Lens Testing

[Corydon Anderson]

Just wondering if any experienced DPs could explain step by step the way they test lenses in pre-production? I know it can vary a lot depending on what the production is but i'd like to learn a detailed process of how a professional would undertake lens testing.

[Jimmy Gilmore]

Looks like no one is going to answer your question so I'll get the ball rolling here. Caveat, I'm not a DP - I'm a writer/director and unfortunately too often the producer too.

 

In my experience, either the DP owns his own lenses and is familiar with them or they're rented. The rental house will prep the camera and lens set so they work perfectly together. I'm not sure where you live but if you wander into say Panavision in Hollywood you'll see a bunch of techs with cameras on benches lined up with charts on walls. They test the lenses to make sure the focus marks match up to the actual focus distance, that the exposure is where it should be and that there are no obvious problems with the image quality. They also run the cameras through a series of tests to make sure you won't have any problems on set.

 

If you're really interested in how this all works I'd suggest visiting a local camera rental house. Most of the ones I've done business with over the years are staffed by some pretty damn friendly and helpful people. Your success is their success.

 

Camera prep isn't really a DPs job. I certainly would not pay one their day rate to screw around with back focus. But I don't work in the land of big budget features and the process may be quite different that world.

[Gregory Irwin]

I need to weigh in here. As a career first assistant cameraman, I've been testing lenses for over 30 years. My first point is that ACs generally test lenses - not DPs. This is done during the camera prep. My second point cannot be stressed enough. The rental house does prep the lenses and everything else involved for that matter but it is the responsibility of the AC to certify that all of the gear is up to standard and ready to shoot with - especially the lenses. It is not the rental house's burden.

 

For a feature film, I generally prep at the rental house for 2-4 weeks. The better part of the first week is spent on nothing but the lenses. Now, I do realize in this day of age and with smaller production budgets that prep time can be as little as one day. In this case, there is no time to properly test the lenses. Your priority is to make sure that you have all of the proper gear and that it generally all works and that the lenses are at the very least, focusing properly. But what I'm going to explain ahead is what I do for a complete lens prep.

 

First of all, I arrange ahead of time for the rental house to supply between 4-5 sets of similar primes and zooms, or as many as they can. On my first day of prep, I'll make sure that the camera body that I'm testing the lenses on is prepped as far as ground glass collimation, back focus, flange depth, etc. then I do my first pass of all of the lens sets by checking their focusing ability on a simple lens chart. This officially starts the elimination process. If I don't like the feel of the lens, my initial reaction to it's sharpness and contrast, it's eliminated out of the pool.

 

After going through all of the lenses in this fashion, the survivors of the first cut now go onto the lens projector. This projector beams a lens chart big on a wall in a dark room through each of my lenses. This is where I can really see the characteristics of each individual lens, ie. color, stigmatism, chromatic abberation, internal flare, the eveness of sharpness across the field of view, etc. Now I see a drastic cut of lenses. Second round of elimination completed.

 

The third round, if shooting film, is now actually testing the remaining lenses on film. THE FOLLOWING IS EXTREMELY IMPORTANT!!! I make a large lens chart, no smaller than 6-8 feet wide by 4-5 feet high. This chart is made up of a collage of duplicates of very contrasty, sharp BLACK AND WHITE magazine photographs. Magazines like Vanaty Fair, Cosmo or any other publication that would have slick full page ads of jewelry, close ups of models faces, etc. In other words, any photograph that has NO COLOR BIAS and that contains very sharp detail. Watch ads are very useful. Once I've collected numerous photographs, I select one for the center of the chart. It can be anything that you want for your centerpiece. After that, I begin building outward, horizontally and vertically from the center with all of my duplicate photos to achieve symmetry. Once this task is complete, I light it evenly to a T2.8 and begin the photography with my widest lenses to the tightest. I like to use Post It Notes to write the millimeter and the serial number of each lens, stick it on the chart so I can identify each lens on screen. I move the camera back as I get tighter with each lens so I fill my field of view with as much chart as I can get.

 

When I project my lens test on the big screen, it is easily discernible to see the COLOR differences between each lens whether they are warm or cool. This is because I used black and white photos that contained no color bias allowing me to see nothing but the color of the lens' glass. I can also see contrast differences as well as sharpness differences. I now can select my final choices for my lens set and have any final adjustments made to the selects. I also check the selected lenses that the iris settings are accurate.

 

As far as digital lens prepping is concerned, all of the above applies with the exception of actually recording the test. This assumes that you have a calibrated monitor to judge your lenses on. Of course you can record it if you need a reference for later. Having said all of this, I have noticed that many of the new series of lenses such as Arri's Master Primes are very consistent with all of the optic variables.

 

This completes my testing process and I now feel confident that I can go forth and trust my lens choices. Good luck with all of your own lens testing. Test as much as your schedule allows. At the very least, I would always project the lenses. This gives loads of valuable information to assist you in making some good choices.

 

G

 

 

 

 

[Jimmy Gilmore]

Thanks for the detailed response. A lot of really great info.

[Gregory Irwin]

Here is an example of a lens testing chart. I didn't make this one but it illustrates what I described in my above posting. Mine are usually more dense with the photographs.

 

 

G

Edited December 23, 2012 by Gregory Irwin

[Gregg MacPherson]

Do you have a normal URL for that. I couldn't make that work.

 

Thanks.

[Gregory Irwin]

Do you have a normal URL for that. I couldn't make that work.

 

Thanks.

 

Sorry. I can't make it work either. :(

[Rob Sanders]

Most cinematographers or still photographers send any lenses for testing, collimating, CLA...ect to a professional lens repair facility. Taking apart lenses is NOT their job and its something you do NOT want to do yourself. We have a enough trouble with the lighting, composition, film choice...ect! ;) And most DP's do not have there own collimator, although I am sure there are a few that do. For cine lenses on the USA West Coast this is #1 place for repair / testing of cine lenses. And here is lens sharpeness test chart.

 

http://www.ducloslenses.com/.

 

 

 

 

 

http://cdn-static.cn...story2large.jpg

 

Edited December 30, 2012 by Rob Sanders

[Rob Sanders]

You can download the resolution chart in pdf here

:

http://www.graphics.cornell.edu/~westin/misc/res-chart.html

 

To do basic lens sharpness and color testing. Take notes at every T-stop or F-stop, focus, focal length of the lens.

 

Basic lens Test Equipment Needs

- Two Diffused Light Sources

- ISO 12233 Test Chart

- Xrite Color checker

- Kodak Color Separation & Grey Scale Large

- Light Meter

[Gregory Irwin]

Here is an example of a lens testing chart. I didn't make this one but it illustrates what I described in my above posting. Mine are usually more dense with the photographs.

 

 

G

 

 

Edited January 2, 2013 by Gregory Irwin

[Rob Sanders]

"Here is an example of a lens testing chart. I didn't make this one but it illustrates what I described in my above posting>"

 

Very nice Gregory, thanks for sharing. I have never seen this lens test before only the ISO 12233 Lens Test Chart pdf download I shared earlier in this thread.

Edited January 3, 2013 by Rob Sanders

[AlejandroGomez]

but how actually work this chart? For what is what?