Aha! Now I get why 58mm lenses!

I have a fairly large set of Minolta cameras and many lenses, but I never could figure why their top normal

lenses in the early days were 58mm rather than the more modern standard 50mm. Other older cameras had the same

quirk and I wondered why. I used the 50mm lenses pretty exclusively until one day I decided to haul out the

58/1.4 and put it on my XE-7. I noticed something as I brought it to my eye, it seemed that I could get a similar

size view of objects as seeing without the camera. Then I opened my other eye. The size of objects in each eye

were identical. So simple and logical, like a 1:1 finder.

You may be right. I never noticed that before. I just tried that with a Helios 44M (f2/58 mm). Hmmmmmmmmmmm...

With many early 1960';s slr cameras such as Nikon and Topcon the fast F1.4 lens was 5.8cm; ie 58mm to clear the return mirror; the goal was a 50mm F1.4 but the didn have the back focus distance long enough to clear the slr mirrors in these designs yet. Thus these F1.4 faster lenses on early slrs were longer than 50mm for a mechancial reason; to clear the slr's mirror.

You may be right that there was a mechanical limitation, but they certainly (at least in Minolta's case) made a virtue of necessity.

I tend to agree with Kelly - that it was a solution to a practical lens / camera design problem rather than an aesthetic choice. If you look at the lenses supplied as standard with cameras which had no mechanical limitations such as a 4x5 view camera you find that standard lenses varied from 135mm ((roughly equivalent to 35-40mm) through the normal standard of 150mm (about 50mm) up to 180mm (about 60mm). It all depended on the use the camera was put to. Press cameras often came with the wider lenses so the photog had more options in a hurry. The later fixed lens compact cameras such as the Olympus Trip and that range of cameras had fixed lenses about the 40mm mark.

 

For cameras such as the non-reflex Retinas and many others the 50mm was standard though Voigtlanders sometimes had a 55mm lens and there were many other variations.

 

The 58mm of the Minolta might be related to the minimum focal length of the wide angle lens they could make without the mirror hitting the lens. The 58mm would then fit in a sensibly spaced range of lenses.

 

The widest lens normally available during the 1960's was the 20mm such as the Nikkor 20mm f3.5 UC lens for the Nikon F series. This was quite a breakthrough when it first came out as it was the first of that focal length to have a back focus big enough to clear the mirror.

The original reasons for the size as regards Nikon are likely the case (I didn't want to argue the reasons for other makers, especially pioneering ones), but I was only referring to Minolta specifically. They could easily have changed the 58mm lens size for a wider one by the time of the introduction of the SRT, but didn't do so until the early '70s (for the 1.4) or the late '70s (for the 1.2). Now they may have done it to provide a balanced line of lens sizes (though in those days, their next wider was a 35, a pretty standard size), but they used the "normal" 58mm to give a viewfinder that gives the size of objects the same as viewed by the eye. I can't believe that was an accident, but instead a design decision (to sell more 58mm lenses?). It may have been harder for Minolta to design a 50/1.4 to fit with their smaller flange-to-focal plane distance (compared to Nikon and M42 mounts), but Canon's FL/FD series had an even smaller flange/FP distance and their 1.4 lens was 50mm. To add something more to the mix, I have a Mamiya/Sekor 1000DTL with 55/1.4 lens. I hauled it out of the closet to check, and the size of objects in the viewfinder are the same as the eye, just like the Minolta 58mm. The standardization to 50mm for all normals didn't occur with SLR makers until the 1970s.

Hi,

 

While I tend towards Kelly's explanation as reasonable and sensible, the human eye can't be overlooked either. I never really gave it much thought before, but since the Helios and many other 58mm use a "Planar" type formula, this may be what's behind the slightly longer focal length.

Are there any mathematician / lens designers here?

My first good camera was an Exakta with 58mm f/2.0 Biotar. I now have a bunch of cameras with various focal lengths for their "normal" lenses. I prefer the field of view of a 58mm lens.

 

However, I think, as was mentioned, that the technical reason for 58mm lenses was to clear the SLR mirror.

