Sanders McNew
9-Oct-2005, 23:51
I want to mount a ca.1910 Goerz Dagor Series III No. 2, 7-inch lens (Compur dial shutter) on a 5x7 Deardorff. I want to use it as a convertible lens. I know this has been discussed in earlier threads, but I have additional questions that I hope someone can address before I go to the expense of a new lensboard for the lens.
I know that, using only one element, the focal length grows 1.75 times, to just over 12 inches. This is good.
I gather that the maximum aperture shrinks from f/6.8 to f/13.5. This one is a shocker to me.
Question one: How does one compute the aperture values at less than wide-open? I see the maximum aperture is basically multiplied by two. Is that true for the other apertures? For example, does f/11 become f/22, f/16 become f/32, and so on? If not, how does one compute aperture sizes? Basically, am I losing two stops across the board?
Question two: How does shooting with one element alter depth of field? If I'm shrinking the effective aperture, am I getting more DOF in the bargain?
Question three: Does shooting with one element affect lens coverage? A 7-inch Dagor should handle 5x7 work. Will a 12-inch demi-Dagor do as well?
Question four: In portraiture, I often shoot with this Dagor wide open at f/6.8, to get some slight diffusion in the highlights. Will I see the same effect when shooting the demi-Dagor wide open at f/13.5? Are there issues presented by shooting the single element wide-open, that the complete lens does not present? (I am shooting entirely in B+W, so color issues are of no concern to me.)
Question five: Is there a "sweet spot" for the aperture when shooting with a demi-Dagor?
I am grateful for your wisdom.
Sanders McNew
www.mcnew.net
I know that, using only one element, the focal length grows 1.75 times, to just over 12 inches. This is good.
I gather that the maximum aperture shrinks from f/6.8 to f/13.5. This one is a shocker to me.
Question one: How does one compute the aperture values at less than wide-open? I see the maximum aperture is basically multiplied by two. Is that true for the other apertures? For example, does f/11 become f/22, f/16 become f/32, and so on? If not, how does one compute aperture sizes? Basically, am I losing two stops across the board?
Question two: How does shooting with one element alter depth of field? If I'm shrinking the effective aperture, am I getting more DOF in the bargain?
Question three: Does shooting with one element affect lens coverage? A 7-inch Dagor should handle 5x7 work. Will a 12-inch demi-Dagor do as well?
Question four: In portraiture, I often shoot with this Dagor wide open at f/6.8, to get some slight diffusion in the highlights. Will I see the same effect when shooting the demi-Dagor wide open at f/13.5? Are there issues presented by shooting the single element wide-open, that the complete lens does not present? (I am shooting entirely in B+W, so color issues are of no concern to me.)
Question five: Is there a "sweet spot" for the aperture when shooting with a demi-Dagor?
I am grateful for your wisdom.
Sanders McNew
www.mcnew.net