28mm lens sizes - Why so big?

Xpres · Expire: 2014-10-28

One for the boffins this, although the answer maybe straightforward.
I've just got a Mir 10A from 'RichardD' (thanks Richard!) which although an f3.5 seems rather big. It's about the same size as the Viv' 28/2.5 with a large front element whereas, for example, the zuiko 28/3.5 is comparatively small.
Anybody know the reason for this? Richard thought it might be something to do with correcting distortions, but the zuiko is small and well corrected.

Question

Orio · Expire: 2012-12-04

It surely depends on the optical scheme and the number of elements.
You can see a big difference also, in the Contax catalogue, between the Distagon 2.8/28 and the Distagon 2/28: same focal lenght, but a considerable longer lenght for the latter.
In theory, an uncorrected 28mm lens should be long exactly 28mm, that is, 2,8 cm.
In practice, this rarely happens - I saw this happen only with the Tessar 28mm f/8 for Contax rangefinder. With reflex lenses, the necessity of installing a retrofocus group (inverted tele) causes the lenght of the lens to be much bigger than nominal focal lenght.

poilu · Expire: 2019-08-29

you must check zuiko to see some miniature

Nesster · Expire: 2014-02-20

I imagine it is easier and economically advantageous to build larger: there's more edge image to throw away, for example, and so the elements don't need as much fine work... or this was true pre-computer designs. So: wider elements, perhaps choked down by the aperture, permit a bit looser tolerance and/or more forgiving design.

Lately, for example the 4/3 system's lenses tend to be fat: this has something to do with the geometry of how perpendicular you keep the rays hitting the sensor. Or that is my understanding from when I read the promotional materials.

LucisPictor · Expire: 2013-12-03

As Orio has already said, it has to do with the design of the lens elements.
Zuikos are known for their compact size, they are much smaller than the average lens of a similar focal length.

Sometimes, esp. with a wide angle lens, the front element (like the one of the Vivitar 2.5/28 that you mention) is designed particularly large in order to prevent vignetting from filters.

It is very entertaining to compare different lenses of the same focal lenght and put them next to each other. Wink

Case from Holland · Posted: Thu Jul 03, 2008 8:50 pm Post subject:

Xpres · Expire: 2014-10-28

Orio · Expire: 2012-12-04

I think the focusing distance plays a role in the barrel lenght, too.
The MIR-10A can focus very, very close.
This means it needs a longer "run", and the barrel must act like a tube at the closest focusing distance.

Xpres · Expire: 2014-10-28

I did wonder about that, but the vivitar 28/2.8 CF, for example, is no bigger than the Hexanon in the pic and doesn't have a lrge front element.

Orio · Expire: 2012-12-04