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Canon patent for 0.82x optical viewfinder

canon

Canon patent for an optical viewfinder with 0.82x magnification. The viewfinder magnification is not to be confused with the frame coverage.

For instance, the EOS 5D Mark IV has a viewfinder magnification of 0.71x and a frame coverage of 100%. The Canon EOS 80D has 0.95x magnification and 100% frame coverage. The EOS 7D Mark II has 1x magnification and 100% frame coverage. Finally, Canon’s entry-level Rebel DSLRs have a magnification between 0.8x and 0.87x. Hence it’s legit to assume this patent refers to a viewfinder for a future Rebel-class DSLR.

  • Patent publication number 2016-191760
    • Release date 2016.11.10
    • Application date 2015.3.31
  • Example 5
    • Diopter -1 – 3 + 1
    • Focal length 61.30 58.73 64.32
    • Eye point 20.0 20.0 20.0
    • Magnification 0.82 0.85 0.78
An extract fro the patent literature:
[Claim(s)] [Claim 1] In a finder optical system which observes an object image formed in a predetermined side with a taking lens,
From the predetermined side side to order, it is a condensing lens of positive refracting power,
A reversal optical system,
The 1st lens of positive refracting power,
The 2nd lens of negative refracting power,
The 3rd lens of positive refracting power
The 4th lens of positive refracting power
A finder optical system comprising the 5th lens of negative refracting power.
[Claim 2] A finder optical system being aforementioned claim 1 and satisfying the following conditional expression in a finder optical system of a description.
K: -2.0<f12-/f<-0.9 .. (1)
L: -0.45<f5-/f<-0.3 .. (2)
Here, f expresses a focal distance of the finder system whole system, f12 expresses a composite focal length of said 1st lens and the 2nd lens, and f5 expresses a focal distance of the 5th lens.
[Claim 3] A finder optical system satisfying the following conditional expression in said finder optical system according to claim 1.
N: nud1>54 .. (3)
O: nud2<30 .. (4)
Here, the number of ATSU ** of the 1st lens and nud2 express the number of ATSU ** of the 2nd lens nud1.
[Claim 4] In said finder optical system according to claim 1,
A finder optical system, wherein the 1st lens of positive refracting power and the 2nd lens of negative refracting power are cemented lenses.
[Claim 5] A finder optical system satisfying the following conditional expression in said finder optical system according to claim 1.
Nd4>1.80 .. (5)
Nd5<1.55 .. (6)
Here, Nd4 expresses a refractive index in d line of the 4th lens, and Nd5 expresses a refractive index in d line of the 4th lens.
[via Egami]
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