[DownhillGR]

Hello everybody this is my first post here, sadly with a problem...

I bought the pentax 35mm f2.4. At first i was impressed by how good it was. Especially at portraits and close range subjects. Then i noticed some softness when i was trying to focus on distant subjects. Most of the time they were out of focus. Then i tried to focus to infinity but i found out that this was not possible. Raising aperture at f4 somewhat remedys the problem but doesn't eliminate it. I thougth to fiddle with the K-x debug menu but instead i decided to test it against a tamron 18-250 at 35mm and f4. Bottomline, the tamron always outperformed the pentax lens when it came to far away subjects. Not to mention that the Tamron lens focuses to infinity easily.

now the question is, is that possible? Does such a defect exists (near focus is sharp but at longer distances is very soft) or this is normal behaviour for this kind of lens? I'm asking because right now i have two choices.

First is to return the lens to the shop and accept a replacement or pay the extra money and buy the tamron 17-50.

[Adam]

Does it work fine when focusing manually? If so, the lens is probably exhibiting back-focus. Since you have a K-x (which doesn't make lens adjustments easy), I would go ahead and get the lens replaced.

These articles might help:
Fixing Front and Back Focus - Introduction - PentaxForums.com
DA* 16-50mm vs. Sigma and Tamron 17-50mm F2.8 Comparison - Introduction - PentaxForums.com

[DownhillGR]

i tried manual focus but it doesn't get any better. What puzzles me though is that at close distance (portraits) even at f2,4 the lens focuses fast and accuretly

[Deiberson]

I would think that shooting to infinity at f/2.4 or f/4 and expecting sharp images corner to corner would be impossible on any lens. I wouldn't try it without stopping down to f/16-22 then focusing 1/3 into the frame.

[Marc Sabatella]

When you say you cannot focus to infinity, I suspect you are making the mistake of simply turning the focus ring all the way until it stops and assuming that will be infinity focus. It isn't, usually - that's normally a bit *past* infinity. Otherwise, I'd say, post some sample shots including 100% crops of the focus area, comparing the DA35 to the Tamron or some other lens. I'm guessing it will turn out to be a simple matter of the camera not having focused quite where you expected - not "back focus" or "front focus", but just the simple fact of life that the focus point cannot be placed *precisely* (focus "points" are actually broad rectangles).

[DownhillGR]

considering the fact that this lens has no distance scale i couldn't set hyperfocal distance, but i've tried manual focusing till i could get an acceptable pic (even then tamron seemed sharper), but no matter how i tried, i couldn't get acceptable focus with autofocus. Tamron hunts a bit but gets the job done. I'll post some pics. even though it's not a scientific approach it will show the problem. I'll even post some pics that show strange behaviour (clearer focus on the right part of the pic while the left part seems soft even though i had center fovus point). I'll post as soon as i get home in the evening

[DownhillGR]

looking around about my problem i bumped on this site

PENTAX - smc PENTAX DA 35mm F2.4 AL

Look at the picture of Zakynthos wreck. (the cliff and the sea)

this picture to me looks very soft, as if it's misfocused! If this is a common issue about this lens still needs to be clarified...

anyway i'll post my images from budapest in the evening...

[Marc Sabatella]

There's no way you can tell anything from an image taken by someone else and posted resized down to web resolution. You have no idea where the photgrapher chose to focus and what he choose to put outside the focus zone, nor do you know anything about the conditions under which the photo was taken, nor do you have another o hoto of the same scene taken with the same exposure settings at the same time under the same conditions to compare it to. Looks to me like used a form of hyperfocal focusing - focusing simewhere in the middle ground in order to get as much of the picture as he could "mostly" in focus. On any case, there is absolutely no possible way you'd ever be able to see the differences between two lenses at that size - you'd need to examine very closely at 100% to see any difference.

[DownhillGR]

i agree with you on that it just seemed very similar to the results i was getting

http://www.flickr.com/photos/75762547@N03/

I've uploaded some of the files on flickr (i haven't used it before. I uploaded in full resolution but i don't know if you can download the full file. As mark pointed out in previous post compression makes some details less obvious). So if somebody has the patience to take a look please share your opinion. Thanks.

01. Pentax Back Focus 01 - focus was on the man but the pic is sharp behind him



02. Pentax Backfocus 02 - Focus was on red window, pic is sharp behind it



03. Pentax f2.4 on buildings - Focus is on buildings which are very blurry. doesn't show well in the compressed image. tell me a way to upload the original.




