How can the Pentax 40/2,8 be so small?

[btgc]

Over time I've come to conclusion pancakes aren't my dish, I leave it for kids 🙂 Seriously, focus ring on Revuenon 45/2.8 (quite similar design to other manual focus 40-45mm pancakes) is very narrow (one line of knurling), it's slower and thus very little harder to focus than Rikenon 50/2 lens which by many ebay sellers is wrongly described as a pancake (which it isn't, but is just a little bigger) but has proper 6 elements instead of 4 in real pancake (well, good photos aren't by number of optical elements, we know) and is a bit brighter. And costs 10-20 times less than that 🙂

This is like w/ phones - there were time when everyone wanted to go smaller but now when phones aren't just phones and screen is everything, they instead get bigger!

 

[gavinlg]

Obviously most people dont care a lot about size in SLR lenses. I find the bulk of a Canon 50/1.2 L ridiculous compared to manual lenses of the same speed.

The EF 50/1.2 L is almost 9cm in diameter at around 600g. Progress?

The 50L is also one of the best fast 50mm lenses in existence - so it sort of makes up for its weight problem.

 

[Griffin]

Thanks for the replies all. I was really interested in the boring technical stuff about how this lens is so small and if it would be possible to make other focal lengths this small. I was in fact referring to the manual focus lens, but the one for digital Pentax' cameras is pretty much the same size (or so it seems from web pics).

My conclusion is that a Tessar design, combined with the 40mm focal length, hits some sort of sweet spot size-wise, whereby the various elements/groups can be placed closer together. Am I correct?

 

[charjohncarter]

Tessar has 4 elements in 3 groups, while the manual Pentax 40/f2.8 has 5 elements in 4 groups. So probably not a classic Tessar. Someone that knows more about lens design might jump in, I'm certainly not the person to ask.

 

[user237428934]

The larger filter covers the whole lens, not only the front element which should be about the same in diameter as any other 50mm f1.2 lens.

Here is a picture:
http://www.kenrockwell.com/canon/rebel-xti.htm

They use the ring-usm autofocus. Lot's of advantages but on the downside it makes the lens bigger because the AF is around the lens elements.

 

[jpfisher]

Almost sliding off topic here, has anyone tried that Canon 40mm? opinions?

Super small, very sharp, and relatively cheap. ($150 at B&H right now!)

The only downside is the focus-by-wire design--if the focus motor goes, it's a dead lens. If I owned a Canon EOS system I'd buy one in a second.

I've also shot with the Pentax 40mm XS (bundled with the K-01) a little bit and more extensively with the 43mm Limited. The latter is one of my favorites--fast, compact, and it feels like a real lens--I'm looking forward to using it on full-frame digital via an adapter + EVF when the "M" is released.

The latter doesn't do me much good on film (my Pentax bodies are too old to control the aperture), but was happy enough with its performance on APS-C. Glad to know what it can cover a 35mm frame.

 

[ruby.monkey]

Super small, very sharp, and relatively cheap. ($150 at B&H right now!)

The only downside is the focus-by-wire design--if the focus motor goes, it's a dead lens. If I owned a Canon EOS system I'd buy one in a second.

I've also shot with the Pentax 40mm XS (bundled with the K-01) a little bit and more extensively with the 43mm Limited. The latter is one of my favorites--fast, compact, and it feels like a real lens--I'm looking forward to using it on full-frame digital via an adapter + EVF when the "M" is released.

The latter doesn't do me much good on film (my Pentax bodies are too old to control the aperture), but was happy enough with its performance on APS-C. Glad to know what it can cover a 35mm frame.

Are you referring to the 40mm XS? Because the 43mm (like all the FA Limited lenses) offers manual aperture control.

 

[jpfisher]

Are you referring to the 40mm XS? Because the 43mm (like all the FA Limited lenses) offers manual aperture control.

Yep--the latter "the latter" should read "the former" -- my bad!

 

[titrisol]

The Pentax 40 is a great lens IMHO
It is a 5 lenses, 4 group design....

I guess 40mm is a natural length that can be a pancake, but it is not the only one

The Tessar was a pancake of its time....

 

[tunalegs]

The Pentax 40 is a great lens IMHO
It is a 5 lenses, 4 group design....

I guess 40mm is a natural length that can be a pancake, but it is not the only one

The Tessar was a pancake of its time....

TBH I don't think "pancake" has any technical meaning. It is just a nickname for lenses with very short barrels. Many of the older CZJ Tessars had a built in hood, so the barrel was not any shorter than used on faster lenses, but the exact same glass also came in short "pancake" style barrels at various other points in time. When double gauss designs became the standard for SLRs, it was typical to put triplets and tessars into large barrels to make them look more modern. Half the length of this Steinheil lens is just a built in shade for instance:

Steinheil Edixa-Auto-Cassaron by berangberang, on Flickr