Why 1.7 ?

Just wondering if anyone knows why the largest aperture on the M 50mm f1.7 is f1.7 ?

I could understand f1.8 as it is in the 1.4,1.8,2.8,4 etc scale.

I presume that you could have a lens with any maximum aperture that doesn't have to have a conform to the above scale but why not have made it f1.8 ?

Jason

Because f1.7 sounds better or because it became possible with a lens redesign to get just a little more speed from the typical 6 element standard lens.

Someone managed a f1.6 50mm lens, I think it might have been Fuji.

It was a marketing ploy. Pentax thought some people would be more likely to buy a camera with an f1.7 standard lens rather than one with the more usual f1.8, like an OM1 or an FE, AE1, etc.

Edit:
The same thing goes on today, with pixel count. Camera manufacturers compete to stuff ever more pixels onto their sensors because they know that the average Joe Punter equates more with better. We camera W**kers though, know that pixel count, on it's own, means bugger all.

The lens aperture can be anything that you can actually design to.

The larger the maximum aperture the brighter the picture you get in your viewfinder and the more critical is the focusing of the lens due to the reduced DoF.

The probability is that f1.7 was more favourable for the actual lens computation, when came down to it.

Aren't the values approximate square roots

1.4 - 2
1.7 - 3
2 - 4
2.8 - 8
4 - 16

etc.::

and isn't something to do the area of the aperture - hence the square roots.

::
Howard

Indeed they are

http://en.wikipedia.org/wiki/F-number

f/1.7 sits on the half a stop scale, while f/1.8 sits on the third a stop scale

Matt

You're a clever bunch you lot

Think i`m in the wrong forum,
I though a square root was a carrot gone wrong

Davex.