NikonGear'23
Gear Talk => Lens Talk => Topic started by: Peter Forsell on April 28, 2018, 22:10:00
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There's still two telephoto lenses in Nikon lineup that are not AF-S, namely the 135/2 and 180/2.8. I'm just wondering how light/small could a PF version of 200/2.8 be? Current Nikon AF 180/2.8D weighs 760 g and is 144 mm long and a corresponding Canon 200/2.8 (no DO glass, no IS) is about the same.
The weigh probably cannot be halved like the 300 PF did to the 300/4D, but a pocketable 200/2.8 PF would be interesting. Can the phase fresnel optics reduce the size and weight of a hypothetical 200/2.8 much, or are there other limits?
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Interesting discussion, but, although I don't want to sound like wet blanket, that would not going to happen.
I think that the f2.8-class mid-teles of 70-200 range has long been converged on one highly efficient zoom. No matter how small and light a PF 200/2.8 would be, it is still much lighter and handier than a couple of f2.8 mid-teles switching back and forth.
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My guess is that a 180 or 200mm f/2.8 lens with a Fresnel lens is unlikely. Nikon have not applied for any patents for such a lens, and it would only be marginally smaller than the same lens using conventional elements. If you compare the size of the 105/1.4, 135/2 and 180/2.8, which all have similar size entrance pupil, you'll see that the size does not increase much in spite of the longer focal length, the 180/2.8 is relatively compact so there is not much scope or value in making it smaller.
It would be nice to see more compact telephoto primes such as 105/2.5 and 135/2.8, as they would be much smaller and cheaper than the 70-200/2.8 zooms, and offer more speed compared to the slower 70-200/4 and 70-300/4-5.6 zooms.
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Circumstantial evidence of registered patents - and recent direct leaks - all point to Nikon investing their PF lens technology into longer telephotos. Obviously this is where optimal advantages are gained in ergonomics: a shorter and hopefully much lighter lens. Their 300 f4E PF is one winner of a optic and it makes sense to present more tele options to the market. Birders and other genres of wildlife are sure to take up new offerings - especially for a single telephoto for travelling that works well with teleconverters.
https://nikonrumors.com/2018/04/16/nikon-to-announce-a-new-nikkor-600mm-f-5-6-pf-lens-soon.aspx/
Compared a f4 telephoto, a 600 f5.6 has a lower TeleConverter Factor (T1C-0.75) but it will still retain some AF functionality using modern DSLRs (D5, D500, D850) cf https://chambeshiphotographyblog.wordpress.com/2018/02/17/the-tc-factor-with-telephoto-lenses/
A 840 f8 using TC14 will certainly be useful :-)
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I would like to see something like a 135/2.8 AF-S, not PF but a modern, well-corrected lens with the latest autofocus technology. It would serve to reduce bag weight compared to existing options in the Nikon system and be more pleasant to handle than something like the 105/1.4. For 105mm I would like to see an update to the Micro, which has some optical issues (fringing at 1:1), and could use E diaphragm control and possibly AF-P for improved focus shift series.
It seems Nikon's focus for PF applications is in the intermediate aperture long primes, probably there the gains are largest and there is not much competition at the moment (at least not based on diffractive optics).
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Going on a tangent here, but why are the Canon lenses called "Diffractive Optics" (DO), and Nikon called "Phase Fresnel" (PF) ??
Fresnel lenses are refractive lenses.
Refraction is the phenomenon of light, radio waves, etc. being deflected in passing obliquely through the interface between one medium and another (such as air/glass) ...
Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle.
And what does "phase" have to do with a Fresnel lens? Lens coatings use destructive interference to suppress reflections. Destructive interference is the interference of two waves of equal frequency and opposite phase, resulting in their cancellation where the negative displacement of one always coincides with the positive displacement of the other.
Are the Canon and Nikon names just silly marketing terms, or is there more to it than that?
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Going on a tangent here, but why are the Canon lenses called "Diffractive Optics" (DO), and Nikon called "Phase Fresnel" (PF) ??
Both use a diffractive element. The two companies may use different approaches in the design and manufacture of the elements though; perhaps the design method led to Nikon choosing a different marketing name.
