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09/29/2007 07:22:29 PM · #1 |
Hi,
I seem to be having issues with nailing my focus. This is especially evident in low light, but also at other times. I don't know if my expectations are too high, but the average picture I take seems to have just that bit of blur to it. I've tried my lens on a 30D & it focuses sharp, so the lens does not seem to be the culprit.
I have been thinking of upgrading to an XTi after a bit, but I am now beginning to wonder if I might need a higher jump than that (eg. 40D) to nail the focus consistently (I'm into candid portraits)
Anyone have thoughts on this, and whether the XT should have as much of a problem here as I find it does?
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09/30/2007 12:29:16 AM · #2 |
Test the camera and lens in good light conditions and see if you can make it give you bad focus. There are many issues that can cause focus problems, including low light and trying to focus inside the minimum focus distance for your lens.
You haven't really provided enough information or examples to make any real conclusions on the source of your problem.
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09/30/2007 12:46:07 AM · #3 |
| Check the in-camera processing settings. There is a menu setup that prescribes the amount of in-camera sharpening that is performed. All DSLRs use a different amount of in-camera sharpening by default. Recently I have had the opportunity to play with an XT, an XTi, and my new 40D. All produce different results with my same set of lenses. I had the XT in-camera sharping turned up a little. I never could find this setting on the XTi and it produced much softer results than the XT. The 40D default settings are more sharp than either of the other two. Typically folks that are new to DSLRs expect resulting photos to be very sharp and I believe the defualt values are just that - default - allowing more final processing freedom for the photographer. |
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10/01/2007 09:53:41 AM · #4 |
Thanks for your replies--it's one of those issues I need to get to the bottom of as I'd hate to be taking pictures for others and have a technical failure like this.
I'll do some testing later in different strengths of light & apply the same sharpening amounts in camera & I'll post back later |
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10/01/2007 10:12:53 AM · #5 |
For what it's worth I've recently acquired a Sigma 10-20mm lens for my 350D and at 10mm it seems to misfocus badly (often a long way short of the correct focus) as measured by the distance scale (something at "infinity" causes it to focus at about 0.7m) and results (much sharper results if I manually focus to infinity, or autofocus at 20mm). I've experienced similar with my 17-55mm so I don't think it's the lens, and after performing brief tests with the same lens on a friend's 40D (sadly I was indoors so limited choice of subjects) it appears that it's the camera at fault.
The camera can nail focus with other lenses (e.g. the 60mm macro and 70-200) so it's not that it can't focus at all, it just seems to not cope with the wide-angle end of shortish zooms.
Given the general improvement on offer with a 40D I am tempted to upgrade. I can then either try and get the 350D fixed at my leisure or live with it as it is.
Just posting this in case it's similar to your experiences...
splidge
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10/01/2007 11:04:28 AM · #6 |
The Canons focus based primarily on contrast. In order for there to be contrast, there must be a combination of light and detail at the point in which focusing is being attempted. The ultra-wide lenses make it very difficult for the camera to find detail at the selected focus point sometimes.
As you move up the scale towards the pro bodies, the focusing system gets much more precise and sensitive, so that's what you're seeing with the 40D; it's simply BETTER at focusing.
I keep AF switch in the OFF position on my 10-22 and manually focus; it's very easy since DOF is huge anyway.
R.
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10/01/2007 11:32:45 AM · #7 |
Originally posted by Bear_Music:
The Canons focus based primarily on contrast. In order for there to be contrast, there must be a combination of light and detail at the point in which focusing is being attempted. The ultra-wide lenses make it very difficult for the camera to find detail at the selected focus point sometimes.
As you move up the scale towards the pro bodies, the focusing system gets much more precise and sensitive, so that's what you're seeing with the 40D; it's simply BETTER at focusing.
I keep AF switch in the OFF position on my 10-22 and manually focus; it's very easy since DOF is huge anyway.
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Thanks for replying, you've probably explained my problem.
But then, for every test I've done I've been sure that there is a big contrast for it to pick up on (and always using the centre point), and it's never been at all hesitant in focussing, it just gets it wrong - and if you focus at 20mm, zoom back to 10mm and focus again it unerringly moves the focus from the (almost) correct place to a worse one.
On the AF/MF front I don't bother with the AF switches on most of my lenses - I use a dedicated AF button and if I want to manually focus I don't press the button (this puts USM/HSM pretty high up my wishlist on lenses!). On the 350D this costs AE lock but then I never use that anyway (Manual mode makes a pretty good exposure lock). But having said that, I find it very hard to focus the 10-20 through the 350D's viewfinder; I actually can't see much difference between the in-focus and out-of-focus shots through the viewfinder (but the difference definitely shows in the files). Although as you say the DOF is large so I can just guess on the distance scale (and that is what I have been doing, but it's annoying).
As you say the 40D would be a huge upgrade in general AF performance anyway given that the 350D's is worse than the 20D/30D - so I'll see an improvement regardless of whether my 350D is broken or just poor. There's cashback in the UK starting today I think so it could be the time to buy... ;).
splidge
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10/01/2007 06:58:01 PM · #8 |
Wierd--and I hate this feeling:
I can't find a huge difference in focus between the 20D & my Rebel XT.
I printed off a sheet of text and set it 10 feet away, aligned both diagonally and horizontally, lowered the light so I was on ISO 400, 1/60 @ f.4.0, and shot away on 105mm IS. Sometimes the Rebel would search more for focus lock, but once it obtained it, the results were comparable.
And yet there's got to be a reason it performed so badly on Saturday. Maybe it's my technique :-(
Is there anything more to do technique-wise for candids than gaining focus lock on a high-contrast feature of the face (eg. eye or corner of the mouth), then re-composing?
I'll re-post if I discover any more on these bodies... |
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10/01/2007 07:09:56 PM · #9 |
Originally posted by Medoomi:
Is there anything more to do technique-wise for candids than gaining focus lock on a high-contrast feature of the face (eg. eye or corner of the mouth), then re-composing? |
Well, that depends on how much you are re-composing.
See //visual-vacations.com/Photography/focus-recompose_sucks.htm.
splidge
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10/02/2007 11:58:18 AM · #10 |
Originally posted by Medoomi:
Is there anything more to do technique-wise for candids than gaining focus lock on a high-contrast feature of the face (eg. eye or corner of the mouth), then re-composing? |
Yeah... It's called "manual focus" and it works like a charm.
R.
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