How hard is it to focus @ 1.2?

[devilla101]

Hey guys

I've had my 85 1.2 mkII for around a month and noticed that shooting wide open on my 5D, most of the my shots where I focused on was blurry. Instead it seemed the area behind was focused or if its flat surface and on an angle the area next to it is sharper. However manually focusing at 1.2 seemed to work and doesnt exhibit the problem.


Eg. Shot a friend and focused lock the eye close to me. When I viewed the image on my computer the other eye was sharper. Is this back focusing and if so will Canon charge me to get it re calibrated.

Other than that the lens is sweet. Above 1.4-8 the focusing seems accurate. At 5.6 where I shoot most of my portraiture its bloody sharp and aweseome!!

[aim54x]

That seems a little strange, and what a wonderful piece of glass you have there Ronald, something us Nikon users dont really have an equivalent to (f/1.4 is the closest). Hopefully someone with a the same lens can help you, but have you tried to call Canon?

Cheers
Cameron

[robert]

I cant comment on your set-up, other than be jealous of that lens!
Does stopping it down slightly to f2 create a larger depth of field to cover it? (edit- reread and see it does) Although even if it does if you pay that much for a lens you want it to be spot on.

I often had the 'unintended' area in focus with a 50 1.8. It was pretty consistent and I figured it was a back focus issue- one of the reasons i just got the 50D- it has AF micro adjustment. Now it is spot on.

I think you can send the setup in to Canon for adjustment- not sure if there is a cost.
Maybe not a helpful reply, just my experience of the issue.

[ATJ]

I would be very surprised if the set aperture had any influence on the focusing by the camera. The camera should be focusing first and then changing the aperture to take the photograph. What I think you are seeing is that the focusing is slightly out, no matter what aperture you choose, but when you stop down, the increase in depth of field is enough to mask the focusing issue.

Now, as to whether it is the camera that is focusing incorrectly or there is something wrong with your settings or usage, the best way to test that would be to put the camera on a tripod and experiment with focusing on a static subject. This is to see whether what you are possibly seeing is slight movement in the camera between when the camera focuses and when the shot is taken.

[devilla101]

Thanks guys.

I downloaded a focus test chart, followed the instructions and shot a couple of frames with the 5D and 50D. I am happy to announced that it is within specs. With the 5D slightly back focusing 1mm or so and the 50D pretty much bang on. Maybe crop factor plays a part but I'm happy enough that the lens is pretty much spot on.

Therefore I can conclude that its very hard to focus @ 1.2

[DebT]

Hi Ron,
would appreciate the link for the focussing chart ...
I have been thinking similar things with a couple of my lenses and not sure if it was just my eyes ..so I would benefit from doing similar tests
DebT

[devilla101]

Hey Debbie

Sorry for the late post, been busy all of Nov and starting to ease up now. Anyhoo here is the link where I got the chart from. Whether or not its scientifically proven to be accurate. Who knows, but it gave me that 'feel good' feeling my 85mm was just fine

http://focustestchart.com/chart.html

[Yi-P]

Congrats Ron on your early xmas pressie

Even on the Nikon f/1.4 version, focusing wide open is really a pain, specially with close subjects. But then it really comes to practice and understanding how your camera's autofocus work.

It is more likely operator error and technical forgiveness that gives your blurry image... Or simply art if you put it the other way.

[devilla101]

Hahahh thanks Yip, its been on my shopping list for a loooooooooong time.

Regarding the blur, i'll tell my portrait clients its the latest craze not to have faces or parts of their face in focus anymore...think I can get away with it

[mickeyjuice]

Regarding the blur, i'll tell my portrait clients its the latest craze not to have faces or parts of their face in focus anymore...think I can get away with it

It's the 'soft' look. All the rage in Eurpoe, don't you know?

[ATJ]

This thread has been bugging me for a while and I can't keep it in any longer.

Unless you are using a very old and completely manual lens, the aperture chosen makes absolutely no difference at all to the process of focusing. Modern SLRs and their lens are always wide open, regardless of the chosen aperture up until the point the shutter is released. Focusing, whether manual or auto occurs while the lens is wide open. It makes no difference if you set the camera to f/22 or f/1.2, the focusing will be exactly the same. It is only after the focusing occurs that the lens gets stopped down to the chosen aperture. Note that this is true even using manual focus.