When you have photons hitting the diffractive element, they are scattered in different directions from the edges and the phase of the photons depends on the pathlength traveled. At the detector the photons which have similar phase combine to amplify the image and photons that have opposite phases vanish. The diffractive element is designed in such a way that a useful image is formed. Fresnel diffraction is discussed:
https://en.wikipedia.org/wiki/Fresnel_diffraction
I guess Nikon's "Phase Fresnel" refers to both Fresnel diffraction as well as modeling of the Phase of the photons as they travel through the lens as a method of simulating the effect of the diffractive element. If you want to read more about how wave phenomena of light can be explained by considering photons particles with phase, Richard Feynman's book "Qed: The Strange Theory of Light and Matter" describes it eloquently.
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It would be nice to see more compact telephoto primes such as 105/2.5 and 135/2.8, as they would be much smaller and cheaper than the 70-200/2.8 zooms, and offer more speed compared to the slower 70-200/4 and 70-300/4-5.6 zooms.
I totally agree. In the film days before AF hit the market my Ai 2.8/135mm was the one lens I used for outdoor portraits. A great lens, small, light and of very high definition with a smooth bokeh, plus very cheap in the used marked. I really should get one of these again!
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I totally agree. In the film days before AF hit the market my Ai 2.8/135mm was the one lens I used for outdoor portraits. A great lens, small, light and of very high definition with a smooth bokeh, plus very cheap in the used marked. I really should get one of these again!
Very handy lens. I keep the 135/3.5 Ai as a tiny tele. Having had the 135/2 AiS, 135/2.8 AiS, and the 135/3.5 Ai all at the same time until recently, I'd like to have a 2.8 version that's a little more 'APO' than the old Ai one.
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Both use a diffractive element.
https://en.wikipedia.org/wiki/Fresnel_diffraction
but I am with Roland about this one - a Fresnel lens (element, here) is refractive, and while diffration occurs, it is not the image-forming phenomenon.
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I don't really understand the optophysical theory, but the element used in PF300 seems to be called "Blazed Grating" which is a special refractive optics utilizing the diffraction effect:
https://en.wikipedia.org/wiki/Blazed_grating
This is an interview to the Nikon engineers in charge of PF300:
https://dc.watch.impress.co.jp/docs/news/interview/688994.html
Sorry, the texts are all in Japanese, but you will recognize the illustrations of the blazed grating.
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I own an AF-S 105/2.8G ED VR Micro and like it but... the lens is a honker and it's a pain when I forget to set Axial CA correction. I'll usually find I forgot to set Axial CA when I'm nearing completion of edits in Photoshop. I start in CNX-D and then move to PS with a TIFF. The heavy breathing of the hasn't bothered me as I don't think I've ever used the lens on a tripod. I own a 105/4.0 AI and 105/2.8 AIS Micro for tripod use. If Nikon replaced the AF-105/2.8G ED VR they need to make it smaller and do a better job with the CA. It takes way tooooooo much space in my bang.
I would welcome an AF-S 105/2.5 and 135/2.8 but they would need to be reasonable in size.
Dave Hartman
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Going on a tangent here, but why are the Canon lenses called "Diffractive Optics" (DO), and Nikon called "Phase Fresnel" (PF) ??
Fresnel lenses are refractive lenses.
Refraction is the phenomenon of light, radio waves, etc. being deflected in passing obliquely through the interface between one medium and another (such as air/glass) ...
Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle.
And what does "phase" have to do with a Fresnel lens? Lens coatings use destructive interference to suppress reflections. Destructive interference is the interference of two waves of equal frequency and opposite phase, resulting in their cancellation where the negative displacement of one always coincides with the positive displacement of the other.
Are the Canon and Nikon names just silly marketing terms, or is there more to it than that?
"Phase Fresnel" is just Nikon's proprietary term, like "VR".
A Fresnel lens can use either refraction or reflection to collimate light, as in a lighthouse, or focus it, if it is turned round, as when a Fresnel lens is used to focus sunlight on a solar power cell. There is always also diffraction at the edges of the elements, which is why a Fresnel lens are unsatisfactory for image forming lenses in photography. According to Nikon, it is only the diffraction that their PF elements make use of, taking advantage of the fact that the effect of wavelength on the degree of diffractive bending is opposite to that with refraction, so a Fresnel lens can compensate for longitudinal chromatic aberration; have a look at https://www.nikonimgsupport.com/eu/BV_article?articleNo=000006500&configured=1&lang=en_GB
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I don't really understand the optophysical theory, but the element used in PF300 seems to be called "Blazed Grating" which is a special refractive optics utilizing the diffraction effect:
Since the light has to go through the element, by necessity there is refraction but you cannot model the light propagation through this kind of an optical element without modeling the diffraction, and the latter certainly contributes to the image. The difference between a Fresnel lens and a Phase Fresnel lens is that the latter has a grid which has structure on spatial scale close to the wavelength of the light (390-700 nm) which leads to the diffractive phenomena. A conventional Fresnel lens (without diffraction) doesn't form a useful image.
