What is the lens (with a shutter) that has the smallest depth of field

[Ben Syverson]

The giant 12" Aero Ektar (ƒ/2.5) has got to have some of the shallowest depth of field at that focal length.

[Leigh]

I just ran some numbers on DoFMaster (http://dofmaster.com/dofjs.html)

for 4x5, 300mm, subject distance = 10 feet:
@ f/2.5 DoF = 0.15 feet = 1.8"
@ f/4.0 DoF = 0.24 feet = 2.9"
@ f/5.6 DoF = 0.35 feet = 4.2"

If the OP really wants minimum DoF then the Aero Ektar f/2.5 would be the best of the ones listed so far.
But it and other exotic lenses probably do not have shutters.

- Leigh

[benrains]

That link Hugo Zhang posted is for a 12.5" f/1.5 Taylor-Hobson. Since it weighs 83 lbs (37.6 kg) I'm not sure how practical it'd be.

[Steve Hamley]

There are uncommonly seen 360mm/36cm f:4.5 tesars (Schneider Xenars for example) in Compound #5 shutters. I also had S.K. Grimes put a 36cm f:4.5 Heliar into a Compound #5. You might post a WTB ad for a 36cm Xenar in shutter since it seems the most common of the fast lenses in shutter.

If you don't want to wait for the tessar/Xenar to appear in shutter, the more obvious choices are any of the 360mm f:5.6 plasmats like the Symmar, or a 14" f:6.3 Kodak Commercial Ektar.

Cheers, Steve

[Frank Petronio]

A 360/5.5 Schneider Tele-Xenar in a compound shutter (like I just sold for $250) does short depth-of-field on 4x5 nicely, without movements because of its telephoto design. Most of the shutters for these longer lenses will have maximum speeds of 1/125th or 1/60th (or slower in reality) so in some conditions you may need neutral density filters to reduce the amount of light.

[rjmeyer314]

There's a good discussion of depth of field at http://en.wikipedia.org/wiki/Depth_of_field. The operative formula is complicated, and I couldn't get it to paste here. In general however for a fixed distance of focus, lens aperture (set f-number) and circle of confusion size, the depth of focus goes roughly as 1/f^2, where f is the focal length of the lens. Thus, there is no particular lens that has the least depth of focus, but long focal length lenses in general tend to have shorter depths of focus. To get appreciable depth of field from most large format lenses you need to go to a very high f-number (small aperture).

[Paul Ewins]

The 300/4.5 Xenar was the one in the Compound 5, the 360/4.5 was only available in Barrel.

[Mark Sawyer]

In a conventional shutter and 300mm (anything longer needss an even bigger shutter), you're pretty much limited to f/4.5 by the shutter choke. Maybe there's an f/4, but I can't think of one...

If you can get by with a Packard shutter, there's a 300mm f/3.5 Tessar.

The most extreme that's still remotely practical (that f/1.5 Cooke is way heavy/large, and I doubt it covers 8x10), would be the 12" f/2.5 Aero Ektar that Ben mentioned. They usually have an "aircraft camera shutter", but I have no idea how to work one or what its restrictions are. A very large Packard (the back element is 4 3/4 inches across) might be the best solution. There are some equivalents to that lens too, like the 12" f/2.5 Goerz Type I.

If you lose the shutter requirement and aren't fussy about quality, the condenser lenses on an 8x10 enlarger are usually 10x10 to 12x12, and have a focal length in the 12 to 18 inch range. You could have an f/1 8x10 lens if you have a big enough front lens board...

[Sevo]

The most extreme that's still remotely practical (that f/1.5 Cooke is way heavy/large, and I doubt it covers 8x10), would be the 12" f/2.5 Aero Ektar that Ben mentioned. They usually have an "aircraft camera shutter", but I have no idea how to work one or what its restrictions are.

On-board power typically is 28V DC+200V 400Hz AC - cameras probably will only need the former.