AF out or user error

[ldasignup]

1. With a 50d, you only have one choice of focal length, so with your f2.8 fixed max aperture lens, use 55mm.

2. Here's an article I found interesting: http://www.slrgear.com/articles/focus/focus.htm
The gist of it seems to be that there is a LOT of variability in the AF system.

3. Do you use mirror-lock-up and the 10-second timer for less camera movement?

4. I'd suggest much more light (or flash?) to have a much higher shutter speed to minimize camera movement.

5. You can't necessarily depend on the super-imposed AF point really using the "Focus here" point for focus. The DataColor and LensAlign devices have a more prominent, contrasty target that is to the side of the ruler.

6. My practice with a 50d and 5dm2 was to take pictures of a target on a large brick wall, outside with tripod and square to the wall, with micro-focus-adjustment values of -20, -15, -10, -5, 0, +5, +10, +15, +20 and go from there. All my lenses ended up fine with MFA 0.

[Colin Southern]

Hi Lynne,

5. You can't necessarily depend on the super-imposed AF point really using the "Focus here" point for focus. The DataColor and LensAlign devices have a more prominent, contrasty target that is to the side of the ruler.

This is something that's quite often said, but in my experience they're usually pretty darn close. And thinking about it, why wouldn't they be ... they're part of the precision design of a camera and just one of many fine tolerances that shouldn't be particularly difficult to achieve.

6. My practice with a 50d and 5dm2 was to take pictures of a target on a large brick wall, outside with tripod and square to the wall, with micro-focus-adjustment values of -20, -15, -10, -5, 0, +5, +10, +15, +20 and go from there. All my lenses ended up fine with MFA 0.

+1 to that (no pun intended!). Anything less that +/- 5 steps is just too fine for me to see, but on top of that, folks need to appreciate that there are other variables such as differing focal lengths and AF performance that usually mean that any tiny advantage at one setting may well equate to a tiny disadvantage at another. My 1Dx now has the ability to specify corrections at both ends of a zoom range ... and I STILL concluded that it just wasn't worth the effort.

Might be a different story if the process could be automated, but I'm still yet to be convinced.

The irony is that many photographers will drive themselves nuts in this area -- and then completely forget about using an appropriate sharpening workflow that has a far bigger impact on image quality.

[Equilibrium8]

1. With a 50d, you only have one choice of focal length, so with your f2.8 fixed max aperture lens, use 55mm.

2. Here's an article I found interesting: http://www.slrgear.com/articles/focus/focus.htm
The gist of it seems to be that there is a LOT of variability in the AF system.

3. Do you use mirror-lock-up and the 10-second timer for less camera movement?

4. I'd suggest much more light (or flash?) to have a much higher shutter speed to minimize camera movement.

5. You can't necessarily depend on the super-imposed AF point really using the "Focus here" point for focus. The DataColor and LensAlign devices have a more prominent, contrasty target that is to the side of the ruler.

6. My practice with a 50d and 5dm2 was to take pictures of a target on a large brick wall, outside with tripod and square to the wall, with micro-focus-adjustment values of -20, -15, -10, -5, 0, +5, +10, +15, +20 and go from there. All my lenses ended up fine with MFA 0.

Thanks Lynn. I'll try wrap my head around that article.
3. I didn't use any mirror lock-up or timer. Just tripod as I was trying to recreate the focus errors I been getting in real shoots.
4. Same as above (trying to use low-light scenario for focusing), but I probably didn't think this through. Does low-light have any effect on how well it focuses? Or would the lens either focus lock or not?
5. I wanted to try the other charts today, but forgot to get them printed. I'll do it tomorrow.

[Equilibrium8]

One thing that might help find examples of photos; Does LR have a function to show the focus point? I assumed it would because DPP has it. I think I have examples of what I mean from real world shoots, but I need to be sure the focus did lock where I think it did, else it is irrelevant.

[Colin Southern]

Does low-light have any effect on how well it focuses? Or would the lens either focus lock or not?

Usually it'll just struggle to lock focus, but it's also very possibly for it to just plain old "get it wrong".

I remember one glorious sunrise that I'd driven 1/2 hour in the night to get to ... camera was struggling to focus, so once I got confirmation I switched the lens to MF and didn't touch it ... and proceeded to take dozens of out of focus shots. Doh!

[Equilibrium8]

Usually it'll just struggle to lock focus, but it's also very possibly for it to just plain old "get it wrong".

I remember one glorious sunrise that I'd driven 1/2 hour in the night to get to ... camera was struggling to focus, so once I got confirmation I switched the lens to MF and didn't touch it ... and proceeded to take dozens of out of focus shots. Doh!

That becomes a problem with back-button focusing too. Once I think it is in focus, I just leave it and shoot... only to see later that nothing was well-focused.

[Colin Southern]

That becomes a problem with back-button focusing too. Once I think it is in focus, I just leave it and shoot... only to see later that nothing was well-focused.

You should still be getting (occasional?) focus confirmation lights though.

I normally use a 6x D Cell torch as a "focus assist light) if the subject isn't too far away - and for far away subject (especially with pin light sources) then live view often works well. If all else fails - and it's low-light landscape, I just use my torch to see the distance scale on the lens!

[jcuknz]

Thanks Grahame. One of the links above mentioned using Live View, too. It seems Live View uses contrast detection AF and not the phase detect normally used.

I took my camera out to the front gate some time ago at 11pm and was suprised and greatly gratified at how my Contrast Detection AF system worked by the street lights ....I had a hard job finding patches of contrast-less to stop it snapping into focus

"I never expect a photo to be sharp ... that is what I have an editor for." Anon.

[Equilibrium8]

You should still be getting (occasional?) focus confirmation lights though.

I normally use a 6x D Cell torch as a "focus assist light) if the subject isn't too far away - and for far away subject (especially with pin light sources) then live view often works well. If all else fails - and it's low-light landscape, I just use my torch to see the distance scale on the lens!

Sure, the confirmation light comes on when it locks (I haven't paid attention if it changes after that).

I think I will do the same. The AF assist lights on Yongnuo flashes are bad. I just got a YN160 video light which may work well, but more inconvenient than a flashlight.

[Equilibrium8]

I tried the other test method. Using various combinations of Liveview, Manual, and Manual focus,, they all looked about the same.
[IMG][/IMG]

1/200 sec at f 2.837 mm37 mm ISO 10

Here is one example I found of the focus errors I mean. This was focused on eye. Overexposed, but I can't find any others now.

[IMG][/IMG]