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new Nikon gear
#33
@stoppingdown

 

One cannot patent the use of a fresnel lens, or the use of a fresnel lens with other refractive elements.  A Phase Fresnel lens is also not the same type of fresnel lens as canon is using but rather a different geometry.  That also cannot be patented.

 

@JoJu

 

The length being "exactly" 75mm I would doubt, as all specifications are rounded, but it also doesn't mean anything directly. 

 

@brightcolors

Quote: 

Why is the 300mm f4E PF so remarkably short and light (same goes for the Canon 400mm f4 DO IS USM II)
Yes, but not simply because it exists.  The fresnel surfaces contribute power that would otherwise require shorter radii of curvature.  That reduces aberrations, so more aggressive telephoto ratios may be pursued.  The lightness is partly contributed to (even largely, I would say) by the use of fresnel lenses as they have very little thickness.

 

Quote: 

Does the use of the PF/DO elements mean a whole lot of extra elements are needed to get rid of the aberrations?
Again, not directly.  You requrie one flint to balance the polychromatic aberrations of the fresnel surface.  The structure of the fresnel surface may only be "tuned" to a single wavelength.

 

Looking at  first order, Nikon used a fresnel element to massively increase the power of the P group in the P N configuration.  The direct result of this is that the power of the N group must be massively increased.  This requires stronger curvature, higher refractive index, a GRIN material, or an additional fresnel lens.

 

First order -> http://photonics.intec.ugent.be/educatio...v1ch32.pdf

Smith also wrote Modern Lens Design and Modern Optical Engineering the former of which I am on a team editing the third edition of.  

 

To undo geometrical aberrations, you split and compound elements to distribute the power and "lean on" the refractive index of the material to do some of your work for you if you do not want to use special materials. 

 

This increases the element count

 

Counter-point:

 

Does the use of CAF2, Calcium Fluorite, in and of itself make a lens apochromatic?

 

No, it doesn't.  CAF2's good property is that it has anomalous partial dispersion, which is a big long sciency phrase zeiss likes to use for marketing.  If you look at Nikon's diagrams above you can see dispersion - the spreading out of the different colors.  All materials do this, unfortunately, but they do it to different degrees.  Dispersion stems from the fact that the refractive index is not constant across the spectrum.  If you go here, you can see the graphs of the refractive index of CAF2 and NSK4, a common low dispersion glass:

 

http://refractiveindex.info/?shelf=main&...e=Malitson

http://refractiveindex.info/?shelf=glass...page=N-SK2

 

Visible is approximately .4-1um, or just plug in .38 for the blue of the visible spectrum and .7 for the red side.

 

The big concept to see is that CAF2's refractive index has a point of inflection somewhat close to the visible range.  The refractive index of NSK2 changes .028 across visible while CAF2 changes only .0117 - less than half. 

 

The Abbe number of a material describes its dispersion between green and red - most glasses fall in the range of 65-30 or so.  CAF2's ranges from 95-118 depending on the specific manufacture.  It has phenominal "normal" dispersion but its crystal structure also has a harmonic or some business in the blue range that causes its partial dispersion, the measure of dispersion between green and blue, to be abnormally low. 

 

Does this guarantee apochromatic results?  No, no it doesn't.  It just means that a particular lens may be used to prevent blue CAs, and blue is difficult to deal with, but poor choices may still lead to blue falling to a different focus than green/red elsewhere in the design. 

 

Quote: 

Since I am not allowed to use the 400mm f2.8E
You are not allowed to use any lens - element count has no direct meaning with respect to performance.  Canon's 17mm TS-E has 18 elements - surely that means something here too?  (it doesn't)

 

Quote: 

The increase in elements is pretty normal for modern tele prime design, and is not due to the use of the PF element.
You have no basis for this claim, nor the knowledge to make it accurately.

 

There are generalizations that may be made, such as modern coatings (from the 90s and on) allowing higher element counts without having poor transmission, and CAD becoming better in the past decade or so at guiding the design process that lead to generally higher element counts with newer lenses - but this is independent to the performance of the lens.  Often adding more elements can make your performance worse, as more elements do give degrees of freedom to optimize with but they also impose restrictions. 

 

The use of the PF element in and of itself - i.e inherently did not increase the element count.  What nikon chose to do with it did.

 

Quote: 

By the way. The 500mm f4 and 600mm f4 lenses with IS also have 16 elements.
What do lenses with nearly twice the focal length have to do with this lens?

Canon's 50mm f/.8 has 6 elements.  The 85/1.8 has 9 elements, and the 100/2 has 8 elements.  The focal lengths are spaced the same as 300 -> 500/600, surely there is some correlation between the element counts!!! (there is none)

 

Quote: 

Why do both Nikon and Canon use such elements?
It comes down to weight initially.  If you can cut the thickness of one of your large front elements in half you may reduce the weight by as much as 400-500 grams.

 

Nikon's new 300/4 takes a different approach, using a fresnel surface to drive the telephoto ratio into a very impressive space.

 

The big "takeaway" is this:

 

A fresnel lens does one of two things:

It allows a lens element to become thinner while still having the same power.

OR

It allows an already curved element to contribute more power than it would with the material being used.

 

Neither of these is directly tied to the overall length of the lens.

  


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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