcome!


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dudler Avatar
dudler Plus
20 2.1k 2048 England
8 Jun 2020 8:37AM
There's a short clip on YouTube showing the Contax AX mechanism in operation - for some reason, I can't embed it in the blog itself: but look HERE to see it...
altitude50 Avatar
altitude50 19 23.9k United Kingdom
8 Jun 2020 9:25AM
I wasn't aware that the Contax AX focused in that manner. The earlier Ensign Commando did something similar. My first AF camera was the Minolta 9000 when it first came out, I thought it was excellent then but let down by top lcd issues, I sold it for £30! wish I had kept it.
dudler Avatar
dudler Plus
20 2.1k 2048 England
8 Jun 2020 10:18AM
The 9000 was a thing of beauty, definitely - I think the only manual-wind AF camera ever made. The rewind crank's pantograph design, lots of little touches. The LCD isn't a major feature, or particularly useful, I felt. However, long-term reliability does seem to be an issue...

I bet the Commando didn't use a motor and a ceramic rod for alignment, though...

In principle, it's like a monorail camera, where you can move the back with the screen/film holder as easily as the front standard. But that's a whole different blog...
chase Avatar
chase Plus
18 2.5k 682 England
8 Jun 2020 11:14AM
I'll get it....eventually Wink

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