What defined focal length of lenses?

[M-88]

Hello. The question is, why are the common lenses the way they are - 24 mm, 28 mm, 35 mm, 50 mm (okay we know this one), 85 mm and so on. Why are these lenses more common and not let's say 22, 25, 30, 70 mm lenses, for example?

Thanks in advance!

 

[Chan Tran]

I think you are talking about lenses for the 35mm cameras (because the focal length you listed are common for the 35mm but not for other formats). So the common focal lengths have to do with what they decided as useful angle of view.

 

[M-88]

I think you are talking about lenses for the 35mm cameras (because the focal length you listed are common for the 35mm but not for other formats). So the common focal lengths have to do with what they decided as useful angle of view.

You're right, I'm talking about 35 mm format, but why those angles and not other? How did they define 'useful'? For example 24 mm lens has 84 degrees and 28 mm lens has 75 degrees of diagonal FOV. Why didn't they go with something that would have had 80 degrees FOV?

 

[jim10219]

You gotta pick something. Somebody made a 28mm lens, then somebody came out with a 28mm lens to compete with it. Also, sometimes a lens will be listed as 28mm, but may in fact be 27, 26, or 29.5mm. They called it a 28mm because that's what other manufacturers called theirs, and they wanted to directly compete with them. So basically, someone came up with one focal length, people found useful, then someone followed suit, then someone thought it would be useful to have another focal length, other people followed, and then someone thought it would make sense to fill the gap between the two, and more people followed. There's no specific reason for the most common focal lengths, other than companies decided to make a lens there, and consumers decided to buy that lens. It's more marketing than anything.

 

[M-88]

You gotta pick something. Somebody made a 28mm lens, then somebody came out with a 28mm lens to compete with it. Also, sometimes a lens will be listed as 28mm, but may in fact be 27, 26, or 29.5mm. They called it a 28mm because that's what other manufacturers called theirs, and they wanted to directly compete with them. So basically, someone came up with one focal length, people found useful, then someone followed suit, then someone thought it would be useful to have another focal length, other people followed, and then someone thought it would make sense to fill the gap between the two, and more people followed. There's no specific reason for the most common focal lengths, other than companies decided to make a lens there, and consumers decided to buy that lens. It's more marketing than anything.

It means engineers deliberately chose strange values, be that focal length or FOV. Not cool. As for deviations in actual values, I thought that was a trait specific to Soviet lenses only.

 

[Chan Tran]

Well first of all they chose the normal focal length. Why 50mm and not 43mm I don't know. But from that point they pick other focal length that provides significantly wider or narrower coverage but not too much. I think each focal length is about 1/3 different from the others as far as the FOV is concerned.

 

[RalphLambrecht]

Hello. The question is, why are the common lenses the way they are - 24 mm, 28 mm, 35 mm, 50 mm (okay we know this one), 85 mm and so on. Why are these lenses more common and not let's say 22, 25, 30, 70 mm lenses, for example?

Thanks in advance!

I can only guess that it has to do with customer demand and what people thought useful as well as well selling focal length of the competition. You start with roughly the film-format diagonal as normal and take it from there; half normal is wide angle; double the normal is a short telephoto; make finer corrections for special cases; eventually, prosumers will swear that one is better than another and amateur desire does the rest.

 

[M-88]

Well first of all they chose the normal focal length. Why 50mm and not 43mm I don't know. But from that point they pick other focal length that provides significantly wider or narrower coverage but not too much. I think each focal length is about 1/3 different from the others as far as the FOV is concerned.

This image is missing 28 mm lens, but it doesn't look like 1/3 to me anyway

http://scottsoapbox.com/uploads/2016/04/Focal-Length-Comparison-mini2.jpg

I can only guess that it has to do with customer demand and what people thought useful as well as well selling focal length of the competition. You start with roughly the film-format diagonal as normal and take it from there; half normal is wide angle; double the normal is a short telephoto; make finer corrections for special cases; eventually, prosumers will swear that one is better than another and amateur desire does the rest.

I think Barnack didn't use a lens with 42.43 mm diagonal. Perhaps 50 mm was the closest thing he had.

