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Measuring focus for video


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#1 Daniel Christie

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Posted 17 December 2006 - 10:58 PM

Hi everybody. First post on this site. Can anyone tell me where you would measure focus from if you are shooting video? Someone told me that they were taught at filmschool to measure from the front element of the lens as apposed to the image plane, so I ran some focus tests on a DSR-450 with a fujinon ENG lens and sure enough the barrel markings seemed to be from the front element. Is this just a nuance of ENG lenses, or is it the same with other video lenses. For someone who had, until recently, only ever focus pulled with cine lenses it just doesn't seem intuative to me or any of the DoPs and other ACs I have talked to about it.

Thanks
Daniel
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#2 Allen Achterberg

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Posted 18 December 2006 - 01:29 AM

there's a marking on the body where the plane is. There should be anyway, most Higher end Camera's I've worked with there is. You measure from the Image Plane...NOT the front element, not like it really matters...there'll be room for error with video.

I generally don't even measure most video...more work than is needed sometimes.
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#3 Brad Grimmett

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Posted 18 December 2006 - 06:16 AM

there's a marking on the body where the plane is. There should be anyway, most Higher end Camera's I've worked with there is. You measure from the Image Plane...NOT the front element, not like it really matters...there'll be room for error with video.

Well, I would argue that it DOES matter. I like my pictures in focus thank you... If you're on a closeup at 150mm you will certainly notice if you're measuring from the wrong plane.
Some lenses (mainly ENG type video lenses) are measured from the front element. It can certainly throw some people off sometimes, but it's very easy to find out if you just spend a few minutes with the camera and a chart at the beginning of the job. Normally the front element lenses are about a foot off, so you'll be able to check it by your eye very easily. Once you know which it is, all is well.
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#4 Daniel Christie

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Posted 18 December 2006 - 07:31 AM

Thanks for the replys.

I generally don't even measure most video...more work than is needed sometimes.


Me either, when I'm operating but when you are focus pulling, especially with an operator who comes from a film background who wouldn't usually ever take focus themselves, you don't always have the opportunity to get your eye to the viewfinder . I've also found some operators just feel more comfortable seeing a tape measure being taken. The functional advantage is that you can measure up while the operator is still finding his or her frame.

Daniel
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#5 Phil Rhodes

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Posted 18 December 2006 - 07:42 AM

Hi,

I've seen a lot of soft shots from people who insist on measuring video. The numbers on many ENG lenses are little more than a rough idea - my position is that ENG lenses on SD or HD cameras should always be eye-sharped, although there's nothing wrong with measuring it as a sanity check.

Phil
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#6 Brian Drysdale

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Posted 18 December 2006 - 12:22 PM

The focus scale on the ENG style lenses is awful, with very few focus distances actually marked. Usually I give the camera assistant marks by focusing by eye rather than using the distance marks on the ENG lens and measuring by tape. Although the assistant could make their own focus scale for the lens, it's very compressed. On many scenes the eye focused marks on the ENG style lenses are horribly close together.

Cine style lens have a much better scale and you can use tape. However, you do need to check that the eye focused distance on the lens matches the tape measured distance because sometimes they can be out.
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#7 Rupe Whiteman

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Posted 18 December 2006 - 04:57 PM

... On ENG zoom 'glass, the distance markings should be used as a guide only. If you think of the relative cost of a tv zoom to it's 16/35mm cousins... It's generally best for the operator to read out the markings for 'pulling during a take, let the focus puller stick his triangles and you're off...

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#8 timHealy

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Posted 18 December 2006 - 07:28 PM

Probably my single biggest complaint working with young filmmakers is using consumer or prosumser cameras with the crappy lenses with no footage marks or zoom indications. Nothing seems to be repeatable! Years ago when I was learning about film and video I discovered I could ditch the crappy video lens on a Sony double sytem 3/4 inch system and utilize a C mount Switars. If one of the consumer or prosumer mini DV or HDV camera manufacturers came out with a camera with a C mount it would sell to young filmmakers like hotcakes.

Just my biased 2 cents.

