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03-21-2015, 12:46 PM   #1
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k3 focus issues

Another focus issue with my new k3 and I know it isn't the camera body b/c I already exchanged my first one, thinking that it WAS the body. So I have two lenses: A sigma AF 17-35 F2.8-4, and a rokinon 85mm F1.4 full frame lens. The sigma just can't seem to get a sharp focus, even with fiddling with the AF fine adjustment. Is this just a lower quality lens that I should trade up from?
The Rokinon is a dream to play with, except that once I dip below 5.6 aperature the focus is completely off. I will focus on a eye and get the shirt collar crisp as can be. The fine focus adjustment doesn't work b/c it is a manual focus only. I figure that the focal point is somehow off. Should I program in a different focal point at the start, other than 85mm, since it is a full frame lens perhaps? Any suggestions?
Working in live view seems to be accurate with the 85mm, but it's a pain b/c I have poor near-vision, and then I get camera shake having to hold the camera away from me to see the screen.
Anyway, I'm so frustrated, I'm wondering if it's just me, or if I should scrap pentax and go with canon, or if I need to invest in higher quality lenses just to get a crisp picture. My sony point and shoot is rendering cleaner lines than anything I'm coming up with right now

Please help?!?
BTW- this forum rocks, so I really don't want to scrap the whole thing.

03-21-2015, 12:59 PM   #2
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Pls don't say that as THEY'LL close your thread as they closed mine:
www.pentaxforums.com/forums/172-pentax-k-3/288665-how-improve-k-3-da-shots-contemporary-point-shoot-level.html
The K-3 and Pentax are goddes here so you can pray only.
Pray to Pentax for focus then
Blame Ricoh (and Sigma)

-----
QuoteOriginally posted by ckschempp Quote
My sony point and shoot is rendering cleaner lines than anything I'm coming up with right now
03-21-2015, 01:41 PM   #3
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QuoteOriginally posted by ckschempp Quote
The Rokinon is a dream to play with, except that once I dip below 5.6 aperature the focus is completely off. I will focus on a eye and get the shirt collar crisp as can be. The fine focus adjustment doesn't work b/c it is a manual focus only.
Have you adjusted the diopter correctly? I assume you are focusing using the focusing screen to focus? If so that needs to be adjusted to suit your eyesight before it is accurate. You use the little dial on the right of the viewfinder. Also, modern focusing screens are optimized for auto focus, not manual focus so at apertures below f/5.6 it gets increasingly difficult to tell the precise point of focus. And you should check the focus while on a tripod, most people do not notice but if you watch someone taking a picture it is common for the photographer to sway just a bit as they press the shutter button. With really fast glass that 1/4" of "sway" is enough to move the focus point.
QuoteOriginally posted by ckschempp Quote
Should I program in a different focal point at the start, other than 85mm, since it is a full frame lens perhaps?
I'm not entirely sure what you mean by this? Program another focal point? And it makes no difference that it is a FF lens. Do you mean focal length for the SR?
QuoteOriginally posted by ckschempp Quote
Working in live view seems to be accurate with the 85mm, but it's a pain b/c I have poor near-vision,
If Live view is accurate then there is nothing wrong with the lens or the camera. I suspect your diopter is off.
03-21-2015, 01:43 PM   #4
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Hi CKS,

Sigma make a USB dock to program the PD AF response of their lenses at different focal lengths and subject distances.

The Rokinon is excellent (I have it) but if your vision is not good and you're too shaky to handhold I'm not sure what you hoped to achieve with such a precise (f1.4!) manual focus lens.

You could shoot wide open on a tripod or stop it down otherwise to get more depth of field tolerance.

03-21-2015, 01:51 PM   #5
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QuoteOriginally posted by Prakticant Quote
Pls don't say that as THEY'LL close your thread as they closed mine:
Well, I don't see how you've helped this gentleman, Prakticant - with the personal limitations he's mentioned - at all.

What will you do when he struggles to nail the Rokinon MF on a Canon as well?
03-21-2015, 02:12 PM   #6
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QuoteOriginally posted by ckschempp Quote
Another focus issue with my new k3 and I know it isn't the camera body b/c I already exchanged my first one, thinking that it WAS the body. So I have two lenses: A sigma AF 17-35 F2.8-4, and a rokinon 85mm F1.4 full frame lens. The sigma just can't seem to get a sharp focus, even with fiddling with the AF fine adjustment. Is this just a lower quality lens that I should trade up from?
The Rokinon is a dream to play with, except that once I dip below 5.6 aperature the focus is completely off. I will focus on a eye and get the shirt collar crisp as can be. The fine focus adjustment doesn't work b/c it is a manual focus only. I figure that the focal point is somehow off. Should I program in a different focal point at the start, other than 85mm, since it is a full frame lens perhaps? Any suggestions?
Working in live view seems to be accurate with the 85mm, but it's a pain b/c I have poor near-vision, and then I get camera shake having to hold the camera away from me to see the screen.
Anyway, I'm so frustrated, I'm wondering if it's just me, or if I should scrap pentax and go with canon, or if I need to invest in higher quality lenses just to get a crisp picture. My sony point and shoot is rendering cleaner lines than anything I'm coming up with right now

Please help?!?
BTW- this forum rocks, so I really don't want to scrap the whole thing.
Some sigma's are know to require above +/-10 adjustment, If this is the case use PK tether to go to a +/- 20 scale.
In reference to your Samyang 85mm f1.4 issues, If i understand you correctly you're saying that the focus changes when you close your lens past f5.6 (f7.1, f8, f10 and so on) If this is the case and your subject is too close to the camera then you're dealing with hyperfocal distances (I suggest you bone up on this) meaning your focus is in front of you DOF plane.

ps. Its worth checking wheather your apperture is function correctly as well, the Samyang/ Rokinon have issues with aperture control, they get stuck wide open or don't talk properly to the camera. After you've confirmed that your lens functions properly then look at your hyperfocal distances.
03-21-2015, 03:27 PM   #7
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It really shouldn't be as difficult as all of that. Can you post some examples with EXIF data? Without that, its all just third-party conjecture.
03-21-2015, 03:34 PM   #8
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QuoteOriginally posted by Prakticant Quote
Blame Ricoh (and Sigma)
Blame Sigma. My K-3 AF works great.

