You know, those outermost elements look to be 'one to a block' for both the concave and convex surfaces.
The two outer elements are the same on each side of the stop, and made out of inexpensive glass. Only the doublets are asymmetrical. After letting the optimization run over the weekend, the performance is about as good as an entirely non-symmetrical lens would be. This will help cut cost further.
I made a couple more tweaks to the optimization inputs, and I'll let it run unattended for several days. While that's going I'll put together some information on the performance to give you a better idea of what it can do. When I'm satisfied that it's been tweaked as best it can, I'll generate drawings to get the optics quoted.
I also need to cross-post to the large format photography forum. I wanted to wait until I could get closer to getting quotes.
I tried to cut out the doublets and replace with singlets but wasn't as satisfied with the results.
-Jason
Yes. The design wanted either those curvatures on the outer elements or make them achromatic doublets to control color. I could pull back on the curvature but I think it would blow up.
"... to control colour": does that mean it would be easier to design a lens for B&W use only?
"... to control colour": does that mean it would be easier to design a lens for B&W use only?
No: color means color spectrum...that is, the range of wavelengths which the film is sensitive to. As you know, different colors have different wavelengths, and the angle of refraction through glass is dependent on wavelength. B&W film is sensitive to a range of wavelengths, so you have to correct for all the colors (bring them all to the same focus) within that range. Otherwise what would be color fringes or halos in a color print would be a larger fuzzy blob in B&W.
A follow-up question on the asphere question (actually I suppose this could apply to any shape): why is a ground element considered to be superior in quality to a molded element? I'm also intrigued by your mentioning non-moldable glass.
I understand that, but isn't the range for B&W film smaller than for colour film, thus easier to handle?
And hence the discussion for single coated (SC) lenses for B&W and multi coated (MC) for colour?
Or am I mixing up the wrong ingredients?
I took a look at reducing the curvature of the outside elements and it shredded the performance like I thought it would... just grisly... Huge spot sizes everywhere. The optical design equivalent of the big German guy in the Raiders of the Lost Ark airplane fight scene...
Of course, because you're not worrying about lining up all the spectrum as perfectly as is needed for color. (I'm probably saying this wrong, but I hope my meaning is understood). Different colors have a different "bend" to them so when they pass through the lenses they don't all line up in the same place, so the color lenses that are corrected for this commonly called APO, our little more complex to design because they have to redirect different wavelengths of color to slightly different directions so that they all lined up together on top of each other on the film plane.
Did that make sense? And of course am I wrong? lol
I took a look at reducing the curvature of the outside elements and it shredded the performance like I thought it would... just grisly... Huge spot sizes everywhere. The optical design equivalent of the big German guy in the Raiders of the Lost Ark airplane fight scene...
Probably the 77 mentioned in post #112. I'm almost certain.
Or maybe use the Cokin P system.
82mm filters will be required out front, so that means the Cokin P system.
82mm filters will be required out front, so that means the Cokin P system.
No. 77 mm will vignette as well. (See the layout). But I would hope the cost of the lens and a Cokin P system will be less than the 150 SS XL.
Hi Jason - thanks again for the answers you've given so far to my questions. In relation to falloff, I wonder if you can comment on the "tilting pupil/pupil distortion trick" used by Rodenstock and Schneider in the Grandagon-N and Super Angulon series respectively. As I understand it, this optical trick causes the entrance or exit pupil to "tilt" as it is viewed off-axis, retaining its circular shape and effectively reduces the falloff progression to Cos^3 theta.
Michael
Also noticed that moving the first lens away from the rest of the groups increases "soft focus", ie sph aberration. I can put the first lens in its own threaded cell so you can move it out from nominal position for increased soft focus, but there will be one additional mechanical part (adds to cost).
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