Archived posting to the Leica Users Group, 1999/07/07

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Subject: [Leica] Re: Noctilux Gloom-Buster VS 75mm f/1.4 ..
From: Jim Brick <>
Date: Wed, 07 Jul 1999 17:14:43 -0700

I believe DOF is determined by image size. That is, if you set a Noctilux
at f/1.4 and frame a scene, then set a 75 Summilux at f/1.4 and frame the
same scene exactly like the Noctilux (The Noctilux is closer to the scene
than the Summilux in order to have the exact same image on film) the DOF of
both lenses will be exactly the same.

If you stand at exactly the same place and take the photograph, at f/1.4,
with both lenses, the Summilux will record less of the scene than the
Noctilux. 75mm vs. 50mm. The Summilux will have less DOF, in this
circumstance, than the Noctilux.

The f/1.0 DOF statistics belong only to the Noctilux.

The Summilux at f/1.4, focused at it's closest position, might possibly
have less DOF than a Noctilux at f/1.0 focused at its closest position.
Perhaps exactly the same. This is a good project for someone. I believe the
75/1.4 close focus/image size is the best of the M lenses.

I have a photo of a tulip, printed 16x20 on Ciba, that I took with my
75/1.4, at f/1.4, and focused at its closest position. The DOF is literally
the front surface of the tulip. Barely a few millimeters.


At 07:40 PM 7/7/99 -0400, you wrote:
>If I remember correctly, DOF, to first order, depends on the absolute
>aperture. The noctilux has an aperture of ca. 51mm, whilst the 75/1.4's
>is about 54 mm. I'd expect the noctilux to have greater DOF wide open. 
>As always, I'm open to correction.
>> Mark Rabiner writes:
>> > I'm wondering what the difference would be a say 4 feet away DOF wise
>> > both lenses wide open?
>> > My hunch is the Noct would give you about 1 inch front to back and the
>> > 75 would give you 2.
>> At 4 feet the 50mm f1 gives you 1.44 inches, the 75mm f1.4 gives you 0.72
>> inches.
>> So you were close, but the wrong way round.
>> David Morton