Turning a camera lens to an afocal converter lens

Hello, optics guys of science and technology forum!

question: is there a way to turn a regular camera lens (the one that you mount in front of a sensor/film) to an afocal one (the one you mount in front of a lens) by removing rear glass element or some other glass modification? Changing order of glasses etc?

Internet is full of junk converter lenses. There are few good ones and they are usually very expensive and mostly discountinued. I'm wondering if one can expand the options by modifying regular camera lenses. I assume modification would need to include getting rid of the aperture blades or simply leave them at full aperture would be enough.

Thank you all.

I am afraid people here will be unwilling to answer you. (but I am from those crazy who like your question)
Sure, you can do *something*, but image quality would be worse than dirt cheap converter. Many lenses (e.g. retrofocus 35/1.4, telezoom 70-200) can be thought as afocal converter + master lens and if you saw it in between you get afocal unit and master lens, but their image quality alone will be abysmally bad, because they were designed to be one system to start with.
You might also decide to disassemble some lenses (cheap zooms with 15-18 elements come to mind), measure elements, run calculations, choose which will you use, make new housing, assemble it... but it's so much labor so you might just make new lens from scratch (or better yet: make 10000 of them, market them accordingly, and sell! profit!)

something about similar topic:

You might also need device called spherometer to measure curvatures.
Or deduce measurements from point spread function, but hey, that's difficult, and I am only dreaming of it.

Random bits cannibalised from lenses will be worse than the worst commercial offerings.

Check out what Raynox have available. I haven't tried their converters, but their 3-element close-up attachment lenses are certainly excellent.

rondom said:

Hello, optics guys of science and technology forum!

question: is there a way to turn a regular camera lens (the one that you mount in front of a sensor/film) to an afocal one (the one you mount in front of a lens) by removing rear glass element or some other glass modification? Changing order of glasses etc?

Internet is full of junk converter lenses. There are few good ones and they are usually very expensive and mostly discountinued. I'm wondering if one can expand the options by modifying regular camera lenses. I assume modification would need to include getting rid of the aperture blades or simply leave them at full aperture would be enough.

Thank you all.

Click to expand...

That depends on what use you have in mind for the convertor.

In days of yore, it was common practice to fit a second 50mm lens backwards onto the 50mm lens on the camera using a reversing ring. The result was a remarkably good combo for macro use.

Its RKM said:

rondom said:

Hello, optics guys of science and technology forum!

question: is there a way to turn a regular camera lens (the one that you mount in front of a sensor/film) to an afocal one (the one you mount in front of a lens) by removing rear glass element or some other glass modification? Changing order of glasses etc?

Internet is full of junk converter lenses. There are few good ones and they are usually very expensive and mostly discountinued. I'm wondering if one can expand the options by modifying regular camera lenses. I assume modification would need to include getting rid of the aperture blades or simply leave them at full aperture would be enough.

Thank you all.

Click to expand...

That depends on what use you have in mind for the convertor.

In days of yore, it was common practice to fit a second 50mm lens backwards onto the 50mm lens on the camera using a reversing ring. The result was a remarkably good combo for macro use.

--
Its RKM

Click to expand...

thanks. the purpose is to use it with a fixed lens compact. with any interchangeable lens camera it makes little sense these days. I was aware of the macro trick, thanks again...

D Cox said:

Random bits cannibalised from lenses will be worse than the worst commercial offerings.

Check out what Raynox have available. I haven't tried their converters, but their 3-element close-up attachment lenses are certainly excellent.

Click to expand...

thank you. I am aware of raynox. you're probably right, although part of me hoped that a simple trick, such as removing the rear glass element would turn any lens into a converter or something

Enginel said:

I am afraid people here will be unwilling to answer you. (but I am from those crazy who like your question)

Click to expand...

thank you for sharing my enthusiasm

Enginel said:

Sure, you can do *something*, but image quality would be worse than dirt cheap converter. Many lenses (e.g. retrofocus 35/1.4, telezoom 70-200) can be thought as afocal converter + master lens and if you saw it in between you get afocal unit and master lens, but their image quality alone will be abysmally bad, because they were designed to be one system to start with.

Click to expand...

how so? how do they behave as afocal lenses?

Enginel said:

You might also decide to disassemble some lenses (cheap zooms with 15-18 elements come to mind), measure elements, run calculations, choose which will you use, make new housing, assemble it... but it's so much labor so you might just make new lens from scratch (or better yet: make 10000 of them, market them accordingly, and sell! profit!)
something about similar topic:

http://www.opticsforhire.com/blog/2010/4/5/is-it-worthwhile-to-reverse-engineer-a-lens.html

Click to expand...

thank you for the excellent link. I realize this was a silly idea at best.

thank you!

rondom said:

Enginel said:

I am afraid people here will be unwilling to answer you. (but I am from those crazy who like your question)

Click to expand...

thank you for sharing my enthusiasm

rondom said:

Sure, you can do *something*, but image quality would be worse than dirt cheap converter. Many lenses (e.g. retrofocus 35/1.4, telezoom 70-200) can be thought as afocal converter + master lens and if you saw it in between you get afocal unit and master lens, but their image quality alone will be abysmally bad, because they were designed to be one system to start with.

Click to expand...

how so? how do they behave as afocal lenses?

rondom said:

You might also decide to disassemble some lenses (cheap zooms with 15-18 elements come to mind), measure elements, run calculations, choose which will you use, make new housing, assemble it... but it's so much labor so you might just make new lens from scratch (or better yet: make 10000 of them, market them accordingly, and sell! profit!)
something about similar topic:

http://www.opticsforhire.com/blog/2010/4/5/is-it-worthwhile-to-reverse-engineer-a-lens.html

Click to expand...

thank you for the excellent link. I realize this was a silly idea at best.

thank you!

Click to expand...

If you don't have silly ideas, you will never have any good ones.

He/she is probably wanted to learn something new, and this is good.

Steam engine also seemed silly idea to many in ancient Greece, why engines when you have slaves?

And on the other side, many more people think that socialism works, and it results not it forum questions but real consequences.

P.S. disregard that. I see I was reading your comment wrong.

by the way, it is possible to design a zoom lens which can transform to afocal converter