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09-15-2018, 04:07 AM   #1
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Focus Issues with TAMRON 28-75 2.8 AF on K-1ii

Bought a new TAMRON 28-75 mini telephoto as a complimentary lens to my 28-105mm Pentax kit lens for my K-1ii. I have noticed focusing issues where the AF acknowledges clear focus, yes in Lightroom editing the raw files are blurred and off focus. When I shift to manual, it is less noticeable but the photos are not as crisp as I believe they should be.

Is my K-1ii out of alignment? it has only 800 clicks on it. Has any one else had this issue?

09-15-2018, 04:29 AM   #2
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It's quite likely that you simply need to carry out AF fine adjustment for the lens. Most older-model Tamron lenses that I've used required some in-body adjustment, and in fact one of them - a 70-200 f/2.8 - was so far out that I returned it. I haven't noticed that issue with the newer models, but the Tamron 28-75 f/2.8 (at least, the Pentax compatible version) is an older design.
09-15-2018, 04:33 AM   #3
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QuoteOriginally posted by BigMackCam Quote
It's quite likely that you simply need to carry out AF fine adjustment for the lens. Most older-model Tamron lenses that I've used required some in-body adjustment, and in fact one of them - a 70-200 f/2.8 - was so far out that I returned it. I haven't noticed that issue with the newer models, but the Tamron 28-75 f/2.8 (at least, the Pentax compatible version) is an older design.
Thank you for the feedback....I'll give it a try. The TAMRON was highly recommended so I was a bit disappointed in the images. I'll come back and advise as I have not seen this focus shift in any of the new FA Pentax lenses I have
09-15-2018, 04:44 AM   #4
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QuoteOriginally posted by Merv-O Quote
Thank you for the feedback....I'll give it a try. The TAMRON was highly recommended so I was a bit disappointed in the images. I'll come back and advise as I have not seen this focus shift in any of the new FA Pentax lenses I have
Yes, Pentax lenses tend to be quite well adjusted straight from the factory. Older Tamrons seem to have been less stringently adjusted and tested at the time of manufacture, so there's a bit of luck involved. My own 28-75 f/2.8 for K-mount needed adjustment by the service centre, but since then it only requires -4 AF fine adjustment on both my K-3 and K-3II bodies, which is fine. I now get sharp images at all focal lengths with that setting.

It's a great lens once you get it adjusted properly. Actually, it's my all-round favourite lens for K-mount - at least on APS-C bodies. I'm sure it's good on full-frame too...

09-15-2018, 07:41 AM   #5
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Did you focus in Live View mode? I'm asking because similar lens,Tamron 70-200 2.8 in many cases does not focus in LV at all. There is confirmation from AF, but the focus is, well, 'somewhere' - this how my 70-200 behaves, but I use it only with OVF, so it's not a problem. There were several threads on this in the forum, and I wonder if users of 28-75 experience similar problems.
09-15-2018, 09:05 AM - 1 Like   #6
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I have a copy of this, and it's a nice lens that can produce sharp images, so I'd pursue the fine adjustment as described. If it doesn't sharpen up with adjustment, definitely return it for another copy. It should perform well. It's nice enough that even though I have the D FA 24-70, I have kept it to have a lighter alternative for walking around with my K-1.
09-15-2018, 09:22 AM   #7
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QuoteOriginally posted by clickclick Quote
I have a copy of this, and it's a nice lens that can produce sharp images, so I'd pursue the fine adjustment as described. If it doesn't sharpen up with adjustment, definitely return it for another copy. It should perform well. It's nice enough that even though I have the D FA 24-70, I have kept it to have a lighter alternative for walking around with my K-1.
I'm probably going to buy the Lensalign tool from Adorama and check all my lenses. The fact that there is a front and back focus alignment tool for the K-1/ii is great for aftermarket Lenses. Ironically, I don't see any focus blur on the 28-105mm 3.5 Pentax kit lens. Those images are clear. I also recently bought an IRIX 15mm Firefly that produced some questionable focus issues--even at infinity!! I have attached two sample photos to show this anomaly

