What type of lens do I need for this shot?

H

harmonica44

If you fast forward 3 minutes 58 seconds into the video:

http://www.youtube.com/watch?v=xLXU-Sa_o_I

I can't use a zoom lens because the aperture keeps changing when you zoom. Even if you have it set to a lower aperture, to match the furthest zoom, the light still keeps changing, during the zoom regardless. I can't be the zoom myself and move in closer to an actor, because I would then have to focus pull, and you would be able to see the focus pulling. What lens do I need to avoid aperture loss, and no focus pulling during the zoom? Thanks.
 
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If you want to zoom during a take. you need a constant aperture zoom. All the cheap zooms (like your kit lens) aren't constant aperture, but the nicer ones remain (usually as low as 2.8) throughout the range of the zoom. The two most popular are the Canon 24-70mmL and the 70-200mm L, but there are other slower ones, and different ranges from different brands. I'm not sure that focus remains throughout focal lengths on those lenses though? That's a more common concern for video than stills, and a DSLR is still a still camera first.

A push though is probably a better way to do it nowdays. A dolly helps, but in reality man pulling focus is a part of running a camera. Sometimes it's hard, but it's always possible. A follow focus might help you.

As close as that gets to the eyes, you'd be best off with a Macro lens, probably a 100mm. Alternatively, you would go with a long lens like the 70-200mm and just be far away. Your kit zoom might not be able to focus that close. I think it's closest focusing distance is like .4 m or something? Maybe that's close enough, but something to consider none the less.
 
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Another consideration is the lighting.

The reason the auto aperture keeps hopping all around is because the overall lighting changes as the image changes during the zoom.

Inside or outside, use a broad even light or bounceboard to evenly illuminate your character and design the shot so that there are as few wide contrasts in the image throughout the zoom (foreground and background) - WITH - the locked/fixed aperture Paul just suggested.
 
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rayw said:
Another consideration is the lighting.

The reason the auto aperture keeps hopping all around is because the overall lighting changes as the image changes during the zoom.

Inside or outside, use a broad even light or bounceboard to evenly illuminate your character and design the shot so that there are as few wide contrasts in the image throughout the zoom (foreground and background) - WITH - the locked/fixed aperture Paul just suggested.
Click to expand...

It's nothing to do with auto exposure - it happens in manual mode too, because a) the lens doesn't have a constant aperture and b) the camera can only communicate aperture changes to the lens in steps, not a smooth curve.

Harmonica, I'd be inclined to do it with a dolly move rather than a zoom. It's hard enough pulling focus accurately on stills lenses as it is; zooming while shooting will make it nigh on impossible.

A macro lens as Paul suggested would be good. I'd also start with the camera up close and then pull back, and reverse the footage in post, because the closer you are the more critical focus becomes. If you do it this way you can guarantee your end frame will be sharp.
 
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chilipie said:
It's nothing to do with auto exposure - it happens in manual mode too, because a) the lens doesn't have a constant aperture and b) the camera can only communicate aperture changes to the lens in steps, not a smooth curve.
Click to expand...
Super.
Gotcha on the aperture changes in steps.
So, if the aperture is set to manual and "locked" at whatever setting it states the aperture doesn't remain fixed? The auto programming still overrides the setting?
(This might be specific to the equipment one is using.)
 
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rayw said:
So, if the aperture is set to manual and "locked" at whatever setting it states the aperture doesn't remain fixed? The auto programming still overrides the setting?
Click to expand...

Right, the lens is physically different from zoomed all the way in to all the way wise, and as such if you're set at f/8 all the way in, without changing you'd be at f/4 or something when all the way wide. Or maybe visa-versa, I can't remember which way it goes. To compensate, it blades adjust as you zoom in or out getting a little brighter then the blades clicking to the right spot, then getting a little brighter and clicking to the right spot, etc..

Constant aperture lenses a designed to stay the same throughout the focal range.
 
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rayw said:
Super.
Gotcha on the aperture changes in steps.
So, if the aperture is set to manual and "locked" at whatever setting it states the aperture doesn't remain fixed? The auto programming still overrides the setting?
(This might be specific to the equipment one is using.)
Click to expand...

It remains fixed until you change the focal length - then as soon as you stop zooming, the picture snaps brighter/darker as the aperture corrects itself. If you use a lens with a constant aperture (i.e. can achieve the same f-stop at the wide and tele ends) you won't have this problem.
 
