I'm currently pulling focus for a 16mm SRII freebie/non-commercial/personal
project for someone. I'm far from a Focus Puller by trade. But given the
nature of the shoot, this is my way of getting such experience.
We've been shooting today with 8mm, 12mm, 16mm, + 25mm Zeiss lenses, plus
a 10-100mm zoom. On tape-measuring distances, finding focus through the
view-finder, and creating new marks on the lens, I am surprised at how
far out they can be from the barrel markings.
I don't have anything near the experience of a quality Focus Puller that
most of you are used to working with, but am a little amazed that I cannot
measure the distance and set the focus ring, or the white follow focus
ring, without having to start-from-scratch via the view-finder, and disregarding
the lens markings.
Is this common? Or just common with the cheap, old lenses I seem to work
Lighting Cameraman, Camera Assistant
Before you do anything, run a viewfinder focus check test.
This is the only way you know if what the operator is shooting is what
you'll get on the film. Take a dollar bill (or a pound note - that stuff
has a picture on it doesn't it? ), tape it with double stick to an insert
slate. Cover the dollar with 2" clear tape (like Scotch tape, just
bigger). Put the insert slate on a C-stand somehow.
Take your widest lens and put it on the camera in question. Position the
slate at minimum focus for that lens. Pan the slate away from the lens
axis until its about 45 degrees away from the camera. Arrange the slate
so the focus, again, is at its minimum. You should see a decent shift
from fuzzy to sharp to fuzzy. Light the chart without glare and at the
LAD color temp of the film stock (I like to use reversal film. It's really
sharp, very little grain and I can see a nice positive without needing
to go to a work print).
Lighting the chart at the LAD color temp will allow the best resolution
and balance of all the dye layers in the film (thus guaranteeing you the
sharpest possible image - no loss of res. due to blown out layers). Scrim
the light down until your at the widest stop on the lens possible.
By now, you should have a good change from fuzzy to sharp to fuzzy. If
not, then pan the slate away until you get a good shift area, but not
so much that the face on the dollar bill is un-recognizable. Mark the
centre of the focused area with small tape arrows (top and bottom). Take
time with this, making sure you hit the exact centre of the sharp area
(usually the bridge of the face's nose).
Shoot this arrangement at 24 fps and process. If you're using neg stock
and not rev., don't get a work print. View the negative directly. Look
for the area of most focus and see if its shifted. If it has, uh oh. If
not, you now know that what you shoot is what you'll get.
Normally, this test turns out fine, but its great to check things out,
'cause that way you can do what has to be done to fix things (i.e., re-scale
lenses, trade lenses out, have the back focus adjusted, etc.,). But if
the camera goes into the shop for a depth change or any other work, re-test.
It's the only way you'll know with out a doubt that what you shoot is
what you'll get.
First AC, Los Angeles, CA
Can't beat Michaels excellent advice, but I'll add :
You are using pretty wide lenses. It's possible that your getting a sharp
image through the finder that is not on the mark because of your depth
of field. Set the lense to the mark and see if it is sharp at that distance,
then shift the focus a hair in either direction and see if it's any sharper,
softer or unnoticeable. The important thing is that when you hit the mark,
the lense is sharp at that distance. The lense may also be sharp off the
mark, but that is irrelevant as long as it is as sharp or sharper (sharpest)
on the mark.
Test the 10-100 at 100mm and see how it comes up. If it hits the mark,
the camera is probably okay. If none of the lenses hit the mark, it is
probably a camera issue.
ICG, New York
There are a few potential problems when the focus scales don't match what
you're seeing. Either the lens is wrong, the lens mount (flange depth
or back focus) or the groundglass depth could be off; or even a combination
of all three (what I like to call an Ebola camera problem, where one is
bleeding from every orifice).
The quick test for your flange depth is to put on the zoom lens. Zoom
all the way in, focus, then zoom out. It the image falls out of focus
then your back focus is out. This is a service call to have the depth
reset with a collimator.
