Concept - Switchable Dual focal length prime lens?

Allrighty... Here is a question for the would be optical engineers out there.

Imagine a 17 - 55mm lens. From what I understand to facilitate for a dynamic range of zoom some sacrifices are made in regards to image quality.... As aposed to a fixed prime.

My question is this. Would it be possible to design a lens that switches from one fixed focal length ( 20mm) directly to another ( 50mm) without needing to facilitate for tHe range between, and if so would this be conducive to greater image quality ( as apposed to a zoom lens thAt needs to perform throughought the entire range?

Hope I worded that correctly, I know it's quite a heavy question but would like to see what others think.

http://us.leica-camera.com/photography/m_system/lenses/2193.html
--
http://www.thedrunkenboat.net

How does the tri-elmar compare, optically, to similar-length "primes"?

(and, for you Leica-philes: how does it fit into the Leica brand image and philosphy?)

Hey David, thanks for the link.

Such "variable focal length" lenses have been around for ages, long predating zooms. Probably appeared in the 1920s--for sure by the 1930s. There are such Leitz lenses for 35mm Leicas. I don't think any Japanese manufacturers have ever gone that route--at least not since they stopped copying German rangefinder lenses in the 50s.

--
RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'

An interesting request.

Some time ago I was encouraged to look at the data on shots taken with a medium length zoom.

The proportion of shots taken at the two extremities far exceeded those taken at intermediate focal lengths.

So there is a demand for the product, as long as the restriction comes with some genuine benefits, such as wider aperture, weight, price or whatever.

Tony

And here I was, thinking i was onto something big!

The idea came to me as I am trying to minimise on changing lenses inthe field.

I thought if i could have my 70-200 on one body, and a variable focal lengh fast/sharp "prime" on the other, this would cover a large portion of what i shoot.

i shoot on nikon bodies, and am yet to find that perfect wide - normal lens.

the 17 - 35 2.8 i find to have ugly distortion on the edges, and isnt super sharp ( not mine anyways )

the 14 - 24 2.8 nano is an amazing lens, but doesnt cover the mid or normal zoom range, which leaves me reaching for my 50mm.

17 - 55mm 2.8 is DX which im not interested in

I know that im looking for the utopia, but its interesting to hear that such "variable" focal length lenses are available.

would love to see some info/reviews/mtf charts, or hear from someone who can identify the pro / cons of the optical design.

i personal would LOVE a lens that i could switch from 16 - 30 - 50, or even 20 - 50 - 85?

what would your ideal range be?

OSAM said:

How does the tri-elmar compare, optically, to similar-length "primes"?

Click to expand...

Not as good, but it's still a pretty nice lens.

The Tri-Elmars exist because Leica cameras have a certain number of fixed frame lines. So, although it's not really more complex to make the lens work at all the focal lengths between the three, it has to only work at three so it can work the mechanical linkages and bring up the right frame lines.

OSAM said:

(and, for you Leica-philes: how does it fit into the Leica brand image and philosphy?)

Click to expand...

The philosophy used to be "do anything", and the Tri-Elmar was a tool for that.

Then the philosophy became "serve the collector market" and the Tri-Elmar was unusual, which made it collectible.

The current philosophy is "sell the most stuff" and zooms typically cost more than primes.

--
Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

http://www.swissarmyfork.com

Leica had the Tri-elmar, Konica had their rather exotic dual focal wide angle M lens. Soligor in previous years past had the dual focal ( there is infact a couple of them , one for long focal, one for wide angle ). And way way back then Tamron, and some others had that too in different fashions

there is nothing new about this conpcpt, the old convertable lens ( way back in plate ) is doing that. Today the concept in a small system made little sense because of the zoom and becasue as of all things , a fix focal or another one is not that hard to carry along and then some ...

--

• Franka

Joseph S Wisniewski said:

OSAM said:

How does the tri-elmar compare, optically, to similar-length "primes"?

Click to expand...

Not as good, but it's still a pretty nice lens.

The Tri-Elmars exist because Leica cameras have a certain number of fixed frame lines. So, although it's not really more complex to make the lens work at all the focal lengths between the three, it has to only work at three so it can work the mechanical linkages and bring up the right frame lines.

Click to expand...

You can certainly make it "work" very easily, which is different from "work well".

Here's a lens that shows a degree of "Tri-Elmar" behavior. It works best at 18mm, 50mm and 135-200mm. It's a Sigma superzoom, of all things:
http://www.slrgear.com/reviews/showproduct.php/product/1007/cat/31

"The verdict for this lens is an interesting one. At certain settings, this lens actually produces decent results, but you have to be very careful to know what these are. Fortunately, they include the most frequently-used focal lengths and apertures; wide-open, and either full wide-angle (18mm), the mid-range (50mm) or full telephoto (200mm)."

Sounds like Sigma could have made soft detents to remind users of the good focal lengths.

Seems like it's certainly possible to optimize for a few discrete focal lengths within the range the lens is actually capable of zooming in.