January 21, 2018, 08:15:06 AM

Author Topic: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens  (Read 5669 times)

Canon Rumors

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Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« on: December 14, 2017, 12:08:12 PM »
A patent application showing a new mirror lens design from Canon is confusing to say the least. I figured the days of the catadioptric lens were well behind us, but here we are.

Specification from the patent:

  • Focal length: 400mm
  • Aperture: f/5.6
  • 2 ω: 1.96
  • Image height: 13.66mm
  • Back focus: 33.07mm
  • Lens length: 247.73mm

The image below from Northlight shows the light path through the lens. The light path is in red, and the mirrors are outlined in blue and labelled.

The blue bits are mirrors. The light comes in through L1, bounces off M1/M2 and through a hole in M1 back to the camera.

neuroanatomist on the forum thinks this could be an EF-M mount lens. You can view the patent at the Japanese Patent Office here.

« Last Edit: December 14, 2017, 12:24:06 PM by Canon Rumors »
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Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« on: December 14, 2017, 12:08:12 PM »

neuroanatomist

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #1 on: December 14, 2017, 12:10:37 PM »
An EF-M lens, it seems (from the image height and back focus distance).
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Antono Refa

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #2 on: December 14, 2017, 12:41:14 PM »
An EF-M lens, it seems (from the image height and back focus distance).

First thing I noticed was it's for APS-C sensor with shorter back focus.

I'm not sure it's small enough to be produced for EOS-M bodies, as it's about as long (or short) as the 400mm DO lenses. It would probably be lighter, though.

Mt Spokane Photography

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #3 on: December 14, 2017, 12:56:33 PM »
What the patent actually claims is that it can vary the effective aperture by dimming the light as it basses thru the lens elements.  (LCD?).  As many know, it is not possible to put a variable aperture in a mirror lens, so ND elements must be used if f/8 is not sufficient.  They have rear drop in lens holders to do that.

"The imaging system which was caused conventionally, especially used the reflection system as the method of overall-length shortening of a telephoto lens is proposed. However, when a physical diaphragm is placed as problem peculiar to a reflection system, at the time of a small diaphragm, the light volume of an image periphery is reduced substantially, or may be intercepted altogether. In recent years, needs to make animation correspondence also in a digital camera are growing, and it has become an important element to have a mechanism in which light volume is adjusted. On the other hand, it is not a physical diaphragm and there is a means to change voltage and to adjust light volume. 
 [0003]
 The example with above means to change voltage to a catadioptric system and to adjust light volume to it is disclosed (Patent document 1). It has a bending reflection member and the example which carried out the luminous energy regulating means owner is disclosed"

The invention could be applied to a mirror lens for any lens mount.

I was hoping they had solved the bokeh issues with mirror lenses, but thats not the case.

Mt Spokane Photography

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #4 on: December 14, 2017, 12:57:58 PM »
What the patent actually claims is that it can vary the effective aperture by dimming the light as it basses thru the lens elements.  (LCD?).  As many know, it is not possible to put a variable aperture in a mirror lens, so ND elements must be used if f/8 is not sufficient.  They have rear drop in lens holders to do that.

"The imaging system which was caused conventionally, especially used the reflection system as the method of overall-length shortening of a telephoto lens is proposed. However, when a physical diaphragm is placed as problem peculiar to a reflection system, at the time of a small diaphragm, the light volume of an image periphery is reduced substantially, or may be intercepted altogether. In recent years, needs to make animation correspondence also in a digital camera are growing, and it has become an important element to have a mechanism in which light volume is adjusted. On the other hand, it is not a physical diaphragm and there is a means to change voltage and to adjust light volume. 
 [0003]
 The example with above means to change voltage to a catadioptric system and to adjust light volume to it is disclosed (Patent document 1). It has a bending reflection member and the example which carried out the luminous energy regulating means owner is disclosed"

The invention could be applied to a mirror lens for any lens mount.

I was hoping they had solved the bokeh issues with mirror lenses, but thats not the case.

Don't look for this to show up soon in your store, mirror lenses are not popular enough to warrant the Canon high prices.

andrei1989

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #5 on: December 14, 2017, 01:33:47 PM »
An EF-M lens, it seems (from the image height and back focus distance).

