'Best' AF Pentax DSLR?

Hi all,

I've recently been using a M43 system with a very nice Panasonic/Leica 100-400 lens, all very convenient but the digital viewfinder and the slow speed of the lens are a bit frustrating. Getting fast lenses on M43 is ruinously expensive.

I'm therefore looking picking up the Pentax gear again. Aside from size relative to M43, perhaps my only bugbear with my Pentax gear was the slow and inconsistent AF and issues getting consistent sharp focus - I could go out for a day and all of the images would have back focus or just general sharpness issues, which might not be as notable on other days but no amount of focus adjust in the camera body would seem to permanently sort. M43 just doesn't suffer this, despite only having contrast AF.

Accepting that some of this is undoubtedly user error, I'd still appreciate any thoughts on which body people have found have had the best AF performance - particularly continuous - and which has the most rock-solid, guaranteed lock-on in single AF.

For info, I've got a K3 and there is a K30 body I can retrieve once lockdown is over. My set of lenses include a sigma 70-200 f/2.8 and a Sigma APO 300mm f/4 which are the ones I use most frequently. Both are screw-drive AF. Interested to hear if KP, K3II, K70 etc are seen to offer any advances over the K3, or whether old lenses are prone to this sort of issue - recall a few sigma lenses had backfocus issues but think the affected lenses were different models.

All advice gratefully received.

I use K1 and paired with a modern D-FA lens is a very fast accurate autofocus. It is also fast and accurate with 20 year old screwdrive lens. Just needs to be calibrated properly.

Suggest you wait for the new aps-c model to be released, expected this year, but you should expect to get the latest lenses to get the best performance both optically and for AF speed.

First off I would say I have always had problems with Sigma lenses and autofocus. You can fine tune them to your hearts content but they always seem very inconsistant when it comes to critical focus. WIth Pentax lenses there seems no such problems, I rarely have to fine tune mine and they are spot on, I ended up swapping out my Sigma lenses for Pentax because of this. (12-24mm for 15-30mm, 24-70mm HSM for 24-70mm WR, 70-200mm OS for 70-200mm WR, 50-500mm for 150-450mm) but then you are talking serious money.

Secondly, I have the K-1 and compared to other makes I have used (7D/D500) the autofocus speed is useable for most things but it's certainly not mind blowing and I personally think that is down to the size and spread of the focus points more than the AF system now. The centre point covers far too much space so on small birds and such like it is forever hunting to lock on.

Last but not least, AF-C tracking is basically pants, I'm going to get blasted for saying this here but it's rubbish, always has been with Pentax (had the K-5, K-5IIs, K-3, K-3II, KP) and is the reason I use other makes for fast moving small objects. The new crop body may well do something about both the focus point spread and the AF-C tracking and (as they are saying on the other forum) become a D500 beater but as far as I am concerned we don't have the lenses to take advantage of it.

So I would say if you want a good solid performer that excels at 75% of what people do with a camera then Pentax is a great choice but if you are in the other 25% then look elsewhere.

Interesting about Sigma lenses. I have two (both bought at someone's recommendation) and I've never been happy with either. The best "standard" range AF lens I've had was the original kit lens for my K10D.

I rarely photograph things that move quickly so I'm never sure whether it is me or the kit, but trying to photograph quickly moving chickens has been trying...

Cheers to all for comments

Mike, you're not alone, I've never found the tracking/continuous AF to work to any degree of sophistication on any Pentax body or with any lens. The tracking on my M43 is notably improved, although I do note the the GH5 and the 100-400 are a lot more recent than my K3 and sigma glass - my good quality telephoto lenses are all quite dated.

I'll keep an eye out for a decent pentax telephoto, I've used sigma mostly as the bang for buck is very good but I'm increasingly frustrated by the inconsistency you note, so if Penatx lenses offer an improvement I may give it a try.

On a final note, Is it me or do DSLRs need a lot more attention paid to the AF compared to film? I really can't recall having these issues with my old MZ-3, although I didn't shoot much moving wildlife just due to the cost of the film!