04. Pentax Strange Behaviour - Focus was on buildings behind which are sharp enough but the strange thing is that the tree branches on the right are Sharp while the yellow leafs are blurry. Doesn't show very well in this compressed image. In full size image it's very pronounced. (please tell me a way to upload full sized image)




05. Pentax strange behaviour - Buildings are sharp but this time the focus was on lamp pole, yellow leafs are sharper than right branches.



06. Iceskate- focusing in front otherwise skaters look blurry like in next photo



07. Strange behaviour again - Right part sharper than left part. Skaters blurry



08. 01. Pentax autofocus. Best i could get but focused on girls



09. 01. Otherwise best i could get is this




10. 01. pentax f8 manual focus. Actually very nice...




11. Pentax 10000000th attempt. worse results than tamron



12. Tamron first attempt. Acceptable focus.



13. Tamron monument - Photo of the monument taken with tamron at f4 - sharp no need for second focus attempt



14. Pentax monument - Blurry. not accurate focus


I haven't used flickr before so i don't know if you can download the full sized image. Actually i think that compression doesn't show the problem in some of the pics while it exaggerates it on some others. if anybody is intrested please pm me to mail the original images.

[krgroothuis]

I recently bought a DA 35 mm 2.4 also.

I am not impressed of the lens quality of the sample that I have now.

Where did you buy your DA 35 2.4 ?

I bought it "new" in an auction on Amazon.uk in dec. 2011.

May be you bought from the same batch and are they sold cheap because of known failures.

[Docrwm]

I recently bought a DA 35 mm 2.4 also.

I am not impressed of the lens quality of the sample that I have now.

Where did you buy your DA 35 2.4 ?

I bought it "new" in an auction on Amazon.uk in dec. 2011.

May be you bought from the same batch and are they sold cheap because of known failures.

There aren't any "known failures" of the 35/2.4. Are their bad copies, of course. Is it likely that several people have gotten a bad copy - yes again. But, so far nothing to indicate anything specific other than unhappiness with infinity focus by a couple folks. Mine works fine at long distances.

[DownhillGR]

i also bought new, stocked item, from a respectable seller in UK Through Ebay. I contacted him and he told me to send the lens back. I'm trying to figure out if i'm going to ask for a replacement, or go for the tamron 17-50 (which is also a risk, knowing all the back/front focus issues). It's true though that when i searched for 35 f2.4 i didn't find significant reports about "bad copies".

But what actually puzzles me is that at close range this lens is superb! Focuses fast and sharp! Also i've noticed that even though i set it at f2.4 when i try to focus on different subjects that are not far apart, the camera won't refocus. I'm starting to think that there might be somekind of incompatibility between k-x and 35 f2.4?

i'll post some pics showing tamron and 35 f2,4 behaviour

[DownhillGR]

http://www.flickr.com/photos/75762547@N03/sets/72157629149629077

01-04 are 35mm samples - read the captions

a-c are tamron - read the captions.

the 35mm seems reluctant to refocus whenever needed.

[Marc Sabatella]

Nothing I saw in any of the images I looked at seemed at all surprising to me. Most of them just happened to have focused somewhere slightly other than you intended. That's not a lens flaw or a camera flaw; it's a fact of life that cameras can't read minds. You can specify the approximate area you want the camera to focus using the selectable focus regions, but it focuses anywhere it wants within that region. And the region is much larger than the tiny red square in the viewfinder.

So what you called backfocus is really just a difference of opinion. Basically, you just have to learn to be more careful about where you focus when shooting large aperture lenses. Unless you can show me a single pair of images that shows even the most in focus region on the DA35 is not as sharp as on the Tamron, but again, nothing I saw showed anything of the sort. Just cases where you didn't focus as accurately as you could have. Not a problem with the lens.

[DownhillGR]

marc i don't quite understand what you are saying. those where a few representative shots of about 1200 shots taken at a trip. i use the tamron which by the way is a much inferior lens, for more than 3 years and now i have to start to learn to be more carefull? any crossreference to tamron was at the same aperture (f4) not at f2.4. all night shots are out of focus. most of any shot taken of a distanstant subject is soft. i never said that tamron is a better lens. i just find my copy of 35mm unable to focus.