It is also worthwhile mentioning that focusing should actually be EASIER with a f/1.2 lens than f/1.4, f/2.8 or even smaller maximum apertures. This is because a) more light gets in so it is easier for the camera or the person to judge focus and b) the shallow depth of field makes it more obvious when something is in focus.

What is happening here is either or both of the following scenarios.

First, the depth of field at f/1.2 is going to be very shallow indeed. Unless just everything in the frame is in the same plane, things in the image will be anywhere from soft to downright out of focus. If you were shooting a portrait, and you focused on the eyes, you may find the nose is not sharp and vice versa. Basically, if you don't focus on the right thing the image will look unsharp and even if you do, some parts of the image will be unsharp.

Second, depending on the focus mode used, movement of the subject or the camera after focus was acquired but before the shutter was released will result in a loss of focus. The shallow depth of field will make this worse. I don't know about Canon, but with AF-S on a Nikon, once the focus is acquired after half depressing the shutter button, the camera will not focus again unless you release the button. This means it is possible to acquire focus and then moved the camera significantly such that the image is so out of focus it is not funny, but the camera may still indicate proper focus. Using AF-C decreases this effect significantly, but it is still possible, through movement of the camera or the subject, to have something out of focus even though the camera thinks it is.

So... I suspect the problem here is simply shallow depth of field and focus errors rather than focus being any more difficult.

[DaveB]

Andrew, I think it's just a case of the DOF being shallow. I didn't get a sense when reading this thread of people thinking the AF worked differently at different apertures (but maybe that's because I just assumed everyone understood how it worked ).

I must admit that with my new 85mm/1.8 combined with my new FF camera I'm noticing how hard it is to get focus right on "grab" shots at f/1.8-2.0. I did check the body's focus and no microadjustment was required: it's just my technique. I can only imagine that f/1.2 is even tougher.

[ATJ]

Dave,

You may be right. I just kept reading "hard to focus @ 1.2" and thought they actually meant "hard to focus @ 1.2". As you say it is really "it is hard to get a photograph that looks in focus @ 1.2".

[Grev]

I find it hard to focus my AiS 50mm f1.2, no depth of field at all... one little too much either way and it's out of focused...

[ATJ]

I find it hard to focus my AiS 50mm f1.2, no depth of field at all... one little too much either way and it's out of focused...

If you think about it logically, it is actually easier to focus - or at least easier to get accurate focus.

Depth of field is all about how much of the scene appears to be in sharp or as my old Manual of Photography puts it: "the distance through which the subject may extend when the subject is focused as sharply as possible on one part of it without the image becoming noticeably unsharp." As you say, at f/1.2 there is no depth of field at all so the only thing that is not noticeably unsharp is the part which is focused as sharply as possible. i.e. you know immediately what's in focus and what's not.

Compare that to a f/2.8 lens where not only the part which is focused as sharp as possible appears sharp, but some distance either side. i.e. you may consider a certain part in focus when really it is the depth of field making it appear less unsharp. It may not be focused where you want it so it was actually harder to focus.

Using an f/1.2 lens may be more frustrating (especially a manual one) but when you nail the focus you know it.

[aim54x]

Using an f/1.2 lens may be more frustrating (especially a manual one) but when you nail the focus you know it.

That I can agree with, just like focusing on the edge of a glass knife using the dissecting scope that is built in on a ultramicrotome, you just know when you have it right!

[Grev]

I find it hard to focus my AiS 50mm f1.2, no depth of field at all... one little too much either way and it's out of focused...

If you think about it logically, it is actually easier to focus - or at least easier to get accurate focus.

Depth of field is all about how much of the scene appears to be in sharp or as my old Manual of Photography puts it: "the distance through which the subject may extend when the subject is focused as sharply as possible on one part of it without the image becoming noticeably unsharp." As you say, at f/1.2 there is no depth of field at all so the only thing that is not noticeably unsharp is the part which is focused as sharply as possible. i.e. you know immediately what's in focus and what's not.

Compare that to a f/2.8 lens where not only the part which is focused as sharp as possible appears sharp, but some distance either side. i.e. you may consider a certain part in focus when really it is the depth of field making it appear less unsharp. It may not be focused where you want it so it was actually harder to focus.

Using an f/1.2 lens may be more frustrating (especially a manual one) but when you nail the focus you know it.

Well it's not that hard to do ultimately and I don't find that much difference in focusing wide open or stopped down in reality... I can do it pretty quickly and precisely now, just that if I'm close focusing then there'd be a problem.