 

[Dennis-B]

The focal length of a lens is determined by the ability of the lens to cover the diagonal of the film format. 35mm needs 43mm +/- for a "normal" lens. Wide angle and telephoto lenses also have to cover the same format, so they have to be designed with 43mm of resolution in mind.

When it comes to telephoto lenses, and because of ergonomics, the optical center of the lens is in front of the front lens element. If you measured the focal length from the film plane, it would be in front of the lens.

When wide angle lenses are designed, they can only be around 28mm in focal length without going to a retro-focus design, so as to prevent interference with mirror movement. Wide angle lenses wider than around 24mm focal length, usually start distorting the image when the camera is tilted off-axis.

Glass formulae are also in the mix. Nikon's glass formulae and different from Canon, Minolta, or Pentax. Those formulae cause refraction to vary, as well as resolution.

If Nikon's 28mm is actually 27.6 mm, the company will advertise 28mm.

 

[MattKing]

The focal lengths that are "common" for 35mm format today are that way because of familiarity and market forces.
When the first lenses were being developed for the 35mm format, optical and engineering factors were more prevalent, including the fact that manufacturers were often adapting work done for larger and smaller (primarily motion picture) formats.
Why does a significant portion of the world drive on the left side of the world, when much of the world drives on the right? Because that is the way things evolved.

 

[Kino]

I would assume that certain focal lengths in part were derived from breakthroughs in the lens making arts. Maybe certain types of lens groupings lend themselves better to certain focal lengths and so on...

 

[johnha]

Pentax have made some odd ones: 30mm, 31mm, 43mm (that's obvious) & 77mm, many ranges have a 40mm pancake (must be an easy recipe).

 

[M-88]

The focal length of a lens is determined by the ability of the lens to cover the diagonal of the film format. 35mm needs 43mm +/- for a "normal" lens. Wide angle and telephoto lenses also have to cover the same format, so they have to be designed with 43mm of resolution in mind.

When it comes to telephoto lenses, and because of ergonomics, the optical center of the lens is in front of the front lens element. If you measured the focal length from the film plane, it would be in front of the lens.

When wide angle lenses are designed, they can only be around 28mm in focal length without going to a retro-focus design, so as to prevent interference with mirror movement. Wide angle lenses wider than around 24mm focal length, usually start distorting the image when the camera is tilted off-axis.

Glass formulae are also in the mix. Nikon's glass formulae and different from Canon, Minolta, or Pentax. Those formulae cause refraction to vary, as well as resolution.

If Nikon's 28mm is actually 27.6 mm, the company will advertise 28mm.

I completely forgot that 35 mm cameras were rangefinders long before there was an SLR thing and their flange distance is indeed 28-29 mm (M39 and Contax I mean).

Thank you, that makes a lot of sense.

 

[M-88]

Pentax have made some odd ones: 30mm, 31mm, 43mm (that's obvious) & 77mm, many ranges have a 40mm pancake (must be an easy recipe).

I believe that 40 mm, especially with f/2.8 aperture is somewhat optimum for price/performance/compactness when it comes to pancake lenses, because I've heard of more than one such lens. And 42-43-45 mm lenses are most often encountered by me in various rangefinder cameras.

 

[AgX]

For SLRs there are kind of "standard" FLs.
But then there is also 20, 25, 29, 30, 40, 55, 58mm etc.

Yes, I too since long wondered how those standard FLs originated, but also why then for instance Meyer kept the 29 and 30mm until the bitter end. Likely never recalculated since the 60s.

 

[Sirius Glass]

It means engineers deliberately chose strange values, be that focal length or FOV. Not cool. As for deviations in actual values, I thought that was a trait specific to Soviet lenses only.

Are you expecting adults to act rationally??

 

[jim10219]

Well first of all they chose the normal focal length. Why 50mm and not 43mm I don't know. But from that point they pick other focal length that provides significantly wider or narrower coverage but not too much. I think each focal length is about 1/3 different from the others as far as the FOV is concerned.

My guess is because 50 is an easier number to remember than 43. The easier it is for the customer to ask for it, the more you'll sell.

 

[Dennis-B]

For SLRs there are kind of "standard" FLs.
But then there is also 20, 25, 29, 30, 40, 55, 58mm etc.

