Image Circle of Hasselblad 110mm f2?
Hi, Was just wondering if anyone knew what the image circle is for the Zeiss 110mm f2 FE lens? Have looked at the site that addresses this
but don't actually know what all the numbers mean. I realise that it optimised to cover the 6cm x 6cm frame but am wondering how far off it would be from covering a 8cm x 8cm frame. I have previously held up a Pentax 67 105mm 2.4 up to my large format camera and this covers the area (8cm x 8cm), so am wondering how far off the 110mm is. The other one I was also wondering about is the Noritar 80mm f2. Am really interested in these fast lenses... Ok, thanks so much, any information would be greatly appreciated!
Best Regards Andrew
Zeiss supplied this lens in two versions in the Rollei 6000 mount, which I am familiar with. The second version had improved flare control, including a mask on the exit pupil side. If the same is true in the 'Blad mount, look for the early version without the mask, as the mask will physically limit the image circle.
Image Circle Diameter for a Given Projection Angle
The specifications for this lens are impressive. The reference you cited gives a diagonal coverage angle of 39°, but doesn’t specify at which aperture. Lenses generally give the least coverage wide open.
As the diaphragm is progressively closed, the projected image circle increases in size up to some maximum. Many 4” x 5” format lenses produce maximum diameter image circles at or close to f/22, a middle value for many lenses of this format.
If we suppose that the 39° coverage angle occurs at the middle value—f/5.6 in this case—then we can calculate the diameter of the image circle at infinity focus at the f/5.6 aperture as
d = 2f*tan(ϴ/2)
We have f = 110.8mm
ϴ = 39°
d = 2(110.8mm)*tan(19.5°) = 78.47mm
Of course the diameter of the image circle gets progressively larger as the lens is focused closer than infinity.
If Zeiss reckoned the 39° projection angle at an aperture larger than f/5.6, then you might get an even larger image circle as the lens is stopped down.
The diagonal angle of view as stated by Zeiss is what you get on film, at any and all (!) apertures.
This diagonal angle of view, though perhaps a measure for the minimum size of the image circle at f/2 (we know that it covers that at least), is not a measure for the size of the image circle itself.
It cannot be used to calculate the image circle projected by the lens: it's the result of a crop by the film format that happens to be in use. And there are other factors involved as well, such as physical vignetting by the barrel.
They do show the coverage for two f-stops. The u(mm) is distance from the center (radius) in millimeters. So, like the calculation above, you can see that at just less than an 80mm circle (40mm radius), the image quality falls off quite a bit.
The "relative illumination" graph is not zero at 40mm, so the circle of illumination will be somewhat bigger than 80mm, however, as the MTF graphs show, there will not be good image forming light at the far, dim edge beyond 40mm from center.
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Hi, Thanks so much for the responses, much appreciated! I am looking to use this lens wide open but mainly for portraits and such, so maybe it could be a goer. Would never really look at focusing to infinity and probably a full length portrait is the widest i would be looking at.. Might just have to wait till I can get hold of one here in Melbourne and hold it up to the GG of my camera.. Thanks again for all the responses.. Cheers Andrew