Shield wrote:
You had me until the last sentence. Why couldn't you use MF? The whole point was the autofocus inconsistency; this has 0 to do with manual focusing.
I mean I would just manual focus it, but can't even do that because of focusing screen
"CW: The EOS 5D Mark III’s focusing screen has about the same overall brightness and depth-of-field characteristics as the EOS 5D Mark II‘s Eg-A standard focusing screen. This is a brighter screen than the Eg-S with most lenses, but it does not depict depth of field accurately for apertures wider than about f/4. Manual focusing accuracy using the optical viewfinder is about the same, lens for lens, on the 5D Mark III as it is on the 5D Mark II with an Eg-A focusing screen."
goosemang wrote:
"CW: The EOS 5D Mark III’s focusing screen has about the same overall brightness and depth-of-field characteristics as the EOS 5D Mark II‘s Eg-A standard focusing screen. This is a brighter screen than the Eg-S with most lenses, but it does not depict depth of field accurately for apertures wider than about f/4. Manual focusing accuracy using the optical viewfinder is about the same, lens for lens, on the 5D Mark III as it is on the 5D Mark II with an Eg-A focusing screen."
Many/most people that do MF in the Alt forum here think the 5D3 is better than the 5D2 for MF. And they have also posted thousends of pics done with MF from f/1,4 or faster lenses. Anyway this is the camera or your eyes you are complaining at, not the Sigma lens which can be MF focused at all apertures including the f/1,4
I wonder if that light theory is correct. It makes sense, and appears very plausible.
If that is the case, is it worth swapping my lens? It performs so perfect otherwise, and if that is going to be a common trait lens to lens why exchange? Maybe Sigma will release a firmware update later on to fix this issue... Who knows.
Still debating myself... I got approval to get an exchange, but my lens is just amazing other than the artificial light MA shift... I also think it may be normal but many are not in the same lighting situations for it to show up. So I am still debating... Focuses so perfectly near to far, wide open, and amazing sharpness. I am not sure if I want to risk another lens that will have the same issue and some other focusing quirk.
Hmmmm.... Roger, any theories you may have for my issue?
Lasse Eriksson wrote:
Many/most people that do MF in the Alt forum here think the 5D3 is better than the 5D2 for MF. And they have also posted thousends of pics done with MF from f/1,4 or faster lenses. Anyway this is the camera or your eyes you are complaining at, not the Sigma lens which can be MF focused at all apertures including the f/1,4
They are using MF confirm. Im not sure if its right, but MF confirm most likely depends on camera AF. Tho if it will work or not with Sigma 35mm f1.4 is a good question. Would be good idea to test it, cause it might or might not work, depending if Im right or wrong.
Mescalamba wrote:
They are using MF confirm. Im not sure if its right, but MF confirm most likely depends on camera AF. Tho if it will work or not with Sigma 35mm f1.4 is a good question. Would be good idea to test it, cause it might or might not work, depending if Im right or wrong.
It's not like all people are using MF confirm. But if it is like you say in your post, then the 5D3 would be better for MF than the 5D2. Because you say the MF confirm depends on the AF. And the AF is much better with the 5D3
Lasse Eriksson wrote:
Many/most people that do MF in the Alt forum here think the 5D3 is better than the 5D2 for MF. And they have also posted thousends of pics done with MF from f/1,4 or faster lenses. Anyway this is the camera or your eyes you are complaining at, not the Sigma lens which can be MF focused at all apertures including the f/1,4
I'm not blaming the sigma, I'm saying that I would just manual focus the sigma but the focusing screen doesn't accurately display DoF at f1.4
Just got mine yesterday. Experiencing front focus also. About an inch to an inch and a half worth of front focus at close distances. I'll be returning mine.
RogerC11 wrote:
Just got mine yesterday. Experiencing front focus also. About an inch to an inch and a half worth of front focus at close distances. I'll be returning mine.
I'm using a T2i. No MA feature for AF. I'm actually contemplating on either exchanging it for another copy or for a combination of the sigma 30 1.4 and tamron 17-50 2.8 for roughly the same price. I really like the lens though and wish it would have been a properly focusing unit. Still on the fence about if I want to try another copy though. Knowing my luck, I'd prob experience the same trouble if I choose to try the sigma 30mm.
Could be just bad luck of the draw - does it front focus at normal distances (that you can tell?)
I ask this because I've run into plenty of 1st party focus problems also, so I'm curious if you have a close-focus front-focus or it's front-focusing everywhere.
A good example is my former Nikon 35 1.8G DX lens.
That lens, on my former D90, was astoundingly sharp at f/1.8. Seriously, it was amazing. It was probably a "magic" lens in that whatever tolerances it had (slight front or rear focus, whatever), etc. must have been completely countered by the D90 because it was scary sharp from wide open at every focal distance.
I took that same lens and mounted it to a new acquisition at the time, a D7000, and the lens was much, much less impressive - it frankly stank. Turns out I had to dial in some MA, but even then I was never as happy with it as I was with the D90.
I think I may just keep my copy of the 35... Even with the MA shift indoors... The lens performs so amazing everywhere else, and I think the issue may be universal with this lens (and maybe just the 5D3?) with this behavior. Its not like the lens is doing it all the time in all types of light, or has varying MA with distance... Mine nails everything at any distance super sharp and accurate... It is just indoors in *some* light, it front focuses but only with artificial light.
They sent me an exchange RMA, but I think I just may skip on it... It is not THAT bad to switch the MA to +9 indoors when I need it, it is quite easy to test for and change when needed. Takes maybe half a minute.
If anything I may just send to Sigma service at some point and maybe they will have some firmware update or something they can do. I am so happy with this lens and its performance I would hate to exchange it with one that may have MA shift with distance or some other quirk.
Im sending mine in to Sigma for calibration. Mine is exhibiting similar behavior. Lots of shots will hit but at the same time it front focuses an inch to inches at around mfd to 3-5 feet as well
The different lighting thing makes perfect sense - although in thinking about it I'm surprised we don't see it more often.
The phase detection sensors have lenses that split the light from each side of the image, then bend it back to focus on a pair of sensors. I think it's safe to assume those tiny lenses are not apochromatic, that is they aren't correcting so that different wavelengths of light are all bending in the exact same manner.
Halogen lights, like most artificial lights, are going to put out a very narrow spectrum. This is an graph from wikepedia for streetlights, but it gives the idea.
Sunlight, on the other hand, gives a broad peak of multiple wavelengths.
I assume that the AF sensor in a Canon camera is tuned to one wavelength of light, probably something in the green spectrum, but I don't know for sure. If the coatings on a Sigma lens are a bit different than Canon (they probably are) then they'll pass a slightly different spectrum through the lens.
It probably won't matter with sunlight, where there spectrum is very broad without narrow wavelength peaks, but could matter with artificial light - halogen, LED, some fluorescents. The different spectrum would bend a slightly different amount than the focus algorithm in the camera is planning.
If this is the case, I'm curious if we will see something similar with other third-party lenses (although it probably will require a sharp third-party autofocus f/1.4 lens to see it, so that limits our options to observe it). It would also seem that a Nikon camera with a Sigma lens might not exhibit this behavior but a Canon camera might or vice versa.
Then again, I'm probably way off base. Is there a doctor (of optical physics) in the house?
It just does not seem to be to me, a lens fault that could be 'fixed' by exchanging my copy for my situation. The lens is flawless otherwise... I can work around this little quirk. Reliable and accurate as can be outdoors and inside even, as long as I switch the MA value if the lighting requires it.
