Focus on the 75-300mm - user error?

[Persephone]

Thsi really is puzzling me. Sometimes, my 75-300mm will not focus right...

http://img.photobucket.com/albums/v32/hbdragon88/focus_cropped.jpg

That's a 100% crop of an image I took tonight. I was using the 20D with the 75-300mm, One Shot, 1600 ISO, f/5 at 1/60. I was standing about 20 feet away (across a pond) and had my 420EX aimed at 90 degrees. It's subtle, but she's not in focus. I'm not 100% sure but I believe i used center point focusing, aligned it with her face, and I heard the beep to indicate that focus was attained.

I shot in JPEG with contrast, sharpness, saturation, and color tone all slid over one bar ot the left.

Thsi just wasn't one image - most images have the soft quality to them, nothing strikes out as really sharp.

I was wondering - did I do something wrong? I'm inclined to think I was, but, I can't just figure it out.

I can post more pictures on request.

[John_B]

hbdragon88,
It looks like the lens/camera front focused. However you aren't 100% sure you used the center focus point which could explain it. Its also possible the camera moved between focus and capture and the shutter speed was a bit slow for hand held telephoto photo with lens at 140mm on a 1.6 sensor 20D

Try this: put your camera on a tripod or sturdy flat surface and find a non moving subject ex. brick wall and let the camera AF with the flash and then take a photo without moving the camera. If the test photo comes up sharp then it probably was user error.

I also have the EF 75-300 f/4-5.6 III USM lens and don't have focus problems with mine...

Good Luck :)

[Persephone]

I said I wasn't 100% sure, because I was using the joystick to move AF points during the event. I'm 99% sure that it was center point for all the stage pictures.

Is 1/60 really too slow for handheld flash photography? It didn't appear to have motion blur on it and I was holding the camera fairly still. Does the AF have trouble focusing over a much greater distance?

I looked through more of my photography and here's a prime example. Shots were taken one right after another, after the people got into a group. Here it is, presumably front-focusing. I 100% cropped the same lady again. Image shot at 75mm. The whole picture is OOF - I can post the whole thing, but it's pretty clearly blurry on every subject, which means that focus was not attained at all.

http://img.photobucket.com/albums/v32/hbdragon88/75300_2.jpg

I switched to the 18-55mm right away and it's sharp as a tack.

http://img.photobucket.com/albums/v32/hbdragon88/1855focus.jpg

Before I switched to the 75-300mm, I tried to use the 18-55mm. Again, center point focus, focused on the lady on the podium, not in focus at all. How does this picture fit in with the scheme of things?

http://img.photobucket.com/albums/v32/hbdragon88/1855focus_2.jpg

[John_B]

hbdragon88,
Well its not uncommon for a photo using an 18mm lens shot at 1/60th sec to be sharper then a similar photo with same shutter speed at 75mm when hand held, or in your last case 55mm (which looked way under exposed). In the first photo you shot with the 75-300 lens wide open which also gives very little DOF (depth of field).

A standard rule for hand held photos is for the shutter speed to match the focal length on a 35mm camera ex. 1/50th (or faster) for a 50mm lens. However when using a 1.6 sensor like on your 20D you need to times the lens mm number by 1.6 ex2. 1/80th for a 50mm lens on your 20D (focal length x 1.6 = shutter speed). However it really depends on the person holding the camera. Then you have moving subjects (yes us humans even when staying still move, we do have to breath etc...) which can contribute to getting a sharp photo.

How long have you had the lens? ??? Is this the first time you noticed it not focusing correctly? ???

Like I said before try to test your lens on a tripod, if you get sharper results then your shutter speed was too slow.

[Persephone]

I've had it since June. I believe this is the first instance where I've ever pushed it this far - a nighttime event. Never had to take the diffuser off. Never had to point it at 90 degrees (in some shots I can see the light hitting their eyes, tha'ts how much power was behind the flash) just to properly expose it. It's also the first time I've had to shoot this far away with the telephoto lens.

The shutter speed explanation makes sense. That means I should have shot it at 1/250th of a second to get it sharp (if the problem was solely related to handheld motion). But doesn't flash negate the need for speed - somewhat? And I don't know if I could have shot any faster especially given the distance away I was from the stage.

EDIT: http://img.photobucket.com/albums/v32/hbdragon88/75300_3.jpg

I did take a tripod-like shot early on. I kept getting significant motion blur, so I balanced the gripped 20D on the bridge with the 75-300mm and fired. Center focus point on her head - she doesn't look exceptionally sharp. DOF calculator - if she was 20 feet away, 1.42 feet would be in focus.