Aspherical lenses availability

[Bernice Loui]

Stopping down more than f16 is not going to reduce distortion of the spherical object in your image. Using a longer focal length lens (say 300mm) and backing up lots will help. The other factors is camera position. Appears the image was made at ground level which can alter the geometric shape of a round object being imaged on to a flat sheet of film. If possible, try setting up the camera from a location that places the spherical object on axis with the lens. Might not be possible, but suspect this will make a significant difference using the same 150mm lens.

As for geometric distortion of view camera lenses of the modern variety (Schneider Symmar S ) it is very low, but how they are used and shape of objects being imaged will have an effect of how the object being imaged transfer on to a flat sheet of film.

As for Aspheric lensed for LF, there were only ~one~ series of lenses made in volume production for LF photograph, they are the Schneider Super Symmar XL series which are wide angle lenses. Any wide angle lens would very likely make this distorting worst due to the shorter focal length.

Found the Schneider data sheet for the APO Symmar which is the later variant of the Symmar S, honestly they are not that different for distortion spec. Distortion is not more than 0.5% which is typical for lenses of this type and generic formulation. If there is a need to achieve lower geometric distortion, use a "APO" process lens they have much lower distortion, but in this specific image case, the possibility of lower the geometric distortion of the spherical object of using an extremely low geometric distortion APO process lens is not good. Longer focal length and camera position will change this distortion of the spherical object.





Bernice

[ic-racer]

I am experiencing distorion to my images...
I did my research and as far as I could find out...

More research is in order.

[Oslolens]

In my head it would make a difference if lens and film plane is directed directly towards the sphere, then shift the lens plane (or film plane if available) to make a more interesting picture, as opposed to what you have been doing. Also take note of differences of circle vs sphere when it comes to how it look on film when film plane and circle is parallel, shown on picture above. This is what made the copy camera work. My LF teacher missed out on this, borrowed my 180mm Fujinon-W with less sharp corners on 8x10", as opposed to use a wide angle 150mm to achieve sharp corners.

Sent fra min SM-G975F via Tapatalk

[Bernice Loui]

Since the Schneider data sheets were out, here is the 240mm f9 APO Artar (Originally Goerz process lens) for comparison. It's geometric distortion is virtually nil. Yet if the same focal length (150mm, will not properly cover 4x5, image circle is too small) APO Artar or similar process lens geometric distortion of the spherical object will not change.







Bernice

[simdil]

Stopping down more than f16 is not going to reduce distortion of the spherical object in your image. Using a longer focal length lens (say 300mm) and backing up lots will help. The other factors is camera position. Appears the image was made at ground level which can alter the geometric shape of a round object being imaged on to a flat sheet of film. If possible, try setting up the camera from a location that places the spherical object on axis with the lens. Might not be possible, but suspect this will make a significant difference using the same 150mm lens.

As for geometric distortion of view camera lenses of the modern variety (Schneider Symmar S ) it is very low, but how they are used and shape of objects being imaged will have an effect of how the object being imaged transfer on to a flat sheet of film.

As for Aspheric lensed for LF, there were only ~one~ series of lenses made in volume production for LF photograph, they are the Schneider Super Symmar XL series which are wide angle lenses. Any wide angle lens would very likely make this distorting worst due to the shorter focal length.

Found the Schneider data sheet for the APO Symmar which is the later variant of the Symmar S, honestly they are not that different for distortion spec. Distortion is not more than 0.5% which is typical for lenses of this type and generic formulation. If there is a need to achieve lower geometric distortion, use a "APO" process lens they have much lower distortion, but in this specific image case, the possibility of lower the geometric distortion of the spherical object of using an extremely low geometric distortion APO process lens is not good. Longer focal length and camera position will change this distortion of the spherical object.





Bernice

Really thanks for such detailed and precious info.

[simdil]

In my head it would make a difference if lens and film plane is directed directly towards the sphere, then shift the lens plane (or film plane if available) to make a more interesting picture, as opposed to what you have been doing. Also take note of differences of circle vs sphere when it comes to how it look on film when film plane and circle is parallel, shown on picture above. This is what made the copy camera work. My LF teacher missed out on this, borrowed my 180mm Fujinon-W with less sharp corners on 8x10", as opposed to use a wide angle 150mm to achieve sharp corners.

Sent fra min SM-G975F via Tapatalk

Thanks for the suggestion. Actually I had to tilt the lens standard toward the tower in order to increase DOF. But I didn't notice any change in the geometry, overall.

[Doremus Scudder]

Objects at the edge of the field will always have this kind of distortion to a certain degree (depending on the focal length of the lens) simply due to the fact that you are projecting the image on a flat surface (the film). That stretches and distorts the edges kind of like the way the continents are stretched on a map projection (Greenland really isn't bigger than Australia...).

There's nothing wrong with your lens and an aspherical lens won't help here. Moving back and using a longer focal length lens or recomposing the image (or living with the distortion) are about all you can do.

BTW, aspherical lenses allow complex lens designs and designs with fewer elements. However, Plasmat designs, like your 150mm Symmar are well corrected for distortion and chromatic abberation.

Best,

Doremus

[simdil]

More research is in order.

Thank you so much, it´s a very precise example.

[Drew Wiley]

Longer lens. It's that simple.

[simdil]

Longer lens. It's that simple.

What focal length would you suggest, let's say for the same picture, in place of my 150mm?