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Thursday, 29 November 2007

Focus Confirm Adapters v's Split Screen Focusing

As you may have read in this blog, I like to use some manual focus Olympus OM lenses on my 1Ds2 and this of course, is done by way of an adapter that converts the Olympus mount to a Canon lens mount. This is such a simple process of "click on-click off", that I also carry mounts for M42 Screw and Nikon lenses.

Using other manufacturer's lenses opens up a whole new world of imaging, with access to specialty glass and their unique qualities.

The downside is of course that AF (auto focus) does not work and that the lens' f-stop needs to be shut down manually.... but for most of my images (landscape) this is not a drama, as there is plenty of time to get setup and to get things right.

For those times that are a bit more hurried though, I find the lack of AF a bit of a pain. Yes in the old days that's how everyone did it (inc. me)... but those days are long gone and without regular practice, accurate manual focusing is a skill that can quickly be lost.

Also, today's AF cameras are not really designed for manual focusing and the necessary aids have generally gone missing from the view finder and in their place are focus confirm lights and beeps. So this leaves all the hard work up to the automated system that delivers us a pretty light or beep, so we can feel good about the clever bit of electronics that we have in our hands.

So now that we place an old school manual lens in front of all this high tech, our cams all of a sudden are not so clever after all and we find the standard focusing screen hopelessly inadequate for us to judge focus and the silence of our friendly beeps deafening.

If you are lucky enough to have a camera with interchangeable focusing screens, it's a simple matter of popping out the standard screen and dropping in a new "designed for manual focus" split-screen. This screen's center circle has be divided in two and it is a simple matter of lining of the two halves on the subject that you want in focus.

This a very accurate system and one that has been used for years. It does have it's drawbacks though.... It's not fast unless you practice and it can, at times, interfere with the camera's exposure readings, especially in low light as one of the halves has a tendency to go black.

With this in mind, some clever Dick has come up with an adapter that not only converts the lens mount, but it also carries the AF circuitry that would normally be found on the regular AF lens. This tricks the camera into thinking that there is an AF lens attached and like magic, the flashing lights and beeps of the AF confirm come back to life.

This sounds like the ticket yes? Well.... "for me" this system has a bit of a problem. As you focus the lens there is no real visual stimulus that you are approaching correct focus.

Sure the entire focus screen is getting sharper, but as I said earlier, the screens are not really designed for this these days and the visual help is minimal at best. Unlike the split screen where you can clearly see the two halves approaching "line up".

So with the AF confirm adapter it's more of a "lights on - BEEP your there!!" and you need to put the brakes on REAL quickly! If your not quick enough, you have actually passed correct focus and need to back up a little.

But just how far do you back up? I have found that the AF light will actually stay on for prob a degree (or perhaps 2) of the turning of the focus ring. So without the visual stimulus of the "exact moment of focus" like the split screen gives you, it can be very hard indeed to obtain a truly accurate focus.

Now this will not be an issue with broader scenes that you are covering with heaps of DOF, but in a situation such as macro or shallow DOF portraiture where absolute accuracy is required, the focus confirm adapter becomes very difficult to use in my opinion.

So perhaps the best thing to do is to become VERY familiar with the quirks of each system and use whichever one is going to suit the photography that you are doing at the time. ...either that, or stick with AF lenses, as those suckers have really good brakes! ;-)

Also see:


Australian Digital Photo Of The Day:

Quality Fotodiox lens adapters for various camera/lens brand combinations are available from Amazon, as are camera focus screens more suited to alternate lenses...

Tags: lens adapter lenses nikon pentax canon sony dslr body slr focus confirm af chip auto focus alternate lenses

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