From: Roger <nospam@veggie.org.net>
Subject: Re: Physical size of lenses
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From: "Roger" <nospam@veggie.org.net>
Newsgroups: rec.photo.digital
Subject: Re: Physical size of lenses
Date: Wed, 29 Nov 2017 10:44:24 -0000
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"Paul Carmichael"<wibbleypants@gmail.com> wrote in message
news:f87fa0Fh1fjU1@mid.individual.net...
> Good morning everyone.
>
> I have a trivial question:
>
> On my desk in front of me are two lenses. Both Samyang primes. One is a
> 35mm f1.4 and the other is an 85mm f1.4.
>
> I'm just curious as to why the 35mm is so much physically longer than the
> 85mm.
>
> And a related question: I have a Vivitar 35mm f2.8 that fits in the palm
> of my hand, whereas the Samyang is huge. I suspect the answer is obvious,
> but not to me.
>
> -- 
> Paul.
>
>  https://paulc.es/
>  https://asetrad.org

Hello Paul.

I suspect that the difference between your two 35mm lenses is due to their
maximum apertures. f1.4 is much larger than f2.8.
The difference between your two Samyang lenses is probably because the wide
angle lens is optically more complex than the telephoto lens.
Bear in mind that the effective focal length of a lens is not always the
same as the physical length of a lens. I have a 55-250mm lens which is
(front element to lens mount) approx 11cm long at the 55mm setting and
approx 16.5cm long at the 250mm setting. I have a 10-22mm lens that is a
constant 9cm long.
I suppose the best example would be a mirror lens where the light path is
folded within the lens and so its effective focal length(typically 400, 500
or 600mm) is a lot longer than its physical length.

Let's see what other people have to say.
Regards, Roger.