Focus issue w/ Rebel XTI & 85mm f1.2

t300 · Feb 11, 2013

Hi guys,

I'm definitely stumped on this issue that I've been noticing, but for the life of me, cannot figure out!

So, I've been shooting with an 85mm for the past two months for headshots and they've been super sharp and have been extremely happy with the results. However, what I have noticed is, when i shoot a full body of a subject, it tends to be fuzzy/not sharp.

I'm using a rebel XTI and AF (One Shot) with a EF 85mm f1.2L USM attached.

Image: http://i.imgur.com/jfvOl4q.jpg
Metadata: http://i.imgur.com/ialLsLG.png

I think the lens can produce sharp quality images, so I must be doing something incorrectly when it comes to focusing?

Anyone have an idea why this must be happening?

o hey tyler · Feb 11, 2013

Your shutter speed could be too slow. Your effective FoV is 136mm, and your shutter speed was 1/125. You can up the ISO to 200, or even 400, and make a faster shutter speed. You can also try shooting between f/2-3.2 as well which will allow more shutter speed leeway and may be sharper. I'm not sure when sharpness starts to fall off on an 85L, I don't have the lens, have no desire to, and haven't checked the MTF charts. Those are just my thoughts. Worth doing some experimenting before you rule out user error.

t300 · Feb 11, 2013

o hey tyler said:
Your shutter speed could be too slow. Your effective FoV is 136mm, and your shutter speed was 1/125. You can up the ISO to 200, or even 400, and make a faster shutter speed. You can also try shooting between f/2-3.2 as well which will allow more shutter speed leeway and may be sharper. I'm not sure when sharpness starts to fall off on an 85L, I don't have the lens, have no desire to, and haven't checked the MTF charts. Those are just my thoughts. Worth doing some experimenting before you rule out user error.

Hey Tyler, very observant! It could be that the shutter was a tad bit too slow, though do you think the f.stop had anything to do with it? What's the best way to take a full body portrait to be in complete focus, head to toe.

Do you think if I shot at 1/500 and f2, it would've been sharper? Or should the f.stop be even more closed? I try avoiding ISO 200/400 because of grain, especially since this is for print.

o hey tyler · Feb 11, 2013

t300 said:
o hey tyler said:

Your shutter speed could be too slow. Your effective FoV is 136mm, and your shutter speed was 1/125. You can up the ISO to 200, or even 400, and make a faster shutter speed. You can also try shooting between f/2-3.2 as well which will allow more shutter speed leeway and may be sharper. I'm not sure when sharpness starts to fall off on an 85L, I don't have the lens, have no desire to, and haven't checked the MTF charts. Those are just my thoughts. Worth doing some experimenting before you rule out user error.

Click to expand...

Hey Tyler, very observant! It could be that the shutter was a tad bit too slow, though do you think the f.stop had anything to do with it? What's the best way to take a full body portrait to be in complete focus, head to toe.

Do you think if I shot at 1/500 and f2, it would've been sharper? Or should the f.stop be even more closed? I try avoiding ISO 200/400 because of grain, especially since this is for print.

Being a Canon user myself, I'm pretty confident in the ability of your camera to make a usable image at ISO 400. Sure, you might need to use some noise reduction in post. But you can definitely make prints with it. Also, it depends on the size of the print (quite a lot).

I shoot all prime lenses, 35/1.4, 50/1.4, and 85/1.4. I pretty much stop down to f/2 and go from there. Varying between f/2 and f/3.2 generally. Or more, if I need additional DoF.

From photozone.de:

Looks like you'll have pretty good sharpness all the way up to f/8. The centers and borders are the only areas you need to be concerned with as you have an APS-C camera. It could be that your lens has front or back focusing issues, but I'd rule out user error prior to that.

t300 · Feb 11, 2013

Very interesting table! So, if i shot at 1/500 with a higher ISO, it shold've been able to produce a sharper image you think? Even if the f.stop was at 2 or 5.

I notice that all close-ups, and even medium shots can get extremely sharp and in-focus....but whenever i move further back to include the entire body, it isn't as sharp---maybe because it's trying to focus on the entire image? Should i be on AF-One Shot or AI?

o hey tyler · Feb 11, 2013

t300 said:
Very interesting table! So, if i shot at 1/500 with a higher ISO, it shold've been able to produce a sharper image you think? Even if the f.stop was at 2 or 5.

I notice that all close-ups, and even medium shots can get extremely sharp and in-focus....but whenever i move further back to include the entire body, it isn't as sharp---maybe because it's trying to focus on the entire image? Should i be on AF-One Shot or AI?

I use back button focus and only the center point on my 5D series cameras. I focus on the face or eyes and then recompose the shot. I also exclusively use AI servo. Back button focus allows you to independently control when your camera AFs even if you have your shutter half pressed. Having the ability to separately engage AF is important to me.

pixmedic · Feb 11, 2013

o hey tyler said:
t300 said:

Very interesting table! So, if i shot at 1/500 with a higher ISO, it shold've been able to produce a sharper image you think? Even if the f.stop was at 2 or 5.

I notice that all close-ups, and even medium shots can get extremely sharp and in-focus....but whenever i move further back to include the entire body, it isn't as sharp---maybe because it's trying to focus on the entire image? Should i be on AF-One Shot or AI?

Click to expand...

I use back button focus and only the center point on my 5D series cameras. I focus on the face or eyes and then recompose the shot. I also exclusively use AI servo. Back button focus allows you to independently control when your camera AFs even if you have your shutter half pressed. Having the ability to separately engage AF is important to me.

I shoot nikon, not canon...but I also use back button focus. i find it much easier to control the shot than by using the shutter release. when i have the camera on a tripod, I use a wireless trigger once im focused.

t300 · Feb 11, 2013

Back button focus is a good point, but unfortunately I don't have that feature on my XTI

Mach0 · Feb 11, 2013

t300 said:
Back button focus is a good point, but unfortunately I don't have that feature on my XTI

Program the AE/AF button

t300 · Feb 11, 2013

I also realized that I had my AF on automatic, so I just changed it to Manual so I can set the focal point much more precise. Hopefully this will help future shoots.