3 ms·

With the wide assortment of imaging sensor sizes, the "normal" focal length varies accordingly. Probably better to think of it as "angle of view", typically ~4

by jrapdx3 10y ago

With the wide assortment of imaging sensor sizes, the "normal" focal length varies accordingly. Probably better to think of it as "angle of view", typically ~45-50 degrees for a normal lens. That's usually the easiest lens to design, so typically the most compact and inexpensive lenses are "normal" primes. Today the most popular "normals" are moderate, mid-range zooms, equivalent to 28-80mm or so on a 35mm equiv sensor.

dom0 10y ago
For some SLR systems 50 mm (or more often 51.6 mm) isn't actually all that easy (in the 60s), eg. Nikon with a comparatively large flange back distance. We still see some artifacts of this today, e.g. the classic short reproduction macro was always around 55-60 mm, because it's a spot where the lens design is easier.
- jrapdx3 10y ago
  Macro lenses were more useful with a longer focal length, in 35mm terms, 80-100mm or more longer was desirable to give more working distance to the subject at high ratio, like 1:1. For example, for my MFT system, the macro is 60mm equiv to 120mm for a 35mm frame. As I understand, lens design in the digital era has changed due to the characteristics of the sensors vs. film. Mirrorless designs have also changed requirements and eliminates some restrictions due to flange distance. I'm not an expert in that field, maybe you know more in that regard.
  - dom0 10y ago
    For most macro uses yes, the longer focal lenses where and are preferred due to working distance. The shorter macros where developed specifically for reproduction use (photographing records, books, paintings and the like), where the larger reproduction ratios (1:2, 1:1) where rarely if ever needed, so the problem didn't arise. The shorter flange back distance in mirrorless systems makes some things easier and some things harder (if you want short lenses that is), but overall give more freedom to the lens designer. Sensor vs film and manual focus / first AF systems vs modern AF systems is a huge difference and for many older lenses esp. in the wide angle spectrum that is the reason for a large performance difference between film and digital.
- paulmd 10y ago
  Even the number "50mm" is massively debated. The 51.6mm number is drawn from the focal length of classic Leica normal lenses, which is 100% arbitrary. There's pretty strong arguments that something more like 43mm is the normal focal length for 35mm. And designing lenses with adequate coverage for 35mm as well as a sufficient flange distance to clear a SLR mirror was definitely a problem back in the day. Older "normal" lenses for SLRs used to commonly be 55mm or even 58mm. Wide angle-lenses suffered a similar problem, and for a great while rangefinder lenses (or similar lenses that protruded into the mirror cavity of a SLR) were the dominant options for wide angle photography. It took quite a while to develop good "retrofocal" lenses where the optical center is actually behind the lens (basically the opposite of the telephoto lens where the optical center is in front of the lens). The very first examples of the type are the Angénieux retrofocus and the Voigtländer Prominent's Skoparon, both introduced in 1950. The Skoparon design was essentially a Tessar lens backwards and went on to be one of the earliest wide-angle lenses used in SLRs, notably as the Asahi Pentax 35mm f/3.5. It had an extremely long lifespan, in its medium-format variant (Pentax 75mm f/4.5) it continued to be produced until around 2000. The funny thing is it all happened because Voigtländer patented it for rangefinders but neglected to patent it for SLRs! The other thing to remember about 50mm-ish macro lenses is that it's still somewhat reasonable to build a helicoid that can get out to 1:1 reproduction without extension tubes. I have a 50mm and a 90mm that will both go to 1:1 reproduction on their own, and I can tell you that while the 50mm may be somewhat ungainly the 90mm is absolutely absurd when you crank it all the way out. The 50mm uses a double helicoid, the 90mm is actually four helicoids running inside each other.
  - dom0 10y ago
    Yes, the old unit focusing macro designs can look rather weird and somewhat unstable when fully "racked out". With internal focusing this has been "fixed", although they still need a lot of displacement of the focusing group (in the Nikon 200/4 AF for example it's about five cm if I remember right, which is a lot for an IF design). Most macros still have a lot of external movement, but internally floating elements reduce the required displacement still. (E.g. Tokina 100/2.8, about 6 cm displacement of the main groups, since helicoil - a cam our two for tiny adjustments of two other groups.
paulmd 10y ago
While "angle of view" is the technically correct way to think of this, very few people actually think that way, myself included. It's pretty much limited to people who work heavily with large format and use multiple formats. "35mm equivalent" focal lengths and "crop factors" are by far the most common ways to mentally visualize this. It's not entirely a direct conversion since not every format is a 3:2 ratio like 35mm is - for example 6x7 feels tighter because it's much closer to a square format. My 55mm lens is technically closer to a 22-mm equivalent in diagonal FoV but it feels like a 28mm does on 35mm. I think it's honestly a shame that primes have died out. Dollar for dollar, most primes are massively better performers than zooms in terms of sharpness and aperture.

