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Deep focus in large formats

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Erik Lokegaard

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Are large format cameras such as IMAX and the upcoming Red Epic 617 unable to achieve as deep focus as, say, 35mm cameras? Is it an issue of, the larger the camera sensor, the less depth of field?
Thanks
 
It is an issue of the larger the sensor, the longer the lens required to get the same framing. For example, if you get a closeup of a face in 16mm film, the same shot with the same lens will look wider in 35mm film, so you compensate by using a longer lens. Longer lenses have shallower depth of field, so in practical terms, larger formats usually lead to shallower depth of field.
 
Actually if you have a medium or large format camera and you want deeper depth of field you can just stop down more than you would on a smaller system.
Because of the larger sensor you should encounter diffraction at a much smaller stop than 35mm or 16mm. So shooting at f22 or f32, or even f45 would be plausible and get you a deep focus. The only thing of course is shooting interiors at those apertures at 24fps would require a lot of light. So, yes you can get deep focus, but its not always going to be as practical as it would be with a smaller format.
 
It is definitely harder to get "full" depth of field with larger sensors (or film). On a 4"x5" view camera, it is common to stop down to F32 or more -- with exposure times of 1/4 second or more (for exterior shots during "magic hour"). Other than the longer exposure times, lens performance at very small apertures (f45, f64) also becomes an issue. This is where the "movements" of a view camera become critical, as they allow you to adjust the plane of focus to maximize depth of field without having to stop down quite so much. View camera movements also allow you to adjust the geometry of a scene and are essential to some photographic genres (architecture, product photography, landscapes). Which, of course, brings up the question: Will we ever see a bellows mount for the Epic 645 or 617?

Cheers,
Jim

(real name: James Coker)
 
chuck colburn said:
No it is not.
Click to expand...


Not wishing to be cantankerous but I have to disagree here - it is a case of this. You can spin the argument around to discuss focal lengths vs field of view but the practical upshot is exactly what is asked above - a given field of view on a larger neg = less DOF. Stopping down is not always practical unless you happen to only make films which are set in midday exterior locations.

In the world of "ideal" discussion (ie: web forums for example) where the choice of lens or t-stop might seem like an entirely 'artistic' choice, this is fine, but on location with failing light, cranky directors and trying to get a wide shot at the top of the crane reach - your choices narrow.

Similarly, lighting up a set to T5.6 is a costly process and bound to (A) take more time and (b) cost more - which will raise production eyebrows over time. The norm on stage is to light up to (for example) T4 but rarely beyond this, unless there are special requirements. So to all practical purposes the focus puller at 2.8 on IMAX has a much harder job than he does on the other formats (35mm, 16mm).

Watch the opening bank raid in The Dark Knight to see the drop off in DOF that a larger neg brings (Now that FP would have had a few sleepless nights I'd imagine).
 
James T Mather said:
Not wishing to be cantankerous but I have to disagree here - it is a case of this. You can spin the argument around to discuss focal lengths vs field of view but the practical upshot is exactly what is asked above - a given field of view on a larger neg = less DOF. Stopping down is not always practical unless you happen to only make films which are set in midday exterior locations.
Click to expand...
Completely agreed.
 
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