QuoteOriginally posted by clackers Quote
Sigma make a USB dock to program the PD AF response of their lenses at different focal lengths and subject distances.
Not for the 17-35/2.8-4. It is an older generation lens and not compatible with the dock. Reviews on that lens going back several years have been mixed with general softness along with AF performance wide-open and at shorter focal lengths being a common complaint.

QuoteOriginally posted by clackers Quote
Well, I don't see how you've helped this gentleman, Prakticant - with the personal limitations he's mentioned - at all.

What will you do when he struggles to nail the Rokinon MF on a Canon as well?
I agree. 85/1.4 is incredibly difficult* to focus under idea conditions and is actually beyond the capabilities of the camera's focus confirmation system. Even with a well-calibrated split image screen the task is not easy. And no, the stock focus screen is not up to the task. The focus sensitivity with the stock screen is only about f/4. Tripod mounted using magnified live view is the most reliable, but oh, so clumsy.


Steve

* Actually 85mm at f/2 is quite hard enough. I got soft results with my Jupiter-9 until I switched to a split image screen.


Last edited by stevebrot; 03-21-2015 at 03:47 PM.
03-21-2015, 04:13 PM   #9
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QuoteOriginally posted by Stavri Quote
In reference to your Samyang 85mm f1.4 issues, If i understand you correctly you're saying that the focus changes when you close your lens past f5.6 (f7.1, f8, f10 and so on)
No, the OP said that the focus is way off "below f/5.6". I think they mean wider aperture (f/1.4-f/5.6). They focus on the eye apparently using focus confirm and the collar is sharp, indicating missed focus. Overshot when focusing near-to-far? Things are good with live view so it is not a problem of focus shift or the lens being poorly aligned.


Steve

Last edited by stevebrot; 03-21-2015 at 04:21 PM.
03-21-2015, 04:45 PM   #10
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QuoteOriginally posted by ckschempp Quote
Anyway, I'm so frustrated, I'm wondering if it's just me, or if I should scrap pentax and go with canon, or if I need to invest in higher quality lenses just to get a crisp picture.
Your Sigma may well be to blame, though it is hard to say without a known-good lens of moderate focal length to compare it too.


Steve
03-21-2015, 05:35 PM   #11
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QuoteOriginally posted by stevebrot Quote
Blame Sigma. My K-3 AF works great.



Not for the 17-35/2.8-4. It is an older generation lens and not compatible with the dock. Reviews on that lens going back several years have been mixed with general softness along with AF performance wide-open and at shorter focal lengths being a common complaint.

Thanks for the info, Steve ... I'd not even read anyone here talking about that lens before!
03-21-2015, 05:35 PM   #12
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QuoteOriginally posted by ckschempp Quote
So I have two lenses: A sigma AF 17-35 F2.8-4, and a rokinon 85mm F1.4 full frame lens. The sigma just can't seem to get a sharp focus, even with fiddling with the AF fine adjustment. Is this just a lower quality lens that I should trade up from?
Can you post some samples? It could be a combination of misfocus, low lens resolution (with the 17-35), and camera shake. Live view magnification plus focus peaking is the way to go for sharp manual focus. If you're trying to use AF confirmation with the 85mm, it's most likely to blame, since it can't be relied upon 100%.

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03-21-2015, 07:52 PM   #13
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QuoteOriginally posted by clackers Quote
I'd not even read anyone here talking about that lens before!
Me neither. I had to Google it.


Steve
03-21-2015, 09:27 PM - 1 Like   #14
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So I'm getting that the Sigma was a less than ideal choice. I'm actually fine with that concept- I find that I don't like it at all The Rokinon, I love. I love the fixed frame and I do like the manual focus. I will definitely try the diopter fix (I am a beginner and thought it was just to fine tune the digital readout of the parameters). I guess I need to concede that my older age is going to limit my abilities (I'm only 44, but my eyes think I'm 84) with focus and I will have to learn to love my tripod. Rats.
When I put on the lens, the screen asks me to put in focal length, so I put in 85 mm. I am figuring that there may be a different focal length that may jive a little better due to the full frame lens on a less than full frame body. I will do some trialing and erring on that. Thank you all so much for your input! Any suggestions for a better lens for wide angle, since I will be ditching the sigma?
Sorry about the sideways pic- I still don't have good software for editing. (F3.5, 1/500, 85mm, but it says 127mm equivalent).
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03-21-2015, 09:49 PM   #15
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QuoteOriginally posted by ckschempp Quote
When I put on the lens, the screen asks me to put in focal length, so I put in 85 mm. I am figuring that there may be a different focal length that may jive a little better due to the full frame lens on a less than full frame body.

That'll be just fine, Ckschempp. It's for the benefit of the Shake Reduction mechanism only.




QuoteOriginally posted by ckschempp Quote
Any suggestions for a better lens for wide angle, since I will be ditching the sigma?

Pentax have a newish DA 20-40 you might be interested in.


If you want to go wider or longer there are many possibilities at different price levels.
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