[Evolution]

Hello all. First time post here. I started out shooting Canon, and eventually my dad (faithful to Minolta) convinced me to jump... but I'm not thrilled with the A100 and the Sony outlook, so I've decided to try out some Pentax gear.

Today I received a k10D from Amazon and an smcp-fa 50 f/1.4 from B&H. I'm dismayed to see the combo consistently front-focusing by a good 1/2 inch wide open. Is the problem more likely in the lens or body? The 50 is the only lens I have right now, and I'm worried even the kit lens which is on the way won't be too helpful in determining the culprit given DOF with the f/3.5 aperture. I'm just wondering whether I should exchange the body with Amazon, the lens with B&H, or send the combo into Pentax... though I honestly don't feel like waiting a few weeks to find out what's wrong. I've read a lot of posts about FF problems with the k10d, so I'm thinking that's the most likely source of trouble. Any suggestions?

Thank you in advance. From reading, everyone here seems to be quite nice and helpful.

[skydragoness]

I'm curious to know myself how many people are having this front-focusing issue and if it is the type of lens or the body itself doing it.

[slip]

Hello all. First time post here. I started out shooting Canon, and eventually my dad (faithful to Minolta) convinced me to jump... but I'm not thrilled with the A100 and the Sony outlook, so I've decided to try out some Pentax gear.

Today I received a k10D from Amazon and an smcp-fa 50 f/1.4 from B&H. I'm dismayed to see the combo consistently front-focusing by a good 1/2 inch wide open. Is the problem more likely in the lens or body? The 50 is the only lens I have right now, and I'm worried even the kit lens which is on the way won't be too helpful in determining the culprit given DOF with the f/3.5 aperture. I'm just wondering whether I should exchange the body with Amazon, the lens with B&H, or send the combo into Pentax... though I honestly don't feel like waiting a few weeks to find out what's wrong. I've read a lot of posts about FF problems with the k10d, so I'm thinking that's the most likely source of trouble. Any suggestions?

Thank you in advance. From reading, everyone here seems to be quite nice and helpful.

I would try this...
If you have a local place that sells any pentax DSLR's, the take the camera to that shop and ask if you can try out a different lens. bring a memory card, do some testing, then check it out at home. if the lens produces the same results, then it is more then likely the body. If the lens you tried out has no front focus, then take back the lens. either way you will find out.

hope this helps

randy

[joele]

I haven't noticed an FF or BF with my FA50/1.4, will try tonight though...

[Evolution]

I would try this...
If you have a local place that sells any pentax DSLR's, the take the camera to that shop and ask if you can try out a different lens. bring a memory card, do some testing, then check it out at home. if the lens produces the same results, then it is more then likely the body. If the lens you tried out has no front focus, then take back the lens. either way you will find out.

hope this helps

randy

thanks slipchuck. that's not a bad idea. my local independent camera store doesn't carry pentax, but the ritz around here is one of the largest in florida. i guess it's worth a shot to see if they have a fast prime i can try out. i'll give it a shot. I'm inclined to think it's the body, only because i've read so many reports of FF with new k10Ds and because the 50/1.4 is so standard by now one would hope the manufacturing process is fairly consistent.

[dleung]

I briefly tested my 50/1.4 but didn't see noticable ff, but I get it consistantly with my Sigma 30/1.4 and didn't with my DS. Seeing all these ff problems with the 50/1.4 I'll retest it again to be sure.

[Ivan Glisin]

How did you test? If you used that popular testing chart by Tim Jackson (with mm scale on both sides)? Beware that AF sensor is MUCH bigger than that little red dot indicating correct focus and with only a slight AF sensor/focusing screen misalignment, or camera tilt ant it may catch top/bottom lines and text falsely indicating front or back focus, while in fact just properly averaging center line and top or bottom line.

Try this instead: use tripod or fast shutter speed, M mode (fixed Av/Tv), manual WB, and point at a flat surface with some texture (simply write thick black X on a sheet of paper and tape it to the wall) and take one AF then one MF shot. For each shot start focusing from minimal distance for given lens so you will provide a fresh start for both camera AF system and your eye. Repeat procedure several times, say 3 times. Examine the result. If sequence looks like blurred, sharp, blurred, sharp, blurred, sharp then you have some sort of AF problem. If the whole sequence turns out sharp or if it is hard to tell the difference between AF and MF frames then you are fine. (You may try this at different distances, but 1-2m / 3-7ft should work OK.)

[Ivan Glisin]

More details to be aware of:

1) AF system requires an area to work well. That is, focusing on a single dot or a line may not be sufficient for AF system to properly measure contrast. Make sure your pattern fills inner frame indicating location of 9 AF points regardless of the lens used.