Attached Images
View Picture EXIF
PENTAX K-1 Mark II  Photo 
View Picture EXIF
PENTAX K-1 Mark II  Photo 
09-15-2018, 09:24 AM   #8
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That looks more like blur due to slow shutter speed (1.3s for the first shot, 0.8s for the second)...
09-15-2018, 09:33 AM   #9
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QuoteOriginally posted by BigMackCam Quote
That looks more like blur due to slow shutter speed (1.3s for the first shot, 0.8s for the second)...
Got it...I didn't have a tripod with me as I was on the roof following a function I was taking pics at. The view and the sky was so interesting that I took the shots. I still think the lend is off though.
09-15-2018, 09:39 AM - 1 Like   #10
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QuoteOriginally posted by Merv-O Quote
Got it...I didn't have a tripod with me as I was on the roof following a function I was taking pics at. The view and the sky was so interesting that I took the shots. I still think the lend is off though.
One thing to bear in mind with the Tamron 28-75 f/2.8 is that its performance towards the outer areas of the frame - when used on a full frame camera - is, at best, "OK"... not spectacular. That's a function of size, simplicity and therefore price. So you shouldn't expect to get shots that are equally sharp across the entire frame.

For your AF tests and fine adjustment, you want to be shooting on a tripod, in good light, at ISO 100, with an aperture setting of f/2.8. When you've adjusted as necessary so that your test target is sharp at the centre of the frame, it should work fine at all apertures. It's quite usable (though not pin sharp) wide open, but you'll get best results from f/4 onwards.
09-15-2018, 09:48 AM   #11
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Really appreciate the time that you're taking in discussing this issue....I like shooting in manual focus regardless, but the improved AF on the K-1 ii should be better than what I've been seeing. The TAMRON is a comparably priced to some PENTAX glass, though I liked the idea of f/2.8 in a mini telephoto. I'll keep the FF issue in mind as well. I wish I had joined this Forum before I bought some of my other kit lenses (i.e, PENTAX 50mm 1.4, 35mm f/2 primes) . Better late than never I guess.
09-15-2018, 09:57 AM   #12
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QuoteOriginally posted by BigMackCam Quote
That looks more like blur due to slow shutter speed (1.3s for the first shot, 0.8s for the second)...
Looks like motion blur to me too.

If you are opting for Lens Align, buy the Focus Tune Software too. Get all the info you can on Lens Align and watch Michael Tapes, they are very helpful.
09-15-2018, 10:29 AM   #13
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QuoteOriginally posted by Merv-O Quote
Really appreciate the time that you're taking in discussing this issue....
You're very welcome

QuoteOriginally posted by Merv-O Quote
I like shooting in manual focus regardless, but the improved AF on the K-1 ii should be better than what I've been seeing. The TAMRON is a comparably priced to some PENTAX glass, though I liked the idea of f/2.8 in a mini telephoto. I'll keep the FF issue in mind as well. I wish I had joined this Forum before I bought some of my other kit lenses (i.e, PENTAX 50mm 1.4, 35mm f/2 primes) . Better late than never I guess.
For a 28-75mm f/2.8 constant aperture lens, the Tamron is actually pretty cheap - especially when you consider street prices and look for deals. It's right at the low end of pricing for that class of lens. In fact, I don't know of another full-frame constant f/2.8 zoom covering those focal lengths that is anywhere near the same price. You can get better image quality from other the lenses for the same or even less money, but then you don't get the focal length range and constant f/2.8 aperture.

Contrary to one of the earlier posts in this thread, the Tamron 28-75 f/2.8 focuses perfectly well using Live View, and that doesn't require AF fine adjustment as it uses contrast detect for auto-focus. So, to see what your lens is capable of, take some shots in Live View instead of focusing through the viewfinder. Make sure to keep your shutter speed at 1 / focal length or faster, and don't go below 1/60s. Do this in good lighting conditions. You should find that you get good results, especially when stopped down to f/4 or smaller (but even f/2.8 should be decent). Then, work on AF fine adjustment so you get comparable results when focusing through the viewfinder.

If you can't get good results using Live View, there's something wrong - either with your chosen exposure settings, or the lens. It will most likely be the former - but there's a small chance the lens could be at fault. Feel free to post any test pics if you'd like any more input
09-15-2018, 04:06 PM   #14
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The live view worked better. I ordered a Spyder LensCalc unit from Adorama--I'll report back when I fix the focal point on my lenses.
09-15-2018, 04:30 PM - 2 Likes   #15
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It's a good lens on K-1. Performs nicely, particularly stopped down just a tad.

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