[ckschempp]

Thanks! I'm still new with the jargon, so I did mean wider aperatures than 5.6 are not focusing, not the higher numbers (stopped down?). BTW, I am a lady, not a gentleman, hence the emotions dripping all over my queries

[Fauxton]

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.

The Sigma lens you have is not a good performer. Have a look here - Tests and reviews for the lens Sigma 17-35mm F2.8-4 EX DG Aspherical HSM Canon mounted on Canon EOS 7D Measurements - DxOMark Granted the test is on a 7D but it will not perform any better on your K3. Notice that at any focal length and under f5.6 it is fairly mediocre as far as sharpness goes. The lens seems to be at its best at the wider end - 17mm but its still not sharp. Your K3 will bring that lack of performance out.
So my advice would be to retire it and get something better. Even the Pentax kit lens 18-55 will provide better performance. Compare here Tests and reviews for the lens Pentax smc PENTAX DA 18-55mm F3.5-5.6 AL II mounted on Pentax K-3 Measurements - DxOMark
As to your Rokinon; unless you have a tripod and some patience it will likely frustrate you. That lens is a good FF portrait lens meant to be used in a studio setting. Ideally used tethered - something the K3 doesn't do. So put that one aside as well.
Your best choices would be to get the current generation 18-55 or if you wish the Pentax 35 mm f2.4 - either are inexpensive but better and easier to use than what you have. You can then enjoy your photography, improve your technique, explore the capabilities of your K3 and when you are ready step up to something more expensive and higher performing. If you have money burning a hole in your pocket you could try for the new Pentax 16-85 - that would be a tremendous step up in performance from where you are. If you are near a brick and mortar shop ask them to get one in for you to try.
Lastly it has been my experience that all my lenses (I have Pentax, Sigma and Tamron) require focus adjustment to reach their capability. You can read how to do it by doing a search on these forums. Also to really learn join a local photography club. There you will find many people that would be glad to help you in person.

[stevebrot]

Your best choices would be to get the current generation 18-55 or if you wish the Pentax 35 mm f2.4

I was going to make that suggestion as well, even though the 18-55 is an inexpensive lens, it is competent and will delivery nicely on the K-3. If the OP has a few more dollars in the pocket, I can enthusiastically recommend the Sigma 17-70/2.8-4 DC (Contemporary). I bought my copy when I got my K-3 and have been very happy with the pairing. The f/2.8 maximum aperture adds some weight, but it is worth it IMHO. The Sigma 17-50/2.8 might also be on the radar.


Steve

[Prakticant]

All my life I've heard 'get the cheapest body, but go for the best lens', and you are suggesting opposite .


-----

I was going to make that suggestion as well, even though the 18-55 is an inexpensive lens, it is competent and will delivery nicely on the K-3.

[Stavri]

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.

I just came upon a review on the Samyang/Rokinon talking about the "focus shift" problem on the 85mm f1.4.

quote: A major improvement in this lens( 35mm f1.4) over the Rokinon 85mm f/1.4 is the lack of focus shift. The 85mm had a large focus shift when stepping down, which required it to be focused at the aperture you were shooting at (using the depth of field preview or live view).

[ckschempp]

I just came upon a review on the Samyang/Rokinon talking about the "focus shift" problem on the 85mm f1.4.

quote: A major improvement in this lens( 35mm f1.4) over the Rokinon 85mm f/1.4 is the lack of focus shift. The 85mm had a large focus shift when stepping down, which required it to be focused at the aperture you were shooting at (using the depth of field preview or live view).

Is there a way to compensate for this focal shift, or somehow correct for it?

[stevebrot]

All my life I've heard 'get the cheapest body, but go for the best lens', and you are suggesting opposite .


-----

The body is already bought. The rest of my suggestion included more expensive and higher performing glass. FWIW, I have had very good luck with the 18-55 kit including several accepted in the PPG.


Steve

[stevebrot]

I just came upon a review on the Samyang/Rokinon talking about the "focus shift" problem on the 85mm f1.4.

quote: A major improvement in this lens( 35mm f1.4) over the Rokinon 85mm f/1.4 is the lack of focus shift. The 85mm had a large focus shift when stepping down, which required it to be focused at the aperture you were shooting at (using the depth of field preview or live view).

Link?

The in-depth review on this site did not discover this problem nor is it mentioned in any of the PF user reviews on this site. That being said, focus shift would not surprise me (common in large aperture primes), but usually it happens at narrower apertures and is offset by greater DOF. The situation described by the OP is probably not focus shift since there were no problems when using live view.

With any luck, Lowell will pop in and give his opinion on the reported focus shift. He was an early Samyang 85/1.4 adopter and is one of this site's more knowledgeable users in regards to the lens.

Edit: Klaus at photozone.de reported mild focus shift as a side note in his review. Bob Atkins reported none and made a point of it in his review.

Steve

[stevebrot]

Is there a way to compensate for this focal shift, or somehow correct for it?

The compensation is to focus with the lens stopped down. Good luck since DOF is not on your side. Since you have no problems when using live view, this is probably not your problem. Focus shift is usually measured in millimeters and would not account for the missed focus you describe. Where focus shift is significant is with close-up photography where you stop down to increase DOF, but where the DOF is still very shallow.

Some users on this site are very concerned about focus shift, I guess primarily because it can be seen when pixel peeping or when attempting to do AF fine adjustments. With some lenses it is a fact of life and not much more. At some point you might want to check your 85/1.4 to see if it has this problem, but I would wait until you are confident with the lens and then do whatever testing using a printed test target and the camera on tripod.


Steve

[stevebrot]

do whatever testing using a printed test target and the camera on tripod.

The technique is to establish fine focus on tripod with the lens wide open using a flat, high contrast test pattern and do several exposures at sequentially narrower apertures. The shift (if present) should be readily apparent.


Steve