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new Nikon gear
#10
The increase in the number of elements can be accounted for fairly easily.  The new lens is just 5.8" long - compared to 8~9 inches for previous lenses.  That gives the lens a telephoto ratio of .466, which is simply stunning and certainly the highest telephoto ratio I've seen on any consumer lens, though there may be higher out there. 

 

Because it's a long focal length lens, it is extremely easy to achieve diffraction limited performance when the telephoto ratio is near 1 - you need very mild curvatures to form the long focal length, and mild curvatures do not produce very large aberrations.  The large airspaces can also be used to correct monochromatic aberrations effectively, the trouble just comes with the polychromatic aberrations.  If one ignores them it is possible to create diffraction limited lenses with focal lengths between 200~800mm in just 2 or 4 elements.  To correct them to an "okay" level can be done in perhaps 5 if one uses CAF2 (fluorite), and 6 if you choose not to, though blue may still be a bit bothersome at that level. 

 

With both telephoto and reverse telephoto lens design, the further the telephoto ratio (over all length of the lens - peak of the front element to the focal plane - divided by focal length) strays from 1 the stronger your aberrations will become.  Often it is said that a telephoto ratio of .7 is superb.  To decrease the telephoto ratio in a telephoto configuration (positive lens in front of negative lens) the first thing to do would be to increase the power of the front group of elements.  Here, absolutely enormous power has been added through the fresnel lens.  Not only does it have a strong focusing power on its own with a short radius of curvature, it looks like it's in the range of 70-90mm, but the fresnel "element" of the lens will add even more power.  All of that power will come at the cost of quite large aberrations.  We can see that the first cemented doublet in the "rear" section of the lens has had its power increase (or decreased one might say, as it has negative power).  The role of this doublet is to roughly collimate the beam of light traveling through the lens, it is aided by additional negative power from the lens just behind it.  The massive increase in positive power up front must be met with a massive increase in negative power, so that single negative lens has had a thin negative lens cemented onto the front.  It likely increases the negative power some while aiding in color correction.  There used to be a meniscus lens cemented to a planoconcave lens making up the focusing group, those have been replaced.  The focusing group is now a meniscus lens cemented to a positive lens.  Behind that is a series of lenses do all many of things - I am not sure which are part of the IS group and which are not but I would suspect that the first three after the focusing doublet make up the IS unit and the following two are just for correction. 

 

Lastly, there is a single positive lens to re-focus the collimated beam onto the sensor.

 

The telephoto ratio is extremely impressive, the extra elements are needed to correct the aberrations you pay with to achieve that ratio.

  


