A few 135mm lenses that I own, from left to right: Carl Zeiss 135mm Sonnar on the Zeiss Contarex Bullseye, Olympus 135mm E.Zuiko on a OM-1 and the Nikon Nikkor-Q 135mm on a Nikkormat FT-N.

I was talking to one of my life-long friends, and fellow shutterbug, Mike Boses the other day. We were discussing our latest projects and he asked me why no one uses the 135mm lens anymore. We both agreed that it is the candid photographers secret weapon. People will pay $50-150 for a 50mm which is OK for portraits and $300+ for an 80-100mm "portrait" lens, but just ignore that bargain basement price for a 135mm lens, even the f2.8 ones. I took a quick look at eBay and found a Minolta MD Celtic for $7.98, Topcon $for 12.62, Vivitar for $7.99, Canon FD for 14.95, Pentax-M for $17.90 and a bunch of Sears, Hanimar, etc for less than $5.00! Almost every one had a "make offer" option on the listing. The empty cases for the same lenses were going for more than the lenses. The prices above are for the slower f/3.5-4.0 apertures, the f/2.8 are about twice the amount and the f/2.0 lenses are 20X the f/3.5-4.0 lenses.

To be honest, the 85mm-100mm are usually classified as "professional" portrait lenses and they work better in a smaller studio because of their shorter focal length when compared to a 135mm. Let's look at some working distances for a standard head photo. 

Using the "standard" 50mm focal length for lens to face distance is approximately 30"

Using the "portrait" 85mm focal length for lens to face distance is approximately 48"

Using the "telephoto"135mm focal length for lens to face distance is approximately 68"

Is 68" too far away? I like the distance because it is not as intrusive as the 85mm or 50mm. See the photo below.

Zeiss Contarex with the 135mm f/4.0 Carl Zeiss Sonnar, Kodak TMax 400

I also like to use this lens for candids!

Zeiss Contarex with the 135mm f/4.0 Carl Zeiss Sonnar, Kodak TMax 400

As you can see from the above photos, you do not need the faster, and more expensive, f/2.8 lenses. Are the higher cost lenses sharper? Probably, but most photographs, especially portraits and candids, are all about the subject and not corner to corner sharpness. That topic is a for future discussion.