My lens is annoying me.

[Fiendish Astronaut]

This seems at first to be a similar thread to another one up here, but it isn't the same!

I bought a used 24mm 1.4f Canon lens from a shop and tested it out and it seemed fine. I bought it to take to concerts so I could use it in dark conditions and get good results. But on viewing my images it seemed that the in focus parts of my shots were a few inches in front of the points I focussed on. I found this was the case consistently in all my shots from this and in a subsequent concert.

Check out these examples. On both occassions I focussed on the subject's eyes, yet the sharpest parts of the image seem to be on the mic stand just in front.

http://bighugelabs.com/flickr/onblack.php?id=2902458877&size=large

http://bighugelabs.com/flickr/onblack.php?id=2935720790&size=large

As I said this seems to be consistent, so I don't believe it's due to the movement of the artist. Using a zoom at the same concerts I got many tack-sharp images of my subject's face.

Firstly, am I crazy? Secondly, doesn't auto focussing use th image through the glass to find the focussed part of the image so shouldn't this be impossible (lack of technical knowledge here so I may be wrong about this)? Thirdly, I've tested this at home, and the lens seems fine in my well-lit house - albeit perhaps not fiocussing to the same distance.

So yes it sounds like I'm being paranoid, but I'm getting a consistent series of images where the focussing is perfect on the mic stand but not on my subject's face! If this is a possible problem one can get with a prime lens, what is the best way of testing this?

Thanks in advance to anybody who can shed some light on this...

:x

 

[Moglex]

Can you try manual focusing?

It sounds as if your auto-focus is failing at low light levels with this particular lens. I doubt that it is the lens per se that is at fault.

 

[Battou]

Can you try manual focusing?

It sounds as if your auto-focus is failing at low light levels with this particular lens. I doubt that it is the lens per se that is at fault.

+1

Low light and AF is a bad combination even with current AF technology. try manual next time, I am willing to bet you will be much happier.

 

[chrisburke]

before i read other replies, i said to myself, "he needs to manual focus" its very hard to get a good auto focus in low lighting... plus with the movement of the musician, its very easy for him to movie very slightly and be out of focus.. also if you half press the button, get a focus, then for some reason let go of the button and hit it again, its going to AF on the forfront image, which is the mic stand... i do a lot of concert shots, and trust me, AF is NOT the way to go

 

[Fiendish Astronaut]

Thanks for your replies. Will start practising manual focussing more. But still wondering if the lens has a problem... why should my 1.4f L series prime perform less reliably than my 2.8f zoom?

 

[Battou]

Thanks for your replies. Will start practising manual focussing more. But still wondering if the lens has a problem... why should my 1.4f L series prime perform less reliably than my 2.8f zoom?

Take it out and shoot in in the daylight, you will see a marked difference in focusing accuracy, garenteed.

 

[table1349]

Just a guess based on the composition of the two photos posted and the nature of low light, wide open shooting.

http://visual-vacations.com/Photography/focus-recompose_sucks.htm

 

[Moglex]

But still wondering if the lens has a problem... why should my 1.4f L series prime perform less reliably than my 2.8f zoom?

I doubt there is anything wrong with the lens.

There are a couple of subtle differences that could account for the problem:

Are you using the prime wide open?
Are you using them at different focal lengths?

Either of these conditions will cause the auto-focus system to be presented with slightly different 'data' which could vary its operation.

 

[K_Pugh]

I have a Tamron 20mm-40mm F2.8 SP for Nikon with the same issue. Basically the focusing point is a little bit on front of where it should be. It's more noticeable on the D80 than the D200, i believe it the CAM system or something, i dunno.

I tend to use manual focusing on this lens most of the time unless i'm shooting F11 or higher (F8 on the D200).. it's also more obvious at the wider end of the lens than the longer end. It's a shame as when it's on auto focus the lens is really fast at doing so!

I feel you pain!

Oh and i've tried the lens on my old film SLR and it's fine at AF. I think it's just compatibility issues with new AF systems and some old lenses. I would have hoped that Canon lenses and Nikon lenses would be ok, being Tamron i sort of accepted it.

 

[Fiendish Astronaut]

Funnily enough I was at the Hard Rock Cafe in London for a gig tonight and we were so close to this tiny stage that I had this 24mm prime lens on my camera body waiting for Travis to come on to do their set. One of the other photographers had the same lens and started whining to me about exactly this issue! This time the lights were very bright, I had the aperture set down (I was able to shoot at about 300ISO - amazing at a concert!). Still, the same problem - not one sharp result in the parts of the image where I wanted to focus - even with the larger depth of field (should have upped the ISO to set an even smaller aperture). Switched to my zoom... all tack sharp!

It's all very well manually adjusting it, but really I couldn't see the difference through my viewfinder, especially as this is a wide lens and the part I'm focussing on is quite small in my viewfinder. Ah well, I'll have to accept this - I'm pretty sure it's definitely front focussing like K_Pugh's Tamron. Perhaps I'll have to learn to manually adjust my focussing as a matter of habit with a small turn after I auto focus - that'll only work with relatively still subjects though.

What a gyp. Cheers again for replies.

PS: Apparently Canon is planning to release out an updated version of the 24mm 1.4L. Could it be it's an issue they know about?

 

[tsaraleksi]

If it's an old lens you'll have to pay but you can have a lens calibrated by Canon.

 

[dEARlEADER]

i don't know canon products.... but some nikon bodies allow you to custom calilbrate a front/back focus issue on a particular lens.... check to see if you body allows this option....

 

[JerryPH]

Besides the issue of low light and your camera's autofocus potentially failing you a little, with a lens that can do F/1.4 or bigger apertures, it is almost ciritical that you focus properly, as it is normal to have a DOF that is razor thin.

I have the 85mm F/1.4 Nikkor and I can show you a picture where the DOF is under half a centimeter!

The first question I ask myself is... do I *really* need to take this shot wide open? Unless there is no other choice, I won't because besides the fact that my DOF will be so shallow, it is harder to hit a good focus AND any lens out there is not it's sharpest at wide open so my pushing it up a bit, I increase DOF and increase sharpness some more.

Oh, you could also have a lens that just basically front focuses. Have you tried the lens out in the day? Have you tried testing it out on a focus test chart?

Good luck and I hope its the autofocus and not your lens.

 

[Early]

http://bighugelabs.com/flickr/onblack.php?id=2902458877&size=large

http://bighugelabs.com/flickr/onblack.php?id=2935720790&size=large


:x

I keep looking and looking, and I don't see a problem, at least in the first photo. In the second photo I really can't decide, and would probably have to see it blown up.

I consider that one excellent lens, btw.

 

[Fiendish Astronaut]

Thanks everyone. The lens is not awful, just annoying. It's nowhere near as good as my 27-70mm. And the sharpest parts of the image seem to be in front of where I focus.

The reason I got this lens was so I could use it in dark venues (and these are often the small ones where I would be closer to the stage) so it's no good to me if it's perfect in the daytime - although obviously that is better than nothing.