One also needs to bear in mind that along with focal lenght, viewfinder magnification would affect the "1:1" image shown in the finder with that lens. In other words, the same lens on a finder with a different magnification will not look 1:1 versus the naked eye.

 

I always enjoyed using my 58mm f/1.4 on my SR-T's though. Was a great lens.

I totally agree with the last post. It's just a matter of viewfinder magnification whether the image on the screen is "life size" or not. Most designers prefer "smaller than life size" because then it is easier for the human eye to overlook the entire field.

 

A powerful lens with f/1.4 or f/1.2 usually needs more optical elements (i.e. more glass) than a less powerful one to correct for lens aberrations. On most designs this problem was solved by adding addtional rear elements (probably since their diameter is smaller than the front lens elements), thus increasing the distance between the nodal points and the last surface - and decreasing the distance between last surface and mirror mechanism. To increase the latter again, designers had to choose a slightly longer focal length.

 

BTW there were a few cameras needing less room for the mirror. The Minolta SRT101 and 303 had a special mirror lift mechanism which lifts the mirror prior to tilting it (you can watch this when operating the manual mirror release on the later 303 models). The pre-war Exakta66 had a divided mirror, one part flipped downward and one part upward.

I believe the Miranda G also had a special mirror lift mechanism for its oversize mirror. Viewfinder magnification was one of the things I was getting at. The lens focal length was designed to match the VF magnification, which is why an M42 lens of a certain focal length will work with a 1:1 view on the camera it was designed for, but not on another maker's camera with a different VF magnification.

Topcon, who also used a modified Exakta mount, also used 58mm focal length for their normal lenses until the mid-1970's. Both the 58/1.8 (sharp as a tack) and the 58/1.4 (a handsome beast). Also the 58/3.5 Macro lenses were this same focal length.

 

It was only when they came out with the RE GN Topcors in the 1970's (with Guide Number coupling in that interval before Thyristor flashes) that they switched to a 50/1.8 and 50/1.4. But, they didn't discontinue the 58mm lenses, either.

Pentax did the same thing with the KX. When used with the SMC-Pentax 55mm lens, the KX's viewfinder magnification yields a 1:1 size.

Before the Nikon F was introduced, the makers of RF cameras (including Nikon) made a big deal out of their 1:1 "natural" viewfinders. I'm with Mark on this one.

The very first eye level 35mm SLR, the Zeiss Contax S, came with a 58/2.0 Zeiss Biotar which gave a perfect 1:1 magnification in the finder. However, the same camera was also offered with an f/2.8 Zeiss Tessar, and in this case the focal length was 50mm instead of 58.

 

The reason for the 58mm in fast lenses (you'll notice that Minolta used 58mm for the f/1.4 but 50 and 55 in slower formulas) was not for the 1:1 viewfinder but because the fast lens has a thicker optical assembly which would not clear the mirror if they set it at 50mm from the film. Later lens designs solved this problem, by applying the retrofocus design principle from wide angle lenses to the normal lens..... but the retrofocus wide angles did not exist when the Contax was introduced.

I believe you that it was a design decision originally done to make the faster lens clear the mirror, but I still insist that (some? all?) camera companies were taking advantage of this by making a virtue of necessity inasmuch as they made sure their viewfinder magnification caused the 1:1 ratio with their faster lenses. I mean, the 58/1.4 gives 1:1 even on my XD11, which was long after all other normals were 50mm but the 58/1.2 which was a fairly low production lens and replaced with a 50/1.2 a couple of years into XD11 production. It had a purpose beyond the design limitations which were anyway solved by the mid-60s (otherwise how could Canon have a 50/1.4 FL lens?), and I think it helped ease people into the faster lenses using 1:1 as one selling point. I'm not disagreeing with anyone who says it wasn't the original purpose, but it hung on longer than necessary, and I bet that 1:1 was the reason. After SLRs became dominant, the "feature" was no longer necessary. It's too bad I don't have an X-700 to check out if it still worked even into the '80s, when zooms were beginning to take a large market share.

