[Stavri]

The term is seldom used on this site, but "focus breathing" usually is described as a change in relative FOV as the lens focuses down from infinity. The term is a bit of a misnomer and is a property of many internal focus zoom lenses. For example, my Sigma 17-70 FOV at 70mm and 2 meters is about the same as a 50mm lens at the same distance.

Focus Breathing (Focal length variation with focus distance)- Bob Atkins Photography

What you are describing is called "focus shift". It is caused by residual spherical aberration and occurs when the lens stops down at exposure time. Usually, the shift is relatively small (a few millimeters +/- at plane of focus at common shooting distances) and is covered nicely by increased DOF. Where it becomes a problem is when doing macro work.


Steve

Focus shift is what I meant, thank you...

[ychousa]

BTW, maybe a bit off topic, but I got a $30 M 50mm f1.7 off eBay delivered today-oh my, this beast is stunning!! Just a quick sample pic (just autotone & resize only in PP) of my patio and I was just stunned! I'm so glad that I've switched to pentax system. Just need a little care for my K-3's autofocus, then there should be no complaint.

[Stavri]

BTW, maybe a bit off topic, but I got a $30 M 50mm f1.7 off eBay delivered today-oh my, this beast is stunning!! Just a quick sample pic (just autotone & resize only in PP) of my patio and I was just stunned! I'm so glad that I've switched to pentax system. Just need a little care for my K-3's autofocus, then there should be no complaint.

The M 50/f1.7 and the super-tak 50/f1.4 are THE lenses that non-pentax users immediately think off when asked about pentax legacy glass. They have been adopted by Canonites and others because of the excellent performance/price. The M 50/1.7 is one of the best performing normal prime lenses across all brands.

I know these are in demand at the moment, buti think a super-takumar 50/f1.4 should be in every pentaxians cupboard, You haven't earned your moniker till you do.

[tibbitts]

Does anyone have an experience like me? i'm kinda losing confidence in buying lenses.

Yes, and not just with Pentax lenses. I think there are several factors:

1. We have so many MP today that when you look at an image at 100%, you're demanding a lot more from the lenses than we did in the film era, or earlier digital eras. Since we can test much more thoroughly now than we could with film, at very low cost, we do;

2. With regard to 3rd parties, there's just less volume in Pentax (which is one reason so many third-party manufacturers have at least partly abandoned Pentax.) So some issues with AF and firmware etc. are just less likely to get worked out;

3. I'm guessing that Pentax (and maybe some other brands) manufacturing and QC haven't kept up with the increasingly complicated optical and mechanical complexity of newer lens designs.

Hopefully manufacturing quality and consistency will catch up with some of the engineering/design advances, and we'll have better quality, more consistent lenses soon.

[normhead]

I've never had a problem. 7 Pentax lenses. Had a sigma 70-300 once for a different mount - sucked so bad I didn't want it around to use even as a paper weight.

Sigma-70-300 Photos by Norm_Head | Photobucket









I guess everyone has their issues.

[Eagle94VT]

I have a couple other Sigma's for my Canon. The 70-300 was the only lens I ever returned. The pictures looked like they came from my purple Holga. But I still take that purple Holga along with me on many outtings! A Hollywood edition I found for sale for $10.
One fruity day by eagle94vt

[Stavri]

The main reason why 3rd party manufacturers do just a terrible job making lenses in the K-mount, is that all the lenses get made during the weekend, (TRUE STORY) During the weekdays they built Canon and Nikon lenses, then on the weekend when they are all burnt up, they make the Pentax ones. They don't want to built lenses on the weekend, they wanna go home. But they Can't.....and it's sad

This is why the QC is so bad....(your heard it here fist)

[normhead]

The main reason why 3rd party manufacturers do just a terrible job making lenses in the K-mount, is that all the lenses get made during the weekend, (TRUE STORY) During the weekdays they built Canon and Nikon lenses, then on the weekend when they are all burnt up, they make the Pentax ones. They don't want to built lenses on the weekend, they wanna go home. But they Can't.....and it's sad

This is why the QC is so bad....(your heard it here fist)

And here I though the Pentax lenses were all built Monday morning and Friday afternoon. The reality is so much worse than I thought. They are probably watching sports on their iPads while building the Pentax lenses. But,looking at the 10% return rate on the Tamron 70-200, there has to be a reason for that. Built on the weekends makes as much sense as anything.

