Archived posting to the Leica Users Group, 2005/03/20
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Simon, For typical camera CCD's the active site is recessed in a well frequently covered by a microlens. If the light bundle strikes the lens at some suboptimal angle, that light energy will not reach the sensor resulting in loss of information. This can result in color fringing and/or loss of speed. As Henning demonstrated in his vignetting studies, lens design matters. I recall Erwin commenting that Leica designers tend to be more gentle with the light rays than other designers; I would have a discussion with him regarding just what that means. Specifically, talk about the Noctilux design and the ray tracing coming off the rear element. Don dorysrus@mindspring.com -----Original Message----- From: lug-bounces+dorysrus=mindspring.com@leica-users.org [mailto:lug-bounces+dorysrus=mindspring.com@leica-users.org] On Behalf Of animal Sent: Saturday, March 19, 2005 11:58 PM To: Leica Users Group Subject: Re: [Leica] Digital cameras with large aperture lenses don i don,t understand would you explain in more detail i understand that the angle of the incoming light will be perpendicular to the surface of the microlens will the larger refraction towards the well cause a loss off light energy ?where does that go ? heat? bremsen radiation ?what,s it called cerenkow radiation ? or do the off angle photons bounce around a bit and arrive slightly later then the center ones.the increased distance and arrival time does that make a measurable difference? thanks for all the replies however i merely wanted to point out that optical systems are still built that have ultra wide apertures and digital sensors. i read somewhere via a nemeng link i vaguely recall that an astronomer has modified a SLR to work with one of those wide xray lenses and that the lens is much closer to the sensor then with film. can speculate at nauseam on the technical details but don,t know much about optics anymore simon ----- Original Message ----- From: "Don Dory" <dorysrus@mindspring.com> To: "'Leica Users Group'" <lug@leica-users.org> Sent: Sunday, March 20, 2005 1:55 AM Subject: RE: [Leica] Digital cameras with large aperture lenses > Adam, > For a fast lens you typically have a large diameter rear lens element. > Yes, the light going through the center of the lens will stay the same. > But consider the rays coming from the outer edges of the rear element > and refracted into the off axis region of the sensor. This light is > also striking at a relatively high angle and may not reach the sensor > behind its lens and in the well. This effect will increase as the focal > length of the lens decreases; a 200 F2 will have almost full speed, a 24 > F1.4 may be as much as a half a stop off for a full frame sensor. > > This is one reason the Olympus efforts at lens design are worth looking > into, their whole line was designed for a specific sensor size with > known physical properties. > > Don > dorysrus@mindspring.com > > -----Original Message----- > From: lug-bounces+dorysrus=mindspring.com@leica-users.org > [mailto:lug-bounces+dorysrus=mindspring.com@leica-users.org] On Behalf > Of Adam Bridge > Sent: Saturday, March 19, 2005 3:22 PM > To: Leica Users Group > Subject: Re: [Leica] Digital cameras with large aperture lenses > > Okay - I STILL don't understand what you say is happening. > > I can understand that less light may be captured by the microlenses > over the sensor elements located at the edges of the sensors because > the lenses, I suppose, are designed for light arriving perpendicular > to the plane of the sensor when, in fact, they are not. > > BUT how does this affect what's going on in the middle of the sensor? > It doesn't make any sense to me at all. If you open from f2 to f1.4 > you should receive twice the number of photons arriving at the > micro-lens (since the lens works identically as that for film up to > this point.) > > So you are saying that something non-linear is happening at this > point. What would this be? Is the reflection at the air/microlens > interface involved? The microlens/sensor interface? It's about > photons, right? I can't believe we've dropped into the quantum realm > where QED explainations are required in order to understand the > interactions. But I sure could be wrong. > > anyway - I'd like to understand the physics and so far it's all > hand-waving and assertions. > > There must be a way to do some science here - but I think the camera > software, even in RAW mode, tends to cover up any effects that might > be happening. > > I'm really curious and dumbfounded - I'm not doing this for the sake > of argument. > > Adam > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information