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Sam David Zhang

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  1. Wonderfully explained. I actually reached out and emailed Roland from photosynthesis.co.nz which is a wonderful resource for cataloging Nikon lenses and has a lot of info regarding older vintage lenses like serial numbers, tech specs, etc. He said the following: Hi Sam, Lens coatings are very thin layers applied to the glass. The layer is ¼ the wavelength of light thick, and works by destructive interference to reduce reflections. If you imagine light striking the lens. Some light is reflected off the air/coating surface but most passes through. Then some more light reflects from the coating/glass boundary. The light reflecting from the glass surface is now ½ wavelength out of phase with the light reflecting from the coating ( ¼ in plus ¼ out). Because the two reflected rays of light are ½ wavelength out of phase, the peaks of one coincide with the trough of the other, which cancel each other out – destructive interference, which reduces the amount of light reflected. Because coatings cause destructive interference for a particular wavelength of light, reflections from other wavelengths (colors) are more obvious, which gives the coating its color. Coatings only work well with one wavelength (color) of light. Multilayer coatings have layers of different thickness so each layer works with a different color to give better suppression of reflections across the visible spectrum. Coatings work best if the light passes at right-angle through the glass. When it passes through at an angle the distance it travels between the air/coating layer and coating/glass layer becomes bigger so no longer causes destructive interference for that wavelength (it would work for a longer wavelength). That is why coatings are not so effective from light coming at extreme angles. This also explains why coating change color when you view them from a different angle. Nikon apply different coatings to each lens to optimise the performance of the lens as a whole, which is why different lens surfaces often have reflections of different colors. I hope that helps! Roland
  2. Picture is from someone on mflenses.com, not mine, but it's a great example of the title. I do however have a small set of Nikkors that I use for stills and video use. I was cleaning them and noticed that some had a blue-purple sheen associated with the coating, while one of them had a greenish one. I know that Nikon switched up the coating colors along the way of manufacturing many different lenses in their Nikkor line, but what really did the different colors mean and why did Nikon opt to switch it up? Was it just a manufacturing/engineering reason or maybe inventory? I'm sure the coatings, even if they were differently colored, were pretty much identical in function and design up until Nikon switched to their modern coatings. I'm just suddenly very curious about this topic and thinking about the possibility of rehousing my Nikkor set in the future. My OCD wants to have identical colors so that the lens set looks really sexy together. But, I understand that this is a bit much, hahaha.
  3. Looking back at the video, you can hear the audio track have a noticeable cut/edit right around the timestamp I give for when he talks about it. Maybe two sentences that were out of context with each other got spliced together with the magic of editing. I think it could have been a weird decision by the editor to just frame the sentence that way. While it did make English sense, it doesn't make much lens sense. Deadlines and etc who knows what happened. I like Shane he's got mountains of experience and wisdom. I'm betting that the video got pressed to tape fast, and Shane didn't edit the video himself.
  4. I was watching Shane Hurlbut compare lenses in the Cooke, Leica, Canon, and Rokinon lines using a pretty standard comparison setup. He mentions something at 08:45 in the linked video below about how the vintage Cooke lenses were able to retain circular globes of bokeh even when stopped down when shot on film. However in the digital age, sensors will show the more angular bokeh on lenses like these with a lower number of iris blades. I understand the relationship between the shape of bokeh and the iris blades and aperture, but I couldn't wrap my mind around the physics of why a stopped down lens would retain globe shapes on film versus a digital sensor. Does anyone have a nifty wiki article or an explanation about this phenomenon? Shane Hurlbut explains stop-sign bokeh on older lenses on digital vs film
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