Best

Tim
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#9 Michael Collier

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Posted 18 December 2006 - 10:24 PM

For ENG lenses with those markings, its quite useless to measure. I never have measured anything, just make sure you have a good backfocus. Backfocus anytime the lens goes on a plane or long bumpy car ride, or if the focus feels off when taking your focus.

Then zoom in and focus. Zoom out and you know your criticle is set. If your still unsure, iris to wide open, shutter down so you can see detail and focus. Works brilliantly. If you have several marks to measure, wrap white electrical tape around the barrel, zoom to get your focus at every point and make a mark by that point. Fujinon lenses and canons and just about every ENG lens I have used does not have marks close enough to make them useful at all. setting it by tape often is as good as guessing. Zoomed in you get a very clear look at the focus, and just a 1/2 degree turn becomes the difference between absolute focus, and slightly soft.

Works unless your already shooting at full telephoto, or your backfocus is off. But at least since your looking through the chip so to speak, you see if its off or not.
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#10 Allen Achterberg

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Posted 19 December 2006 - 11:12 PM

Well, I would argue that it DOES matter. I like my pictures in focus thank you... If you're on a closeup at 150mm you will certainly notice if you're measuring from the wrong plane.
Some lenses (mainly ENG type video lenses) are measured from the front element. It can certainly throw some people off sometimes, but it's very easy to find out if you just spend a few minutes with the camera and a chart at the beginning of the job. Normally the front element lenses are about a foot off, so you'll be able to check it by your eye very easily. Once you know which it is, all is well.


Never given my DP a soft shot. Never ever had someone complain that something was soft in the Dailies.

I think I've AC'd once with a stock lens, and it was the XDCAM, we were testing the camera a good year or two back I believe. everything came back sharp. At the time, I was using a tape measure always with video.

If we were at 150mm, with a tight shot like you describe, I wouldn't measure it.
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#11 not valid

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Posted 02 January 2007 - 05:56 PM

Maybe you dont trust your eyes?
Michael Collier has got the idea zoom to focus then pull back to your desired frame Ive never shot on film myself only on digital and have never measured focus. On digital cameras particularly cheaper ones i trust my eyes more then i would trust the markings anyway.
have a little faith and go by eye. Ive never had a soft shot using this technique.

The only time my shots are soft is when im using one of those Horrible sony pd-170 focus rings and i cant find out which way i have to turn the thing to get my focus back it just keeps turning and turning damn useless thing if you ask me
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#12 Stuart Brereton

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Posted 02 January 2007 - 06:21 PM

Maybe you dont trust your eyes?


There's not always time to give eye sharps (and I know a couple of operators who refuse to give them) so your AC needs to have a focus scale they can rely on. ENG lenses are terrible for this, but if you've got time in prep (or lunch on the first shoot day, if necessary!) you can run the tape out and remark the barrel.
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#13 Daniel Madsen

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Posted 02 January 2007 - 07:00 PM

This is sort of an off-topic question, but does anyone know the circle of confusion for 1/4in and 1/2 CCDs?
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#14 Brad Grimmett

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Posted 03 January 2007 - 06:40 AM

Never given my DP a soft shot. Never ever had someone complain that something was soft in the Dailies.

I think I've AC'd once with a stock lens, and it was the XDCAM, we were testing the camera a good year or two back I believe. everything came back sharp. At the time, I was using a tape measure always with video.

If we were at 150mm, with a tight shot like you describe, I wouldn't measure it.

Never given a soft shot? Sorry, but I don't believe you. I've worked with some amazing 1st's, and I've seen at least a moment of softness from every single one of them. I'd love to say that I've never composed a shot poorly, but it's just not the case. No one is perfect.
If you don't want to measure and it works for you that's fine. It wouldn't bother me at all if I was operating as long as you weren't soft a lot. Most operators and DP's wouldn't mind I don't think. The problem is, if you make a mistake or two they're not going to ask you to get out your tape measure, they're going to ask the producer to start looking for a replacement. So if it's your ego that's keeping you from measuring, maybe you should re-consider.
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#15 Jonathan Bowerbank

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Posted 03 January 2007 - 04:52 PM

I generally don't even measure most video...more work than is needed sometimes.


