35mm zoom and DOF
 

I am interested in purchasing a 35mm zooms lens, like a cooke 20-100mm. However the fastest zoom lens seems to be 3.1 . Would this lens be able to get the shallow depth of field as my 1.4 primes? Do you think a 3.1 zoom lens would be practicle in terms of exposure and DOF for this system or just a waste of money? I know that films have been shot with zooms. Any advise on zoom lenses would be appreciated.

Hi Dan,

To answer your question, an f3.1 lens will not deliver the shallow depth of field of an f1.4 lens. To evaluate whether or not you are willing to live with the compromise, you can simply dial your prime lens to that stop (call it a 2.8 and a half for all practical purposes) and see if the results are something you can live with.

Exposure-wise, you are putting yourself into a challenging situation as far as interiors go with this slow of a lens coupled with the light loss of the Mini35. Be prepared for some big lighting units!

I have used zooms with this system (see my article on the Seinfeld/Amex spots and it's great as long as you have enough light to accomodate, as well as the proper support gear (heavy-duty head/sticks, zoom motor and controller, appropriate mattebox etc).

Hi Dan,

I will have to caution you about trying to use a Cooke 20-100 zoom lens on the Mini35. This particular lens was designed before the full frame was widely used as a film format. It was designed to cover only the academy format (that preserves the optical audio on the side of the frame). On the Mini 35, the corners of the full frame will have a visible light loss. Most of the zooms except the most recent have this problem.

Guy Genin.
ZGC Inc.

Guy:

Interesting, that's news to me. I guess I always assumed the Mini35 used Academy framing. So, is it effectively the same as the Super 35 TV frame (sometimes known as BigTV?). Thus I should assume wider field of view for a given focal length than a standard TV "pumpkin"?

Guy,
Thanks as always for the great tech support and info.

Can somebody who knows, please tell exactly what the captured image size on the mini35 ground glass is? Is it 24 x 36 mm (still) or 21 x 15,3 mm (cine)?

It's cine, not still.