Diffraction, reflection, and refraction all originate from the same physical phenomena: the scattering of light from matter. A pure refractive element is one which is smooth (on the spatial scale of the order of the wavelength of light) so that you can model the light propagation using approximations such as reflection and refraction. When the element has structure on the spatial scale of the wavelength of light, then you cannot ignore the wave-phenomena of light, or diffraction. Quantum electrodynamics (QED) provides a way of modeling all these phenomena without having to consider them as distinct effects.
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aha. thanks for the explanations.
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This is an interview to the Nikon engineers in charge of PF300:
https://dc.watch.impress.co.jp/docs/news/interview/688994.html
If you drop it into translate.google.com does quite a good job
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I don't really understand the optophysical theory, but the element used in PF300 seems to be called "Blazed Grating" which is a special refractive optics utilizing the diffraction effect: [...]
Thanks Akira. I would need someone to explain it in more simple terms for me to understand, but it is obvious these are more than just simple Fresnel lenses.
I suspect besides the obvious Fresnel steps in the element, there must be a substructure which is the size of the wavelength of light, which is responsible for the diffraction effect. The wikipedia page says the blazed grating is optimised for one wavelength only, so I wonder how the lens works with white light (has anyone tried it for UV or IR photography?). Very interesting technology.
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If you drop it into translate.google.com does quite a good job
So, the interpreter will soon be filed to the redbook...
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Thanks Akira. I would need someone to explain it in more simple terms for me to understand, but it is obvious these are more than just simple Fresnel lenses.
I suspect besides the obvious Fresnel steps in the element, there must be a substructure which is the size of the wavelength of light, which is responsible for the diffraction effect. The wikipedia page says the blazed grating is optimised for one wavelength only, so I wonder how the lens works with white light (has anyone tried it for UV or IR photography?). Very interesting technology.
Indeed it is an interesting technology. I wonder when or if people would find the way to suppress the PF flare...
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Thanks Akira. I would need someone to explain it in more simple terms for me to understand, but it is obvious these are more than just simple Fresnel lenses.
I suspect besides the obvious Fresnel steps in the element, there must be a substructure which is the size of the wavelength of light, which is responsible for the diffraction effect. The wikipedia page says the blazed grating is optimised for one wavelength only, so I wonder how the lens works with white light (has anyone tried it for UV or IR photography?). Very interesting technology.
The 300PF works quite well with IR, as exemplified by muliple images posted here before. Here is one, wide open on D40x. Notice the lack of flare on the shiny chimneys.
(http://otoien.zenfolio.com/img/s/v-2/p1593147141.jpg)
Backlight hitting direclty can create some good flare and ghosting in IR, as I previously exemplified here: http://nikongear.net/revival/index.php/topic,7350.msg118637.html#msg118637 , repeated here for convenience. With some effort one can show off the ghost of the fresnel pattern:
(http://otoien.zenfolio.com/img/s/v-3/p2823793011.jpg)
I doubt there are micro patterns overlayed on the Fresnel pattern. The DC watch article indicates otherwise. Perhaps the increasing frequency of the pattern towards the edges is at play?
I do not think there is much hope for UV transmission with the modern coatings of the lens.
Indeed it is an interesting technology. I wonder when or if people would find the way to suppress the PF flare...
Akira, the PF flare is usually not a problem in practical visible light photography, and I believe the design already suppresses most of the effect compared to the original designs that came out (for instance Canon's first use of this technology). Other lenses will also flare in those situations: To make the PF effect show up one needs severely blown light points. Then instead of a monochromatic halo in regular lenses one can get a little of the rainbow pattern. I believe I posted a comparison to the AF 300/4 in the original 300PF thread. I have also used it for solar imaging and astro photography without any problems.
A much more important property of the lens is the almost complete lack of longitudinal/highlight fringing; a little rainbow showing up in the most extreme flare cases is a very small cost to bear. For astro photography it is also worth noting that coma/astigmatism is much better with the AFS 300/4 PF ED VR E than the AFS 300/4 ED. The latter will give pronounced "winged" stars not very far away from the center (on a DX sensor) unless stopped down below f/5 or so. My AF 300mm f/4 ED has pretty bad purple/green fringing. (I almost always had to work on removal in reflections of sunlit eyes). This in spite of that all 3 lenses are highly regarded resolution wise.
