ef 28 1.8 focusing problems in low light

First of all sorry this is such a long post...

A bit of a background first, I have the ef50 1.4 and the ef85 1.8 and have been using them on my two bodies (xt and xti) since I'm still on an aps-c sensor I'm in need of a wider lens. So I asked my best friend if he could let me borrow his 28 1.8, I took it for a test run a couple of months ago on some backstage runway events and the field of view of this lens is exactly what I was looking for, however on the two events I tried it on the IQ seemed a little off compared to my 85 (the 50 is the lens it was replacing), and in one of the events there was a really low light situation which showed that my rebel xt could deal with the 28 better than my rebel xti, but because te circumstances of light where so extreme I didn't really put too much attention on the focusing problems of the 28 1.8, still it left me with some concerns on buying the 28 for myself.

Last saturday I took some photos at a concert at night for a paying client, and I borrowed the 28 again, the focusing problems showed up again though this time it was not acceptable because I was photographing a band on stage with enough lighting for video recording (I didn't ask for the specifics but from what I've experienced if the lighting is bright enough for video I have no problems focusing with my 85 or 50). I was shooting at F2.0 at ISO 1600 and about 1/60 to 1/100 and the focusing got really problematic, for example I was on stage using the center point to focus and then recompose on the singer that was about 9 feet away and instead of focusing on the singer it focused about 6 feet away from me. Since this was a paying gig and the concerns I had with the lens I moved the focus ring to unfocus and then let the camera focus again, this helped a bit and I got some usable shots out of the whole thing. What later dawned on me but I didn't experiment was to move the focus point so I didn't have to recompose each time, although experimenting while on a paying job and I only had 6 songs to photograph the band on stage made me decide not to, specially since I have not had this problem with my 50 or 85. Only the 28 gave me problems with focusing because on my other body I used the 85 at similar values with no problems at all and not only was the focusing on the money but the IQ was really good.

So to all the 28 1.8 owners have you gotten this kind of focusing problems? Are there any ways to counteract them? or Could it be user error? Or that my bodies are showing their limitations? when I've used the 28 sometimes what I'm focusing on is smaller than the actual square of the focusing point could this be a problem? I had some similar problems with a fashion shoot I did a month ago where I borrowed the 28 again though this time it back focused a bit (about 1 foot).

Any feedback about this would be appreciated, I tried googling this but seems that the 28 isn't all that problematic when focusing

It sounds like the lens is generally focusing on what it's being told to focus on. The body decides what to focus on, and that's probably where the problem is happening. Given the various focus/recompose scenarios and not changing the focus point, I'd say this is something you can improve by more practice and experimentation. It could be that on the longer lenses the same thing is happening, but the actual focus point is also on the same subject so you never notice.

The lens doesn't know anything about focus or focus points; it just does what the body says.

However, if you do start to use some of the outer focus points, you may end up with more missed-focus shots because those points don't have the same performance as the inner one. That's something you fix by upgrading the body.

No; I've been very happy with the focusing of mine. VERY. IQ isn't the best but it's rarely a problem for me.

I have both the 28mm f/1.8 and 85mm f/1.8, and I always found that the two lenses performed almost identically with regards to auto focus. That was with a 7D body, though, as I have not owned the 28mm for nearly as long as the 85mm. The 28mm also focuses quite well on my 5D3.

AntonLargiader wrote in post #15039495
It could be that on the longer lenses the same thing is happening, but the actual focus point is also on the same subject so you never notice.

Can you elaborate more on this?

I'm making an assumption about how you use your lenses, but the way I shoot, my subject will fill the frame more when I'm shooting longer lenses.

So, if I were shooting a singer with a 200, the singer would likely fill the frame and most of the focus points would be on the singer. Therefore, if the camera were using something other than center-point spot focus, it would probably still work out OK because it would just be focusing on a different spot on the singer.

But with the 28, only the center point would be on the singer (because much of the stage would be in the frame) so if the camera were to use something other than center-point spot focus, it would likely compromise the focus on the singer.

Posting some OOF examples here (with the active focus points shown and complete EXIF) might be helpful.

got an email I can send the photo to?

Post it to the thread so others can have an opinion too.

don't have a place to host it so I prefer to send it...

There are three key factors that effect focus speed and accuracy.... The camera, the lens and the user.

I've been using 20/2.8, 28/1.8, 50/1.4 and 85/1.8 for many years (and added 135/2 about 3 years ago when I added a full frame camera to my kit).

