Hi all,
In a website that someone posted here in mid-April,

www.dantest ella.com/technical/rangefinder.html

there is a reference to lens design obviated by the lack of the mirror box on a rangefinder (scroll to the very bottom).

Sonnar, Tessar, retrofocus design, etc. Can anyone suggest a resource to learn about this? My question- are all RF lenses fundamentally different from their SLR counterparts? Is a 35/2M of a fundamentally different design from a Pentax 35/2 SMC-A? On what focal lengths are the lens designs much different? On which ones are they much the same, and of same imaging characteristics?

As a result, are certain RF lenses somehow 'better' than their SLR counterparts? Can the same be concluded about view camera lenses?

-- Tse-Sung Wu (tsesung@yahoo.com), May 25, 2002

Answers

Tse; Some designs are the same; these tend to be 50mm and longer lenses. Some Nikon RF/LSM lenses became the same lens design when the Nikon F evolved.. (such as the 135mm F3.5 nikkor; I own both ) By the same I mean it had the same lens formula and lens spacing...The auto diaphram mechanism for the Nikon F required extra space; the lens diaphram mechanics are more complex. The diaphram on an instant return mirror SLR requires a more complex fast acting diaphram; which is closed down by the camera body..

The large SLR mirror constains the design of wide angle SLR lenses. The swinging mirror occupies space that a Leica RF lens designer is free to use...Since all lens design requires compromises; the RF wide angle lens may be a better lens in some occasions...These tend to be wide angles; where the mirror reduces the lens designers freedom......Kelly

-- Kelly Flanigan (zorki3c@netscape.net), May 25, 2002.

Sometimes all of this theory is simply not relative to the real world. The greatest lens design on earth means nothing if the camera type doesn't lend itself to certain types of shooting. I love my 50mm Summicron M and feel it is a great lens, but I have ran into situations where I resorted to a "lesser" lens so that I could use an SLR. In this single example, the problem of the rangefinder was parallax and framing inaccuracy. I laid in the grass and tried to frame a lighthouse between the rails of an iron fence. I knew of the problem of looking through one optic (the finder) and getting the image on film through another optic (the lens), so I bracketed my composition. I shot three shots, moved ever so slightly for each successive shot, feeling like I had my bases covered. I got my film back, and the Leica shot here was the best out of three. On another day, I had my Nikon in the car and saw the lighthouse. I pulled up, snapped a single shot just for kicks and jumped back in the car. Of course the 100 Dollar old beat up Nikkor got the shot in one frame, while the superior Summicron didn't quite allow for the framing I needed. I guess I could go back and measure the finder / lens differential and move a tripod that exact distance, and shoot several insurance frames... But I won't. The crappy Nikon shot is fine. Leica 50mm Summicron , Nikon 50mm f/1.4

So even if a lens for an SLR can be shown to be less refined, there are times when that would be a secondary consideration. If the lighthouse in the Leica M shot is better resolved than the one in the SLR shot, I can't tell... the damn fence is in the way!

-- Al Smith (smith58@msn.com), May 25, 2002.

"Rangefinder lenses can be higher contrast, partly due to the reduced number of elements (e.g., non-retrofocus design) and flare from fewer elements too. As an example, the Zeiss Biogon design is a classic lens design that produces superior contrast and low distortion in wide angle lenses. But to use this design, Hasselblad had to build a viewfinder SWC superwide body around the lens, without a mirror as in their regular SLR bodies. Nikon made a non-retrofocus 21mm lens for their 35mm SLRs, but you have to lock up the mirror to mount this lens too."

-- Kelly Flanigan (zorki3c@netscape.net), May 25, 2002.

The dogma has been that optical engineers have greater freedom in designing RF lenses because of 1) the shorter flange to film distance; 2) the ability to design lenses in which the rear element protrudes further into the camera body (due to absence of mirror); and 3) the absence of an autodiaphragm.

