Which lenses will cover “Open Gate” on the Alexa XT?
Super 35 film has an image circle of 28.5mm and the Alexa 16:9 is a little smaller at 27.8mm. Using the “Open Gate” mode on the Alexa XT camera requires an image circle of 33.5mm for complete lens coverage. Many of the lenses in use today will not completely cover this larger sensor size. What lenses will work with Open Gate? I decided to take a look using the Gulf Camera inventory of lenses to find out what will work – and what will not. If you have a favorite lens you would like me to add to the list – by all means get one to me and I’ll add it to the test.
Alexa “Open Gate” produces an image with a 1.55:1 aspect ratio. Apart from visual effects photography the 1.55:1 aspect ratio is too ‘square’ for most modern production. An aspect ratio of 1.78:1 (16X9) is most often seen in television production and 1.85:1, 2:1 or 2.4:1 are commonly used in feature film production. I have selected 1.85:1 as an Open Gate “cropped” aspect ratio as it is very close to 16X9 for television and also is used frequently in feature film.
Lets take a look at some commonly used lenses with An Alexa XT in Open Gate mode. I pointed the XT camera at a very evenly lit wall and recorded a clip of Arriraw at 3414X2198 pixels – the Open Gate size image. I then debayered using the Arri software and snapped a jpeg of each clip. I’ll show you first the full 1.55:1 Open Gate image and then a cropped 1.85:1 version at 3414X1845 pixels. The pictures are shown at a low resolution to keep the file sizes under control. Consider the following a database. . .
I won’t hold it against you if you skim!
First, the zooms:
So. The 17-80 looks more like a 40-80 using Open Gate and the 24-290 is great at 30mm/1.85 but then starts to show more vignette as it gets toward the long end. I think the hand held zooms all look pretty good at 1.85 depending on your tolerance for the fall off in the corners. The mild vignette with some of the lenses will be very hard to see when not pointing at a blank wall.
Now, lets take a look at some primes: Zeiss CP-2, Leica Summilux C, Cooke S4, Cooke S5i, B & L Super Baltars, Arri Master Macro 100, Arri 10mm, Arri 14mm
First, a couple of CP2 lenses. With the big full frame coverage there should be no problem.
Ok, as expected the CP-2 lenses designed for Full Frame sensors work fine in Open Gate – so I’m going to move on to other glass.
The Leica Summilux C lenses are spectacular in all regards so working with them on the Alexa XT in Open Gate would be fantastic. . . if they cover:
How about the much loved Cooke S-4 lenses?
The fast Cooke S5i lenses look good with the Open Gate:
What about some vintage lenses? Lets see how they do. . .
The Arri wide primes are about as expected. . .
Alexa XT Open Gate is no problem for the Arri Master Macro 100mm. . .