So I just found out about the phenomenon of "focus breathing".  I was trying to make a nice rack focus, and the frame zoomed in pretty noticeably.  I'm using a photo lens because I thought that made sense for stopmo, but as I understand it, they don't correct for the breathing like cinema lenses do.

How do you guys handle the breathing effect?  Is it better to get cine lenses, or can you adjust for it in post?

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One Technique I've used is to play with the iris and shutter rather than the lens.  On a telephoto lens, closing the iris and opening the shutter means the exposure can remain the same while the depth of field changes.  This means items in the back/foreground sharpen up (or soften) without the frame changing. You've not got quite the same degree of control this way, but it's a possible workaround when using stills photography lenses. 

Alternatively - and theoretically, I've never tried it -  you can track the camera in or out at the same time as racking the focus and that will minimise the movement at the frame edges.

I had never heard of it before, had to look it up:

"Breathing refers to the change of angle of view of a lens when shifting the focus. Some (often higher quality) lenses are designed to lessen the degree this effect. Lens breathing does not prevent one from racking focus or following focus with this lens, but it lessens the desirability of any type of focus adjustment, since it noticeably changes the composition of the shot.

Not to be confused with the suction and expulsion of air from within the lens as its internal volume changes."

Hmm... it doesn't sound like a deal-breaker to me - more like normal stuff I'd expect a lens to do. I'm sure I've got it in my focus pulls and never noticed it. I suppose if you really hated it or thought of it as a problem rather than just normal stuff that happens when you refocus, you could crop each frame and minimize it pretty much - that would be pretty fiddly meticulous work though I'd think. 

Personally I like the things real lenses do in the real world, and don't want to try to duplicate the sterile perfection of CGI (and more and more in CGI films they come up with new algorithms to try to duplicate the real-wlrd effects of good old fashioned film lenses anyway). 

Here's an example of it:

I first watched this before reading about what focus breathing ism and I couldn't see what was supposed to be the problem - aside from the fact that everything goes way out of focus! But now I see it's just referring to how the field of view enlarges or compresses as he adjusts focus. It looks completely natural to me, not something I would consider a defect. I'm assuming all movies included this until maybe recently, now that they're making ridiculously expensive, computer-designed lenses for HD filming? Or did cine lenses compensate for it even in the 70's and 80's? I don't know - I'd need to check on that. 

I just checked a shot I've done with rack focus - yep, it breathes. Never noticed and it doesn't bother me a bit. In fact it might seem a little odd if it didn't. Not sure about that - I probably wouldn't notice actually. But not something I'd think anyone would care about, unless they're an obsessive pixel-counter, a breed that never existed until recently. 

I suppose if you wanted to compensate for it you might be able to do a key-framed zoom to coincide with the re-focus. Might take a few tries to get it matching pretty close. 

Or pick a point on an edge of the frame and go into each frame and crop right to that point using the same aspect ratio and keeping it centered perfectly. Similar to the way you keep track of a moving-camera shot by drawing marks on the monitor or using the framegrabber's drawing tools. 

I remember noticing the effect the first time in a pull-focus shot in The Wrong Trousers.  Don't know what lenses they used, probably a Mitchell 35mm movie camera but could easily have been re-mounted Nikkor lenses like I used when I shot with a Mitchell.   I don't think my Bolex lenses did it, though I didn't do a change of focus very often.   I knew it as "barrelling" but it's the same thing, a slight zoom effect when you change the focus.  Isabel had me do a focus change for a shot in Butterflies and it did add a slight zoom using her Pentax lens, but nowhere near as big as that telephoto zoom lens in the video Strider posted.  

All lenses "breathe", even high-end ones such as the Nikon 70-200mm VR demonstrated in the video above. Actually, its successor, the Nikon 70-200mm VRII has more pronounced focus-breathing, and they retail for over $2000.

Prime lenses are not immune, and some macro lenses can "breath" terribly. It varies considerably from one lens to another.
Optics are usually optimised for consistency of sharpness from centre to edge of picture, and from wide to long zoom, or to minimise other effects such as distortion, chromatic aberration, ghosting, flare, and so on. These lenses are designed for still photography, where "breathing" is not a problem -- it's only when you use it for live-action or animation that the effect becomes apparent.

Some solutions to this problem:
* Avoid it by not doing a pull-focus shot. ;)
* Ignore it, since most people won't notice it. People tend to look at the action, the character doing the talking, or where focus is sharpest; they don't often pay attention to the very edge of the screen. Helps if you set-up the shot so there isn't much eye-catching detail or contrast near the edge.
* Fix it in post -- frame the shot a little wider and then crop it in post to some stationary reference-points near the edge of the frame. This is in effect a slight "digital zoom" that you adjust to compensate as the lens "breathes". With the huge resolution of today's cameras it isn't a problem for image-quality. It can be tricky depending on what editing software you use, though you might be able to do it at the same time as other corrections such as barrel/pincushion distortion. 

Cheers,
Damien

The problem seems to be to do with the scale we're working at.  I've checked out a couple of my old film camera lenses and they all do it to a certain extent.  In a life-size setting the effect is barely noticeable but close down to miniatures and it becomes an issue.  But I agree with Strider, it's the action of the shot that the audience are watching and not the frame edges. Fret about it less.

Thanks for the advice, guys! I think cropping after the fact makes the most sense for me. I don't have the equipment or desire to set up a simultaneous zoom or track movement.

Ben, changing the DoF like that is an interesting idea; are you able to accurately maintain the exposure?

Wiz, if even highend lenses breathe, how would I find one that isn't as bad? (They don't seem to put it in the specs.) Is it just a matter of trying it in person first?

I would imagine that, like you said in the OP, the cine lenses would be optimized more than ones made for still photography. Though no telling which ones might be the most optimized or which the least. 

I've bought some old 16mm cine lenses, c-mounts made anywhere between the 30's to around the 60's. The earlier ones aren't great though for a couple of reasons, chief being they don't have the better optical coatings that became standard later (I don't recall exactly when just offhand). Also some of them are difficult to focus mostly due to age or neglect. Those older ones go fairly cheap, but I'm sure newer cine lenses would be a lot more expensive - but probably a lot less likely to breathe. I suspect cine lenses made from the 80's forward will be really expensive though, not sure. 

In fact I think I'll put one of them on and see how it fares. 

I agree that cropping, after the fact, is the best option.

Yer, it's pretty good, but the exposure settings are quite far apart so it only works for a sudden shift rather than a slow ease across the focal plane.  I'll see if I can dig out and process the test I did.  It was a few months ago.

Gemedet said:

Ben, changing the DoF like that is an interesting idea; are you able to accurately maintain the exposure?

I tried out one of my TV lenses and it breathes a bit - but not as much as the SLR lens that I think I shot the scene with I checked earlier. So I guess it's a matter of needing to check lenses individually and see how much they breathe if that's important to you. 

Well, after a little research, it seems they don't really make low-end cinema lenses.  Unless I'm missing something, I can't find much for less than a few thousand.  Wow.

Strider, what kind of TV lenses do you have?

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