With the Nikon F one had the 5cm F2 normal and the 5.8cm F1.4 normal. The F1.4 required the longer focal length to clear the mirror.This has been know since the F came out; its ancient knowledge. The rangefinder 5cm F1.4 didnt have a mirror to fouls and hit. The F1.4 normal lens in the F later became a 5cm/50mm when it was redesigned with a retrofocus design. The 5.8cm F1.4 lens had NOTHING to do with a 1:1 finder; it was to clear the mirror. MOST folks DID NOT get a fast F1.4; they got a F2 lens; a 50mm lens. Here I got a used 5.8cm F1.4 Nikkor in 1962.

Regarding the similarity of size, through the viewfinder vs with the naked eye: the viewfinder *may* be reducing image

size a bit.

 

Looking through the viewfinder of a Canon 5D (full frame sensor) with a 50mm prime, the view is slightly smaller than

naked eye, but I know there's a reduction factor with this viewfinder, something like 90%.

With my Nikons (F4 and F5) I need a 70mm FL lens for the viewfinder to match what I see directly.

Hello

I remember that for many years ago I read an article about 58 mm lenses, what stroke me was that the 58 mm was particlarly made to match the human eye in magnification ! Later lens-makers made 60 mm lens and even to day some make 60 mm lenses. I can not to day remember which article it was - I have been through thousands since that, but I do remember just that about our human eye and the 58 mm. So in a way I have allways been disapointed to all the camera-manufactures that they started to make 50 mm lens and not 58 mm. In 24x36 mm - format I certainly can not use a 50 mm, but a 58 or 60 mm is ok and maybe just because it just right to the human eye !

Henrik

Hi Mark:

 

You're absolutely right that they took advantage of it; Zeiss Ikon promoted the 1:1 magnification of its viewfinder from the very start (this was 5 years before the first rangefinder to feature a 1:1 viewfinder was introduced). Viewfinder magnification in an SLR is defined by the lens focal length divided by the focal length of the viewfinder eyepiece lens... the former is (sometimes) restricted by the need to clear the mirror, and the latter is restricted by the length of the optical path through the pentaprism to the screen. I don't think anyone has ever managed to get the eyepiece focal length quite down to 50mm, though the Olympus OM1 came very close ... but given the limitation of the f/2 Biogon to 58mm in the Contax, the choice of 58mm for the eyepiece may well have been a conscious design decision to obtain an exact 1:1 finder image.

I've always believed the 35mm lens came closer to matching the human eye (at least my eye). I've never thought the "normal lens" was really normal.

I've never understood the "equals the human eye" explanation for any lens. The human eye has a field of view of something like 140 degrees, of which it has critical definition in a circle of only a few degrees in diameter in the center... performance which would be considered at once remarkable and rather disappointing in a normal camera lens. Perhaps if you add in the comfortable range of rotation of the eye along with the field of critical definition, you might get something approaching the field of view of a 58 ... or a 50 ... or a 43 ... or a 35mm lens (all of which have been mentioned at one time or another as having a "human eye" FOV); but I don't know if among that group one is particularly more human-eye-like than the others.

Rick is right: the 58mm focal length was borrowed straight from the Contax S.

 

Only the very early fast 50mm for SLRs were "retrofocus" (in the case of the 50/2 Nikkor, only a weak concave

element was placed in front of the usual double-Gauss design.) Soon glass types with higher refractive indices

were available and the designs revert to Gaussian. http://imaging.nikon.com/products/imaging/technology/nikkor/

n02_e.htm

 

OTOH, the early 1970s "Zeiss" Ultron (designed by Voigtlander) for the Icarex still had a concave front

element.

http://www.cameraquest.com/zvicarex.htm

 

It was even carried forward to the Rollei SL35. Zeiss of course did away with the "stop gap" construction for

the Contax RTS system.

I have 58mm f/2.0 Biotars in Exakta, Contax-S (M42), and Praktina mounts. It's a superb lens by almost any

measure. The Soviet version, the Helios-44, is quite good as well. I like the slightly longer "normal" regardless

of why it was done. Winfried has the best story, I think, about how and why. The combination of fast (for the

time) and mirror interference led to longer lenses being easier to design. Witness the 55mm length of the early

Nikkor f/1.2 lenses.