Back Focus in the 50mm 1.2 and how to correct technique in order to prevent it

[theleestudio]

So I have a Canon 50mm 1.2 paired with a 7D. I got it recently calibrated and clean, and it produces wonderful images. Except. sometimes in low light, at 1.2, it bugs out on me and back focuses terribly. Maybe 1/4 shots are good. I know that the DOF is shallow, but I was wondering if someone could explain to me how shallow exactly is it in layman’s terms.

I’ve been utilizing back button focus in order to be able to recompose my shots, but apparently with f/1.2 it’s not wise to move even just a little, or the subject will be out of focus.

[cameraclicker]

Focal length, aperture and distance to subject all affect depth of field.  We know from your post the focal length is 50 mm and aperture is f/1.2.  At 10 feet, depth of field is .86 feet or just over 10 inches.  At 5 feet, depth of field is .21 feet or just over 2 1/2 inches.  I suppose the good news is your 7D has an APS-C sensor so you are apt to be further away from your subject than if you had a full frame body.

Time to get out your tripod and tape measure.  Mount the camera a couple of feet from the floor, level.  Stretch out the tape measure in front of it.  Stand a book beside the tape measure to act as a target.  Set the aperture to f/1.2.  Take shots focusing on the book as you move the book from a couple of feet from the camera, a foot at a time, to about fifteen feet.  Look at the tape measure in your photos, to see the depth of field.  Let us know what you discover.

 

[soaringturkeys]

Hmm technically i don’t know in mms. But I do know that by 1.4. If you are shooting someone’s face. Then only their nose would be in focus and their eyes would be out.

I imagine 1.2 would be worse with Close Ups.

[fstopper89]

The lowest I own is a 35 f/2.0. I feel I get my best images when I’m a few feet away (for a single person, so that their facial features are all sharp) and at the same time get a nice soft background blur. But for something I want more a “macro” of (it’s not truly a macro lens, but I can get quite close and isolate other objects in the image) I generally move in much closer. My friend has a 50 1.8 and she can get such nice portraits of multiple people (with being a bit further away in distance) yet still achieve the shallow DOF. Previously I was shooting on a crop-sensor (Rebel T2i and 40D) but recently got a 5D Mark II, so it’s now a true wide-angle on the full frame (my 35mm) which at the same time, renders it a bit less accurate for portraits as it distorts close-ups a bit.

f/1.2 would be a challenge to shoot with I think, though I bet when you nail it you can get amazing shots.

[reality check]

Every lens has a sweet spot.  Sweet spots are never found wide open.

Example: my fastest lens ( not lowest, like PP refers to it) is a 50mm 1.4. The sweet spot is at 2.8  any wider and it just isn’t going to be tack sharp.

There is a lot more to depth of field than aperture.  Time to google and brush up on some basics.  Good luck

oh and camera clickers exercise is a good one, be sure to give it a try.

also you can find your lens sweet spot by shooting in AV setting up a tripod to eliminate factors such as camera shake. And shooting an object  at all stops and comparing.

[stef]

The 7D isn’t great at low light focusing and even if it says it locks focus, it might not be in focus. You have only a sliver of DOF at the minimum focus distance of 1.5 feet (like a millimeter!), so focus/recompose is a bad plan way up close. At a more reasonable distance like 5 feet, it’s around an inch.

Toss a flash on the top and set it to only do focus assist, but not to flash. That will really help you focus in low light. Use sub-point focus (the focus box that’s filled in with a spot) and instead of recomposing, use the joystick to move the point where you want in focus or as close as you can get.

If you can’t use a flash with focus assist, you’ll have to use one the vertical center focal spots and recompose. Turn the camera and move your head with the back of the camera. Don’t just turn your head with the camera attached.

The 7D built-in flash can be set to assist, too, but it’s kind of blinding.

You can also use live view and zoom in. This works pretty well, esp from a tripod.

Lastly, you could use an led keychain light to focus assist, half shutter, release light, fire shutter.

 

There are tons of ways to do it. I’ve been using a hotshoe-mounted assist light for dark venues.

 

Also, “back focus” usually refers to a faulty lens/camera locking focus in back of the subject. It does not mean using the rear AF button to focus.

[fstopper89]

Nitpick much? I was referring to lowest f-stop. Yes, should have said fastest.  Sorry for my complete disregard for the correct term.

A lot has to do with the focal length, subject-to-background distance, and subject-to-camera distance.

[theleestudio]

Thanks for all the help! This was an image I took about like 3 feet away from the subject’s face at 1.2.

http://sphotos-a.xx.fbcdn.net/hphotos-ash4/484968_4279705721238_1096029818_n.jpg

[theleestudio]

Also does anyone know why this post of mine keeps getting marked as spam? I keep trying to post it in the fauxtog forum and it keeps disappearing.

 

I am not a photographer.

But I’d like to be someday. But am I a fauxtog? Not entirely, I don’t think. Some areas most def.

A little background about me: I’ve always had a passion for the still image. I’m a film major so I have some background and knowledge of lighting, composition, framing etc. (I KNOW THE RULE OF THIRDS OMFGGG).

