Do MF lenses need AF adjustment?

Earlier I was demonstrating (showing off?) my A50 f1.7 to a friend who has never used a MF lens and got some surprising results.

When shooting using the focus indicator/trap in focus techniques the images seemed out-of-focus.

However, when I took the same shot focusing using my eyes/matt screen (normal method) the images were in focus.

So...

Do MF lenses need AF adjustment when using the camera to confirm focus? I can't think of a reason why they would be spared but I have never thought about it before.

Cheerz

MZ

The most important thing is to make sure that the dioptre adjustment on the eyepiece is correctly set. And then we can use our eyes to focus. There should not really though be much difference between what the camera indicates as in focus and what we see as in focus.

So, point the camera at a blank surface and adjust the dioptre until the lines etched on the focusing screen are sharp. It's surprising how many photographers do not do this and hence have manual focusing problems.

Incidentally, we make a lot of AF errors these days, but 1970s manual focusing tests in Photo Technique magazine showed that the average human cannot focus easily in the same place twice. The amount of error found was huge, presumably because the eye adapts and gets tired and is thoroughly unreliable.

I calibrate the focus indicator for my manual lenses the best I can. Or at least check it.

but I try and use eyes to focus with them. the more you do it the better you get at it. I rock the focus barrel back and forth between front and back focus and settle on the sharpest setting in between. It helps avoid the 'getting used to it' syndrome.

Especially not easy @ f/1.2

And yup the viewfinder dioptre is the first port of call.

I've never had this problem when manual focusing as I just focus by eye... then again, I can't see the little green hexagon anyway because its so dim.

Incidentally, I can get better / more consistent focus manually than the camera does automatically. And, yes, I have tried adjusting the camera...

That's where I'm going wrong!

When I've got my new focus screen in I'll give that a try John and see if it makes any difference.

True!

In my recent problems with my K20 back focusing, I had noticed that the relying on the green hexagon caused my MF pictures to be OOF, focusing by eye was accurate of course.

I ran into this issue when I installed a Katzeye screen. The Katzeye focus screen was ever so slightly thicker than the standard Pentax focus screen on my k20d. As a result, I needed to adjust focusing for my manual lenses also.

Adjusting the auto focus using this method:

http://pentaxdslrs.blogspot.com/2008/06/part-1-autofocus-adjustment-for-pentax.h...

got me perfect focus with auto focus lenses. But I noticed after the auto focus system set focus, the image appeared slightly out of focus in the viewfinder screen. The split image finder of the Katzeye is most critical in displaying focus. Discussing this with Rachel at Katzeye led me to changing a shim above the viewfinder screen. Pentax shims are readily available cheaply. Now manually focusing an image displayed in the viewfinder matches exactly the focus as determined by the camera's auto focus system.

Of course, this process calibrated focus for all my manual focus lenses at the same time.

Dick

The red 'focus' indicator only shows which focus point is being used. It does not confirm correct focus. I keep mine set to the centre focus point.

It is the green hexagon in the bottom of the viewfinder that shows confirmation of correct focus.

I find the best way to set the dioptre correctly is to remove the lens and fit a translucent body cap, or no body cap. Point the camera at a bright light source (not the sun), then adjust the dioptre until the framing lines are sharp. Then refit the lens and you are good to go and can be confident that it is set correctly.

It's worth checking the dioptre adjustment occasionally too.

To set the dioptre I AF on to say a box that has lettering on it and then adjust the dioptre so that I can easily read the lettering on the box. This way even if the screen has excessive shims WYSIWYG

Not the right way to do it Algi, the last thing you want is an in-focus image. When you set the dioptre on the eyepiece you want to be focusing your eye on the etched lines on the focusing screen,

Point the camera at a blank wall or sky, defocus if necessary, or even use no lens at all, adjust the setting until all the viewfinder etched lines are as crisp as possible. Now your eye focuses naturally on the ground glass screen and yo0u will be able to judge when an image is in focus.

If your happy about focusing on etched lines that's probably OK. Personally I only trust small lettering that I can only just read. I wouldn't be happy focusing on anything else such as a flower. Also taking the photo with MF I'll always try to focus on some lettering.

Our eyes can be easily fooled into thinking that somethings sharp when it isn't... they automatically sharpen it. They can't do that with lettering either it's readable or it isn't.

Video players such as Media Player Classic let you make a contact sheet of a video. If your jpeg viewer doesn't automatically zoom to 1:1 pixel view, its impossible to say looking at the pictures when the view is 1:1. The lettering is the giveaway in the top left hand corner it only looks right and readable at 1:1

Unfortunately Algi you're missing the point. If you focus on an image to set the dioptre then the eye adapts as you're doing it and the result is variable. The correct technique, as I've outlined and as per the manual, can make a huge difference.

Trust me, you only need to set it up once and then your MF will be spot on. If you can't see the point of sharp focus on the etched lines, then I think manual focus is not going to be effective for you and AF may be better option.

I had previously been a bit crude with my dioptre adjustment. It's a bit better now after following your method John. I had never perceived an issue before but it's nice to have a slightly sharper image in the VF. Cheers for that!

There's more than one way to do most things John and this is certainly one of them, so not really a problem In the past I've usually had cameras with plain screens and I usually manual focus even with AF. With earlier M cameras it was only possible to buy fixed +2 Dioptre etc. correction lenses. My Bronica had a plain screen and the magnifier was adjustable.

You couldn't use the etched lines on say the Pentax ME-60 Plain Matte Focusing Screen on a K-7 (K-5) because there aren't any and this screen is advertised as "greatly enhancing manual focusing". You would have to use my method
in that case? link