Lens design #3

[Stefano]

If f/2.8 is not fast enough for you, here's an f/2 lens. The focal length is about 47 mm.

 

The lens is not yet optimized for "buildability". Also, the distance from the rear element to the sensor required for infinity focus is less than that of lens #2. Mounting a helicoid would be more difficult.

 

The lens does not correct for chromatic aberration.

 

Lens simulated using WinLens3D Basic. Simulated at 340 nm.

 

 

 

 

The lens has some barrel distorsion and vignetting at wide apertures.

 

I will post more detailed information when I will optimize the lens for buildability.

[Avalon]

Not sure I would be able to build more complex lens but thanks for interesting suggestion. I could try building single element FS aspheric lens just to experiment and learn more. Maybe you know best UV capable vintage lens made from glass I could try finding?

[Stefano]

Ulf has measured some lenses, the Soligor 35 mm f/3.5, Focotar-2 and a few others go deep in UV. If you want to go below UVB you need lenses designed for UV.

[ulf]

I think building a lens structure with more than one element can be quite challenging if you are not using precision building blocks like the ones sold at optical component companies like Thorlabs. 

With designs including several elements it becomes quite important with centring of the optical axises of the elements and their individual spacing.

If the optical design is well done there is still quite a big job to correctly adjusting and fine tuning everything.

Here trial and error is unlikely to work.

 

Some high quality lenses have a precision need of some tens of micrometers to work optimally.

Normally some of that is created while producing assembly components specially made for a lens type.

[Stefano]

I plan to refine this lens (approx. 45 mm f/2), and eventually build it, using Thorlabs' tubes and components. The greatest challenge, apart from trapped dust, would be positioning the elements at the correct distance between each other, but in the lens above I think even a 1 mm deviation wasn't critical for sharpness. Thorlabs sells graduated screws for their tubes to precisely measure the depth at which a retaining ring is inserted, for example.

[ulf]

That is how it must be done. 

Such building blocs are not that cheap so the total cost for that experiment will not be very low.

Good luck with your build! I really hope it will turn out good even if it is not chromatically corrected.

 

The sensitivity for spacing naturally differs.

In the UV-Nikkor there is one distance stated to be within ±30µm

[Stefano]

53 minutes ago, ulf said:

Good luck with your build! I really hope it will turn out good even if it is not chromatically corrected.

Thank you!