Yes, I too since long wondered how those standard FLs originated, but also why then for instance Meyer kept the 29 and 30mm until the bitter end. Likely never recalculated since the 60s.

When a manufacturer finds a formula which works, regardless the product, there's a tendency not to spend money on what might be considered limited, or even declining, benefits. If Meyer had a 30mm lens, and it was competitive, why develop a 28mm if the profit from the development is only marginal? The giants in the industry such as Nikon, Canon, Pentax, Minolta, Leica, etc., could outspend Meyer at the drop of a hat. They also had an arsenal of lenses off which they launch new designs. Nikon switched to AI from non-AI without missing a beat; Canon likewise improved it's original FD lenses.

On a much larger scale, the automakers just didn't redesign engines, if they had a reliable design already out there. Chevrolet used a 350 ci engine for years; Ford the 5.0L V8; Chrysler the 426ci Hemi. Now, the originals of these engines bear little resemblance to the latest models, but those were evolutionary improvements.

 

[wiltw]

FL 'standardization' is actually quite a disarray, viewed historically. In the case of SLR focal lengths offered...

• 50mm normal today: in the 1960s we saw 50, 52, 55, and 58 all as 'normals', sometimes several different FL by the same SLR manufacturer
• 100mm 'portrait' today: in the 1960s we commonly saw both 100mm and 105mm

During the 1960s, the FL offered by a single manufacturer were not as numerous as today. For example,

• Topcon had 20, 25, 28. 35, 55/58, 85, 105, 135, 200
• Miranda had 21, 24, 25, 28, 35, 50, 105, 135
• Petri had 28, 35, 50/55, 135

 

[Dennis-B]

FL 'standardization' is actually quite a disarray, viewed historically. In the case of SLR focal lengths offered...

• 50mm normal today: in the 1960s we saw 50, 52, 55, and 58 all as 'normals', sometimes several different FL by the same SLR manufacturer
• 100mm 'portrait' today: in the 1960s we commonly saw both 100mm and 105mm

During the 1960s, the FL offered by a single manufacturer were not as numerous as today. For example,

• Topcon had 20, 25, 28. 35, 55/58, 85, 105, 135, 200
• Miranda had 21, 24, 25, 28, 35, 50, 105, 135
• Petri had 28, 35, 50/55, 135

The three you mention were for the most part, minor players. While Topcon and Miranda made a lot of cameras, with Topcon having Navy contracts, they've not lasted past the 70's. Miranda was wrecked by its distributor, and Petri died from lack of development and quality. In my life, I've gotten to use all three, and their glass was no slouch by any standards. They just lacked the capital to last in a competitive market. Petri had to change its breech-lock mount to a K mount. With that, why buy Pentax, when you could buy a more advanced Pentax for a bit less money? I owned two Petris, FT and FT-EE. Neither was very reliable in their metering. You had to stop down, and mine spent too much time in the shop having the meters repaired.

The survivors today, Nikon, Canon, Pentax, Leica (boutique), all survived by developing camera bodies which bolstered the performance of their lenses. Canon redefined by changing the mounts for its new EOS cameras, and Nikon has survived with it's venerable F mount. Pentax, changing to its K mount does fine.

On a more humorous note, I was stationed in Rhode Island in the Navy, and attached to a Public Affairs office, so I got to know a lot of the photographers stationed at Quonset Point NAS. One afternoon while developing some film, one the the photographers showed me a box of parts. In the box was a (nearly) complete Beseler Topcon. Seems an unnamed Photographer's Mate dropped it out of a plane while doing some shots of the runways. From 8K feet, I don't think there were any assemblies left. They had to close the runways for hours for the cleanup.

 

[wiltw]

The three you mention were for the most part, minor players. While Topcon and Miranda made a lot of cameras, with Topcon having Navy contracts, they've not lasted past the 70's. ...The survivors today, Nikon, Canon, Pentax, Leica (boutique), all survived by developing camera bodies which bolstered the performance of their lenses. .

