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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 08 Feb 2012 (Wednesday) 04:01
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DIY lens?

 
C2S
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Feb 08, 2012 04:01 |  #1

Hello,

I've been thinking about a possibility to make a custom lens for a Canon DSLR using an APS-C sensor. It would be for low-light video use only, so the sharpness shouldn't necessarily have to be really stellar. There's no need for really fancy features either.

So the design would be relatively simple:

- Fixed focal length: the closer to 20mm, the better
- Fixed focus: to infinity, or at least 100+ meters
- Fixed aperture: around f/1.8, slightly larger if possible

You're probably thinking of the Sigma 20mm f/1.8 at this point. Yes, it's a good alternative, but first I'd like to hear if this project is feasible. What kind of an undertaking do you think this could be, and what would be the estimated price range, roughly?

Any thoughts, and links, are welcome. :)


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ZoneV
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Feb 08, 2012 04:42 |  #2

I suppose a full manual lens, with no automatic iris, no EXIF data.

Fixed foxus is good. f/1.8 or faster and 20mm focal length for a DSLR with EF-S mount is not good.
I am not a lens designer, but I have worked with some of them. The lens design (optics) itself is only one thing in this calucation, the mechanical design is needed, and the the cost for production of the lens is a big further factor.
Are you talking about one single lens, or about hunderts or thousands?
One single lens sample production will be roughly estimated about USD 10.000. For the design I would think the same amount should be calculated in the very first apporach.
If you are ok with these costs, you could ask some lens design companys, best someone with a production facility at hand.

Whats wrong with the Sigma?


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phreeky
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Feb 08, 2012 04:57 |  #3

Who says "DIY" and then asks for costs? Do you really mean DIY or do you mean custom made?

You could certainly do the mechanicals yourself if you had the toolset (i.e. lathe) and skills. You could do electronics too for aperture control and perhaps even AF if you spent enough time on the reverse engineering. The optical design as well as the glass manufacturing is where I'm lost and would not even be sure where to start.

The question that cannot be ignored: why?




  
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C2S
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Feb 08, 2012 05:09 |  #4

Nothing that large scale at all: this would be simply a modest personal project for curiosity - so a single lens only.

If I've understood, you are saying that the short focal length combined a large aperture for this mount would be something very challenging, perhaps impossible, for a DIY project at home. From what I've read, I know that focal lengths of about 45mm are more common for simple lens designs, and trying to shorten it to 20mm will make things more complicated. On the other hand, some simple lens designs can apparently reach f/1.0. But I don't find it hard to believe that an even less extreme combination might prove difficult to achieve.

As for the Sigma, just the price. Yes, it's not much, but I would like to find out if it's at all possible to learn to create something close to similar yourself for even less, since the feature set would be quite simple (or so I thought!).

phreeky:

For this project, electronics, aperture control, AF, metering, EXIF, things like that would not be necessary at all.

Thank you both for your thoughts.


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SkipD
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Feb 08, 2012 05:20 |  #5

C2S, do you realize why the EF-S specification was adopted by Canon? It's because making a very short focal length lens for the APS-C format cameras, while maintaining the quality of Canon's existing EF line of lenses, is an engineering problem that drives up cost for several reasons. Thus the concept of allowing the lens to project further into the mirror box was generated.

For your project, I feel that finding a good quality fully-manual lens such as those produced in the 1960s for Nikon F family cameras and using a simple mount adapter would be the way to go. I periodically use all of the Nikkor lenses that I bought for my two Nikon F cameras back in 1967 with my 20D. These lenses have manual focus (which could be locked with a piece of tape if that were necessary), manual manual iris (aperture) control, and excellent quality optics.


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C2S
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Feb 08, 2012 05:45 |  #6

Sigma makes 4.5mm fisheye lenses for APS-C sized sensors (ok, it's a fisheye), and 10-20mm zooms (which I've purchased), so I was hoping that maybe a prime lens with a focal length of ~ 20mm could still be achievable. Not that it's really crucial for the focal length to be really that short if that's a major problem, but I'd rather not go much higher than 24mm either, because at that point it's starting to make more sense to just use the 50mm f/1.8 I already have.

The old manual lenses are actually an option I've very often thought about, especially for video work. But I could use more information about the lens types and their adaptors, and whether it's still easy to acquire them these days or not.

Although, the important question here is, what are the chances that those old manual lenses include something talked about in this thread, that also works on APS-C? I'm assuming the chances for that are slim, unfortunately. But I'd be happy if I was proven wrong.


