Hugo, thanks for the suggestion. 36 bids, from $299 up to $2,550... that lens is hot! Looks like a challenge to me, but I don't know if COTS lenses will allow me to get anywhere. I'll have to take a look.Originally Posted by Hugo Zhang
Hugo, thanks for the suggestion. 36 bids, from $299 up to $2,550... that lens is hot! Looks like a challenge to me, but I don't know if COTS lenses will allow me to get anywhere. I'll have to take a look.
Matt, if you're not acquainted with dioptrique.info, take a look at it. It is in French, has prescriptions for > 1,000 lenses, many taken from patents. Eric Beltrando, its owner, is one of my friends. He was a friend of CEDIS-Boyer's owner and reoptimized Boyer prescriptions for properties of newly-arrived batches of glass. He wrote the program that produced the performance curves etc. on his site. I mention Eric and dioptrique here because he insists that Dagors (f/6.8 and f/7.7) have much less coverage than the 85 degrees Goerz claimed. He says the same about f/9 w/a Dagors, see http://www.dioptrique.info/OBJECTIFS11/00533/00533.HTM. He calculated that the f/18 Protar V has much more coverage. See http://www.dioptrique.info/OBJECTIFS1/00034/00034.HTM
I hope that I'm mistaken, but I doubt you'll be able to assemble anything like these lenses using COTS lenses.
Dan,
Yes a Protar V covers more, but not by that much than Zeiss Dagor. 16 inch image circle vs 15 1/2 for this 18cm. F/9 is much brighter than f/18. Believe me as I have used both. This 18cm lens covers more than a 24cm f/6.8 Dagor. If you are hiking with an 810 camera and need a small wide angle lens, it's a good choice. I know people can get coated 210mm G-Claron and Computar for less tha half prices with similar coverage.
https://www.cameraeccentric.com/stat...fs/zeiss_3.pdf
Hugo, I referred the OP to Eric Beltrando's calculations. Eric insists that Dagors of all speeds don't meet their coverage claims. In fact, he calculates that for "exacting applications" f/6.8 Boyer Beryls (Dagor clones) cover only 55 degrees.
I think our disagreement is due to different coverage concepts, the limit of illumination and the limit of good image quality.
In any case, making a working 6/2 double anastigmat from COTS lenses will take considerable luck. The glasses have to have the right combinations of refractive index and dispersion and the lenses have to have the right curvatures, otherwise cementing them together won't be possible.
Thanks Dan. This looks like another great resource. If you haven't seen it, there's a similar collection of lens designs from patents, etc. at http://www.lens-designs.com/. All of the designs are apparently in the public domain.
I definitely agree that it'll be rare to find COTS lenses to approximate the original prescriptions. The trick will be to see whether there are some lucky substitutions that permit acceptable quality.
As for the split triplet designs I've posted, I think I'll hold off continuing with the mechanical design until there's some DIY interest expressed in building it.
You're describing a Super Angulon type wide angle, which is a significantly more complex design than a Cooke triplet, with more elements and much greater bending of the elements.
If you take two off the shelf achromats like these and put them in a symmetric configuration (convex lenses out) about an aperture stop, you'd be making a lens like a Rapid Rectilinear. One could likely make at least adequate images this way. Once the lenses are chosen the only degrees of freedom are the lens spacing and the position of the aperture stop, so you don't have the same ability to optimize as the designer of the RR, but if the lens system is symmetric that minimizes several of the aberrations.Could you also do a similar thing using Nikon 5t, 6t, Canon 250d or 500d achromatic diopter lenses in combination with a minus-element?
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Butbut, no. The super angulon has 100 degrees and f8. Mine is 121.3 super symmar (120mm nominal) f5.6 plasmat -bastard or worse according some
I'm sure someone will find of-the-shelf lens elements to build a "miracle" large format lens. Mine would be a small 170-200mm covering 8x10" with room to spare. Sold the 180mm Fujinon-W inner ring. Going to test the 210 G-Claron against an early Nikkor-W with 77mm front.
If one can add elements from slr kit-lenses, the choice is widened, but it would take some time to investigate what the early AF 35-70, 18-70 and 28-80 are made of.
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I was inspired by Nodda Duma's original thread to look around at what one could make with inexpensive off the shelf lenses. As he says in that thread, a problem for even simple designs is that it's hard to find COTS flint glass elements. Many basic lens designs start from convex crown glass and concave flint glass. But in standard optics catalogs, most of the single elements are made of the same crown glass for the convex, concave, meniscus, etc (typically N-BK7 or an equivalent, which is the least expensive type of optical glass per pound AFAIK). Jason wound up using a fused silica lens for the concave "flint."
Surplus Shed sells a fair number of achromatic doublets and they also sell some of the elements as individual lenses, which means you can get a concave flint, but without any tech details other than diameter and focal length. Many of them are cheap enough (<$10) to fool around with. I got a variety of crown and flint elements with the idea of experimenting with a few rough designs. I am not an optical designer nor do I have Zemax, but there are some tools to visualize simple designs, such as https://arachnoid.com/OpticalRayTracer/, also found some calculations at pencilofrays.com and some Python modules. But next step, I need to make a spherometer to measure the radii of curvature of the elements I have.
I'm curious about the lens mounting methods. Not having machine tools, I got some threaded barrels and rings that are used to assemble telescope eyepieces (also from Surplus Shed), but it is still unresolved how to center and retain the elements in these.
If we had ham we could have ham and eggs if we had eggs.
Here is a link to a sample chapter from a book on lens design that discusses designing and optimizing a Cooke triplet. Lens designers know this stuff, but it is useful for non-lens designers to see the level of complexity and degrees of freedom that are used in designing what most photographers think of as a modest lens. A lens that is either much faster or has a much wider field, like a Super Symmar, is a much greater level of complexity.
https://www.willbell.com/tm/ChapterB.3.pdf This is Chapter B.3 from G.H. Smith, "Practical Computer Aided Lens Design," published by Willmann-Bell, and unfortunately Willmann-Bell just closed up shop so you should download it now. For educational purposes, read the text about the choices made and skip over the computer printouts.
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