To prevent having to measure during production, it's probably a good idea to do focus tests during prep. Measure out with the tape, set the focus on the lens and see if they match up. This is mainly to find out how accurate your lens is. But as always, you should zoom in and get your critical focus for every shot you do.
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#16 Allen Achterberg

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Posted 06 January 2007 - 02:40 AM

Never given a soft shot? Sorry, but I don't believe you. I've worked with some amazing 1st's, and I've seen at least a moment of softness from every single one of them. I'd love to say that I've never composed a shot poorly, but it's just not the case. No one is perfect.
If you don't want to measure and it works for you that's fine. It wouldn't bother me at all if I was operating as long as you weren't soft a lot. Most operators and DP's wouldn't mind I don't think. The problem is, if you make a mistake or two they're not going to ask you to get out your tape measure, they're going to ask the producer to start looking for a replacement. So if it's your ego that's keeping you from measuring, maybe you should re-consider.



it's not my ego that keeps me from measuring. No need to get all huffy and puffy over my claims. if you do not believe them, thats ok. To make things clear, I am not claiming that I am something special, or a focus God, but I will maintain that I've done very well without measuring with 2/3in optics.

I will not deny having a quick buzz, but it doesn't go unnoticed in the digital world with an HD monitor and someone's face constantly in it, but it's never been an issue for me, the take before was sharp all the way through, the take with a qucik buzz has useable footage, and the take after that is great. You act as if I am a Die Hard no measuring AC. I'm not. When necessary, I do. If I have doubts, I find the solution!

for the record, I've never been Fired, yet. Hopefully never. Been rewarded though...
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#17 Brad Grimmett

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Posted 06 January 2007 - 09:33 PM

it's not my ego that keeps me from measuring. No need to get all huffy and puffy over my claims. if you do not believe them, thats ok. To make things clear, I am not claiming that I am something special, or a focus God, but I will maintain that I've done very well without measuring with 2/3in optics.

Actually, you WERE claiming to be something special. You were claiming you never had a soft shot. But of course you amended that in your next post.
I wasn't getting huffy, it was just obvious that you were making a claim that is obviously untrue.

You act as if I am a Die Hard no measuring AC. I'm not.

Your previous post made it sound as if you didn't even bring a tape measure to set. I was just reacting to your post.

for the record, I've never been Fired, yet. Hopefully never. Been rewarded though...

That's good. I don't believe I implied that you weren't a good 1st.

Who was it that said, "You haven't made it in this business until you've been fired"? I believe it was a DP, but I can't remember who.
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#18 Allen Achterberg

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Posted 08 January 2007 - 05:56 PM

we'll leave it at that Brad, I'm not one to argue...or to nit pick
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#19 Brad Grimmett

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Posted 08 January 2007 - 08:41 PM

we'll leave it at that Brad, I'm not one to argue...or to nit pick

I assume you're taking a shot at me with this comment, but that's fine. I AM one to argue when I believe in something, and I AM one to nit pick when it concerns my career and the quality of my work and the work of the crew working with me. I don't think there's anything wrong with that.
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#20 Daniel Stigler

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Posted 09 January 2007 - 10:43 AM

Two years ago i had to work with a Sony videocamera with two horrible Fujinon zooms. I remarked the barrels with my Putora chart but found out painfully that the marks were only good for the focal length and iris setting they were done with. Of course back focus changed all the time. It was frustrating as I never knew where my focus was. Eye focus helps out, but when actors miss their marks or improvise I need reliable marks to correct.

Measuring sometimes is a psychological procedure. I remember a shooting day (SR3 with Ultra Primes) where we shot in a stairway the whole day. I measured the width of the stairway, the size of the platforms and the doors and I was good with that. During lunch break my DoP told me that the director nervously asked him if I knew what I was doing because for his understanding I was using my tape measure so little.

Edited by Daniel Stigler, 09 January 2007 - 10:43 AM.

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