Unfortunately I had no easy way to discern the Nikon lenses of the 1960s vs. those from the 1970's and later. So I chose Topcon for the list of lenses because, like Nikon, the RE Super/Super D was a 'system camera' with a very wide array of lenses, macro- and micro-photography accessories, high speed motordrives, etc. The Nikon line, as I recall, had a complement of lenses similar to Topcon, as the two were priced as premium products ($430 Topcon Super D with 58mm f/1.4 lens).
I just consulted a Sept 1964 Modern Photography, and lenses listed in a store ad show the same FL as I previously listed for Topcon, except Nikon had no 20m or 25mm lens but it did have a 400mm lens in the list. Unfortunately the US distributors for Nikon or Topcon did not list lenses in ads of the day, and by 1967 the retail store ads listed no more lens FL than what was available in 1964!

 

[Dennis-B]

Unfortunately I had no easy way to discern the Nikon lenses of the 1960s vs. those from the 1970's and later. So I chose Topcon for the list of lenses because, like Nikon, the RE Super/Super D was a 'system camera' with a very wide array of lenses, macro- and micro-photography accessories, high speed motordrives, etc. The Nikon line, as I recall, had a complement of lenses similar to Topcon, as the two were priced as premium products ($430 Topcon Super D with 58mm f/1.4 lens).
I just consulted a Sept 1964 Modern Photography, and lenses listed in a store ad show the same FL as I previously listed for Topcon, except Nikon had no 20m or 25mm lens but it did have a 400mm lens in the list. Unfortunately the US distributors for Nikon or Topcon did not list lenses in ads of the day, and by 1967 the retail store ads listed no more lens FL than what was available in 1964!

Spot on! Most makers changed lenses incrementally. Nikon's changes were very much like Topcon, not imperceptible, but I don't remember any "explosive" lens announcements by anyone. I'm sure, though that there were ads featuring prominent technology changes (Canon fluorite coatings, Nikon AI). I do remember an ad by Canon for their EF 50mm f/.95 lens. Not saying that Nikon didn't announce big jumps, I just don't remember them all.

Lenses performed similarly if they were built with a good level of quality. And, the camera mags were in the business of hyping the latest bodies.

 

[Alan Gales]

Well first of all they chose the normal focal length. Why 50mm and not 43mm I don't know. But from that point they pick other focal length that provides significantly wider or narrower coverage but not too much. I think each focal length is about 1/3 different from the others as far as the FOV is concerned.

I read somewhere that a 50mm focal length is the least expensive to make. I don't know why it would be cheaper to make than a 40mm, 43mm or 45mm though. I figured that 50mm was just thought to be a good number.

I used to own a 25mm Zeiss lens for my Contax. I always thought 25mm made more sense than 24mm because it's half of 50mm. Most manufactures didn't think so though.

 

[ciniframe]

…….., but why those angles and not other? How did they define 'useful'? For example 24 mm lens has 84 degrees and 28 mm lens has 75 degrees of diagonal FOV. Why didn't they go with something that would have had 80 degrees FOV?

So someone would have a reason to invent the zoom lens!
Seriously though, personally I've avoided zooms as too big, heavy and slow. That said, I shoot 35mm half frame and with such a small format you don't want to crop....at all, so sometimes I find it useful to mount a zoom so as to frame as precisely as possible.

 

[Theo Sulphate]

I read somewhere that Minolta made it's f/1.2 lens in the 58mm focal length because -- at that time -- they couldn't design f/1.2 with a smaller diameter objective lens and a 50mm focal length. I don't know if that had anything to do with the characteristics of the SRT's mount.

 

[Dennis-B]

Nikon has a couple of older model zooms that are 43-86 zooms - 1x-2x. The first was not a great lens, the second was quite better. I have a copy of the latter, and It's very useful as a "walk-around" lens on my Nikkormat FT3.

I just looked at an owner's manual for a Canon 7 rangefinder, and the 50mm class has either 6 or 7 elements, while the 35mm f/1.8 has 8 elements. The 25mm and 28mm lenses have 5 and 6, respectively. Oddly, the 50mm lenses all have 1.0x magnification even though they're slightly longer than 43.

There's not a lot of rhyme nor reason for the way manufacturers have designed and made lenses, or bodies for that fact.

It goes back to the fact that each manufacturer believes they're doing it right, much the same as why Fords, Chevys, Jags, etc., are all different.