See my edit to my previous post. I didn't notice the broken lines at first glance. They are my neighbour's lenses, I use an SL 66.
I looked at the 120 mm Makro-Planar as a numerical example of the offset. The broken line is at f/8. That corresponds to shift of about 0.64 mm, or 0.5%, if my maths is correct.
They're tiny alright. When I first started using my Hassy I didn't even notice the mark, even though I was used to seeing them on my Canon and Nikon lenses. :rolleyes: I think though that at f/8 (or f/11 on MF) it would be a very minor focusing adjustment for a scenic.
Ed, first off very few lenses have absolutely no chromatic aberration in the visible part of the spectrum. Secondly, very few lenses are corrected for the invisible non-photographically useful parts of the spectrum. Some enlarging lenses are, according to their makers' propaganda, well corrected for 350 nm - 700 nm, few taking lenses are well-corrected for as wide a range.
I disagree. *NO* lenses have "absolutely no chromatic abberation" in the visible (or anywhere else) part of the spectrum. Every design involves a compromise ... cost and sheer possibility are always determining factors. The only question is "How much deviation from pefect correction of chromatic abberation ... or spherical, or coma ... is acceptable."
Why don't you admit that you've overstated your position or made exagerated claims for how wonderful modern lenses are?
??? I did? My point was that the IR focusing line on the Hasselblad lenses was probably omitted fpor a reason ... and that working without it, focusing from the filtered image on the groundglass ... was probably the way to go with modern IR emulsions.
I oversated how "good" something was??? I haven't done that for some time ... well before I started working in a Metrology* Lab.
* No, not "Meteorology" (weather). Metrology is working with eye-watering "fine" measurements.
The current lenses appear to use a broken line instead of a red line - one of the DoF lines is dashed instead of solid, and it isn't red. At first glance, I thought that it was just a little dirt or chipped paint!
As you'll notice from my original post in this thread, I agree with you about focussing with a filter that passes some visible light when combined with the type of 'IR' film currently available in 120. I got the clear impression, perhaps erroneously, that you were disagreeing with my suggestion that focus shift depends on lens design.
To tell the truth, I don't know if I was "agreeing" or not. I only tried to add what little I know about lenses and optical pheonomena. Chromatic abberation - "color correction" - happens to be one of those characteristics widely misunderstood ... usualy one hears something like, "I don't need a Color Corrected lens ... / Chromatic abberation doesn't affect me ... etc.,... because I don't use color film - I only work in black and white." That particular belief is so ingrained among some that it is nearly impossible to convince them that ALL imaging is degraded by the lack of correction in that area. Another widely held - and erroneous belief - is that chromatic abberation has something to do with color fidelity - that overall color balance will be affected ... which is only remotely "true" ... I was going to write what would be a pun - the image would be only affected around the "fringes"...
One "Idea" I'm working on now ... removing the lens from a Hasselblad 503Cx body ... lens mounting flange to film plane will be something like ~ 80mm; taping an approriate pinhole over the flange surface; adding a #25R (or ...?) filter - and blasting away with Dynalite 1000mx strobes - full power onto Konica or MACO IR film.
Something tells me the Polaroid back is going to be used - extensively - here, to BEGIN to determine exposure. I wonder how much IR the Dynalites kick out ... ?