>>4401688 (OP)
Because you touch yourself at night.

But seriously. I'm no expert, but I think it's because of making the lenses at different MM there are mm where it requires more lenses and more expense to get the maximum quality. Those mm ranges are a good range of cheap, compact and good quality.

>>4401688 (OP)
It's not always those numbers, there's 58's, 75's, 70's, 80's, 150's, 200's and of course 70-200's.

>>4401688 (OP)
Japs copying each others optical formulas back and forth forever after the initial theft from zeiss.

Only sigma makes the better lengths like 65mm and 90mm because they’re leica adjacent

>>4401688 (OP)
It depends on the brand and the era, as well as what else is available. I have a Minolta 100mm macro but maybe that length isn't common or made for your mount. You also have to see it from the manufacturer side: If you make an 85 and a 105 for instance, how likely are you to sell the gap fillers if you started offering 90 and 100 too?

>>4401693
Pentax has made some unicorns like 120mm.

>>4401688 (OP)
because at some points there were rangefinder cameras which displayed framelines for different focal lengths in the viewfinder. these frame lines were physically built into the camera, so when the manufacturer of the camera body made one that had 85mm frame lines, it wouldn't have made sense to build a 90mm lens for it.

>>4401688 (OP)
>why only mention the most used focal lengths instead of listing every single possible combination?
are you perchance retarded?

>>4401759
I'm saying why are those 3 arbitrary numbers the most common

>>4401759
>anon can't into context
Yes, you are retarded.

>>4401763
They are apparently sweet spots for maximizing performance with regards to historic lens manufacturing constraints and designs.

yeah