Focusing Issues with EF 50mm f/1.8 II

[Juga]

Hello all. I have a Canon T4i and recently bought a EF 50mm f/1.8 II because it is cheap! However I have had extreme issues with its AF so I switched to MF. When I use MF it appears to be focused in the viewfinder but when I go back to review my photos all of them look out of focus. I am wondering if this is a common issue with this lens or is it because I am a noob. Please advise!

 

[Overread]

Could you show us a few example photos? Detail clearly the method you used to get the photo as well as the aperture, shutter speed and ISO that you used. There could be a variety of issues which you're experiencing so the more details and examples you can provide the better we can work out what the problem is.

As a very basic comment the lens itself shouldn't have any problems delivering a sharp shot, it might be a cheap lens but that is mostly because its a massmarketed product and also a very common and simple (and yet effective) design.

 

[texkam]

Make sure your diopter is adjusted correctly.

 

[Juga]

Could you show us a few example photos? Detail clearly the method you used to get the photo as well as the aperture, shutter speed and ISO that you used. There could be a variety of issues which you're experiencing so the more details and examples you can provide the better we can work out what the problem is.

As a very basic comment the lens itself shouldn't have any problems delivering a sharp shot, it might be a cheap lens but that is mostly because its a massmarketed product and also a very common and simple (and yet effective) design.

I will certainly do that tomorrow as I don't have access to my photos right now. I know the lens is capable which is why I purchased it...maybe an adjustment period to go use to it I guess. Either way I will post some stuff tomorrow with details.

Make sure your diopter is adjusted correctly.

Did this prior to my post and didn't seem to make a difference.

 

[TCampbell]

One of these days I suppose one of us should make a video on focusing.

1) If you use the lens wide-open then focusing is tough. The depth of field can become paper-thin. At that point, it's very critical that you make sure the focus point in your camera is directly on the critical focus point for your subject AND it's also critical that once the camera locks focus, neither you NOR your subject move.... at all.

Imagine you've got this paper-thin depth of field (and I'm not kidding when I say "paper" thin. Somewhere in my library I have a photo of a coin where the face of the coin is "sharp" and the desk that the coin is resting on is actually blurry... so the depth of field literally is so narrow that the thickness of a coin makes that much of a difference.)

The question is... once you lock focus, do you suppose it's possible that either you or your subject could have moved or swayed by so much as thickness of a coin?

Granted the coin was at very close focusing distance (which makes depth of field extra thin) but my point is to reinforce that the camera normally "locks" focus and then shuts off the focus system until you take the shot. Any movement between the time the camera locks focus and the time you take the shot will make the image go soft.

2) Make sure you understand HOW the focus system works. On your T4i, if you allow the camera to auto-select the focus point of the 9 points available, the camera will ALWAYS lock focus on whichever of those 9 points is CLOSEST to the camera. If you don't want it to do that, then it's up to you to put the focus system into manual point selection mode and YOU pick the focus point. Be very careful that the focus point is on the specific spot you care most about.

3) Most lenses do their best work about 2 stops down from wide-open. Wide open is seldom the best for focus.

4) Contrast-detect auto-focus (in "live view" mode) is always theoretically better (if you can guarantee it's focusing on the point you care about), but it's also much slower than phase-detect mode (the mode you use when shooting using the viewfinder.) If you suspect your lens or camera are misbehaving... switch to live view and see if it changes your results.

5) Use the Canon DPP (digital photo professional) application that they gave you on the disk that came with the camera. It has a mode which overlays the auto-focus points so you can visible see where in the photo the camera locked focus (but if you use the "focus and recompose" method then it wont be accurate. It really shows you which focus point you used... and assuming the camera didn't recompose then that focus point will still be over the point where it locked focus.)

 

[Juga]

One of these days I suppose one of us should make a video on focusing.

1) If you use the lens wide-open then focusing is tough. The depth of field can become paper-thin. At that point, it's very critical that you make sure the focus point in your camera is directly on the critical focus point for your subject AND it's also critical that once the camera locks focus, neither you NOR your subject move.... at all.

Imagine you've got this paper-thin depth of field (and I'm not kidding when I say "paper" thin. Somewhere in my library I have a photo of a coin where the face of the coin is "sharp" and the desk that the coin is resting on is actually blurry... so the depth of field literally is so narrow that the thickness of a coin makes that much of a difference.)

The question is... once you lock focus, do you suppose it's possible that either you or your subject could have moved or swayed by so much as thickness of a coin?

Granted the coin was at very close focusing distance (which makes depth of field extra thin) but my point is to reinforce that the camera normally "locks" focus and then shuts off the focus system until you take the shot. Any movement between the time the camera locks focus and the time you take the shot will make the image go soft.

2) Make sure you understand HOW the focus system works. On your T4i, if you allow the camera to auto-select the focus point of the 9 points available, the camera will ALWAYS lock focus on whichever of those 9 points is CLOSEST to the camera. If you don't want it to do that, then it's up to you to put the focus system into manual point selection mode and YOU pick the focus point. Be very careful that the focus point is on the specific spot you care most about.

3) Most lenses do their best work about 2 stops down from wide-open. Wide open is seldom the best for focus.

4) Contrast-detect auto-focus (in "live view" mode) is always theoretically better (if you can guarantee it's focusing on the point you care about), but it's also much slower than phase-detect mode (the mode you use when shooting using the viewfinder.) If you suspect your lens or camera are misbehaving... switch to live view and see if it changes your results.

