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I am unable to consistently obtain good focus on my t4i

ken_clunis
Contributor

I am unable to get consistently good sharp pictures with my t4i even though I use a tripod. It seems that the auto-focus area is too large and it picks up and focuses on an object in a different plane. Is there any way around this - other than using manual focus? An example might be a bird on a branch in a tree where a foreground branch is in focus but the bird is not. I revert to live view and zoom in to focus manually but by the time I do this, the bird hs flown away.

9 REPLIES 9

Skirball
Authority

Yes, use a single selection point to the autofocus instead of auto selection.  Your camera has 9 focus points, I think?  Those are the nine dots you see in the viewfinder.  There's a button on the upper left of the back panel, it has a checkerboard icon next to it, push that and then select the AF point you wish to use.

I am using the central point only but it too will sometimes select and adjacent area. For example, an eye brow instead of the pupil

ken_clunis
Contributor

Update on focus problems. I have done some resolution testing of my camera and lenses and found that I am expecting too much for the equipment. It is not a focus problem at all, rather it is poor resolution of the camera and lenses. I guess I am too picky and if I want better sharpness in my images, I will need to upgrade.

Thanks for your help.

Ken

Perhaps you're using poor lenses, but it’s not the camera.  The T4i has as good of resolution as you need.  With exception of some megapixel monster like the Nikon D800, you're not going to see a significant difference in the resolution unless you’re blowing these things up into huge prints. 

 

Either your technique needs work, or your expectations are out of the league of consumer (and lower level pro) setups.

I wouldn't call the Canon EF-S 18-135mm STM or the Canon EF-S 60mm Macro "poor" lenses, but used on my T4i, they just don't have the sharpness I require for large prints. Dpn't get me wrong. I think the T4i is a good camera in so far as an APS-C format is conccerned but it is not up to the task at hand: Large prints.

I don't relish the idea of upgrading to a larger camera e.g., Canon 6D, I just may have to in order to get what I need. Certainly cost and size is always an issue but I will probably talk myself into to doing so.

How large are you trying to print & how deep are you cropping? Is your tripod super stable & are you using a shutter release cable?

 

"A skill is developed through constant practice with a passion to improve, not bought."

I would like to do 24 x 36. Right now I am limited to 12 x 18.

Hardly any cropping. I compose in the viewfinder.

Tripod is super stable and HEAVY and yes remote release using any one of several ways - cable, rf link and IR. I also do tethered shooting - but only in the studio. I found that it is impractacle outdoors (weather, lighting, and etc.)

 

 

You're going to need to both switch to L series lenses & lower your expectations. Printing a full file image from an 18 mpixel sensor camera only allows somewhere around 140 DPI which won't hold much detail when viewed close up. You can print that big but you'll need to stand back to view it properly. 

 

"A skill is developed through constant practice with a passion to improve, not bought."

Due to the nature of light, there's are several factors that can limit the resolving power (e.g. the finest amount of detail that can be resolved -- for example being able to notice that two fine hairs next to each other don't just appear as a single bit of hair.)

 

One of those is called Dawes' Limit:  http://en.wikipedia.org/wiki/Dawes'_limit

 

Keep in mind that these are based on laws of physics and assume "perfect" optics (so it's not really a question of whether or not the optics are good enough.)

 

There are also diffraction limits but those rules come into play when you use very high f-stops (small aperture opening in the lens.)

 

A lens will tend the best performance with respect to resolving fine details at around 2 stops below wide open and very often this will be in the f/5.6 to f/8 range -- keep in mind this is a generalization.  The sweet spot will vary by lens model (and might even very by specific lens copy).  Even different focal lenghts in a zoom will yield different performance -- so there's usually a sweet spot there as well.

 

My favorite lens for APS-C bodies is the Canon EF-S 60mm f/2.8 Macro USM -- which provides phenominal detail resolving capability for a surprisingly low price.

 

Also it's good to keep the old addage in mind "If your pictures aren't good enough, you're not close enough."  When you want to see detail... get close!

 

Tim Campbell
5D III, 5D IV, 60Da
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