F-Theta (laser equipment) as taking lenses

[alex ph]

F-Theta lenses are used in machines for laser scanning and engraving. For this purpose they are produced following high standards applied to distortion, CA, temperature tolerance, coating quality. All this sounds intriguing. As for their focal length, it corresponds to tele in "common" photo universe, varying from around 100mm to 450mm.

They are also quite large which is not such a big advantage, but some of them are telecentric, which means a very even distribution of sharpness all over the visual field.

Second hand or offered by Chinese makers they enter pretty accessible budgets, of circa 60-80 euros or dollars per unit.



I wonder if some of you, experimenting with printing, enlarging, engraving and projection glass, fell into one of F-Theta lenses and out of curiosity tried to adapt it.

Datasheets spread in the net sound contradictory concerning the back focal length (flange distance) of the F-Thetas. According to some of them, this B measure varies from 11mm to 22.5mm. Not that great, being mostly too short. According to others, it varies from 194.62mm to 486.66mm. Too long! Such a fork may concern different types and applications. And still there must be some standards in the industry, to let them fit the same machines. So, the adaptability is a question, and I am not prepared well enough to conclude it from the datasheets.

Long story short, do you have any experience and maybe ideas about the adaptability of these lenses to our photography equipment?




Images credit: Ronar-Smith web site

[simple.joy]

[iangreenhalgh1]

Usually, these lenses are only corrected for a narrow bandwidth ofthe light spectrum, that can make them rather poor lenses for conventional photography, but without actually trying them, who knows.

[alex ph]

Thank you, fellows, for your substantial reactions. "Hardware" limitations might certainly explain the lack of posts reporting successful adaptation. Another reason might consist in a relatively young age of the market for such lenses which has not become yet the field where ML photographers stepped in.

I'll keep an eye on the second hand market. If an offer under 30 euros appears, I'll be tempted to give it a try. For the moment, I have no friend or contact around who has passion for laser engraving. That could be the best way to reach a lens to try, and before to have a well grounded opinion on its applicability.

[visualopsins]

Iirc the mounting distance from back of lens is very short even for mild.

Lenses must be flat field and telecentric, used within specific distance range.

[kds315*]

Used a few for 365nm and used an external iris as such need to be stopped down for an acceptable result - not bad actually!

And I found one from Zeiss Jena, a f1.4/100mm which I used for some tests, called it "soft focus" as those results looked like that, quite a bit CA as expected but I liked it...but I don't have it anymore I think.

https://www.flickr.com/photos/kds315/albums/72157671100239984

[alex ph]

This is most interesting, Klaus! The images are very stylish, thanks to the combination of sharpness and glow. Thank you for sharing.

Could you focus your Zeiss only close up, under 1m, as your flickr album shows?

Otherwise, do you have some tests to show from your other F-Theta lenses, maybe even "quick'n'dirty", to see how they render?

[paulhofseth]

I borrowed one from a friend once; spectacular "italian flag" colours; so it is obviously only correected for the hgh oower laser frequency. Stacking two ordinary filters to get a reasonabloe B&W did not help,

I presume a sharp cutoff filter for the design freqyency would be ideal for specialized snaps.

p.

[alex ph]

Really interesting! Have you kept some original shots, to see the rendering?

[paulhofseth]

Immeediately discarded.

p.

[alex ph]