|
Forums >
Photography Talk >
Focusing problems with prime lenses
I normally use zoom lenses but I recently got the Sigma 50mm 1.4 art lens and while I really like it overall, the focusing is very inconsistent especially when shooting wide open. The only other prime lens I've used is the Canon 50mm 1.8 and I had the same problem with that. Is there anything I can do to improve focusing apart from using a tripod? Oct 31 15 01:36 pm Link lots of solutions are mentioned here: https://www.modelmayhem.com/forums/post/951742 suspect the you may have the same problem(s). inaccurate focus use poor hand holding technique not dealing with & understanding narrow dof understanding minimum shutter speed limitations Oct 31 15 01:39 pm Link Another possibility: camera variation. Every camera and lens has some acceptable variation in where the sensor, lens mount, rear element, etc. sits. It's very small, but there is one. Say for sake of argument that a sensor can be misaligned by up to 5 microns/nanometers/whatever they use to measure it, and the same for lenses. If the sensor was 4 microns off in one direction, and the lens was 4 off in the other direction, now you're off by 8 microns, which puts that camera/lens combination out of spec. I don't see this a lot, but a few years ago I used to see it all the time from literally every camera company and AF lens maker. It used to be accepted among pros that when buying new, you should try a few copies of the same lens if possible. These days, it seems like those tolerances have gotten tighter, but it still happens once in a while. The use of on-sensor AF detection helps too, since that effectively removes camera variation from the equation when using it. It was ALWAYS a bigger issue with pro lenses than kit lenses. For one, newbies aren't generally as critical. But beyond that, wide aperture lenses(like primes) have a narrower DOF, which means that alignment is much more important. When you zoom out to the long end on an 18-55 you're at f/5.6, which gives you a lot more leeway. You see this in other industries too. It's a lot easier to keep an AK-47 or a Toyota Corolla in spec than a target rifle or a track car. Oct 31 15 03:52 pm Link AF systems are geared toward shooting at F8. You are a fool if you think that your camera will focus accurately at F1.4 no matter the focal length. Oct 31 15 04:42 pm Link I used zooms for a long time then bought my first Sigma prime last year. I had a lot of the same focusing problems at first. It took some patience and practice, but my photos are a lot better now. It really just came down to the things mentioned in this post: LeonardG Photography wrote: Oct 31 15 05:43 pm Link Dave McDermott wrote: "During autofocus, the camera automatically opens the lens to its widest aperture, only closing it down to the aperture you’ve chosen just before the shutter curtain opens". Oct 31 15 07:01 pm Link Even if you use some 800mm prime lens you can get badly focused shots. Ask any birder who shoots with one. Watch them fire off a barrage of a dozen shots and one will always be sharper than the rest of the series even if they focus-locked onto the bird's eye. Pot luck really. The LensRentals guy equates AF to shooting with shotgun at times: Some hit. Some miss. It's just not that accurate as we'd like it to be. I can set mine up on a tripod and punch the shutter button and watch the lens spin off a bit each time due to hysteresis - although nothing has changed in distances. Sure, you can tune and fiddle to get it close, but 100% accuracy is unachievable, imho. Maybe in another 20 years... Oct 31 15 08:07 pm Link tcphoto wrote: There is no Canon DSLR autofocus system that focuses at f/8. All these systems focus using the widest aperture of the lens. If you ultimately make the photo at f/8 it only serves to partially mask focusing errors, it doesn't enhance focusing accuracy. Nov 01 15 12:19 am Link JAE wrote: Remember Kids. Canon and Nikon does not have to give out their AF Systems to 3rd Party Lens Makers..ie Sigma. And when firmware is updated to Nikon and Canons...they sneak that in, so your Sigma's and Tamron's do not focus quite right. I have the Sigma 50mm Art, I use Nikon..and no problems. But I have heard in the past that Sigma has issues with Canon Cameras, from time to time. But there is a very simplistic solution. Manual. Nov 01 15 12:27 am Link DOUGLASFOTOS wrote: Most modern focus rings don't have fine enough adjustment for manual focus because it slows down the speed of AF action. Even with focusing screen you won't get super sharp focus at 100% view like you can using AF. The only real solution is wasting time by going into live view to zoom in and focus that way. Nov 01 15 01:54 am Link Some interesting points. The new shake reduction tool in photoshop has been very useful and has helped salvage some photos that were otherwise unusable. If I'm using flash I can turn the power all the way down so I can get a shallow DOF. The photos are tack sharp when I do this. It's only when working with natural light that it becomes a bit hit and miss but I've noticed its not as bad at smaller apertures. It's only when I go wider than F4 that I start to get problems. Nov 01 15 01:37 am Link Yingwah Productions wrote: So true. Even using a purpose-built, manual focus lens on a DSLR can be difficult due to the lack of a good focus screen. Under these circumstances, I cheat. Dave McDermott wrote: Flash duration is very fast, and the shutter speed is mostly irrelevant. Based on your observation of flash vs. natural light, I think the issue you're having is related to camera movement as opposed to focus. Nov 01 15 01:44 am Link Yeah I think it is just