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PaulGriffith said:
To compensate, it blades adjust as you zoom in or out getting a little brighter then the blades clicking to the right spot, then getting a little brighter and clicking to the right spot, etc..

Constant aperture lenses a designed to stay the same throughout the focal range.
Click to expand...
Great. Good to know.
So, with it being either/or, with a little experimenting a person can figure out if their camera has that (annoying) zoom-compensating-aperture thing going on or the constant aperture thing.

I don't think I've run across any documentation on my poopy little cam that states such distinction and I've not had a need to test such, either. But this all sounds like reasonable stuff to know- what the limitations of our equipment is and why things aren't doing what we think they should be doing.

chilipie said:
It remains fixed until you change the focal length - then as soon as you stop zooming, the picture snaps brighter/darker as the aperture corrects itself. If you use a lens with a constant aperture (i.e. can achieve the same f-stop at the wide and tele ends) you won't have this problem.
Click to expand...
Wonderful. Good, good, good.



Thanks, Chilipie & Paul!
 
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Sure man. You can actually tell by the name of the lens. The Canon 18-135mm f/3.5-5.6 is not constant aperture, where as the Canon 24-70mm f/2.8 is. The 3.5 is it's most open aperture all the way wide, the 5.6 is it's most open aperture all the way in. 2.8 not having a second number after it means it's as bright as 2.8 throughout.
 
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Goodness.

Well, I guess I have an annoying "I know you think you can set your aperture at f/X or Y, but the moment you start zooming in or out that's ancient history" sort of lens.

Bugger. :grrr:


Thanks, again.
 
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So...

1) Fix aperture
2) No zooming
3) Dolly/Track shot in

But, we're best off beginning at the subject, then...
1) Fix aperture & focus
2) No zooming
3) Dolly/Track shot out, adjusting focus if necessary
4) Reverse in post

Sound about right?



PaulGriffith said:
Though, if you aren't zooming, then having a fixed aperture lens doesn't matter.
Click to expand...
Dumb Dora "Duh!" on me.
Of course you're right.
 
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I think that's right haha.

Though, if you aren't zooming, then having a fixed aperture lens doesn't matter. Granted, fixed aperture lenses are generally nicer all around than the cheaper ones, but as long as you're happy with the f stop you can set it to the you're golden.
 
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yeah, dolly in with a wide lens stopped down as far as you can...

Alternative do the same thin with a LONG lens from a distance away to get that compression shallow DOF look with a bigger rage of in focus distance..

but here's a useful trick..



Start with your dolly all the way in to the tightest position, get that perfect focus on the eyes and then pull out. Pull focus as best you can during the dolly move, but if it goes a little wonky just make sure that at the end of the dolly OUT your focus is good....

in post REVERSE the footage for a sweet dolly into PERFECT focus eyes. This is the ONLY way to do it for a relay fast "dolly in" shot.
 
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when looking and choosing a zoom lens.. two factors make a really useful cine lens..

constant aperture (as we discussed here)
and Para-focal.

Most of your new zoom lenses will not maintain focus over the zoom distance. A lens that WILL maintain focus point over the zoom range is consider a parafocal lens.

This is the main reason all the digital cameras come with a "focus assist" button that digitally zooms in, gone are the old days where you would zoom in, check focus and zoom out for a nice focus shot... your not still doing that are you mr. Internets?
 
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Okay thanks. My 18-55 lens does maintain focus during the zoom, but only if I zoom. If I use a dolly it still goes out of focus as I move closer. I tried doing the suggestion to start out with the camera moved all the way in, and then just reverse it, but it goes out of focus when you dolly the cam back as well. It seems that zooming is the only way to maintain it.

I could get one of those follow focus rig things, but is it possible for an experienced DP to do that shot, without the quick refocusing being noticeable? I was watching the movie Actor Of Valor, and I read it was shot with all DSLRs and I noticed how it went out of focus quite a few times when the actors moved closer to the camera and further back, and the focus puller kept having to pull, but it was noticeable. Not sure if it was because of the limitations of the lenses or if that was done for style. The DP I worked with so far who shot my short said she had a hard time with the lenses not having a lot of focus when actors moved closer in certain types of shots. She never practiced with a DSLR before in school, so she didn't quite now how to work around it, without the focus pulling being noticeable.
 
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