Front Focus Issue - Help Needed

"If the focusing screen or the mirror were out of position all your images would be out of focus with all lenses.
It may be that this one lens is not hitting the focus point properly because of a slight error in the mechanics of the lens."


This is what I also think -

What do you think I should do in this case?
a - Call Chris at SRS and see if they have any ideas
b - Pentax suggested bringing them the lens, I am doubtful, as I am not ready to spend a lot of money of the repair or clean process.
c- do something on my own?

Going to sleep now, thank you all for your help, will pick it up tomorrow morning, and try further experiment.

Good night

Pleasant dreams . . . 50mm . . . FF . . .why why why why . . . .

Seriously, if you get the same result with 2 X K10D bodies, it must be something to do with the lens, not the cameras mirror, prism, or focus screen.

I've asked myself that question many times John.

The only mechanical cause I can think of is that we didn't have shake/dust reduction on film SLR's. Unless materials, design, production tolerances, and/or quality control of modern lenses are to blame. Then again the FA 50mm 1.4 that Nathan is having trouble with is relatively 'old school' as far as those criteria are concerned.

Similarly the only optical cause I can think of is perhaps internal reflections that 'confuse' the AF system.

I haven't heard/read of anybody having issues when using MF either, only AF.

It would be good to know if those Pentax/Nikon/Canon/Olympus/Sony DSLR cameras that don't have these facilities suffer from the same issue and is it lens dependant.

I think Nikon include AF adjustment in one or more of their bodies too so the problem is not limited to Pentax/Samsung hardware.

As far as I know, all makes of digital SLR suffer from this.

Well, in the 'old days' we never used to look at our pictures in quite as much detail as we do now. One of my better selling prints is actually slightly out of focus. I didn't notice it looking at the slide through a loupe, and it was only when I got it scanned that I realised. Printed to 12x8 it's noticeable when you look very closely, but at normal viewing distances, no.

The way we look at photos now, at 100% on a monitor, is similar to projecting a slide onto the finest, smoothest screen possible, then standing 12" away and inspecting every detail. Did you ever do that?

So these problems may well have been there all along, but without the ease of these focus tests they were probably just put down to user error.

I'm sure, if you search long and hard enough, there will be posts on some dim and distant forum about a film SLRs back/front focusing, because even then, there would have been one or two people wasting a few rolls of film to test it.

Dan

You may well be right Dan.

An upgrade to a K20D wouldn't cost £500 if you sold one of your K10Ds to partly fund it. The net cost wouldn't be huuugely more expensive than buying a new lens, and you'd have one better camera as well.

I've noticed slight AF errors with my FA 50mm 1.4 sometimes on my K10D. I suspect there is a design issue with the K10D where focusing precision is sub otimal with certain lenses. I also have AF trouble with my Tamron 17-50.

Meanwhile, I suggest doing more tests with real-world subjects instead of using charts - comparing AF with MF bracketing. It may be that you're not using the chart properly and assuming there is a greater problem than there really is.

Bear in mind that the FA50mm is not that sharp wide open*, and it's at this aperture that the camera is trying to focus. This may play a part in the focusing accuracy when using this lens.

Dan

*Certainly not as sharp as it is when stopped down a little bit. I'm not pointing this out as a failing of the lens, just a property of it. That slight softness can be used creatively etc etc...

Caveat duly noted Daniel!

Some years ago I asked the then Sales Manager how accurate the AF of the Z1-P was. What I wanted to know was would it focus on say the eyes in a portrait and not just some ill-defined area around the face. He couldn't answer the question.

Now we are expecting an f1.4 lens to focus absolutely spot on down to the mm and I suspect it may not have been designed to have that close a tolerance. Most people use a 50mm f1.4 at greater distances than we are talking about with a test target, and rarely at f1.4.

It would be nice to get some alternative measurements from different lenses to confirm it, but we might be chasing the crock of gold at the end of the rainbow with this one.

THank you all very very much for your help and advice.

I will have time on monday to experiment with MF - other apertures - longer distances.

Will report on results as soon as I can.

thank you in the meantime.

Nathan

Any news Nathan?

Apparently not .

Chart here and instructions
http://focustestchart.com/chart.html

Sorry peter, I haven't had any time to shoot recently...

As soon as I get some free time i'll report back.

Cheers!