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08-02-2016, 10:47 PM   #1
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K1 pics vs Sony a6300

So, I purchased K1 and Sony a6300 for different needs, but when I take pic of my niece and nephew ( still photo ), I see Sony has better focusing system and they face especially their eyes look so much sharper than K1 . I even adjusted AF to 9 points on K1 and focus on their face, but still side by side Sony is sharper. If the kids moves a little bit, then forget it, K1 failed all the time. Here is my gear:

Pentax K1 with Tamron 28-75 f/2.8 initially I shot at 2.8, but then switched to f4 and kept the same ISO settings and AF.C to match Sony
Sony a6300 with Zeiss 24-70 f/4

any help is greatly appreciated .

08-02-2016, 11:13 PM   #2
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Unless you put up pics, it's very hard for us to compare, Dr_Romix.

And for starters, that Sony lens is $1200 from BHPhoto, right?

You're comparing it to a budget screwdrive lens!
08-02-2016, 11:40 PM   #3
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I'm travelling now and the internet speed is pretty slow to post the full size image on my Flickr account. I'll post pics next week when I get back home. Also, I'm going to compare Zeiss to Pentax version of 24-70 next week. Thanks.
08-02-2016, 11:47 PM   #4
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It´s not a back/front focus problem with K1?

08-02-2016, 11:51 PM   #5
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I do find that Tamron's AF performance to be slightly sloppy at times - and mine required some AF adjustment (have you calibrated it?) - but when it hits it is pretty sharp. But it is still a cheap lens...if you spend 4x the amount you will probably get better performance, as you have found.
08-03-2016, 12:23 AM - 1 Like   #6
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Well, let's review the facts...oh, I found the problem...Tamron vs ZEISS.
08-03-2016, 12:36 AM   #7
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QuoteOriginally posted by mikeSF Quote
Well, let's review the facts...oh, I found the problem...Tamron vs ZEISS.


I imagine the Tamron designers, at least, would be flattered by the suggestion of equivalence!

Their Zeiss counterparts? Maybe not so much!
08-03-2016, 01:18 AM - 1 Like   #8
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The Tamron 28-75 f/2.8 is a very good lens for the price... However, all three Tamron lenses I've owned for Pentax have front focused significantly (when none of my Pentax lenses required any more than +/-2 adjustment). I returned two copies of the 70-200 f/2.8 to my supplier because neither of those could be calibrated within the +/-10 AF fine adjustment; at least, not so they would focus well enough at all focal lengths both at distance and close in, wide open. And my 28-75 f/2.8 is currently with Tamron UK's service agent for alignment, as - after a fair bit of use - I've finally realised that it, too, front-focused beyond the limits of the camera's AF fine adjustment (especially at close range). I'm looking forward to getting it back, as - overall - I do think it's an excellent lens considering what I paid for it.

Sony's AF is exceptionally good, though, and the Zeiss lenses are just gorgeous... My Sony A99-based Hasselblad HV and Sony Zeiss 24-70 f/2.8 combo focuses incredibly quickly and with unnerving accuracy - I honestly can't think of one occasion yet where it has missed critical focus; very impressive indeed. So, yes... Sony's AF is streets ahead of Pentax. But then again, Pentax wins hands down in other areas... Bring up the shadows in high contrast areas on your Sony images and you'll find nasty, pixelated noise along the dark edges, due to compression in the .ARW raw files. This has completely ruined a couple of my photos which, had I taken them with one of my Pentax cameras, would have been perfectly usable shots. The dynamic range and clean shadow detail that can be recovered from my Pentax images is just remarkable compared to Sony's compressed raw files.

As always, with any camera and/or lens, it's a case of understanding the strengths and weaknesses, and working with those


Last edited by BigMackCam; 08-03-2016 at 04:34 AM.
08-03-2016, 02:30 AM   #9
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I guess as others have said, the issue is your lens -- hopefully just front or back focusing problems that you can fix with focus adjustment. I would try focusing using live view and see if that makes a difference. Certainly if you want a lens that measures up to the Zeiss performance, you probably would need to look at the the Pentax DFA 24-70.
08-03-2016, 02:58 AM   #10
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QuoteOriginally posted by BigMackCam Quote
my 28-75 f/2.8 ... as - after a fair bit of use - I've finally realised that it, too, front-focused beyond the limits of the camera's AF fine adjustment (especially at close range)
Good to see I am not alone . I wonder why front-focus is such a pattern with Tamron on Pentax.