However, Erwin says that one can theoretically generate better lenses by the use of a larger exit pupil (presumably to reduce the diffraction error). Thus SLRs (like the R series), which have larger lens mount diameters than RF cameras such as M have an inherent advantage. I think it's likely that the merits of a particular lens design are more important factors than any of these theoreticqal advantages.

Also, I have always wondered why Leica chose the M mount for their two fastest lenses: the 50/1.2 and 50/1.0 Noctiluxes. Why didn't they ever make a Nocti in R mount, was their a reason that the 50/1.0 design could not be adapted for the R series?

-- Eliot (erosen@lij.edu), May 25, 2002.

Tse; here is another nice link on the subject & it's quote:

"Another hallmark of RF system is its optical performance. Since there is no minimal distance between rear lens element and shutter, the RF lenses are constructed without bulky retrofocus design, resulting is significant advantages in optical quality of wide angle – normal lenses at full- medium apertures. Meaning of this? You can shoot with f/2.0 and results will be barely distinctguishable from those taken at f/5.6 – a dream for street and available light photographer. For comparison, almost any SLR lens in 28-80 mm range must be stopped down to f/8.0- 11.00 to obtain maximum optical quality "

-- Kelly Flanigan (zorki3c@netscape.net), May 26, 2002.

"In 1950 Angenieux introduced the first retrofocus wide angle lenses for still reflex cameras. Angenieux had a reputation as a manufacturer of top quality movie lenses. Their new retrofocus design finally allowed the single lens reflex to become the versatile and dominant design it is today. Prior to the advent of the retrofocus design, single lens reflex were hampered by the lack of wide angle lenses that could be used with reflex viewing, as non-retrofocus wide angle lenses protrude too far into the mirror box to allow the mirror to swing up out of the way."

-- Kelly Flanigan (zorki3c@netscape.net), May 26, 2002.

Eliot; here is why the Noctilux is used on the M and not the R series Leica....."The Leica M is quiet and unobtrusive in use. It can be focused more easily in lower light than can an SLR (even with the help of modern AF systems). With a 50mm lens it can be hand-held at significantly slower shutter speeds than is possible with an SLR. I have made high quality images with this combination at 1/15th second. Some photographers claim to be able to regularly hand-hold down to 1/8th second. (This is due of course to the lack of a vibration-inducing instant-return mirror, but also to the excellent ergonomics of the Leica M camera.)"

The focus quality of using my Nikkor SC 50mm F1.4 wide open under low light with my Nikkormat FTN or Nikon F SLR 25 years ago is not as good as today using the Leica M3 and my Noctilux.....

-- Kelly Flanigan (zorki3c@netscape.net), May 26, 2002.

Hi all

I think the answer is entirely contained in one word "retrofocus"...

It means you have to use supplementary lens elements on wide angles to form the image properly on the film plan on a SLR camera...

Of course with today engineering and production capabilities, this advantage is slimmer than yesterday but it is still something valuable. To compare things on an equal base, let us take the example of Hasselblad wide angles: it is notorious that the specialized fixed wide angle SW 900 series lens produces better imagery than the equivalent retrofocus model which can be used with a classical Hasselblad reflex body. Though the modern retrofocus design is considered far less handicaped than before.

The case of other lenses is generally more related to the way the lenses are engineered and produced. And sometimes the way they can be used... For example as the rangefinder camera will produce less parasite vibrations than an SLR and no black out you may obtain better results at slow speed which give the impression the RF lens is better and, I think it is even more important, the binary nature of focusing on a RF camera, particularly at full aperture where DOF is minimal, can help to obtain better imagery in practical use through a more precise focusing.

Finally I think we are a bit spoiled by Leica lenses performances in any bench tests and we are accustomed to the "Leica way" in terms of compromise (any lens is the result of a compromise) and sometimes it renders fair comparatives difficult...

So my conclusion will be mixed: apart for wide angles, there is no reason an SLR lens should be inherently worst than an SLR lens but sometimes the shortcomings inherent to SLR concept (particularly in hand held photography and at wide apertures)spoil the potential of these lenses.

Friendly.

François P. WEILL

-- François P. WEILL (frpawe@wanadoo.fr), May 26, 2002.

