Image Circles and Lenses

[Michael Erlewine]

Is there a list of image circles for F-Mount lenses somewhere? I am going to get either the new small MF cameras, the Hasselblad X1D or the Fuji GFX. Both have the same sensor,  the size is 43.8×32.9mm.

I am told that the image circle for these cameras is 55 mm for both, calculated as sqrt(22^2 + 33^2).

So the Image Circle is 55mm. What does that tell us as per our Nikon lenses?

What I am wondering is how, short of manually trying them, can I begin to get an idea as to what among my lenses (F-Mount) will be usable on this larger sensor? Is there a list somewhere or a simple formula?

I also understand that I may get away with some smaller image circle lenses if I shoot macro, which I sometimes to.

I have some LF lenses, like the Nikkor 120 mm AM-ED f/5.6, for example.

[Roland Vink]

I assume you meant "55mm = sqrt(44^2 + 33^2)"

There is no shortcut to determining the useable image circle for Nikon F-mount lenses. All older film-based and modern FX lenses are designed for an image circle of sqrt(24^2 + 36^2) = 43.3mm. Some will project a much larger circle, but how much of that is useable is hard to say. All unit focusing lenses will produce a larger image circle as you focus closer, so the older micro/macro lenses would be good candidates.

[Michael Erlewine]

I assume you meant "55mm = sqrt(44^2 + 33^2)"

There is no shortcut to determining the useable image circle for Nikon F-mount lenses. All older film-based and modern FX lenses are designed for an image circle of sqrt(24^2 + 36^2) = 43.3mm. Some will project a much larger circle, but how much of that is useable is hard to say. All unit focusing lenses will produce a larger image circle as you focus closer, so the older micro/macro lenses would be good candidates.

So, basically, wait and do it by trial and error is best?

[Roland Vink]

Basically, yes.

If you know of lenses with comparatively little light fall-off towards the corners and maintain good sharpness, they would likely have a usable image circle beyond 43.3mm. I would start with them first. Lenses with strong light fall-off are already getting very close to the limit of the image circle, so there is probably not much more, although the image circle will increase proportionally with extension so they may do well at close range. Lenses which go soft towards the corners probably have a usable image circle smaller than 43.3mm.

[Frank Fremerey]

In Schneider APO Digitars the "Image Circle" is defined as the area illuminated with at least 90 lines per millimeter resolution. The illuminated area can be much larger of course.

At f/11 the Apo Digitar 5.6/120mm (No 48) has an image circle of 15 centimeters by that definition, same at 1:1 magnification.

At 1:1 the Nikkor AM ED 120mm Large Format lens has an "Image Circle" by some unknown Nikon definition of 23 centimters.

[Akira]

I can only think of PC Nikkors and the old tele lenses (400mm and longer) using the focusing unit.  The image circles of the old teles covered at least 6x6 format (and there were versions for Zenza Bronica, if I remember correctly), although they would not satisfy Michael's need.

[David H. Hartman]

For useable image circle of unit focusing lenses expect the useable diameter to increase with stopping down until diffraction kicks in. I would test center and deep corners from maximum aperture to f/11. Typical published specs for large format lenses is maximum aperture and f/22.

[pluton]

Longer lenses are natural candidates for use on a larger circle, but many tele lenses intended for 35mm use have baffles at the rear to restrict stray light in the camera body.

[Dr Klaus Schmitt]

All quite true what has bee said here. So you need at least a useful (i.e. with high resolution) image circle of 55mm diameter.
As you mainly do macro photography, by aware that the image circle at 1:1 (1x) is 2x (double) the one at infinity. At higher magnifications it gets larger on a linear scale (if that lens has no shielding light baffles, already has been mentioned)

Product information helps, so for instance your Printing Nikkor 150mm has 88mm image circle, your Apo EL Nikkor 105mm (new model) has 80mm diameter

You would need modified mounts / helicoids for using them on these different MF cameras.

[Roland Vink]

be aware that the image circle at 1:1 (1x) is 2x (double) the one at infinity.

When focusing by extension, I assume resolution also declines proportionally, so at 1:1 the resolution (lines per mm) is also half, all things being equal. Of course this depends entirely on whether the lens is corrected for infinity or close range...

Most of Michael's work that I have seen is not high magnification, they are closeups maybe in the range of 1:10, in which case the image circle would only be 10% larger - not enough to cover 55mm unless the lens has a large image circle to begin with.

The image circles of the old teles covered at least 6x6 format (and there were versions for Zenza Bronica ...)

The same telephoto lens heads were used for both Nikon F and Bronica 6x6 (except possibly very early 800/8 and 1200/11 with smaller rear elements may only cover 35mm film/FX format - they were soon upgraded with larger rear elements to cover 6x6). These lens heads were mounted on a focusing unit which attached to the camera, with different focusing units for Nikon F and Bronica. The early telephoto lens heads did not use ED glass so are not APO, unlikely to be well enough corrected for Michael's needs, as Akira said. Also, the focal lengths (400, 600, 800, 1200mm) are not very practical for studio closeups.