clintock
Galleryless Gearhead
With SLR and digital cameras and lenses, it's a fair amout easier to get instant feedback about lenses, since you can directly view the image..
Not so with RF.
So while I'm waiting for a replacement optic module for my sick Jupiter 3, I was trying to figure out a way to observe it's optical properties, some way to compare it to a known good lens without having to shoot film (heaven forbid!) and process..etc..
So here's the fun. You'll need a lens and a computer screen.
At about the normal distance you'd view the computer screen, hold the lens so you look through the film side, using the lens like a loupe to view the dots of the computer screen. Vary the distance of the lens from the computer screen and observe how the dots get larger and larger until they 'flip over' and get smaller and smaller as the distance in increased.
Note the behaviour and image as the dots get near the 'flip over' point. By flip over, I mean the image of the screen's dots gets as magnified as it can, and the image is ideally a single red, green or blue dot.
I noticed something interesting when observing the image as the distance of the lens passed though the 'flip' distance.
On my sick J3, the image of the dots in the center of the lens maximized and flipped well before the image of the dots on the edges..
The illness my J3 has can be seen here http://www.rangefinderforum.com/forums/showthread.php?t=34064
When doing this with other 50mm lenses, I noticed those with better out of focus properties (note I didn't say it) had the image flip all at once, where the center of the observed image of the screen dots as well as the edges got big and inverted together. The Hexanon m 50/2 was the best at being in unison.. the summicron 40/2 not as good, but close.
Like I said, stupid thing to do , but maybe it could serve as a way to predict things like if one put together a lens with a shim in the wrong place or somehing like that.
Not so with RF.
So while I'm waiting for a replacement optic module for my sick Jupiter 3, I was trying to figure out a way to observe it's optical properties, some way to compare it to a known good lens without having to shoot film (heaven forbid!) and process..etc..
So here's the fun. You'll need a lens and a computer screen.
At about the normal distance you'd view the computer screen, hold the lens so you look through the film side, using the lens like a loupe to view the dots of the computer screen. Vary the distance of the lens from the computer screen and observe how the dots get larger and larger until they 'flip over' and get smaller and smaller as the distance in increased.
Note the behaviour and image as the dots get near the 'flip over' point. By flip over, I mean the image of the screen's dots gets as magnified as it can, and the image is ideally a single red, green or blue dot.
I noticed something interesting when observing the image as the distance of the lens passed though the 'flip' distance.
On my sick J3, the image of the dots in the center of the lens maximized and flipped well before the image of the dots on the edges..
The illness my J3 has can be seen here http://www.rangefinderforum.com/forums/showthread.php?t=34064
When doing this with other 50mm lenses, I noticed those with better out of focus properties (note I didn't say it) had the image flip all at once, where the center of the observed image of the screen dots as well as the edges got big and inverted together. The Hexanon m 50/2 was the best at being in unison.. the summicron 40/2 not as good, but close.
Like I said, stupid thing to do , but maybe it could serve as a way to predict things like if one put together a lens with a shim in the wrong place or somehing like that.
pvdhaar
Peter
Sounds like you spent some quality time fondling lenses 
I wonder whether what you're seeing really has to do with how well a lens assembly has been carried out. Isn't it more an indication of field curvature?
I wonder whether what you're seeing really has to do with how well a lens assembly has been carried out. Isn't it more an indication of field curvature?
M
Magus
Guest
Post deleted by posters request
Ash
Selflessly Self-involved
If I'm not completely wrong, isn't that a test that pretty much proved the astigmatic/anastigmat thing?
Astigmatism is where the picture has out of focus areas towards the edges, whereas the Anastigmat lenses were developed for even focus across the whole plane. So in a sense your test proves whether the lens cels are in or out of collimation, as modern lenses should be from Ross/Zeiss/Goerz/tessar/protar/etc designs that are built to be anastigmats.
Astigmatism is where the picture has out of focus areas towards the edges, whereas the Anastigmat lenses were developed for even focus across the whole plane. So in a sense your test proves whether the lens cels are in or out of collimation, as modern lenses should be from Ross/Zeiss/Goerz/tessar/protar/etc designs that are built to be anastigmats.