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DPChallenge Forums >> Individual Photograph Discussion >> Backfocus? Ahh!
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09/04/2006 05:11:42 PM · #1
I just spent a lot of money on a new lens. Its been a while since I've bought a lens or anything like that, and I was never too critical of them before, but I figure if I'm going to be spending 1k+ on a lens it should work perfectly. The lens actually seems great, except that when I try and focus close it looks like the focusing is off...even at f/8...sigh. Here's the picture, let me know what you think! Should I send it in for calibration or try and exchange it?

This WAS focused, the focus lock beeped at me and everything. The red dot was where it was focused.

f/8
ISO 200
1/320s
09/04/2006 05:33:22 PM · #2
What lens is it? I would call them and see if they'll calibrate it to your camera for free, but on the other hand that means being without a camera for however long they decide to keep it, and if your luck is like theSaj's, that'll be months on end and you'll get it back in worse condition.
09/04/2006 05:56:16 PM · #3
Originally posted by MadMan2k:

What lens is it? I would call them and see if they'll calibrate it to your camera for free, but on the other hand that means being without a camera for however long they decide to keep it, and if your luck is like theSaj's, that'll be months on end and you'll get it back in worse condition.


Thats what I was afraid of as far as sending it away. Its the 24-105 f/4L. I got a local store to match the online price at B&H although it was still more with tax. I'm thinking now I might just go back and try out the rest of their lenses they had in stock before I send anything out.

Edit: Since its got a year warranty I suppose I could also just live with it until I go on break from school in november. I doubt I'll be using it much at the closest focusing distance so it shouldn't be TOO much of a problem...

Message edited by author 2006-09-04 17:58:45.
09/04/2006 06:05:02 PM · #4
It seems that there is no focus problem to me. Between 5 and 6 where you see 14 is where you focused. I think if you take the test shot directly above it would make a lot easier to see. Your test shot is taken from diagonal. I think 5 and 6 are not as sharp in your image due to the shallow depth of field.
09/04/2006 06:09:49 PM · #5
Originally posted by pinbokeshatta:

It seems that there is no focus problem to me. Between 5 and 6 where you see 14 is where you focused. I think if you take the test shot directly above it would make a lot easier to see. Your test shot is taken from diagonal. I think 5 and 6 are not as sharp in your image due to the shallow depth of field.


See thats the problem...the Red Dot is where I focused, not between 5 and 6, and the red dot is a good ways in front of where the actual focus point is.

Also, if I took this shot from straight above then the whole plane of the ruler would be in focus. This needs to be done at an angle to show where the focus plane actually falls.
09/04/2006 06:33:41 PM · #6

Here is a shot using 17-40 f8.0 1/30.

I focused at the long line near 3. I got the same effect.
09/04/2006 06:38:44 PM · #7
Never understood these threads. If you think it backfocuses, send it in for repair. It's impossible for 'the public' to validate your results as, without shooting with the lense ourselves, it is equally as likely that your hand moved the camera up a hair as the lense focused incorrectly.
09/04/2006 06:51:34 PM · #8
Originally posted by routerguy666:

Never understood these threads. If you think it backfocuses, send it in for repair. It's impossible for 'the public' to validate your results as, without shooting with the lense ourselves, it is equally as likely that your hand moved the camera up a hair as the lense focused incorrectly.


But if it's normal behavior I'd like to know that. I could do the same test on a tripod and get the same result, becasue I can guarantee you that my hand didn't move a half inch in the milisecond it look between the focus lock and the shot being taken.
09/04/2006 07:03:53 PM · #9
Originally posted by routerguy666:

Never understood these threads. If you think it backfocuses, send it in for repair. It's impossible for 'the public' to validate your results as, without shooting with the lense ourselves, it is equally as likely that your hand moved the camera up a hair as the lense focused incorrectly.


I perfectly understand these threads.

Some people feel that just thinking it backfocuses is not enough to send it in for a repair. Maybe you have lots of back up lenses and you don't mind missing a lens for a few weeks, but if I got a new lens and I have to ship it back for a repair, I want to make sure that there is no mistake.

A lot could go wrong in shipment. If it's not broke, don't fix it.
09/04/2006 07:10:19 PM · #10
Originally posted by bfox2:

Originally posted by routerguy666:

Never understood these threads. If you think it backfocuses, send it in for repair. It's impossible for 'the public' to validate your results as, without shooting with the lense ourselves, it is equally as likely that your hand moved the camera up a hair as the lense focused incorrectly.


But if it's normal behavior I'd like to know that. I could do the same test on a tripod and get the same result, becasue I can guarantee you that my hand didn't move a half inch in the milisecond it look between the focus lock and the shot being taken.


Ok then. No, it's not normal behavior for you to focus at one point and have a point half an inch up from there actually be the focus point.
09/04/2006 08:14:53 PM · #11
Originally posted by bfox2:

Originally posted by pinbokeshatta:

It seems that there is no focus problem to me. Between 5 and 6 where you see 14 is where you focused. I think if you take the test shot directly above it would make a lot easier to see. Your test shot is taken from diagonal. I think 5 and 6 are not as sharp in your image due to the shallow depth of field.


See thats the problem...the Red Dot is where I focused, not between 5 and 6, and the red dot is a good ways in front of where the actual focus point is.

Also, if I took this shot from straight above then the whole plane of the ruler would be in focus. This needs to be done at an angle to show where the focus plane actually falls.


On the contrary, if your lens really has a focus issue, the whole plane of the ruler would be out of focus. I think it would be a good diagnostic test for you to photograph the ruler or something straight on. If it comes out sharp, then it's focusing correctly.
09/04/2006 08:43:48 PM · #12
Originally posted by jpeters:

focus issue, the whole plane of the ruler would be out of focus. I think it would be a good diagnostic test for you to photograph the ruler or something straight on. If it comes out sharp, then it's focusing correctly.


Ok, so thats good. When I shoot the ruler straight on it comes out well focused which is a plus. Its just shooting it on an angle which gives a 'focus bias' (for lack of a better term) behind the actual AF point. I still feel like it should be more accurate than that though for the price.

Either way I'm just going to call the store in a day or two when I've got time and see what they say.
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