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Reading Lens Markings

I am looking for a quick lesson or advice on the proper way to read (interpret) lens markings. My last project was shot all the way open on Elite super speed lenses. On a 25mm, I was trying to judge precisely where 17' and 30' was and where 48' was with only lens makings at 10', 20' and infinity. I know there is a lot of depth out there on that lens but I was trying to use it all to keep a lot of things sharp.

Is there a good rule of thumb for measuring between two markings? And what do you do with all that space between 20' and infinity?

Finally, which lenses have the best markings?

Thanks in advance for any help.

Dana
AC in Boston


Dana,

You can take a piece of tape and put new marks on the lens. A very experienced topnotch AC here did this to a 300 mm Canon and a Nikon (if I remember correctly)

I helped w/ the measuring...tape measure w/ a slate was the way he did it, every so many feet (between the factory marks)-pretty painstaking procedure. We found that the factory numbers were slightly off. My Ang. has such markings, so I have practically every mark on it, very useful.

Jon Fauer's books describe this procedure (can't remember which book right now)

John Babl
Miami

Most lenses are NOT linear. I do not know about the newest Zeiss or Primos, or the Set Geoff had re-housed (which I think are linear).

Basically what it means is that from 10 to 20 feet markings on the lens, the correct focus position (if the lens is in proper shape) will be 2/3 the distance away from 10 feet onthe barrel ( about 1/3 the distance from the 20 mark) NOT half way as if the lens was linear in it's focusing.

-- Steven Gladstone
Cinematographer - Gladstone Films
Cinematography Mailing List - East Coast List Administrator
Better off Broadcast (B.O.B.)
New York, U.S.A.


The only thing I could suggest is to make your own marks. Measure and mark it.


You cannot accuratly judge distances that far away anyway, I'd recommend you get eye foucs marks and interpet the inbetween points
.
Bret Lanius - Camera Assistant - Atlanta GA, USA
http://blanius.home.mindspring.com


I make my own marks, whenever possible, on any lens that has non-linear marks or any other sort of useless marks. For example, the Canon 11.5-138 zoom, or any of the Canon or Fuji HD zooms. I use these lenses all the time and, via this technique, I have finally "made peace" with them.

By the way, many of these zooms have a barrel section (closer to the front of the lens) with a larger circumference. Here's a trick I've found helpful. I start by taping the larger section, on the "dumb side", and performing a complete calibration pass, marking only that side of the lens.

Then, when I'm done, I tape over the original focus marks (on the "smart" side) and, with a helper, I simply rotate the barrel to each of the marks and copy that mark over to the smart side.

Why do I do this? The larger circumference means I have more room for marks, and I can make more accurate marks, and I can write larger numbers.

Andy Stadler
S.F.
Camera Assistant


It's not just the markings that need to be altered but the, erm, gearing as well.


The idea is that as someone moves towards you you have to make a constant rate of rotation for a constant speed of movement.

None of that turning faster and faster as people get closer
.
We also added a lot of in-between distances to the scale as well.

It's what happens when your AC gets asked what he'd really like.

-- Cheers
Geoff Boyle FBKS
Director of Photography
EU based
www.cinematography.net


I've read a lot about people remarking lenses when the actual lenses markings don't match up. I've always been under the impression that if a lense doesn't come up I send it back to the lense tech. I guess most of my rentals have been out of houses so I am at liberty to do so. My reasoning is if the markings are out, what else might be.For example, the focus barrel may be slipping and then any marks manufactured or post are of no use.

I understand there are some zooms that have minimal markings, but even when I do retape I leave the original marks viewable, just so I have something to compare. I love the new housings that they put on the Canon zooms. It's aftermarket, so be careful when pulling on the dumb side, sometimes the marks don't line up with the operating side.

Ian Choplick
LA AC


Thanks everyone for your thoughts. Its comforting to know that I am not alone in the struggle.

Making your own marks works very well for lenses over 50mm. It can also be done on the shorter lengths for stuff less than twenty feet away. Its that darn combination of a short focal length and long subject distance that is elusive. Luckily we have a lot of depth out there, but at 1.3 and at that end of the focus ring I would bet a hair off can be the difference of ten feet.