[TedW]

Just a thought but are you sure you not applying each adjustment to all lens. That would be easy to do. When making focus adjustment you have to specify it to only apply to that specific lens otherwise it will apply the adjustment to every lens. Something seems odd here. I've bought several new and used lens and have not yet found a need to adjust ant of them.

[Stavri]

Just a thought but are you sure you not applying each adjustment to all lens. That would be easy to do. When making focus adjustment you have to specify it to only apply to that specific lens otherwise it will apply the adjustment to every lens. Something seems odd here. I've bought several new and used lens and have not yet found a need to adjust ant of them.

It could be that you're not looking hard enough or that you have indeed an excellent batch of lenses. Either way it's the personal satisfaction with your lenses performance that counts, not achieving the ultimate performance. Pixel peeping is no fun...

[normhead]

IN answer to your original question according to Lensrentals.com Pentax has the lowest frequency of repair rate in the industry.

That being said, I pick up my camera bag the other day, and my DA* 60-250 fell to the floor with a loud bump. It works fine but it had a slight bit of out of the ordinary resistance in one part of the zoom motion. Which has since disappeared. To use it now, you'd never know there was anything wrong with it. But it's a little bit noisier than tt was before. I could sell this to some unsuspecting soul and get a new one.... and it might be good for years to come, but, I plan to send it to have it checked out. It may be that right now my lens works fine, but because of a bit of barrels distortion, the WR seals aren't working. Any used piece of equipment you buy could have had a similar experience. It may even have been working when whoever sold it to you shipped it to you, and been damaged during shipping.

Personally, I simply don't buy used unless I get a fantastic price. It's simply not worth it.

[rawr]

Pentax usually rates quite highly for consumer satisfaction, including lenses:

Pentax DSLRs top global consumer satisfaction survey | Digital Camera World

Basing any findings on Pentax defect rates or AF largely on used lenses bought here or on eBay would be a mistake.

One also needs to be very rigorous in AF testing to get it right. What is your AF testing methodology? Poorly judged AF adjustments can make your AF worse.

Since the Canon T2i does not support AF micro-adjustment, maybe your good luck with lenses on Canon came from never being able to apply any micro-adjusts to them

[TaoMaas]

We have so many MP today that when you look at an image at 100%, you're demanding a lot more from the lenses than we did in the film era, or earlier digital eras.

I think that's a big factor. The other thing that comes into play is focus. I could be wrong, but I don't lay all the blame at the feet of the lens. I think cameras could be having a hard time locking on or may be choosing the wrong area...plus I think there's a high degree of operator error. I'm not saying that this is the problem in this case...but I'm just sayin'.

Edited to add: I've never had a Pentax lens where I thought there was something wrong with it. In almost every case, the fault was mine. However, I will say that I don't really buy many brand new Pentax lenses. So maybe I've been lucky and have only bought used lenses where someone already had all the bugs sorted out. However, I've bought lenses in a WIDE variety of places...and my experience has always been the same.

[tibbitts]

It could be that you're not looking hard enough or that you have indeed an excellent batch of lenses. Either way it's the personal satisfaction with your lenses performance that counts, not achieving the ultimate performance. Pixel peeping is no fun...

My guess is that a lot of users, even fairly serious enthusiasts, don't pixel peep in the extreme edges/corners, particularly with longer focal lengths, because they're more interested in subjects that are near the center. All of my lenses have had good center sharpness (obviously varying somewhat with the model of lens) given careful MF. Most have been ok about 2/3rd of the way to edge, but then mulitiple lenses have fallen down dramatically from there to one edge/corner or another. With zooms that often happens at only certain ranges of focal lengths or distances. So for someone who primarily makes certain types of portraits, animal photos, etc., what would be a huge problem to me might not be a problem at all to them. Similarly, PF from something like the Tamron 70-300 (which can be extreme under the right circumstances) that would be a huge problem for a bird enthusiast, tends to be less of a problem, at least percentage-wise, for me (although no PF at all would definitely be preferable.)

[stevebrot]

It could be that you're not looking hard enough or that you have indeed an excellent batch of lenses.

...or both!

If a person looks hard enough and has the tools to do so, faults (or at least the perception of fault) will always be found. The OP posted an inquiry several weeks ago regarding some of the focus issues mentioned in this thread. After reviewing the example photos there, it is my conclusion that expectations may be a little skewed in regards to objects at distance and that the attempts at fine adjustment may be misdirected, improperly done, and the cause of the problems noted in this thread.

https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/288693-m...-included.html


Steve