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Comment by kamranjon | Hacker News Reader

What is shocking about the f/2.5 f-stop? That’s a pretty fast lens, especially for something diy.

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.

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?

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.

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.

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

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.

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