I did have a recent experience where I did make my own marks and was sorry about it later. The rental house put in a new ground glass after I did the checkout (and checked all the lenses). It was put in wrong. After the DP mentioned three times to me that it looked soft we went and made our own markings on a few lenses. Our eye focus was totally off though because the ground glass was not positioned correctly. Those first two days had a lot of useless footage. We luckily replaced the camera from another rental house after two days. The markings they made on the ground glass were also wrong. Beware of TCS in NYC. I have learned since to check the proper position of a ground glass during checkout.

It seems like I am asking for something with no simple or even possible solution. I can make marks on a zoom lens because its cinch to zoom in and get an eye focus on a 100mm lens but I cant do that on a 25mm in a dark room.

Thanks again
-Dana


Oh I get it, you made the marks in the field, not at the check out.

The fact that every lens was now not coming up the same in the rental should have clued you that there was a problem. What did your insurance company say? No one should change anything in a camera AFTER the checkout is complete without notifying the A.C..

Remember there are two paths of the image that must be set properly. The path to the eyepiece, and the path to the film plane. Checking focus by eye is not worthwhile if the Path to the image plane and the path to the ground glass are not both properly collimated. In this instance it sounds as if the path to the film plane was correctly collimated, but the path to the Eyepiec (g.g.) was mis-aligned. Probably you could have shot with the lens with it's engraved markings, and all would be well.

Next time, when all of a sudden the lenses don't match, you'll know the questions to ask. I'd throw up a zoom (if you had one), and done the zoom in focus and zoom out trick. At least that will tell you if the Viewing system is properly calibrated. On an SR or Aaton, you can use some Scotch Brand Magic tape, taped to the film side of the aperture plate (don't forget to remove the tape and clean clean the aperture when done!), and the zoom lens trick there. A quick in the field sort of check.

-- Steven Gladstone
Cinematographer - Gladstone Films
Cinematography Mailing List - East Coast List Administrator
Better off Broadcast (B.O.B.)
New York, U.S.A.


Funny you should mention this...

I find that on a lot of lenses (maybe ALL lenses? I haven't really checked) the markings on the dumb side are a little bit off in comparison with the operating side. It's only about half a line, so it doesn't really matter. I just find it funny. Maybe there is a reason for it?

Regards,
Wolfgang


I had always used a piece of lens tissue in the gate to accomplish this. Its not as sticky, and less cleanup - though it can be harder to see in low light situations.

I also have a 1" square mirror that Ill put in there to make it easier to see. Also works great for those times production or art surprises you with a CRT (tv or computer monitor) and you don't have that barton box handy....

--Photocon
Conrad Hunziker III


I had never heard of a ground glass being put in wrong so I never thought that it could be a risk to have it put in at the end of the checkout. I unfortunately didn't have a choice because they were putting 1.85 markings on a 1.66 glass. A very clear sign that something was wrong was when we couldn't get things at infinity to be sharp.

Thanks for the tip about using tape (or lens tissue) to do an in-the-field check on the viewing system matches the path to the image plane.

-Dana



If the GG of the camera was out of collimation, the 'factory' marks would have been incorrect.

Angelo Sartore
1st. AC
Melbourne
AUSTRALIA

reading lense markings- in no where land between the last witness mark and infinity

Say a 25mm at T 1.3 at a longer distance it can be extremely difficult to get a mark through the eyepiece (if you are at T 1.3 then it is probably a rainy dark night shoot with a low budget and no patience for mag light focus marks etc!). I can guess between 2 witness marks pretty well but when the barrell only has 20 feet and infinity where is 35 feet????

I think all lense manufacturers should put a Hyper Focal mark on the lense. i.e. our last outpost on the barrel. At least then we have a fair chance of guessing those last points after the last witness mark.

I know a puller who did an entire feature film on steady cam at T 1.3. He had one reshoot because of focus. On a 25 mm at 30 feet (or something similar). Exactly in that unmarked no mans land.

Charles Curran
1st A.C.


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