My 28/1.8 has always been quite reliable and fast focusing. It's certainly no worse in low light than 85/1.8 or 50/1.4. All my lenses with one exception (an ultrawide zoom) are USM, because it's faster and more accurate than micro motor. Of my lenses, the 50/1.4 is probably the slowest, with it's hybrid (and pretty dated) form of USM.

What focusing techniques are you using?

I often always use only a single AF point, and usually just the center one, though with 50Ds and 7D I'll occasionally use other points. I don't have XT or XTi, but I think they both only have one of the better type of AF point at the center (similar to my 5DII), in which case I would only use that center point under more challenging lighting situations. My 50Ds and 7Ds have all cross-type points.... My 5DII and I think your cameras, only have the dual axis, cross type AF sensor at the center, all the others are single axis type AF points, which are less sensitive, slower to respond.

I also use AI Servo and Back Button Focusing much of the time. If my subjects are stationary and focus is really critical (such as I'm using a large aperture to blur down the background), I'll switch to One Shot, or possibly even Live View for focus. However, at a concert, assuming there is quite a bit of movement, I think I'd be most likely to use AI Servo.

Is there a "protection" filter on the 28mm lens? On more than a few occasions I've seen those cause problems. It might help focus too, to use a lens hood... if not already doing so. Oblique lighting might effect AF... though it's not a common problem.

Finally, clean the lens to camera electronic contacts occasionally. It's easy and can make a difference. Just get some isopropyl alcohol (rubbing alcohol is fine), put a few drops on a clean cloth to dampen it, and carefully wipe the contacts on both the back of the lens and the corresponding, spring loaded pins just inside the mount on the camera. While there, make sure the camera's pin contacts aren't sticking at all. Be very careful to keep off the lens' optics and the camera's mirror. This can help lens performance, both AF and aperture control, such as if there are oils on those contacts that might slow or interrupt the small voltages used for camera to lens communication.

There are many places to upload your images for free on the Internet. Flickr.com, for one.

amfoto1 wrote in post #15040947
Of my lenses, the 50/1.4 is probably the slowest, with it's hybrid (and pretty dated) form of USM.

^^^This. Out of my lenses, the only one that has issues focusing at all is the 50/1.4, and even that only in very low light. The 28/1.8 may be the softer of the two lenses, but I've never found focusing to be a problem for it. It's definitely worth practicing changing focus points so you don't have to recompose, once you get the hang of it, it's really quick.

amfoto1 wrote in post #15040947
What focusing techniques are you using?

I use mostly one shot focus and the center point since as you mentioned its the only cross type point on my cameras, I have had very little experience with AI servo and on most of what I do I haven't had any need for it and when I've used it it works ok. As I mentioned sometimes I "unfocus" the lens and let the camera focus again, this technique sometimes works when my 50 or 85 can't pin point the focus correctly, I used this "technique" quite allot for the 28 at the concert. Can it be that with the 28 the focus point is so big the camera doesn't know exactly what I'm pointing at? If that is the case would a 7d be better at this? I checked the screen on the 7d and the focus points seem to be the same size as my rebels (center point I know the 7d has more focus points and that they are cross type)

Here's the example I was reffering to:

http://www.cuervo79.co​m/temp/_mg_0157.jpg

As you can see the focus is set on the area where the keyboards are instead on being on the area of the singer, as you can tell there is a bit of distance between the two and this is what makes me not trust the 28 I would understand a foot of front or back focusing but this much no..
The other thing is that at that distance the center focus point clearly was the same size as the singer (or even a bit smaller) so why did the camera focus on the keyboards....

First,I don't really like this lens performance at night @f/1.8 because it has lots of CAs on the light reflection,also it returns a very soft effect on the object,even the object is in focus.
I think is better to take above @f/2.2 to have a better quality on this lens.

For the focus part,at night is all good but if you tried to take shot with something very dark,
it might take more time to focus.I usually take my external flash,
set focus light only to assist focus.I know you will ask why I don't flash if I have ex. flash,
the answer is sometimes I would like to take the natual light to maintain the color tone.

I think I should pick something to take some samples and upload to here

yeah I don't have a speedlite for my cameras

Under a 60W light bulb in the room,I would say kinda dark(I still need a table light),
but that's not the darkest situation,but I don't need any assist with flash,using center focus point,
focus on "BLUE INK"

All in ISO 800,just want to show how soft @f/1.8

f/1.8

1846 x 1231

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thank you for the examples but I know the sharpness problems with wide aperture lenses (specially the 50 1.4) the problem here isn't about sharpness (although this helps solidify my comment about IQ compared to my 85) its more of a problem of not being able to focus in difficult situations and if it is the lens the problem, user error, or my bodies...