Lou Jost wrote:Using a longer tube lens gives exactly the same image as a shorter tube lens (if both lenses were perfect), just larger. So the CA of the objective is blown up along with the rest of the image.
So a 100mm tube lens on MFT and a 200mm lens on FF give the same image with the same amount of CA in relation to the frame width. But yes, if you are comparing long vs short tube lenses on the same frame sizes, the CA would be more apparent on the more magnified image.
ah, so you are saying that with same sensor, same obj on longer tube lens would cause more apparent CA problem, right? If that is the case, how would a 20x 0.75 objective perform better using a 400mm tube lens? I thought CA is a rather glaring factor when comparing obj's, maybe I am too green with this matter.
As for different sensor size comparison,
So a 100mm tube lens on MFT and a 200mm lens on FF give the same image with the same amount of CA in relation to the frame width.
I understand the same image size, but in terms of chromatic correction, is your statement that, they get same amount of CA, a fact or something you think is true?
As far as I know, though you get same size image, the optical path light travels is very different for MFT with 100mm tube lens vs FF with 200mm tube lens. Most chromatic correction magic heavily depend on the optical path so that lights of different freq will converge at designed point along the optical path.
So I am not sure if your statement is empirical based on your observation as you deal with this stuff on daily basis, ie, what you think, or something that can be supported by theory. I THINK chromatic correction magic of each objective are guarded trade secrets, so exactly how they are implemented, the formula that creates glass material might be really different.
So please point me to some reading material to back your statement (MFT + 100 vs FF + 200 are same in terms of chromatic correction). Thanks in advance.