down to movement. Obviously the flash freezes everything so its not an issue then. I was just a bit disappointed when I did my first shoot with it using only natural light only to find that a lot of the photos were out of focus. Nov 01 15 02:27 am Link Don't give up on it. I have Nikon's 50mm f/1.4G and 50mm f/1.2, but still want to add the Sigma 50mm f/1.4 Art. It's a thing of beauty when it all comes together. Nov 01 15 02:48 am Link Some examples of the problem would be nice.... Nov 01 15 02:55 am Link portraiturebyBrent wrote: Ohh absolutely, I got some great shots with it too. I'll certainly keep using it for a while anyway. Nov 01 15 06:10 am Link Most primes are not the sharpest when wide open (check out some samples at Vimeo). Better to shoot in good light and close the lens down. Nov 01 15 06:24 am Link Dave McDermott wrote: Keep in mind that even though the LENS is at 1.2 when focusing, the AF sensors may not actually be able to use that much light. It's common for them to only accept the 2.8-5.6 range; anything brighter than that is 2.8, and anything darker than that is 'off.' Nov 01 15 08:11 am Link Dave McDermott wrote: Except based on the other comments they were NOT out of focus. You need to be able to differentiate between the softness caused by movement and that from being out of focus. If it is a focus problem there will generally still be something in the image that is sharp. For example, if you are trying to focus on the eye but it is actually the tip of the nose that is in focus then the focus was not accurate (or you focused and recomposed). If everything in the image is soft then it is generally movement. Nov 01 15 10:51 am Link Has anybody tried the Sigma USB dock? My camera doesn't seem to have the micro-focus adjustment so I can't tweak it that way. Dec 14 15 11:12 am Link I have the same problem myself occasionally. I use a 1.8 Nikon 50mm a lot...a lot a lot and I'm learning how to stop the lens down more. Pretty much I try to be in the F2-F2.8 range if it's possible. I only go to 1.8 if the lighting gets really atrocious and if I have to use a lot of iso go get a manageable shutter speed. I've gotten used to more iso, but I still don't like cranking it up too high. I know that's a full frame lens and if it's on a full frame body it shouldn't be too highly effected by iso noise. Dec 14 15 07:03 pm Link Dave McDermott wrote: I've have it and use it. Dec 14 15 07:32 pm Link Dave McDermott wrote: As the Photoshop shake reduction tools help the issue might simply be movement / vibration of the camera. Dec 16 15 09:23 am Link Michael Bots wrote: Yep I think that's all it is considering the focusing is spot on when using flash. I might try using a tripod for my next shoot and see how it goes. That would give me a better idea. Dec 16 15 10:21 am Link not every camera and lens will get along out of the box....that is why you need to set your camera to your lens....you will be able to set the back or forward focus to match them up....some people send their equipment in to have them set right...you can do it your self with aftermarket products to set focus, do your own tests, and remember, some cameras do great auto focus in daylight but just do not get it in flash and indoor light...tripods need to be solid...shutter shake can be an issue...enjoy the journey and have fun.....Mo Dec 19 15 08:15 pm Link mophotoart wrote: How true! Dec 20 15 05:56 am Link GRMACK wrote: This has been a well documented issue for quite some time now... GRMACK wrote: Yep, this works extremely well... problem solved... GRMACK wrote: This has been one of Nikon's strong points... had a second shooter using a flagship Canon which wouldn't lock for her using our studio's modeling lights... had to increase studio ambient so she could continue on the session.... Dec 20 15 06:57 am Link tcphoto wrote: Interesting claim. Where did you get this idea? Put another way, can you provide a reference? Dec 21 15 12:34 pm Link Frozen Instant Imagery wrote: One has to put in a little more work/attention when focusing at wide apertures, including understanding and using the right camera focusing modes (or maybe better stated - not using the wrong ones) - but if you're using better lenses there's no reason to have the false expectation that one can't focus accurately at large apertures. Dec 21 15 01:39 pm Link J O H N A L L A N wrote: Oh, absolutely. I can and do nail focus on a single eye using the 85mm f/1.2 wide open, and that's even shallower depth of field than 50mm f/1.4. I admit I don't always get it, considering that the depth of field can be 6mm, but it's far from impossible. Dec 23 15 08:05 am Link It is a Sigma lens. It used to be that was sufficient explanation. I'd vowed to never get another Sigma lens some years ago and have sold on any that I had and still functioned. Earlier s year I succumbed to the 35mm Art lens. First one would consistently focus in front of the subject and was too great for in-camera adjustments to enable it to focus accurately at any distance. Remember, in-camera adjustments only work optimally at one focus distance, it is a short-term solution. This was sent back. The 'replacement', from Sigma, looked as though someone had sneeze on the front element and both front and rear were very smeared. I found later some documentation that acknowledged it was a used lens, immediate financial loss. Focus accuracy is better but still needs some care, three shots better than one. The USB hub adjustments for this lens are for 3 close distances and then infinity. Not ideal when your main use is likely to see a distance that is beyond the third by a metre. I need to renew my vow. Dec 23 15 11:45 pm Link |