But after a 1000+ shots with the 28-75 on the K-1, at f3.5 or f4 I've found that I can get by with a -10 focus adjustment on the lens, with totally usable results.
08-03-2016, 03:21 AM   #11
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QuoteOriginally posted by rawr Quote
Good to see I am not alone . I wonder why front-focus is such a pattern with Tamron on Pentax.
From what I've read on various forums, it's not isolated to Pentax, though it does appear to be more prevalent. I wonder if Tamron's calibration and test rig for Pentax is somehow slightly out of alignment, though I find it difficult to believe that such a large and capable lens manufacturer would make a schoolboy error like that.

QuoteOriginally posted by rawr Quote
But after a 1000+ shots with the 28-75 on the K-1, at f3.5 or f4 I've found that I can get by with a -10 focus adjustment on the lens, with totally usable results.
Yeah, I've had plenty of good shots at f/4 too - enough that I'm generally impressed with the lens. The thing is, I know it's capable of delivering quite good (if slightly soft) IQ wide open too... it's just that I've had to focus manually to achieve that, especially for the distances that interest me most. When I sent the lens to Intro2020 (Tamron UK's service agent) I explained that my priority is close range AF accuracy for portrait work. I'm interested to see how it performs when I get it back (should be in a day or two)...
08-03-2016, 03:43 AM   #12
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QuoteOriginally posted by BigMackCam Quote
I sent the lens to Intro2020
I'd like to hear how that goes. Did they just take the lens or the body too?
My biggest problem with the lens is that it really needs a variable focus adjustment as whatever I dial in is always a bit wrong somewhere in the range. I doubt they could fix that mind you.
It only really matters wide open - although when it nails focus properly, it does look good at 2.8
08-03-2016, 04:03 AM   #13
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QuoteOriginally posted by victormeldrew Quote
I'd like to hear how that goes. Did they just take the lens or the body too?
My biggest problem with the lens is that it really needs a variable focus adjustment as whatever I dial in is always a bit wrong somewhere in the range. I doubt they could fix that mind you.
It only really matters wide open - although when it nails focus properly, it does look good at 2.8
I'll let you know how it turns out. On this occasion, I only sent the lens... It's kind of an experiment for me - I'm fairly confident that my K-3 is close to ideal in terms of calibration, as my DA Limited lenses require zero or +/-1 AF fine adjustment. So, if my serviced Tammy can be matched to my K-3 within +/-10 AF fine adjustment, I'll know that there was some degree of mis-calibration at the time of manufacture, and that the service facility has been able to more accurately calibrate it with its own equipment. If, however, it still can't be matched within that +/-10 range, I'll send it back to them along with my K-3 and see what happens.

Regarding variance in AF accuracy at different focal lengths, I agree - it's frustrating, but not all that uncommon with zoom lenses, from what I've read. I informed Intro2020 that my priority is the 50-75mm range, as that's my preference for portraiture on APS-C. If the serviced lens will accurately focus at close distances within that range, I can live with some variance at the wider end...
08-03-2016, 04:27 AM   #14
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The a6300 does all your work for you, the K-1 doesn't Also it uses cdaf (in combination with pdaf) which does not need to be calibrated. And on the K-1 only he center point and the two points directly above/below it are F2.8. So check the lens for front or back focus. You can correct this in the K-1. Use only the center points at F2.8
08-03-2016, 04:45 AM   #15
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QuoteOriginally posted by D1N0 Quote
And on the K-1 only he center point and the two points directly above/below it are F2.8.
You may be mixing up two different elements of Pentax low-light AF.

Pentax talks of 'f2.8 luminance flux' as a measure of the ability to AF very fast lenses, despite their shallow DOF - eg:

QuoteQuote:
"The center sensor and two sensors just above and below it are designed to detect the luminance flux of an F2.8 lens for high-precision autofocusing. When using a very fast lens with a shallow depth of field, these sensors greatly improve the focusing accuracy."
Feature 2?K-3 | RICOH IMAGING

And that feature works alongside the general -3 EV sensitivity of basically all the AF sensors in the camera, viz [for the K-3]:

QuoteQuote:
"Dependable AF at super-low minimum luminance of –3 EV

The K-3’s high-sensitivity AF sensor assures dependable autofocus operation down to a minimum luminance of –3 EV (when using 25 middle sensors), preventing the AF mechanism from slowing down or being confused by high-contrast areas in back-lit situations. It also captures low-contrast subjects with great accuracy."
So [as I understand it] there are two things working here to ensure K-1/K-3 SAFOX 12/SAFOX 11 can get the job done very well in low-light. A6300 AF has nothing to match. It bombs out at -1 EV across the whole sensor.
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