Front Focus Issue - Help Needed

Ok,
Maybe my english doesn't allow me to explain myself well enough for you all to understand.

The two K10d I own are absolutely fine with the sequent lenses

100m Macro f2.8
31mm ltd
DA 16-50
DA 10-17
Tamron 18-250
da 18-55

The ONLY LENS that is giving me problems is the FA 50mm f1.4 - which gives me about 4-6 mm of front focus.

I therefore don't need to buy another camera, nor change the focus adjustment on any body, nor send it to pentax to adjust anything.

I need to know if the lens is faulty, and if it can be repaired or the issue resolved. I would be interested in DIY solutions - or perhaps somebody here as had previous experiences similar to mine.

THank you all,

Your English was easily understandable. What you may not be understanding is that people are making alternative suggestions while we don't know if your lens is faulty or not.

My sugestion to upgrade the camera(s), or NorrisTudor's to send the camera(s) to Pentax, would enable an adjustment to be made for the problematic lens without affecting use with other lenses.

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Thank you Norris for the links. Hopefully the info will be of some use to some readers.

Pete,
I appreciate the alternative suggestions that have been made.

If I spend £500 on a new body - I will still have a faulty 50mm - and be out by £500.

If I send the two bodies to pentax - even with the lens - I will have two bodies that work with the 50mm, but that front focus with all the other lenses. [Unless it was indeed possible to update the focussing system as Norris suggested (alike the K20) and have a special setting for the one single lens. ] [ btw pentax do not confirm they are able to do these modifications - nor specify the eventual price]

Because the lens seems to function perfectly, and only has an issue with front focusing, I am not sure if it can be considered 'faulty' - and I am asking for advice on wether it is possible to solve the issue without buying another lens, another camera, or a tripod.

Cheers,

Mostly used is this one.

HIH,
Martin.

cheers martin

The K20D will enable you to set the focus for the one lens and keep that setting just for that lens. The camera will in fact keep the settings for up to 20 lens types.

Don't forget though that the slight error in focusing that you observe will be insignificant at normal distances and smaller apertures. It will only really be an issue close up and at wide apertures.

It would be interesting if you could find another 50mm lens to try out.

Dear John,

I know that the K20 has the option of focus adjustment for up to 20 lenses. I will not buy it anyway, cause I will buy the next in line....

I agree with your point about 'normal use' but it is also true that I use the lens a whole lot, and usually at f1.4 for close up portrait work - so as much as it will not bother me in some of its use, it will make a lot of difference on a rather big part of it.

"It would be interesting if you could find another 50mm lens to try out."
Why so? do you think it might be an issue of the focal lenght? because I have tried 3 zoom lenses at 50mm, and they all perform well. Do you think it might be an issue of the 50mm lens construction? - I am pretty sure that it is something that occurred with time, as I hadn't noticed mis-focus issues until about 1/2 months back, and I've had the lens for 2 years.

Thank you for your help

I was just wondering if the lens itself had become faulty. We have a FA 50mm f1.4 and focusing has never been a problem with either of out K10D cameras.

When you tried the zoom lenses at 50mm it only proved that the zoom lenses focused OK, which doesn't tell us anything about what the 50mm lens is doing.

Are you using auto or manual focus in your testing?
Have you tried both methods?
If you test using both AF and MF, do you get the same result?
Does the lens in question focus to infinity correctly?

As far as I know (and I'm willing to be corrected) the available adjustment affects AF accuracy only. MF should be good every time because you set the focus point yourself, verify it in the viewfinder, and take the shot.

There would be no point making the adjustment for just one lens on a K10D because it'll affect all lenses.

The K20D can hold settings for 20 lenses and having that capability built in demonstrates that it is a recognised problem.

Try http://focustestchart.com/focus21.pdf or http://regex.info/blog/photo-tech/focus-chart/ or http://pentaxdslrs.com/newchart.pdf

It's interesting that it's only become an issue relatively recently. How come we never noticed this with our film cameras?

I wonder if it's something to do with the more critical depth of focus issues with the smaller APS-C format. The smaller the format the less error in the positioning of the sensor/film is permissible.

This is where the 110 cartridge fell down, because film plane position was very sritical and the 110 cartridges were not accurate enough and had no pressure plate.

Depth of Focus relates to the amount of error possible in the focusing of the image on the film/sensor and is quite different to depth of field, which is what we normally discuss.

Ok now we're talking

- I will try to focus to infinity - I have never noticed issues, but I will check tomorrow morning.

- I have not tried MF - mainly because my eyesight is not that good and I wouldn't rely on it for fine adjustment - but what I have done is focus one body with the normal viewfinder, and it seemed in perfect focus (checking multiple times before shooting) and the other body with the magnifying eyepiece I got recently - and this also seemed to be in perfect focus.

I will try both methods again tomorrow -

I appreciate the fact that focus adjustment only fixes AF - but, is it possible as it seems, that the lens is focused correctly in MF and still shows front focus issues? would this be an issue of the focussing screen, and once this flips to capture the image the distance between sensor and lens is indeed not correct?

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.

thanks

Anything is possible with complicated mechanical systems Nathan, but I can't think of a reason why only one lens would be affected. It's also possible that something within the lens is moving.

This may sound daft, but can you hear/feel anything move if you shake the lens (gently of course)?