New 19mm and 70-200

[Roland Vink]

Nikon have had 100 as well as 105 mm lenses, same with 24 and 25 mm (25-50/4).

The usual focal length tolerance is 5% thus a 19 mm could in theory be near 18 or approx. 20 mm. However, this tolerance is the optical design itself, not the variation on the production units.

True, there is the Series-E 100/2.8, AIS 100-300/5.6 and 28-100G, also 10-100 zooms for Nikon 1. Otherwise, all other primes, zooms and special lenses (micro, EL, Printing ...) are 105mm.

Nikon also made a 2.5cm (25mm) lens for their rangefinder camera and the 25-50/4, but other primes and zooms in that range since 1967 have been 24mm.

I agree there is often a tolerance in the focal length, but if the 19mm were really closer to 20mm or 18mm, I suspect it would be labelled as such, otherwise why call it 19mm?

[Bjørn Rørslett]

The design patent determines what the nominal focal length is going to be. Plus convention of course, as most '50' mm lenses are ~51.6 or 52.3 mm by design.

[David H. Hartman]

would monopoly money do...

I could really use a get out of debtors prison free card!

[Akira]

The design patent determines what the nominal focal length is going to be. Plus convention of course, as most '50' mm lenses are ~51.6 or 52.3 mm by design.

AF-S 50/1.8G would be Nikon's first 50mm lens that is truly 50mm: the catalog says that its angle-of-view is 47 degree as opposed to 46 degrees of all the previous Nikkors.

[Roland Vink]

Interesting. The picture angle of the 25-50/4 is 80°40' - 47°50', compared to 46° for most other 50mm Nikkors.

The wider angle of view suggests the focal length at the nominal 50mm setting is also somewhat shorter than other 50mm lenses (which are mostly 51.6mm - see http://www.nikkor.com/story/0049/ towards the end)

[Akira]

Interesting. The picture angle of the 25-50/4 is 80°40' - 47°50', compared to 46° for most other 50mm Nikkors.

The wider angle of view suggests the focal length at the nominal 50mm setting is also somewhat shorter than other 50mm lenses (which are mostly 51.6mm - see http://www.nikkor.com/story/0049/ towards the end)

I think it is understandable that the focal length of the long end of a "wide zoom" is rounded to 50mm.  The situation is a bit different from that of 50mm primes.

Also, a recent interview to Nikon designers of AF-S 105/1.4E revealed that the actual focal length of the nominal 35mm lenses have been 36mm.  (see this new thread of mine: http://nikongear.net/revival/index.php/topic,4593.0.html)

According to Nikon website, the angle-of-view of Ais 35/1.4 is 62 degree wheras those of AF-S 35/1.4G and 35/1.8G are both 63 degree.  It might be only recent years that Nikon started to design 35mm lenses as true 35mm.

[abergon]

Both lenses now officially announced, see press release for the 19mm PC-E here: http://www.nikon.com/news/2016/1019_lens_01.htm.

Price 4000 USD.

[Roland Vink]

Also, a recent interview to Nikon designers of AF-S 105/1.4E revealed that the actual focal length of the nominal 35mm lenses have been 36mm.  (see this new thread of mine: http://nikongear.net/revival/index.php/topic,4593.0.html)

According to Nikon website, the angle-of-view of Ais 35/1.4 is 62 degree wheras those of AF-S 35/1.4G and 35/1.8G are both 63 degree.  It might be only recent years that Nikon started to design 35mm lenses as true 35mm.

Yes I was aware that older "35mm" lenses have a focal length of 36mm - this information is given in lens diagrams from old Nikon Dealer Sales Manuals - I have copies from 1968, 1972 and 1977
Most wide lenses from that period (and I assume through the AIS and AF periods) have a true focal length slightly longer than the nominal value. Once you get longer than 50mm, the focal length is true (for primes at least).

[Erik Lund]

Yes at infinity, all of the IF lenses change more or less as focused closer.

[Akira]

Roland, thanks for the additional info on the discrepancy between the nominal and the actual focal lengths.

Yes at infinity, all of the IF lenses change more or less as focused closer.

And RF (rear focus) lenses, too?

[Roland Vink]

Yes RF lenses, IF, Zoom, CRC ... any lens which has groups of elements moving in relation to other groups when focusing, the focal length will change.

In most cases the focal length gets shorter when focusing closer, this has an advantage of making the lens barrel more compact. In the AIS 55 micro, probably the 85/2.8 PC which has very similar optical design, and a few others, the focal length actually increases on focusing closer.

[Erik Lund]

Thanks Roland

[Bjørn Rørslett]

Yes RF lenses, IF, Zoom, CRC ... any lens which has groups of elements moving in relation to other groups when focusing, the focal length will change.

In most cases the focal length gets shorter when focusing closer, this has an advantage of making the lens barrel more compact. In the AIS 55 micro, probably the 85/2.8 PC which has very similar optical design, and a few others, the focal length actually increases on focusing closer.

Any hard evidence of the assertion about the 55 Micro? Taken at face value, an increased focal length during closer focusing would require even more extension (or equivalently, less magnification for a given added travel of the optics) and greater reduction in effective aperture. Somehow this doesn't sound right.

[Erik Lund]

The way the CRC in the 55mm Ais 2.8 is working is show quite clearly here:

http://www.pierretoscani.com/echo_shortpres.html#shortpres05

When the Micro-Nikkor 55mm f/2.8 Ais is set to minimum focus (reproduction ratio 1:2), the space between the two sub-units is about 12 mm, so the focal length of the lens is about 57 mm (instead of 55 mm on infinity focus).

[Roland Vink]

Thanks Eric 

You can see the longer focal length of the AIS 55 micro in action if you compare with the older AI 55/3.5 - the AIS extends more and the focus distance at 1:2 is greater (0.25m vs 0.241m). The AIS 55 micro actually focuses a little closer than 1:2, so it can get to 1:1 with the PK-13. If the focal length is 57mm at 1:2, it would require 28.5mm extension to achieve 1:1, and the 27.5mm PK-13 is too short, so the lens was designed to focus a little closer to compensate.