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ZoneV
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Feb 08, 2012 06:44 |  #7

C2S wrote in post #13847543 (external link)
... From what I've read, I know that focal lengths of about 45mm are more common for simple lens designs, and trying to shorten it to 20mm will make things more complicated. On the other hand, some simple lens designs can apparently reach f/1.0. But I don't find it hard to believe that an even less extreme combination might prove difficult to achieve...

Yesterday I got two more books with lens design examples from the old days.
The diagramms for the fast photographic lenses ~f/1.0 are with 6 lenses or more as far as I remember - partly with asperhical lenses. A f/1.0 lens for a condensor is much more simple - but there is no real color correction and a very low sharpness.
What simple f/1.0 designs did you find?

For a 20mm EF-S lens you need a retrofocus design type:
http://en.wikipedia.or​g …Ang%C3%A9nieux_​retrofocus (external link)

Every single lens need to have exact front and back curvature, thickness, refracting index and dispersion properties. It is not enough to take some lens elements with about the same shape as in a diagramm and assemble them into a tube :-)

http://en.wikipedia.or​g/wiki/Photographic_le​ns_design (external link)

I bought these books - and the Modern Lens Design book from Smith to get more knowledge about lens design, and to make probably some DIY lens modification. First One try last weekend with a Helios 44 failed.


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C2S
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Feb 08, 2012 07:05 |  #8

What simple f/1.0 designs did you find?

Nevermind that comment, it was about a lens (a single piece of glass) resting directly on the lens mount. :)

Thanks for the reading, and hopefully you succeed with your project(s).


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ZoneV
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Feb 08, 2012 07:41 |  #9

C2S wrote in post #13847610 (external link)
...Although, the important question here is, what are the chances that those old manual lenses include something talked about in this thread, that also works on APS-C? I'm assuming the chances for that are slim, unfortunately. But I'd be happy if I was proven wrong.

I have mount converted a Canon FD 24mm f/1.4 L lens to Canon EF mount (documentation on homepage).
That lens will work on APS-C too. But that lens is still expensive ~ 350-600 Euro.
I have a defective FD 24mm f/2.0, but not converted. FD conversions are not easy.

For sure there are other manufacturers with such focal leghts, but probably it could be hard to find the f/stop you want. Nikon F, Olympus M42, Pentax K mount are no problem to adapt to EF-S.


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C2S
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Feb 08, 2012 08:06 |  #10

24mm f/1.4 would be a workable focal length / aperture combination, but from what I'm being told, apparently impossible to build by a DIY hobbyist, even if the design is greatly simplified and most features stripped away.

The lack of focusing motors makes it less expensive, which is good, but on the other hand, the complex design with many elements (and expensive materials) to maximize versatility and the image quality increases the price even more, which is what I would try to avoid.


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gjl711
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Feb 08, 2012 08:15 |  #11

As a former machinist for a design shop specializing on toys and mock-ups, making your own lens is easy. You can do that in a few hours at a cost of $10 or less. (Just head on out to American Science Center (external link) and pick up a few pre-ground lenses or a lens-o-rama bag)

Making a good or even decent lens is way harder.


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ZoneV
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Feb 08, 2012 08:32 |  #12

C2S wrote in post #13848073 (external link)
24mm f/1.4 would be a workable focal length / aperture combination, but from what I'm being told, apparently impossible to build by a DIY hobbyist, even if the design is greatly simplified and most features stripped away.
...

I made the conversion of the lens mount only - of a existing manual Canon lens.

gjl711 wrote in post #13848103 (external link)
As a former machinist for a design shop specializing on toys and mock-ups, making your own lens is easy. You can do that in a few hours at a cost of $10 or less.
...
Making a good or even decent lens is way harder.

A fast lens with 50 mm focal length would be possible with nearly no problem. But that cheap single lens has cromatic abberations because not even a achromat is used. Furthermore speherical abberations and so on. Probably all optical aberrations.

But a fast 20 mm lens with a back focal length that is longer than the focal length, needs kind of retroficus technic. That could probably be DIY made with some cheap lenses too - but only for monochromatic light and let guess 10° image field usable with a roughly good result (not as good as 18-55 quality with full visible spektrum and much wider field
).


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saranw71
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Feb 08, 2012 08:39 |  #13

This might help :
http://www.lensrentals​.com …/08/lens-geneology-part-1 (external link)
http://www.lensrentals​.com …011/01/cooking-with-glass (external link)


-Saran W. :lol:
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C2S
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Feb 08, 2012 08:44 |  #14

All related articles are appreciated - thanks!


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rick_reno
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Feb 08, 2012 09:02 |  #15

i'm pretty good with epoxy and super-glue, but i wouldn't attempt to make to lens. ;)




  
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