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Comment by coolandsmartrr | Hacker News Reader

I second this. For this focal distance, vintage lens tend offer around f/3.5 - f/4. Compared to that, this is pretty impressive for DIY and just two lens elements. Might be more lightweight too, which makes it suitable for street photography.

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Everything is a compromise. This optical design manages to be f/2.5 most probably because it does nothing to correct the plenty of aberration and defects it produces. Also f-numbers are deceptive regarding brightness and we should see how much light actually comes out from the other side, i.e. calculating its t-stops.

Also, a manual 165mm lens on full frame? I'm sure it could be great for interesting portraits, but street photography?

Once you stop caring about image quality, the f-stop of a lens is only fundamentally constrained by the physical diameter and diopter of the lens. I suspect the f/2.5 figure is only being held back by the size of the lens barrel and aperture mechanism.

If it were actually well-corrected and apochromatic, then a 165mm f/2.5 lens would be fantastic for astrophotography. There's a reason the manual-focus Rokinon 135mm f/2 lens is so popular for that purpose.

And there is a reason why theanual focus Nikon 200 f/2 is, used, at over 2k Euro. Good professional lenses are expensive for a reason. Ehich is the reason why I stick to used ones for DSLRs, those are finally getting cheaper and easily available on the used market now that a lot of people switch to mirrorless and dedicated mirrorless lenses are covering more and more focal length and zoom ranges.

Too long focal length. For street photography in a budget a Nikkor 50 mm f/1.8D is used in excelent condition under 100 bucks. Fast lens, tack sharp, great in low light and small so you do not stand out among the people usibn their phones.

It's only hard to make a fast lens when you also have a narrow lens barrel or a strict internal quality standards to satisfy. In absence of those, an aperture disc is just a disc that can be drilled, and 50[mm]/3.5 = 12.5mm or 0.5" is a nice round number around the context of a 135 format camera.

> suitable for street photography

Good luck using a 160mm lens for street photography, especially given only the center 10% is somewhat sharp

Vintage lenses are slower but at least you can take good photos with them, it's like comparing a diy car based on a lawnmower and a ford focus

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