First thing I noticed was it's for APS-C sensor with shorter back focus.

I'm not sure it's small enough to be produced for EOS-M bodies, as it's about as long (or short) as the 400mm DO lenses. It would probably be lighter, though.

eh? how do you figure it's the same length as a 400 DO?

samyang make a 300mm f/6.3 mirror lens for mirrorless cameras (cool stuff if you miss your dslr  ;D ) which is 74mm in length. the DO equivalent for that focal length would be...nikon's 300mm f4 PF which is 147mm long so by that (flawed?) logic this canon one should be around 100mm in length
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KeithBreazeal

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #6 on: December 14, 2017, 02:01:27 PM »
But it will have awesome donut bokeh!
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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #6 on: December 14, 2017, 02:01:27 PM »

jolyonralph

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #7 on: December 14, 2017, 02:02:25 PM »

I was hoping they had solved the bokeh issues with mirror lenses, but thats not the case.

Issues? What's wrong with donuts?  :)
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neuroanatomist

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #8 on: December 14, 2017, 02:15:16 PM »
An EF-M lens, it seems (from the image height and back focus distance).

First thing I noticed was it's for APS-C sensor with shorter back focus.

I'm not sure it's small enough to be produced for EOS-M bodies, as it's about as long (or short) as the 400mm DO lenses. It would probably be lighter, though.

eh? how do you figure it's the same length as a 400 DO?

samyang make a 300mm f/6.3 mirror lens for mirrorless cameras (cool stuff if you miss your dslr  ;D ) which is 74mm in length. the DO equivalent for that focal length would be...nikon's 300mm f4 PF which is 147mm long so by that (flawed?) logic this canon one should be around 100mm in length

eh?  read the patent...

Lens length: 247.73mm

He figures that because the 400/4 DO II lens measures 233mm in physical length (which corresponds to an optical formula length of 276mm), and patent we're discussing specifically states the optical formula length for the patent is 250mm, which if it's an EF-M lens corresponds to a physical length of 232mm
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KeithBreazeal

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #9 on: December 14, 2017, 02:17:25 PM »
Variable LCD ND filter.  This is an adapter demonstrated but once perfected, could be part of an internal design by lens manufacturers. 

https://vimeo.com/139312965
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Don Haines

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #10 on: December 14, 2017, 02:34:16 PM »
But it will have awesome donut bokeh!

mmmmmmmmmm...... donuts.......

This could be an interesting lens, particularly for food photography!
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Mistral75

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #11 on: December 14, 2017, 02:56:06 PM »
An EF-M lens, it seems (from the image height and back focus distance).

There are five examples in the patent request. All of them are APS-C lenses.

  • two 400mm f/5.6, one with a back focus distance of 33.07mm, the other one with a back focus distance of 45.65mm
  • two 300mm f/4.2, one with a back focus distance of 36.18mm, the other one with a back focus distance of 35.11mm
  • an odd 400-520 mm f/6,7-9.9 zoom lens with a back focus distance of 6.61mm; this one is definitely not an SLR lens.

andrei1989

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #12 on: December 14, 2017, 03:01:57 PM »


my bad. i somehow missed that line
carry on
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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #12 on: December 14, 2017, 03:01:57 PM »

9VIII

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #13 on: December 14, 2017, 03:39:45 PM »
My Samyang 800mm f8 lens is incredibly compact for what it is.
That said, image quality is slightly worse than the equivalent frame cropped out of the 400f5.6L so the two lenses are roughly equivalent, but the Mirror lens is WAY cheaper.

The biggest problems with the Samyang are a slight loss of colour saturation and the lack of autofocus.

If Canon can make a decent 400mm mirror lens (putting the mirror back in Mirrorless) I'm sure it would be an excellent product.

magarity

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #14 on: December 15, 2017, 11:07:40 AM »
Which part justified a patent? It's not like mirror telescopes are something new. The LCD for ND?

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Re: Patent: Canon 400mm f/5.6 Mirror (Catadioptric) Lens
« Reply #14 on: December 15, 2017, 11:07:40 AM »