Next question is the groundglass depth.
The really quick way is to take to a rental house to check, but short
of this just shoot a quick test. Take your longest lens and shoot a close-up
of the prettiest PA on set with her head full frame. Set the lighting
for the widest aperture the lens will allow. Focus on her eyes using the
viewfinder and shoot the test. Project the result and see if her eyes
are still in focus or if the sharp point has drifted back towards her
ears or forward to the tip of her nose. If focus is not still on her eyes
then you need to have the groundglass depth adjusted.
Once you're sure the back-focus and the groundglass are correct, you can
set focus with your eye in the viewfinder and re-mark the lenses. Or you
can go to a rental house and use their lens projector to test and reset
the lens marks, which is by far the easiest and most accurate way to do
>On tape-measuring distances,
finding focus through the view-finder, and >creating new marks
on the lens
If you are having more trouble with the wider lenses than the tighter
lenses you may have a back focus problem. If you are having problems with
ALL lenses, then you may have a back focus problem.
Are you getting eye focus marks with the aperture wide open?
When I was an assistant I discovered that there was usually some "play"
in what I could see as being in focus, especially on wider lenses. You'll
probably experience that, especially with the wider lenses you are working
with. You'll probably have less trouble at the long end of your 10-1 zoom.
When you get an eye focus on an object roll the focus in first from near-to-far
and note where it falls; do that again far-to-near.
If you end up with two spots on the lens barrel that are a short distance
apart you may simply be seeing the depth of field of that lens as you
approach critical focus. In that case your lenses may be fine, and your
eye is simply telling you to stop too soon as you roll the focus towards
where it should be.
The viewfinder, or old soft lenses, may not be showing you all the subtleties
of sharpness available. Make sure you are getting all your eye focus marks
at wide open. And double check your lenses against a chart that you have
measured out at specific distances to see if your lenses or back focus
are whacked or whether you are just looking through some older and softer
lenses that are hard to eye focus.
I'd recommend using a tape measure as much as possible when starting out
as a focus puller. I had a couple of operators who wouldn't let me eye
focus for quite a while when I was assisting unless I was on a really
They said it was good for me. I think it was. Make sure those lenses are
focusing where they should be first.
My strongest recommendation would be to have your camera's flange depth
and groundglass tested and calibrated professionally. Only then should
you use your camera as a back-focus reference for your lenses.
Mitch Gross writes:
>The quick test for your flange depth
is to put on the zoom lens.
I'd be cautious about this approach for two reasons:
1) - A back-focus problem can be a matter of flange depth
(on the camera) or mount adjustment (on the lens). If your camera isn't
calibrated first, you may end up working to a false standard and then
mis-calibrating your lenses.
2) - Zooming out can some times be deceptive because
details naturally become fuzzier as you zoom out.
IMHO all normal-to-short professional lenses should have accessible back-focus
adjustments the way HD lenses do.
Marin County, CA
>IMHO all normal-to-short professional
lenses should have accessible back-focus adjustments the way
HD lenses do.
Begging to differ, the last thing you need on set is another variable
to be set incorrectly...that is what checkouts are for...unless AC's are
all going to go out and buy autocollimators and flange depth kits to use
on set and on location so they can do the job properly (and learn how
to use them correctly)
I think that we would all be better served if lens mounts and optical
block/chip mounts on HD cameras were made out of something other than
aluminium -like something that would be dimensionally stable enough over
a wide temp., range - so that we wouldn't have to keep adjusting back-focus
on HD cameras every damned time we changed lenses...at least one camera
rental house has gone to great trouble and expense to replace the lens
mount/optical block/chip mount assembly on their HD cameras with something
that IS dimensionally stable precisely to address this weakness in video
camera design and manufacture.
I have not worked with the modified cameras yet, so I can't speak personally
to the improvement, but confidence is high.
(yes, some HD jobs have VFX too)