Messages In This Thread
new Nikon gear - by Klaus - 01-06-2015, 08:44 AM
new Nikon gear - by Klaus - 01-06-2015, 08:46 AM
new Nikon gear - by popo - 01-06-2015, 10:47 AM
new Nikon gear - by JJ_SO - 01-06-2015, 11:11 AM
new Nikon gear - by Brightcolours - 01-06-2015, 11:21 AM
new Nikon gear - by Brightcolours - 01-06-2015, 11:42 AM
new Nikon gear - by Klaus - 01-06-2015, 12:18 PM
new Nikon gear - by JJ_SO - 01-06-2015, 12:51 PM
new Nikon gear - by stoppingdown - 01-06-2015, 04:45 PM
new Nikon gear - by Scythels - 01-06-2015, 04:46 PM
new Nikon gear - by stoppingdown - 01-06-2015, 07:06 PM
new Nikon gear - by mst - 01-07-2015, 12:08 AM
new Nikon gear - by mst - 01-07-2015, 12:12 AM
new Nikon gear - by Brightcolours - 01-07-2015, 07:06 AM
new Nikon gear - by Brightcolours - 01-07-2015, 07:14 AM
new Nikon gear - by stoppingdown - 01-07-2015, 08:30 AM
new Nikon gear - by felix - 01-07-2015, 08:51 AM
new Nikon gear - by stoppingdown - 01-07-2015, 09:25 AM
new Nikon gear - by mst - 01-07-2015, 12:10 PM
new Nikon gear - by JJ_SO - 01-07-2015, 05:30 PM
new Nikon gear - by Scythels - 01-07-2015, 06:05 PM
new Nikon gear - by JJ_SO - 01-07-2015, 08:54 PM
new Nikon gear - by stoppingdown - 01-07-2015, 09:09 PM
new Nikon gear - by JJ_SO - 01-07-2015, 10:07 PM
new Nikon gear - by Scythels - 01-07-2015, 10:17 PM
new Nikon gear - by JJ_SO - 01-07-2015, 10:30 PM
new Nikon gear - by stoppingdown - 01-07-2015, 10:34 PM
new Nikon gear - by Brightcolours - 01-08-2015, 12:59 AM
new Nikon gear - by Scythels - 01-08-2015, 04:15 AM
new Nikon gear - by JJ_SO - 01-08-2015, 06:43 AM
new Nikon gear - by Brightcolours - 01-08-2015, 08:24 AM
new Nikon gear - by stoppingdown - 01-08-2015, 11:58 AM
new Nikon gear - by Scythels - 01-08-2015, 04:18 PM
new Nikon gear - by JJ_SO - 01-08-2015, 08:40 PM
new Nikon gear - by stoppingdown - 01-08-2015, 08:49 PM
new Nikon gear - by popo - 01-08-2015, 09:30 PM
new Nikon gear - by JJ_SO - 01-08-2015, 09:52 PM
new Nikon gear - by Scythels - 01-08-2015, 10:18 PM
new Nikon gear - by popo - 01-08-2015, 10:31 PM
new Nikon gear - by JJ_SO - 01-09-2015, 09:12 AM
new Nikon gear - by mst - 01-09-2015, 09:43 AM
new Nikon gear - by mst - 01-09-2015, 09:48 AM
new Nikon gear - by Guest - 01-09-2015, 10:19 AM
new Nikon gear - by Brightcolours - 01-09-2015, 01:08 PM
new Nikon gear - by JJ_SO - 01-09-2015, 06:38 PM
new Nikon gear - by stoppingdown - 01-09-2015, 08:42 PM
new Nikon gear - by JJ_SO - 01-09-2015, 09:12 PM
new Nikon gear - by Scythels - 01-09-2015, 09:15 PM
new Nikon gear - by stoppingdown - 01-09-2015, 09:23 PM
new Nikon gear - by JJ_SO - 01-09-2015, 09:39 PM
new Nikon gear - by borisbg - 01-09-2015, 11:34 PM
new Nikon gear - by Klaus - 01-09-2015, 11:43 PM
new Nikon gear - by Scythels - 01-10-2015, 03:29 AM
new Nikon gear - by stoppingdown - 01-10-2015, 01:16 PM
new Nikon gear - by JJ_SO - 01-10-2015, 05:06 PM
new Nikon gear - by stoppingdown - 01-10-2015, 06:10 PM
new Nikon gear - by JJ_SO - 01-10-2015, 07:54 PM
new Nikon gear - by stoppingdown - 01-10-2015, 08:04 PM
new Nikon gear - by JJ_SO - 01-10-2015, 08:36 PM
new Nikon gear - by stoppingdown - 01-10-2015, 09:32 PM
new Nikon gear - by JJ_SO - 01-11-2015, 09:09 AM
new Nikon gear - by Guest - 01-11-2015, 09:12 PM
new Nikon gear - by Klaus - 01-11-2015, 10:16 PM
new Nikon gear - by JJ_SO - 01-12-2015, 01:51 PM
new Nikon gear - by stoppingdown - 01-12-2015, 02:23 PM
new Nikon gear - by stoppingdown - 01-12-2015, 02:33 PM
new Nikon gear - by JJ_SO - 01-12-2015, 03:31 PM
new Nikon gear - by Klaus - 01-12-2015, 08:47 PM
new Nikon gear - by borisbg - 01-13-2015, 06:03 AM
new Nikon gear - by JJ_SO - 01-13-2015, 08:07 AM
new Nikon gear - by Scythels - 01-13-2015, 04:21 PM
new Nikon gear - by JJ_SO - 01-13-2015, 06:38 PM
new Nikon gear - by stoppingdown - 01-13-2015, 08:18 PM
new Nikon gear - by Brightcolours - 01-13-2015, 09:37 PM
new Nikon gear - by Klaus - 01-13-2015, 10:31 PM
new Nikon gear - by JJ_SO - 01-13-2015, 10:48 PM
new Nikon gear - by borisbg - 01-14-2015, 01:24 AM
new Nikon gear - by stoppingdown - 01-14-2015, 10:56 AM
new Nikon gear - by JJ_SO - 01-14-2015, 03:48 PM
new Nikon gear - by mst - 01-15-2015, 09:10 AM
new Nikon gear - by JJ_SO - 01-15-2015, 10:03 AM
new Nikon gear - by stoppingdown - 02-06-2015, 12:09 AM
new Nikon gear - by JJ_SO - 02-06-2015, 05:10 AM
new Nikon gear - by felix - 02-06-2015, 11:25 AM
new Nikon gear - by JJ_SO - 02-06-2015, 02:56 PM
new Nikon gear - by stoppingdown - 02-06-2015, 04:18 PM
new Nikon gear - by JJ_SO - 02-06-2015, 07:52 PM
new Nikon gear - by JJ_SO - 02-10-2015, 11:15 PM
new Nikon gear - by Brightcolours - 02-10-2015, 11:20 PM
new Nikon gear - by JJ_SO - 03-02-2015, 09:28 PM
new Nikon gear - by felix - 03-04-2015, 09:19 AM
new Nikon gear - by stoppingdown - 04-01-2015, 08:09 AM
new Nikon gear - by Brightcolours - 04-01-2015, 09:15 AM
new Nikon gear - by JJ_SO - 04-01-2015, 09:43 AM
new Nikon gear - by felix - 04-01-2015, 07:10 PM
new Nikon gear - by JJ_SO - 04-01-2015, 08:43 PM
new Nikon gear - by popo - 04-01-2015, 11:34 PM
new Nikon gear - by felix - 04-04-2015, 10:39 AM
new Nikon gear - by Brightcolours - 04-04-2015, 12:10 PM
new Nikon gear - by Brightcolours - 04-24-2015, 04:16 PM

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