List of lenses that can resolve 36mp

Started May 6, 2012 | Discussions thread
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Jim Sims
New MemberPosts: 1
Re: List of lenses that can resolve 36mp
In reply to Einst Stein, 1 month ago

I am new to DPreview, so this has likely already been covered, but there are more gremlins that can be devastating to a lens' performance that its Diffraction Limit - the most common that I have found is longitudinal chromatic aberrations. I have measured some reputable lenses that have as much as .015" (.381mm) focus displacement between red (@620nm) and blue (@480nm). The performance of this lens was just beginning to peak at f:16. It was a broadcast lens that the station sent to me, complaining about poor resolution. Also, I believe that a digital camera's Low Pass filter will degrade an exceptional lens' resolving performance.

Note: As late as the 1980s, Lenses that were made for 3-tube color TV cameras had no chromatic correction.  I suppose the camera manufacturers believed that, since the back-focus of each color channel could be adjusted, there was no need to go to the expense of chromatic chromatic correction.  I had built a device to adjust the back-focus of 3-tube video cameras, optically, with an autocollimator that my shop built for that purpose. We rolled it out at the 1981 NAB conference, in Dallas, TX.  I made a statement, in the exhibit area that Broadcast lenses were not chromatically corrected and a sales rep from one of thevideo lens manufacturers took exception to my statement.  Ho left our booth but soon returned with a very nice Japanese gentleman whom he introduced as the engineer that had designed most of that company's broadcast lenses and then instructed him to tell me that all of their lenses were chromatically corrected. The Japanese looked at me, and then turned to the sales rep. and said, "I never said that". Some time later, I cant remember the hear, I received a call from an engineer a CBS Technology Center.  He asked me if I had made the statement, a the NAB Conference, that Broadcast lenses were not chromatically corrected. When I confirmed the statement, he then said that they had also made the same observation.  I was invited to come to the Center to talk about it.  He said that the significance of the two independent observations opened the door to to a presentation of a paper to the Society of Motion Picture and Television Engineers (SMPTE).  I went to Stamford, CT to visit Technology Center, and it was a very productive meeting. The engineers at the Center gave me very good suggestions about widening the bandwidth od the filters in our Video Tri-Color Collimator, and we talked about setting setting optical standards for the yet settled HD TV format for the United States.  The future looked exciting, but it was all for naught.  CBS closed Technology Center, a victim of major cost cutting measures.  By that time, three channel color cameras were already installing solid state sensors, instead of tubes, and the independent adjustment of back-focus of each color channel was no longer and option.

I can not remember the Diffraction Limit equation contained in Rayleigh's Criterion off the top of my head but if anyone is interested, I will look it up. there is a short cut that does not degrade the accuracy of the original equation. Rayleigh's Criterion assumed that the lens was perfect and that there was no atmospheric issues. Diffraction becomes worse as the aperture diameter is reduced.  Longitudinal Chromatic aberrations are most evident at the lens' largest aperture and its effect becomes less as the aperture size is reduced, causing the depth of focus to increase.

Jim Sims

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