by jrapdx3 10y ago

dom0 10y ago

For some SLR systems 50 mm (or more often 51.6 mm) isn't actually all that easy (in the 60s), eg. Nikon with a comparatively large flange back distance. We still see some artifacts of this today, e.g. the classic short reproduction macro was always around 55-60 mm, because it's a spot where the lens design is easier.

jrapdx3 10y ago
Macro lenses were more useful with a longer focal length, in 35mm terms, 80-100mm or more longer was desirable to give more working distance to the subject at high ratio, like 1:1. For example, for my MFT system, the macro is 60mm equiv to 120mm for a 35mm frame. As I understand, lens design in the digital era has changed due to the characteristics of the sensors vs. film. Mirrorless designs have also changed requirements and eliminates some restrictions due to flange distance. I'm not an expert in that field, maybe you know more in that regard.
- dom0 10y ago
  For most macro uses yes, the longer focal lenses where and are preferred due to working distance. The shorter macros where developed specifically for reproduction use (photographing records, books, paintings and the like), where the larger reproduction ratios (1:2, 1:1) where rarely if ever needed, so the problem didn't arise. The shorter flange back distance in mirrorless systems makes some things easier and some things harder (if you want short lenses that is), but overall give more freedom to the lens designer. Sensor vs film and manual focus / first AF systems vs modern AF systems is a huge difference and for many older lenses esp. in the wide angle spectrum that is the reason for a large performance difference between film and digital.
paulmd 10y ago
Even the number "50mm" is massively debated. The 51.6mm number is drawn from the focal length of classic Leica normal lenses, which is 100% arbitrary. There's pretty strong arguments that something more like 43mm is the normal focal length for 35mm. And designing lenses with adequate coverage for 35mm as well as a sufficient flange distance to clear a SLR mirror was definitely a problem back in the day. Older "normal" lenses for SLRs used to commonly be 55mm or even 58mm. Wide angle-lenses suffered a similar problem, and for a great while rangefinder lenses (or similar lenses that protruded into the mirror cavity of a SLR) were the dominant options for wide angle photography. It took quite a while to develop good "retrofocal" lenses where the optical center is actually behind the lens (basically the opposite of the telephoto lens where the optical center is in front of the lens). The very first examples of the type are the Angénieux retrofocus and the Voigtländer Prominent's Skoparon, both introduced in 1950. The Skoparon design was essentially a Tessar lens backwards and went on to be one of the earliest wide-angle lenses used in SLRs, notably as the Asahi Pentax 35mm f/3.5. It had an extremely long lifespan, in its medium-format variant (Pentax 75mm f/4.5) it continued to be produced until around 2000. The funny thing is it all happened because Voigtländer patented it for rangefinders but neglected to patent it for SLRs! The other thing to remember about 50mm-ish macro lenses is that it's still somewhat reasonable to build a helicoid that can get out to 1:1 reproduction without extension tubes. I have a 50mm and a 90mm that will both go to 1:1 reproduction on their own, and I can tell you that while the 50mm may be somewhat ungainly the 90mm is absolutely absurd when you crank it all the way out. The 50mm uses a double helicoid, the 90mm is actually four helicoids running inside each other.
- dom0 10y ago
  Yes, the old unit focusing macro designs can look rather weird and somewhat unstable when fully "racked out". With internal focusing this has been "fixed", although they still need a lot of displacement of the focusing group (in the Nikon 200/4 AF for example it's about five cm if I remember right, which is a lot for an IF design). Most macros still have a lot of external movement, but internally floating elements reduce the required displacement still. (E.g. Tokina 100/2.8, about 6 cm displacement of the main groups, since helicoil - a cam our two for tiny adjustments of two other groups.

paulmd 10y ago

While "angle of view" is the technically correct way to think of this, very few people actually think that way, myself included. It's pretty much limited to people who work heavily with large format and use multiple formats. "35mm equivalent" focal lengths and "crop factors" are by far the most common ways to mentally visualize this. It's not entirely a direct conversion since not every format is a 3:2 ratio like 35mm is - for example 6x7 feels tighter because it's much closer to a square format. My 55mm lens is technically closer to a 22-mm equivalent in diagonal FoV but it feels like a 28mm does on 35mm. I think it's honestly a shame that primes have died out. Dollar for dollar, most primes are massively better performers than zooms in terms of sharpness and aperture.