I am very impressed with Al's demostration of framing precision of SLR vs RF by shooting a lighthouse through a fence.

The parallax compensation of M6 cannot correct perspective error of 3D scenery.

-- martin tai (martin.tai@capcanada.com), May 26, 2002.

Martin; What is interesting about Al's photos is that the SLR photo is framed correctly; but one would not know if a hand or bird was just in front of the lens during the exposure...!

An RF camera might see the bird or hand; but would not be framed correctly!,Kelly

-- Kelly Flanigan (zorki3c@netscape.net), May 26, 2002.

Al's demonstration is the same reason I went back to my slr when using wide angle lenses. Many times I'm after the near-far effect and found I could not accurately place things in the frame with a rangefinder. I was just guessing and taking multiple exposures hoping I'd get one where everything fell into place the way I saw it.

I enjoy the size and speed and quality of rangefinder lenses, but those things don't help with the composition of the shot...and that's the most important part for me.

-- Jim Tardio (jimtardio@earthlink.net), May 26, 2002.

Kelly, SLR also cannot see whether a flash is fired or not, while RF can see.

Minox GT-E and ML viewfinder is on the same axis as the lens when the camera is held horizontally, thus can handle framing situation such as the lighthouse through fence.

However, if M6 is held diagonally, it too can handle the framing of lighthouse through a fence :)

-- martin tai (martin.tai@capcanada.com), May 26, 2002.

So what I'm hearing is that retro-focus design = you'll have to stop down to get better performance; and non-retro-focus = image quality is quite high at max. aperture.

So a followup question:

Which lenses in the M and R lineups are retro-focus and non retrofocus designs? 21, 24, 28 Elmarit, 35 Summicron, 50 Summicron? Stated differently, are these the same lenses with different mounts? And the 15 VC? is it non-retrofocus design?

-- Tse-Sung (tsesung@yahoo.com), May 27, 2002.

"What I'm hearing is that retro-focus design = you'll have to stop down to get better performance; and non-retro-focus = image quality is quite highat max. aperture."

Not quite that simple - Almost all lenses improve at least a little on stopping down. The 21 ASPH-M is a retrofocus design and is extremely good wide open, as is the 24 ASPH-M. On the other hand Leica's first retrofocus designs (28 f/2.8-M/1972, 21 f/4-R/1968) are not terribly good. It's not just the design, but also the skill of the designer and general advances in technology.

"Which lenses in the M and R lineups are retro-focus and non retrofocus designs?"

M line: 21, 24, 28mm (post 1980) are all mild retrofocus designs to allow metering with the M5 and later the M6/7. The ONLY non-retrofocus designs for the M below 35mm are the very early 21 Super-Angulons, the original 15mm Hologon, and the very first (1964-68) 28mm.

R-line: ALL lenses with focal length less than 50mm are retrofocus designs - they MUST be, because of the mirror.

None of the 50s are retrofocus in either M or R.

"Stated differently, are these the same lenses with different mounts?"

No. The ONLY lenses that share designs between the M and R line are the current 90 2.8M and the last 90 2.8R; and the last goggled 135 f/2.8M and the last 135 f/2.8R. In every other case the R and M lenses are different, and usually VERY different for the wide-angles. The 50s, and the 75/80 f/1.4s, are 'cousins', but not the same.

"And the 15 VC? is it non-retrofocus design?"

No, it IS a retrofocus design. Otherwise it would block the M6/7 meter, as the original Zeiss 15 does.

-- Andy Piper (apidens@denver.infi.net), May 27, 2002.

Andy, According to what you post, there are few lenses in the M lineup that are non-retro-focus design: the early 21 SA, old 15 Hologon, early 28, and the present 15 VC.

And the 35? How does the current 35 Cron compare between R and M versions?

It appears then that there are few non-retrofocus lens designs among the RF offerings. If most lenses, RF and SLR, are mildly retrofocus in design, is there anything that generally disintinguishes the designs of the M from the R lenses?

-- Tse-Sung (tsesung@yahoo.com), May 27, 2002.