Lens design comparison: Canon EF 50mm f/1.8 STM and the Canon RF 50mm f/1.8 STM

Canon Rumors Guy

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Here is a lens diagram comparison between the EF 50mm f/1.8 STM and the upcoming Canon RF 50mm f/1.8.  The new RF 50mm f/1.8 STM definitely looks like a brand new lens design and not simply making the EF mount version work with RF, which likely would never be worth the time and effort anyway.
As pointed out by forum contributor privatebydesign, this is a “double-gauss” lens design.
I expect to see this lens announced next week, if not sooner.

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H. Jones

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Very similar, same number of elements, but definitely different. I doubt this will cost much more than the EF 50mm, if not the same amount.

It does seem like it at least takes advantage of the new mount by enlarging the rear-most element, so hopefully that in itself can improve IQ a bit. I'll be interested to see how it turns out.

It's tough to tell, the diagrams aren't to scale, but looking at the rear mount bit, it does seem like the RF lens is slightly smaller, which is a big perk when you consider it's going on the R cameras without an adapter and will make a very small end result.
 

Andy Westwood

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Sooner the better! it will be interesting to know the price, dimensions, and weight of this little cutie! And to get some early feedback on performance.
 
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Oct 29, 2020
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I was about to purchase a control ring adaptor and an EF 50mm 1.8, I’m so glad I waited! I assume it will be a price of $299, but most comments are mentioning a 149 to 249 price tag, and I’m hoping that’s the case. If it’s that cheap. I’m definitely buying this one, even if I have the RF 35 and 85, just because of its price, and size.
 

privatebydesign

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It is just the standard Double-Gauss design that has been around in innumerable formulae's since 1817.


Uncle Roger has a great series of articles on optical designs too.


What I actually find interesting is the element offset, the RF lens elements are set further forwards than the EF version and are an effective 'adapter', they are not using the advantages of the shorter flange distance here one bit, merely rejigging the thing to do the same. I'd expect performance to be somewhere between the EF 1.8 and EF 1.4, the key will be the way they have used the special element in green.
 
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Mar 4, 2020
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I go back and forth between $149 and $199, the control ring may add a bit of cost.
The Nikon Z50 f/1.8 lens is some 600 euro... I agree, they market that one different, but still, it gives Canon an opportunity to ask 349,- for the RF50 f/1.8. Why not? I'll buy it.
 

quiquae

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It is just the standard Double-Gauss design that has been around in innumerable formulae's since 1817.


Uncle Roger has a great series of articles on optical designs too.


What I actually find interesting is the element offset, the RF lens elements are set further forwards than the EF version and are an effective 'adapter', they are not using the advantages of the shorter flange distance here one bit, merely rejigging the thing to do the same. I'd expect performance to be somewhere between the EF 1.8 and EF 1.4, the key will be the way they have used the special element in green.
They are definitely taking advantage of the shorter back flange distance. Assuming that the diagrams are actually to scale, the RF version has a back flange distance of something like 30mm (20mm behind the lens and ~10mm inside the lens), whereas the EF mount has a minimum of 44mm.
 
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SwissFrank

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Although they're both obviously the fairly symmetric double-Gaussian design that's great from 35 to 85mm, small differences in the lenses can yield big differences in results.

Expectations are that the lenses should therefore cost about the same, but I'm guessing that the special lens here could easily cost 10x more for that one part than a normal variety of or shape of glass. If that part goes from say $10 to $100 then the price for the product as a whole could go up $200 or more after markups.

BTW I think this EF 50mm is the same formula they've used since 1987.

I had every EF 50mm (except the MkII 1.8) and I'd sure like a sharper one. It's such an important focal length that I'd like them to make two: one with portability being first priority (should stick out no further than the front of the grip) and the other being image quality as first priority, like the Leica APO 50/2. Even if it's $3000 for 50/1.8, and huge, why not do it just as a halo product.
 
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syder

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It's such an important focal length that I'd like them to make two: one with portability being first priority (should stick out no further than the front of the grip) and the other being image quality as first priority, like the Leica APO 50/2. Even if it's $3000 for 50/1.8, and huge, why not do it just as a halo product.
The RF 50 1.2 is the high quality 50mm rf prime. This will be the cheap & small one.
 

Maximilian

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I am glad to see that Canon is trying to improve the optical formula, even though they stay with double Gauss design.
I am sure it is for a more cost effective production, maybe simpler mechanical parts and more automated assembly.
I hope the improvement is also for better IQ.

And I hope there will be a 50 mm lens with IS and better optics between this and the RF50L.
 
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Maximilian

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They just moved the elements further down the barrel lol
Not only that.
The basic double Gauss design stayed the same.
But I see different gaps between the elements.
And I see elements cut on both sides where one was only cut on one side (two working steps = more expensive).
And as the rear element seems to be bigger the exit pupil seems to be bigger, too.
= less refracting of the light rays in that last element = maybe less CA (but just guessing)

This is an at least much modifyed optical formula, if not totally redesigned (still based on the same double Gauss design).

Edit: and you don't see just from this drawing if they maybe added some new and better coatings.
 
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Antono Refa

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The RF 50 1.2 is the high quality 50mm rf prime. This will be the cheap & small one.
RF 50mm f/1.2L USM is priced $2,300, about the same as the EF 70-200mm f/2.8L IS III USM @ $2,100

The RF 50mm f/1.8 STM will be priced say $300, 2.5x the price of the EF 50mm f/1.8 STM

Do you really think there's no place for an RF 50mm f/1.4 IS USM at $600 in between?

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Added in editing: Nikon, Sony, Sigma, and Zeiss all have a 50mm f/1.4 priced $1,000-$1,500. IIRC, someone wrote all those lenses are expensive pickle jars because the only way to make them fast & high IQ was a reverse telephoto design.

The RF mount cut the flange distance from 44mm to 20mm. Shouldn't that open the door for Canon to make a 50mm f/1.4 that combines the cheap double Gauss design with the high IQ of the above mentioned lenses? Is the RF 50mm f/1.8 it? Really no place for sub-$1K 50mm f/1.4 IS?
 
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