Can someone explain lens cast by aperture to me

Started 4 months ago | Discussions thread
ProfHankD
ProfHankD Veteran Member • Posts: 7,522
Re: Can someone explain lens cast by aperture to me

fferreres wrote:

I will be paying more attention to this effect. It really can be very dramatic under some circumstances, and it is seldom discussed or observed by anyone.
Could a lens be optimized in such a way that it has an opposite effect? (Colder wide open)

Certainly, but that seems harder to do. This quickly gets to the concept of APO. Especially on older lenses, these color issues were essentially not modeled when designing the lens. The term APO is supposed to mean corrected for at least 3 colors to agree on focus plane, and many non-APO lenses were only computed for one or two colors, so the blue/red behavior may have been a bit of an out-of-band surprise... especially for lenses intended to be used with monochromatic film that might not have had a very broad spectral response curve.

I may owe you $5000 in free consulting already for all the easy scientific explanations across topics, and I am very grateful for your time and participation in this forum.

No consulting fees here -- especially when I'm talking on the fringes of what I understand (which is the case on this particular topic). We really need somebody with optics design experience to give THE explanation.

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