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Thanks Akira. I would need someone to explain it in more simple terms for me to understand, but it is obvious these are more than just simple Fresnel lenses.
I suspect besides the obvious Fresnel steps in the element, there must be a substructure which is the size of the wavelength of light, which is responsible for the diffraction effect. The wikipedia page says the blazed grating is optimised for one wavelength only, so I wonder how the lens works with white light (has anyone tried it for UV or IR photography?). Very interesting technology.
In the simplest terms red light through a prism refracts less than blue light. Red light through a diffraction grating refracts more than blue light. The diffractive lens element is used to counteract the refraction in the other elements of the lens, resulting in an achromatic lens without as many thick lenses which would otherwise be required to achieve the same thing. If you look at the diagrams in the article Akira posted you can see how the phase fresnel element reverses the order of wavelengths.
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Øivind and Jack, thank you for the explanations.
I doubt there are micro patterns overlayed on the Fresnel pattern. The DC watch article indicates otherwise. Perhaps the increasing frequency of the pattern towards the edges is at play?
I think that the illustration in the DC Watch is simplified just to explain the concept of the blaze grating in general.
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Here is Nikon's patent registered earlier this year, for a 400, 500 and 600. These bear close similarities to the 300 f4E PF, but differ in the rear groups. Note what appears to be a protective element (FL coated?) in the posterior of the proposed 400mm
https://nikonrumors.com/2018/02/01/the-latest-nikon-patents-400mm-500mm-and-600mm-f-5-6-phase-fresnel-pf-lenses.aspx/ (https://nikonrumors.com/2018/02/01/the-latest-nikon-patents-400mm-500mm-and-600mm-f-5-6-phase-fresnel-pf-lenses.aspx/)
https://www.j-platpat.inpit.go.jp/web/PU/JPA_H30017857/TKBS_GM302_Detailed.action (https://www.j-platpat.inpit.go.jp/web/PU/JPA_H30017857/TKBS_GM302_Detailed.action)
schematic of the 300 f4E for comparison
https://www.the-digital-picture.com/News/News-Post.aspx?News=14218 (https://www.the-digital-picture.com/News/News-Post.aspx?News=14218)
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In the simplest terms red light through a prism refracts less than blue light. Red light through a diffraction grating refracts more than blue light. The diffractive lens element is used to counteract the refraction in the other elements of the lens, resulting in an achromatic lens without as many thick lenses which would otherwise be required to achieve the same thing. If you look at the diagrams in the article Akira posted you can see how the phase fresnel element reverses the order of wavelengths.
Yes I saw that, but I don't understand the principles that cause it, the diagrams shown seem to be rather simplified and don't really show how it works. For example, it's not clear (to me at least) if the steps shown on some PF lens diagrams represent the large steps visible to the eye, or whether there is some microscopic structure ... I don't see how the large steps could cause diffraction effects. A normal Fresnel lens works by refraction only, which would have dispersion the same as a conventional lens, not reversed as with the FP lens. That's why I wonder if there is a microscopic structure which causes diffraction, similar to the tracks on a CD or DVD which give rainbow reflections due to diffraction. But if there is a sub-structure, then wouldn't it be easier to apply it to a non Fresnel lens? Or do you need both?
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Yes I saw that, but I don't understand the principles that cause it, the diagrams shown seem to be rather simplified and don't really show how it works. For example, it's not clear (to me at least) if the steps shown on some PF lens diagrams represent the large steps visible to the eye, or whether there is some microscopic structure ... I don't see how the large steps could cause diffraction effects. A normal Fresnel lens works by refraction only, which would have dispersion the same as a conventional lens, not reversed as with the FP lens. That's why I wonder if there is a microscopic structure which causes diffraction, similar to the tracks on a CD or DVD which give rainbow reflections due to diffraction. But if there is a sub-structure, then wouldn't it be easier to apply it to a non Fresnel lens? Or do you need both?
You need both, and that fact is in the very name “phase Fresnel”. I am not certain exactly how it is constructed, but the diffraction angles through the transmission grating are fairly high so a flat grating won’t give you what you are looking for unless the angle it makes with the light path is carefully controlled. Fresnels only save weight and don’t control against chromatic aberration so it alone would tend to degrade the image with only slight benefit to weight. It is the combination of effects here which makes it possible to control the diffraction to produce a useful image.