I got my first DSLR about a year and a half ago. Through clever Craigslist and working like 30 hours a week, I was able to upgrade my equipment a little. Picked up a 7D on Ebay for 800, and then the money sink known as photography began. I have two lenses, so I haven’t given into ‘gearfaggotry’ yet. My first lens was a prime lens, so since then, I’ve developed a penchant for primes. I like using ‘walk zoom’ to frame; I feel it makes me more creative.

I feel my weakness is a lack of PS knowledge/general editing know-how, an incomplete knowledge of lighting, and only intuitive/trial and error knowledge of my camera and hours of reading photography forums and my general film knowledge. I’m taking a portrait photography course in December and walking through tutorials on youtube, so I’m always looking to improve.

I have my own “studio” (LOL, not really, just my own domain name) but I haven’t been charging people or anything. I know better than that. That being said, a faculty member liked the way some of my photos came out (I shoot for the campus newspaper) and asked me to take holiday photos of their family for 100$. I’m excited and apprehensive. I’ve let them know I’m not a pro.
Here’s some of my photos:
http://sphotos-a.xx.fbcdn.net/hphotos-ash4/484968_4279705721238_1096029818_n.jpg
http://sphotos-a.xx.fbcdn.net/hphotos-ash4/315585_4128243174769_1232802532_n.jpg
http://sphotos-b.xx.fbcdn.net/hphotos-snc7/576869_4128245574829_649936654_n.jpg

Shot with 7D and 50mm 1.2 L
http://sphotos-a.xx.fbcdn.net/hphotos-prn1/29811_4174464330269_1395257263_n.jpg <– yes lens flares, lack of PS/Lightroom knowledge leaves me perplexed on how to remove.
http://sphotos-a.xx.fbcdn.net/hphotos-ash4/416919_4174473650502_212100873_n.jpg
http://sphotos-b.xx.fbcdn.net/hphotos-prn1/536308_4174474730529_1925553767_n.jpg

Shot with 450D, 17-55 f/2.8

[fstopper89]

Your images look pretty solid and good. They are sharp, and pretty well exposed. I especially like the photos of the couple, they show great emotion. Once you are able to get Photoshop, use it to brighten the faces and color correct a bit, but it looks like you started in the right direction, not relying on photoshop to make your photo, instead, working at getting good images from the start.

[theleestudio]

I think I got a little better results in these photos here:

https://www.facebook.com/media/set/?set=a.502507046450679.119863.486284131406304&type=1

There are a few stinkers in there that the person just wanted me to upload, but I like to think I’m improving. Still doing it for free.

[cameraclicker]

If you have an L lens, it should have come with a lens hood.  If it did not, you can still purchase one.  And you can get them for the rest of Canon’s lenses too.  Sigma lenses come with hoods, as do Canon’s L lenses.

Using a lens hood will greatly reduce lens flare, unless you are pointing the lens right at the light source, then you are on your own.

 

Flare is mostly a change in contrast.  I think it was browneyedgirl89 that put up some photos, with and without flare, so she may be able to comment.

 
This is your photo with lens flare removed. Right click and you can save it. The circle by her head was selected and contrast was adjusted, twice, with a bit of band-aid repair between and at the end. The flare on his leg was selected and contrast adjusted, then a smaller area was selected and contrast adjusted again. The band-aid tool was used to hide the seams, and the burn tool was used to darken the area down more.

You might like Scott Kelby’s Photoshop book. It is a good place to start because it is like a cook book. If you want this effect, here are the ten steps you have to perform to get it done. Then you move on to the next thing you want to do. After a while you can find your way around on your own.

[fstopper89]

Cameraclicker, I love your edit of that image. It looks very seamless, and it’s very difficult in some occasions to remove a flare like that.  I was kind of pondering to myself “how would I remove that flare?” if it were on my photo. The background bokeh make it easier to hide the seams too. I’ve fudged a few things out of the background of several of my images and was able to do so easily due to the bokeh present. Usually I try to move so that these items aren’t there in the first place, but there have been situations in shooting where I couldn’t avoid them and knew if I shot it a certain way I could get rid of it in post (think power poles, occasional trees, etc.) The flare does cause a decrease in contrast. I should also start using my lens hoods, which is probably the reason I’ve gotten flares. Sometimes the flare appears more like a rainbow-colored ring (which in some shots, I find attractive, though it can be a matter of opinion) but a lot of you are right that in a portrait it can often be distracting.

[theleestudio]

Sweet! Thanks CameraClicker!

That shot was with a 17-55mm f/2.8 lens, and I had stupidly left my hood that I bought at home. Live and learn I guess. Is there a link to the Kelby book on Amazon?

This one?

http://www.amazon.com/Photoshop-Digital-Photographers-Voices-Matter/dp/0321823745

Also I reuploaded the image and gave you props on the retouch. Many thanks!

[cameraclicker]

That looks like the book.  I have the CS5 version, and a couple for various versions of Elements.  I haven’t upgraded to CS6 yet.

I’m delighted you like my edit.

[Author]

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