and I thought I was trying to put it simply! You could in theory make the upside down one, but it would be huge and never sell. APS format K-mount wide angle lenses are probably the best bet.
-Scott On Fri, 2003-12-12 at 19:08, Ryan Lee wrote: > Kudos Scott, for a very logical and well thought out think-out (even if the > middle bit was in a foreign language :)) I didn't think it would be that > complicated, but coming from a very non-scientific background, you're much > more likely to be on the right track. What I pictured in my mind was > basically simple trapezoid (is that what it's called? like imagine a pyramid > with it's head cut flat so that the flat top and the base have the same > angles) prism type of element (as opposed to a conventional curved lens). > I'm not even sure if it would bend light like that.. If it did though I > reckon it'd have to be pretty thin to prevent loss of image quality? Anyway > I'm thinking from a very abstract point of view, physics really isn't my > forte.. But even if it's not feasible, in line with your logic and the > upside down image in the viewfinder, I suppose that'd be saleable too, > though maybe bundled with a refconverter type of device, attaching itself to > the viewfinder and re-flipping the image.. What say you Scott? > > Regards, > Ryan > > > ----- Original Message ----- > From: "Scott Nelson" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Saturday, December 13, 2003 12:08 PM > Subject: Re: Sensor size and convertor idea > > > > On Fri, 2003-12-12 at 17:10, Ryan Lee wrote: > > > Just an idea since there's at least one thread discussing lenses and > > > multiplication factor. How feasible would it be theoretically for > > > manufacturers to come up with a teleconverter like accessory to fit > normal > > > lens projections to APS size sensors? I hope it doesn't sound incredibly > > > naive, but I just figured that in some cases people would be desperate > > > enough for a focal length that they might not mind the 1 or 2 stop loss > or > > > the degradation. It doesn't sound terribly difficult to do or expensive > > > either.. Why haven't they done it already (or have they..)? > > > > > > Rgds, > > > Ryan > > > > I've thought about this before, but this little discussion is going to > > get me thinking about it properly. My conclusion is that I don't think > > this is possible without interfering with the SLR mirror. Here's my > > logic: > > > > First consider a regular teleconverter. Just looking at one we can see > > that the focal length is positive because of the way the elements are > > curved. For this very crude calculation, we can approximate it as a > > single thin lens, and use the thin lens equations > > > > 1/f = 1/o + 1/i > > m = -i/o > > > > i = image distance > > o = object distance > > m = magnification > > f = focal length > > > > for the regular teleconverter, o is negative, because the object for the > > TC is the image from the regular lens, which is usually formed behind > > the TC. > > i must be positive, otherwise there is no real image > > |i|>|o| because we want a magnification greater than 1 to expand the > > size of the image. This works fine and the TC refocusses the new image > > farther away, leaving room to stick a TC housing between the lens and > > camera body. This also explains why 2x TCs are almost always shorter > > than similarly designed 1.4x TCs > > > > correspondingly, m is positive, so we don't have an upside down image. > > > > ************************************** > > For the so called reverse teleconverter, we would need to have |m|<1, > > which means |o| > |i| and we have a problem. The wide angle converter > > moves the real image closer to the back of the lens than the original > > image, so there is no spaces for a converter. You could make this work > > if you let o be positive, but then the image would be upside down in the > > viewfinder. > > > > -Scott > >