5) Use the Canon DPP (digital photo professional) application that they gave you on the disk that came with the camera. It has a mode which overlays the auto-focus points so you can visible see where in the photo the camera locked focus (but if you use the "focus and recompose" method then it wont be accurate. It really shows you which focus point you used... and assuming the camera didn't recompose then that focus point will still be over the point where it locked focus.)

Thanks Tim. I don't use it wide open but the part of my DOF being 'paper thin' makes a lot of sense. I knew about the AF system in the T4i because I have read extensively before purchasing it but I felt confident in my ability to use MF. Do you think Al-Servo would help given that I choose my focus point?

 

[TCampbell]

Thanks Tim. I don't use it wide open but the part of my DOF being 'paper thin' makes a lot of sense. I knew about the AF system in the T4i because I have read extensively before purchasing it but I felt confident in my ability to use MF. Do you think Al-Servo would help given that I choose my focus point?

AI Servo should only be used if you know the subject distance is changing. Canon did a 3-part video on the subtle nuances of the autofocus system (done at B&H Photo). They explain that if you KNOW your subject is stationary, some nuances of the AI Servo mode can cause the camera to be fooled into moving to a different focus distance and, if you take the photo at that moment, then you'll get a soft image. They recommend you use "One Shot" when you know the subject is stationary and "AI Servo" when you know the subject focus distance is changing.

A Look at The Canon Autofocus System Part 1
A Look at The Canon Autofocus System Part 2
A Look at The Canon Autofocus System Part 3

(each part is approximately 30 minutes long ... but well worth it for the value of info you'll learn).

 

[subscuck]

What is your shutter speed? If no part of the photo is in focus, you may be using too slow of a shutter speed. If that's the case, it's not an issue of focus, but rather an issue of camera shake. Rule of thumb is minimum shutter speed should be 1/focal length, so 1/50th would be the minimum for hand held. Anything slower would require a tripod.

 

[OLaA]

Manually focusing with newer lenses can be tricky. I shoot with some vintage lenses which make it easier and am still desperately looking for a split prism focus screen for more precision. Just as a test i would shoot in live view on a tripod using the zoom feature and manual focus. That way you can rule out user error.

 

[TCampbell]

What is your shutter speed? If no part of the photo is in focus, you may be using too slow of a shutter speed. If that's the case, it's not an issue of focus, but rather an issue of camera shake. Rule of thumb is minimum shutter speed should be 1/focal length, so 1/50th would be the minimum for hand held. Anything slower would require a tripod.

That was the rule for 35mm (and also "full frame" digital images). With a crop-frame APS-C sensor ... you multiply that by the crop factor (1.6 for Canon and 1.5 for Nikon and most others.) So for a 50mm lens you'd want a shutter speed of 1/75th to 1/80th. Also... this assumes the photographer knows how to brace the camera steady and is actually TRYING to be still. Elbows below your camera and tucked in to rest on your chest/stomach. OR... body turned sideways (like a baseball player at bat) with the camera resting on one shoulder.

When you're at minimum shutter speeds... cheat. Find anything you can to brace the camera steady... lean on a tree, rest it on a fence, whatever you can find.

 

[Juga]

You gotta love it when a plan comes together.

I have kids...what is a plan?

What is your shutter speed? If no part of the photo is in focus, you may be using too slow of a shutter speed. If that's the case, it's not an issue of focus, but rather an issue of camera shake. Rule of thumb is minimum shutter speed should be 1/focal length, so 1/50th would be the minimum for hand held. Anything slower would require a tripod.

Negative ghost rider. I definitely pay attention to my shutter speed if I am handheld but thanks for the knowledge on shutter speed.

Manually focusing with newer lenses can be tricky. I shoot with some vintage lenses which make it easier and am still desperately looking for a split prism focus screen for more precision. Just as a test i would shoot in live view on a tripod using the zoom feature and manual focus. That way you can rule out user error.

Interesting...I will have to try that.

After reading what Tim wrote I am pretty sure it is my DOF being shallow but I will keep in mind all advice given since I am noob-tastic!

 

[cynicaster]

I can almost guarantee it’s a DoF issue and not a faulty product. I say this because I went through the exact same thing. I read up on the internet about how the nifty-fifty is such a great value, is sharper than the kit lens, blah blah blah. So I bought one and eagerly headed out to a family BBQ to take some photos with my new toy. I brought them home and was appalled at how NOT sharp the photos of my niece looked on my big computer monitor.

This went on for a while, I searched the internet to see if focusing issues were common with this lens, etc. Then, I sat down with a DoF calculator and ran some numbers, and learned that the photos I was taking of my niece at 3-4 feet away with wide open aperture were giving me a whopping ~1” of depth of field. And that’s the whole depth, never mind the fact that some of it can get wasted depending on where you focus. This means that focusing on my niece’s nose would leave her eyes in soft focus. That was very enlightening, and now, these days, my results with that lens have improved greatly, although I’m still learning.

When dealing with such narrow DoF, you’re never going to nail it consistently doing it manually, unless you’re a robot or something.

Another thing worth mentioning is that the nifty-fifty is fairly soft at wide open even if the focus is perfect—that’s part of the experience of using a $100 lens. It sharpens up quickly, though, as you stop it down.