Objectives with a Concave front element.
Posted: Wed May 18, 2022 4:52 pm
I decided to start a new thread about this concave front lens design, with a more general focus than the one objective. Reading the original thread would make a good primer for this thread.viewtopic.php?f=5&t=15471
It seems that objectives with the concave front element design feature probably are mostly derived from the 1938 patent linked to in the above thread. That feature along with modifications to the rear lens, at least in the early days of the development of more planar objectives were seminal to that goal.
Although the patent was secured in 1938, both in memory and physical evidence, prior to 1960, I have been unable to identify any commercially available examples that I can positively say are beholding to that patent Possibly, it may have been too expensive to implement until later on or the goal of wide fields may have taken precedence. For sure by 1955, fields of 19-20 mm were possible from several companies albeit not plan. Commercially obtainable plan systems did not become an economic reality until later : I would say the mid 60's but I may be off a few years.
I would hope that since the patent went to Zeiss, they might have commercialized the concept early on but then again I believe German patents may have been extinguished for a period after the war and Zeiss obviously had a period of rebuilding.
I have assembled a group of objectives that were made between 1961 and the early 70's that all seem to have such a design. With some it is a little difficult to tell without breaking the objective down but they all have the concave front element. Although not all are fully plan, those that are not do seem to have superior planarity , some across a fairly wide field for their time. They might be called semi-plan today. Only 3 of the objevtives were made after 1970 but sll stem ftom designs that pre-date 1970.
One of the non plan objectives is a Zeiss Jena objective but I don't know it's age. Perhaps someone more Zeiss knowledgeable does. Another may be an older Zeiss design and is an oddity because it is a water immersion apochromat.Many of the Lomo short objectives were designs pilfered from East Germany along with equipment and people but I don't know if this is one of them. It just has the concave front element and isn't particularly plan in performance. It may be evidence of the use of the design at Zeiss beyond the patent. Someone might know.
I could not find any Leitz objectives with this feature although sold a 40X .95 apochromat 37mm parfocal objective a number of years ago that I am sure had a concave front element. It seemed to be a late 50's , maybe 60's objective?
Picture 1 is a group shot.
Picture 2 , the same group from above. Note the two far right objectives in the middle row. They are both very early AO cat. # 1023 planachros from 1966 or 7. The ring around the front lens is different on each, one being a paint and the other being a smoked dark glass.
Picture 3 is the 10X .30 apochromat, 45X . 80 apochromat and a 45X .66 achromat all from the very first production of the AO infinity scopes around 1961.
Picture 4 is of the Zeiss Jena 40X .95 no cover apochromat (mfg. date unknown) and the possibly Zeiss derived Lomo 70X 1.23 water immersion apochromat. The water immersion apochromat is the only one of the lot that does not show extra glass beyond the lens surface. A metal cone covers right up to the edge.
Picture 5 is the oldest Nikon objective with this feature, a grandaddy to the objective in the original thread. 40X .65 plan achromat from 1968 or thereabouts. This one also has a smoked dark glass quality to the front lens block, similar to the earlier AO objective above. When looking at it from an angle the glass looks to have a black non reflective surface but when looking straight at the lens there is a very low glow of light visible through it, although non when viewing through the back lens.
If anyone wants any particular details about any particular objective, just ask.
It seems that objectives with the concave front element design feature probably are mostly derived from the 1938 patent linked to in the above thread. That feature along with modifications to the rear lens, at least in the early days of the development of more planar objectives were seminal to that goal.
Although the patent was secured in 1938, both in memory and physical evidence, prior to 1960, I have been unable to identify any commercially available examples that I can positively say are beholding to that patent Possibly, it may have been too expensive to implement until later on or the goal of wide fields may have taken precedence. For sure by 1955, fields of 19-20 mm were possible from several companies albeit not plan. Commercially obtainable plan systems did not become an economic reality until later : I would say the mid 60's but I may be off a few years.
I would hope that since the patent went to Zeiss, they might have commercialized the concept early on but then again I believe German patents may have been extinguished for a period after the war and Zeiss obviously had a period of rebuilding.
I have assembled a group of objectives that were made between 1961 and the early 70's that all seem to have such a design. With some it is a little difficult to tell without breaking the objective down but they all have the concave front element. Although not all are fully plan, those that are not do seem to have superior planarity , some across a fairly wide field for their time. They might be called semi-plan today. Only 3 of the objevtives were made after 1970 but sll stem ftom designs that pre-date 1970.
One of the non plan objectives is a Zeiss Jena objective but I don't know it's age. Perhaps someone more Zeiss knowledgeable does. Another may be an older Zeiss design and is an oddity because it is a water immersion apochromat.Many of the Lomo short objectives were designs pilfered from East Germany along with equipment and people but I don't know if this is one of them. It just has the concave front element and isn't particularly plan in performance. It may be evidence of the use of the design at Zeiss beyond the patent. Someone might know.
I could not find any Leitz objectives with this feature although sold a 40X .95 apochromat 37mm parfocal objective a number of years ago that I am sure had a concave front element. It seemed to be a late 50's , maybe 60's objective?
Picture 1 is a group shot.
Picture 2 , the same group from above. Note the two far right objectives in the middle row. They are both very early AO cat. # 1023 planachros from 1966 or 7. The ring around the front lens is different on each, one being a paint and the other being a smoked dark glass.
Picture 3 is the 10X .30 apochromat, 45X . 80 apochromat and a 45X .66 achromat all from the very first production of the AO infinity scopes around 1961.
Picture 4 is of the Zeiss Jena 40X .95 no cover apochromat (mfg. date unknown) and the possibly Zeiss derived Lomo 70X 1.23 water immersion apochromat. The water immersion apochromat is the only one of the lot that does not show extra glass beyond the lens surface. A metal cone covers right up to the edge.
Picture 5 is the oldest Nikon objective with this feature, a grandaddy to the objective in the original thread. 40X .65 plan achromat from 1968 or thereabouts. This one also has a smoked dark glass quality to the front lens block, similar to the earlier AO objective above. When looking at it from an angle the glass looks to have a black non reflective surface but when looking straight at the lens there is a very low glow of light visible through it, although non when viewing through the back lens.
If anyone wants any particular details about any particular objective, just ask.