2) AF system requires fair amount of light to work. In low light AF may be inaccurate or completely fail to lock on subject.

3) Fast lenses have very limited depth of field, especially visible at short distances. Mechanical error of 1mm in moving focusing ring of your FA50/1.4 for a very close subject (less than 1m) may produce visible softening at f/1.4. But for short distances and/or large apertures I recommend using MF anyway: since DOF is so shallow it is unlikely AF system will select the point you want to be in focus.

4) Perhaps something Pentax should improve in AF system: initial focus lock may be inaccurate with some lenses. With my FA35/2.0 lens sometimes snaps quickly into a position (AF locked) but I can clearly see in the viewfinder that image is not sharp. Very light camera movement to provide different pattern for AF sensor followed by half depressed shutter release activates AF system and refines focus. Why is that sometimes necessary I don't know, and it may be that thing people are complaining about when comparing Canon and Nikon AF to Pentax AF.

[trog100]

i think its the body.. made worse by fast glass.. just my experience with the 100d.. by son acquired a new f2.8 28 to 70 zoom lens.. he popped it on my 100d to make some compare shots with a my F2.8 50mm prime.. it compared well..

he popped it on his own 100d and it just would not focus properly at all wide open..

now these were sigma lenes.. cr-p sigma lens would be the normal pentax thought.. i doubt it thow..

trog

[mcm]

My data point:

Used this chart: Nikon D70 Focus Chart

K10D with 16-45mm @ 45mm, F4.0, 0.5m from subject, center AF:

[RiceHigh]

It's mostly something wrong with your K10D body, which has some kind of mis-alignment error between the AF system and the focal plane (CCD plane), or simply an AF system which is designed and built not accurately enough, for a 10MP DSLR.

For more read on focusing errors and the implications, see:-

RiceHigh's Pentax Blog: How AF Errors Can Decrease *Effective* Resolution?

BTW, there is a secret port underneath the bottom cover of Pentax DSLRs, after connecting which Pentax factory calibration software can be loaded. The amount of FF and BF can be dialed in.

Of course, this is to be done with other calibration tools in a "lab", you may ask Pentax to resolve the problem you face and give them a trial.

I think no body here can actually help you except Pentax in the end. Nonetheless, it will always be good to gather more information.

[jnorth]

I wonder why Pentax has not come out with a statement or directions on what to do about front focussing? It seems to be such a serious problem that seems to have inflicted many of their DSLR's yet I have not seen anything from them. Or have I missed it? Does anybody know why Pentax have not made any sort of official statement about this, or where to find it if they have?

[joele]

I tested my FA35/2 and FA50/1.4 as the test a few posts back and they are fine.

Don't read too much into this...

If you have consistant back or front focus the camera can be easily adjusted and just take it to your Pentax service center and they can calibrate it for you...

[RiceHigh]

If you have consistant back or front focus the camera can be easily adjusted and just take it to your Pentax service center and they can calibrate it for you...

I'm afraid that the case is not as simple as what Joele believes..

My experience with my original *ist DS is that Pentax have not much to do with AF errors and any misalignment in the AF system, in mechanical terms, within the DSLR body.

My DS could not focus to infinity for quite some primes of mine and what they could do is to adjust the amount of Front Focusing or Back Focusing by software, as I mentioned in my last reply.

As told by my local Pentax service engineers, the focal plane position by no means can be adjusted *mechanically*.

My DS was finally sent back to Pentax Japan, as recommended by those engineers, i.e., the principal, they opted to adjust the angle of the mirrors for the AF system so as to compensate for the mechanical errors! But then the whole AF module was shifted out of the marked positions in the finder then! (although the BF/FF problem was minimized, putting aside the accuracy of the AF system of the DS is not that good by itself..)

For more details about how Pentax failed to repair my *ist DS which has an AF system alignment problem at infinity and how Pentax Japan finally messed up my *ist DS (including a small piece of finder optics found broken inside the finder), you can read this:-

A Letter to the CEO of Pentax Corporation

Good luck anyway to any Pentax DSLR user who faces similar problem and I hope that Pentax can actually help them to resolve the problem sucessfully in the end!

[Evolution]

Since my original post I've received a K10D replacement body from Amazon, along with a Sigma 30/1.4, Sigma 70-300 APO DG Macro, and Pentax 18-55. The three newer lenses all focus spot on at their most narrow settings on oth bodies. The 50/1.4 however front-focuses on both bodies by the same margin. I'm hoping it's strictly a lens problem and not a problem with the body-lens combination. I will try to get a replacement from B&H and see what happens.