Bob, in fact Imagon uses H stops, that are "close" to F stops and T stops...Originally Posted by Bob Salomon
I guess that regarding exposure H stops are equivalent to F stops, for effective exposure based on the area covered by the holes, as T Stops include the transmission loss in the glass and surfaces, while the H concept is (reportedly, IIRC) about effective geometric aperture and not including coating performance, etc.
All would be numerically close, of course...
I have searched (in vain) for a leaflet (from Rodenstock) which I had explaining the H (helligkeit) stops. The leaflet described the H-stops and the fact that a pure mathematical computation of the actual (vs effective) stops based on the area of the center stop plus the peripheral openings did not yield the same aperture result - in terms of light transmission - as a single opening. Bob's reference to "T" stops is related to this and would seem to indicate that Rodenstocks' calculation was based on the actual transmission rather than the theoretical computation. From all of the literature which I have read over the years, much of Rodenstocks' calculation was based on the anticipated degree of enlargement of the negative.
In my own use of the 250mm Imagon my results on 4x5 were always very satisfactory but I found it unacceptable on 8x10, not because it would not cover the format adequately but because of aberrations which have been addressed in previous posts re: 250mm Imagon coverage. It does what it was designed to do very well (again, my opinion only)... when used in accordance with the manufacturers' instructions.
Joel
AFTER ALL THIS...
The 250 5.8/7.7 arrived. It does not fit on the 200 Imagon lens. While there is no front lens element on the Imagon, there is an empty lens ring. With the ring in on the 200, the 250 disk is too big in diameter to fit. I removed the ring and the disk is then too small to fit. Guess I will have to look to sell or preferably trade for a 200 5.8/7.7 disk.
Ed
As was said before, why not make your own disk? I just used what I had on hand in the studio for a proof of concept. It worked fine. I could always make a fancier one with a fly-cutter on a drill press, a cnc machine, a 3d printer.....
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
Hmm What is the diameter of the new ring? 53ish mm or 68ish mm in diameter? that was meant to be 63mm not 68.
Last edited by cowanw; 1-Mar-2019 at 12:42.
Looks to be 60ish. Definitely not 68. 53 is what I need for the 200 Imagon.
Ed
To be honest, I have neither the tools nor the skill. The idea of a 3D printed copy of the 200mm 5.8/7.7 disk interests me but you need one to copy. Is that something you can do and if so, what might it cost? Just curious.As was said before, why not make your own disk? I just used what I had on hand in the studio for a proof of concept. It worked fine. I could always make a fancier one with a fly-cutter on a drill press, a cnc machine, a 3d printer.....
Ed
You can't make a circle in card stock or know someone local who can?
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
I was think about "fly-cutter on a drill press, a cnc machine, a 3d printer"
I already said this above, but I made what you see in the picture with a compass, ruler, an x-acto knife, a Sharpie, and a scissors. It's not perfectly round, but then neither are the apertures on many old lenses.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
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