I vaguely recall that way back Sigma would reverse engineer lens mounts to remove/minimise licensing fees, and this would sometimes cause weird issues with lenses that seemed alright on one body not behaving quite as expected on others. This goes back to mid 2000s so no idea if it's the case now, and the K-mount series isn't as proprietary as others, but a few older lenses might suffer a bit from this - my experience of sigma is that good lenses are really very impressive, but poor lenses can be notably poor.

I'lk eep an eye on the new body, if it does have improved AF then this might be a good upgrade. The lenses will take a while and quite a bit of cash to change, so if AF upgrades require both body and lens refresh then I'll perhaps have to wait!

I've rarely had AF issues with Sigma lenses as they usually "lock on" pretty quickly - then again, the comment about Sigma's "reverse engineering" approach is probably correct from what I have read.

IMHO, the biggest "issue" with Pentax DSLR AF is the consistent-across-the-range lack of "enough" AF focus points "across the frame" and the h/w "processing power" and good algorithms to control that "power".

What size did you regularly print when using film ? With large MP sensors now we are able to examine the capture in much higher detail than was usually the case with film.

My comments above on the accuracy and speed of Af on the K1 was related to AF-S and generally static subjects. For sports/wildlife it is fair to say Pentax has been lacking when tracking a subject. The newer lenses are better....my DFA 70-200 tracks much better than the older DA* 60-250 for example. I would keep an eye on the latest model however, Pentax must be well aware it is one area they get criticised for and I would expect the K- "new" to address the issue.

My sister-in-law Diane wouldn't class herself as a skilled photographer, although she's much better than she thinks she is. She showed me a whole mass of birds in flight she shot last month using the K-3 and eith a Tamron 70-300mm or the Pentax 150-450mm and she nailed the focus is virtually every one. It was impressive.

As for Pentax AF, I haven't found any slowness or problems since the K-5. The camera will also pick up fine fronds of grasses and birds amongst branches much more reliably than most cameras I use.

When I first got the K1 I was blown away by the sharpness of the Sigma 150-450, much better than I had found on the K50. As for tracking, not something I use much but I recall Cameraville did a comparison between the K1 and a Nikon mirrorless with much faster FPS. His experience was that the Nikon wasn’t able to refocus fast enough to keep up with the frame rate, on top of which he found it harder to keep the bird centre of the viewfinder; conclusion was that the K1 had fewer shots but more of them were useable.

I have been using the 77mm Limited a lot recently with moveable spot focus for portraits and many of the results have been superb; I suspect the rejects are down to the user but when I get it right it performs brilliantly. The same cannot be said of the 100mm macro which hunts a lot so is better in manual. All this tells me is that some screw drive lenses perform better than others but the best are up there with the latest electronic focus lenses.

I have a Pentax 150 - 450 for sale on the PF forum if anyone is interested

https://www.pentaxuser.com/forum/topic/fs---lens-cleanse----pentax-150---450---p...

Running through the four Pentax DSLRs I had ending with the K3 I found there were improvements but only gradual each time. When you switch to any Nikon of the last 5 years it is a different world when it comes to locking on and tracking moving objects or complex backgrounds. I haven't found any problems with my SIgma 150-600mm 'C' lens on my Nikon but of course I can't get that for my K3 anyway.

I don't think this is news to any Pentax owner. Pentax AF has been lacking for moving subjects for a number of years.

I do little tracking so it bothers me not. For my photography Pentax is very quick and accurate.

Until the new K3 III is released you are free to continue to speculate of course.

Why are you bothering to post on here ? Your Nikon does AF for your kind of photography better than Pentax. It does not for mine. So what have we achieved...stalemate ?

This isn't exactly about tracking but I'd welcome other peoples' wisdom. I got fed up with all those AF points long ago because if you focused on something you could guarantee the damn machine would pick the "correct" point by itself and ruin the shot. Consequently, I only use the center point for AF. Am I doing something wrong somewhere? I simply have no idea why they cram more and more AF points into every new camera because (to me) they are absolutely useless. I look forward to being set right.