[Christine Tham]

at 50mm F2.8 , distance to image 50 cm, the DOF is 1.02 cm, the near limit is 49.5 cm and the far limit is 50.5 cm......... that's a equal amount of DOF in-front and behind the subject......


if however the subject is 1000 cm away...the dof will extend further to the rear of the subject than the front...in this case ...DOF is 474 cm, near limit is 816 cm, far limit is 1291 cm........so that's 184 cm in front of the subject and 291 cm behind the subject .


so if shooting focus charts at very close distances you should be aiming for equal DOF, in front and behind the subject.......as the 1/3-2/3 rule is only at much greater distances from the focal plane

Thanks for the useful info.

I believe nearly all my lens come out with 1/3-2/3 focus when I used the Spyder Lenscal, and I have been trying to adjust them to 50-50 focus.

Guess I was an idiot! Anyway, have reset AF fine adjustment to factory defaults.

[Tommot1965]

Thanks for the useful info.

I believe nearly all my lens come out with 1/3-2/3 focus when I used the Spyder Lenscal, and I have been trying to adjust them to 50-50 focus.

Guess I was an idiot! Anyway, have reset AF fine adjustment to factory defaults.

No, you are not an idiot, and if you are focusing at very close distances to the spdyer Lenscal...then you should see 50/50 dof either side of the focal point...

[Christine Tham]

No, you are not an idiot, and if you are focusing at very close distances to the spdyer Lenscal...then you should see 50/50 dof either side of the focal point...

Thanks - no I wasn't on very close distances - probably 2-3m depending on lens

I had to go closer for the wide angles, which were the ones closer to 50-50, exactly as you predicted.

So basically the factory adjustment is fine.

[jolepp]

I think the AF fine adjustment is worth doing for best results. The way I have been going about it has been using center point AF and comparing shots at different settings for best absolute focus in a flat, contrasty area. E.g. comparing +5, 0 and -5, 0 first and then taking it from there. Of course, if it turns out it that the best results are obtained at the setting zero then that is the setting to use . I suppose it is a good idea to test at a "short" and "medium" distance at least: if it turns out that getting good focus with one precludes it with the other then service/return/exchange is called for.

While it is easy enough to understand that the image and AF sensors might have a bit of misaligment amongst themselves and this requires compensation, the idea that the best setting can vary among lenses with the same body is something for which I have not seen a detailed, convincing explanation so far, yet this is apparently the case, otherwise there would not be a point of having per-lens setting.

[Mike.P®]

My Sigma 70-200mm f2.8 and 100-300mm f4 seem to have the same lens ID which is a bit of a pain. The 70-200mm needs +4 on the K-5 but the 100-300mm is just about spot on (doing my lenses right now).

[Christine Tham]

Okay, now that I have better idea of what I am doing, I have completely redone the AF fine adjustment for my lenses.

Most of my lenses require none or very small adjustments (typically 0, +1, +2)

The lens requiring the most adjustment was the DA 21mm Ltd - which required a +6.

I discovered using the Spyder Lenscal that the camera does need to be quite close - enough for the focus area to fill up at least a third of the viewing frame, otherwise there is a chance for the camera not to focus accurately on the target. So focusing 10m away on a wideangle is just not doable for me.

I have not adjusted the Sigma at all, but fortunately the factory setting is close enough for it not to require adjustment.

[jolepp]

From what I have read about it here that sort of values should be typical and no cause of concern: if all lenses end up close to the extreme adjustment in one direction (and/or some would require even more) it might be good to have the body calibrated for a better AF sensor - image sensor alignment. If a single ends up much different from the others having it adjusted would make more sense. Assuming that those smaller (+0-2) adjustments are mostly because of slight inter-sensor misalignment and that +6 is mostly because of the properties of the lens it would seem that there is no need to have anything physically adjusted: there is a +4 click margin for another body to be somewhat more out of the perfect alignment and even for the Sigma it seems as if it might require a bit less than +6 with a perfectly aligned body. Of course it could be that yours in fact is that and most of your lenses just happen to be needing that 0-2 for other reasons, the body being a bit off would seem like the more likely explanation, I suppose the adjustment is there to cover for precisely this kind of thing, though; the inter-sensor alignment tolerance probably cannot be much better without driving up the manufacturing cost inordinately.

[dadipentak]

Thanks - I think I might reset my AF adjustment back to factory. To paraphrase the manual, don't adjust unless you know what you are doing. And it appears I don't.

I know I don't and have taken that 'don't mess with it' message to heart.

[8540tomg]

Hi all,

New K5 owner with a lot of manual focus glass. Does the fine focus adjustment work with older K and M series glass?

Just thought I'd ask before frustrating myself.

Tom

[jolepp]

The 'Apply all' adjustment - well - applies to them all as far as focus confirmation and CIF go.

[jatrax]

I discovered using the Spyder Lenscal that the camera does need to be quite close

Spyder Lenscal manual recommends 5 to 10 times the focal length as the distance to use. So 50mm lens = 250mm - 500mm so yes quite close especially for wide angles.

[jatrax]

Does the fine focus adjustment work with older K and M series glass?

No, it does not. Fine adjustment as discussed in this thread is only for the Auto-focus mechanism. Manual focus lenses depend on the focusing screen being adjusted properly. There are shims available from Pentax to do this, but generally this is not something that needs done unless you are changing focusing screens. The process is entirely mechanical and involves removing the focusing screen and changing out the shims or spacers that determine the optical distance between the lens and the focusing screen.

Although fine focus adjustment would adjust the focus confirmation green hexagon. But I think the camera would treat all older manual lenses as a single lens since the lens sends no id to the camera. Not sure about modern manuals like the Samyang's.

[jolepp]

No, it does not. Fine adjustment as discussed in this thread is only for the Auto-focus mechanism. Manual focus lenses depend on the focusing screen being adjusted properly. ...

Indeed. The fine adjusment will only affect focus confirmation (and CIF).

[8540tomg]

Thanks guys,

That's what I thought. I'm not at all satisfied manually focusing with the K5. I find I can get in the ballpark but seldom seem to really nail focus with my longer (100 macro, 200mm, 300mm, 400mm) lenses.

I guess it's time to get a KatzEye screen for the K5 then. It worked beautifully with the K 10. I didn't need any shims with that one.

Hope I'm as lucky with the K5.

Tom G

[dadipentak]

The fine adjusment will only affect focus confirmation (and CIF).

That might make it worth doing but if it can't distinguish between lenses it's no use.