17-55mm front-focusing...how bad is it?

[neuroanatomist]

Here is a proper test chart designed to help you lock onto the intended line.

The only issue I have with the chart you linked is that the focus target is still a horizontal line, which will predominantly activate the f/5.6 part of the AF point, and not the more precise f/2.8 sensor (which is the one I'd want to use, if the lens was f/2.8 or faster.

[alex]

Well everyone, I performed another test today on the coffee table, using John's (kindly) provided star-burst focus chart. Propped the tape measure up on some building blocks (had to sneak into the napping boys' room to get them!), tried to align everything to the best of my ability, and did some shooting.


This time I took about the same number of shots as previously.


Boy, were these results DIFFERENT from before. unbelievable. John, you must have been right about the requirements for my camera's AF system. The amount of variability between the shots was minimal. Not only that, but to my eyes, my focus problems are negligible. Of course, that's assuming that I lined up the paper focus chart in the same plane as my camera's sensor and also lined it up with the tape measure correctly. Again, I did this to the best of my ability.


I attempted to set the plane of focus so that the line right below the 7 would be in focus.


Settings were the same as before, 55mm, f/2.8, ISO800, either 1/40 or 1/50 depending on the shot.


First shot is the MF, LiveView. I focused on the paper in the LiveView screen, not the number on the tape measure.


[img]/resized-image.ashx/__size/800x0/__key/CommunityServer-Discussions-Components-Files/8/4135.DPP_5F00_0005.JPG[/img]





Number 2, AF (the center point focus is aimed at the paper just above and to the right of the center star burst, directly horizontal and to the left of the 7)


[img]/resized-image.ashx/__size/800x0/__key/CommunityServer-Discussions-Components-Files/8/6378.DPP_5F00_0006.JPG[/img]


nearly identical (to my eyes), and all the AF shots I did were like this.


Finally, a nearly 100% crop of the AF shot above.


[img]/resized-image.ashx/__size/600x0/__key/CommunityServer-Discussions-Components-Files/8/3806.DPP_5F00_0009.JPG[/img]





What do you guys think?


Thanks!


alex

[Trowski]

Very much looks like your lens is performing extremely well. I think the problems you were experiencing before were due to the problems John pointed out with your testing technique. I'm tempted to assemble that chart John linked to, pasting the starburst pattern onto the focusing area, and then test out some of my lenses. That being said, I've never really noticed any problems with my lenses.


John, I really think you should write full articles for a photography website (or perhaps start your own). So often I find your posts to be the most helpful, well-written, and logical responses to the many questions posed on this forum.

[Richard Lane]

John, does it again! I think your images look very good now, so if you are shooting targets you should be in good shape.[]


Now, see if you could use this information when focusing on real subjects and see if you're happy with the results, because the target is easier for the AF system to lock on to, so for real subjects make sure that you choose a focusing location with sufficient contrast and/or delineation, like the corner of someone's eye, or their chin which is approximately in the same plane as the eye.


Maybe, you could post some real world shots. Ones that you weren't happy and some new ones. If you could post the shots with the red focusing square visibly on them, that would be helpful.


Rich

[jake66]

I have the same lens on the same camera and also have the same focus problems as Alex.


A while ago I also tested mine on a flat surface and found the lens to be about spot on.


I think the problem is definately with the limitations of my Xsi's AF and not the lens. I find the same thing on my 70-200 f4 is. Some shots are focused perfectly and some are slightly front focused.


So I'm pretty sure John is right about your lens. (as usual)[]

[alex]

Yeah, it looks like John was right. Too bad he's on vacation and doesn't get to enjoy this. [:P]


So I sit here now, stumped. What is the source of my lack of sharpness?


I'm left with two options that I can think of:


1) Human error/inexperience/unreasonable expectations: I like to keep my ISO as low as possible, which for my camera means ISO100. With these settings, I rarely seem to be in situations where my Tv ends up being faster than 1/100, let alone 1/250 of a sec. It seems, with my camera, if I want fast shutter speeds, I have to be shooting in the middle of a bright, super sunny day. I typically don't do this, as most of my photography is landscapes so harsh light ain't good. Even with IS, maybe I'm just not steady enough to get sharp shots hand-held in these shutter speed conditions? Surprising if that would be the case, I'd think. I'm only 31. []


2) DOF limitations. It's entirely possible, I suppose, that in a lot of my shots, there is at least SOMETHING that's sharp somewhere in the frame. I'd have to check. Maybe I need to make more use of my DOF table in my camera bag.


The fact remains that the shots (landscapes) I can remember being most sharp are the ones I've used MF and LiveView for. I just wish I could get sharper shots handheld for shots of my boys, etc.


Welcome to the limitations of an entry-level DSLR, I guess. []


Thanks everyone,


alex

[jake66]

Don

[HDNitehawk]

Alex


When setting up the target make sure you are square with it, verticaly and horizontaly. The target should be level and the tape inverted at a slight angle. It looks as if you did do this but I couldn

[neuroanatomist]

Too bad he's on vacation and doesn't get to enjoy this.

Not quite yet - I leave on 2/17.


Depending on the scene and conditions, there's a third possibility - even if your camera is steady and your subject is within the DoF, your subject may be moving due to biology, wind, etc. If your subject is a pile of rocks, though, barring an earthquake it seems like the first two possibilities are more likely...


RE DoF and landscapes, if you're not already familiar with it, read up on hyperfocal distance.


--John

[alex]

This will definitely be an ongoing thing, I think. I appreciate everyone's responses, and I'll take it all in and let it stew for a bit.


I'm going to focus (pun intended) on loosening up a bit on ISO, paying a LOT more attention on where I'm focusing to utilize my particular camera's AF system, and in general just take more time setting up each shot, especially landscapes.


I am still considering sending it all in just to get checked. I mean really, why not?


If you want to look at some examples of some of my work, please just go to www.alex.shutterchance.com and navigate to the archive, go back to some shots from last September for some recent landscape stuff.


Thanks so much everyone!


alex