Here we go again, the Canon RF 35mm f/1.4L rumored to be announced next month

[koenkooi]

Just a thought, but given the headline name of a lens is usually a rounding of the actual aperture (T versus f), is the difference between 1.2 and 1.4 potentially even less than it seems?

I bet the wide aperture ones are all rounded down, so it's likely f/1.299 vs f/1.499. And T stops are more for metering than for estimating DoF, so the listed f number is the useful one for stills people.

 

[neuroanatomist]

Just a thought, but given the headline name of a lens is usually a rounding of the actual aperture (T versus f), is the difference between 1.2 and 1.4 potentially even less than it seems?

In that context, it's worth noting that the EF 35/1.4L II was tested by DxO and they report T = 1.7 (and for comparison, the EF 35/2 IS tests at T = 2). So maybe if they release an RF 35/1.2, it will have a T-stop somewhere close to 1.4...

I should also point out that T-stops account for more than just rounding of the aperture value, the measurement of actual transmission also includes light lost due to internal reflections, and it's that more than the rounding that accounts for the difference between f/stop and T/stop. For very fast lenses like this, the sensor also matters. There's more light lost with smaller pixels at the oblique angles of incident light. You can see this, for example, in the fact that the 35/1.4L II tests at 1.7 T/stops on the 50 MP 5DSR, but it's 1.6 T/stops on a 20-30 MP FF sensor.

DxO did a write-up a while back about how manufacturers stealthily bump up the gain with fast lenses (e.g. the camera is really using 1/3 - 1 stop higher ISO than it's reporting in the EXIF, and the boost decreases as the fast lens is stopped down so that by f/2 or so it’s actually using the ISO it’s reporting).

 

[EOS 4 Life]

because of IS?

Yes.
Cinema EOS cameras do not have IBIS.

 

[EOS 4 Life]

It didn't stop Canon releasing the RF400/2.8 - 600/4 vs the EF equivalents and similarly the RF800/5.6 - RF1200/8 (no EF equivalent) with built-in teleconvertors.

I heard that Canon was not planning to release RF versions until their professional sports shooters pleaded with them to do so.
The only other lenses that Canon did that with was the cinema line which was also for pro users.

 

[EricN]

Two words: X-ray lens.

If I recall such x-ray lenses were produced in the 1960s, but why can't they be produced now? It's not too heavy or too expensive because there are 400mm f/2.8 on up to 1200mm prime lenses.

Edit : I meant to say, "... why can't lenses with such wide apertures be produced for photographic uses now?"

 

[EOS 4 Life]

Just a thought, but given the headline name of a lens is usually a rounding of the actual aperture (T versus f), is the difference between 1.2 and 1.4 potentially even less than it seems?

Canon typically would have T1.3 and T1.5 respectively not including the RF 85 f/1.2 DS.
Other brands like Sigma are all over the place.

 

[EricN]

It’s possible to make an optically improved mirrorless 35mm f1.4 considerably smaller and lighter than a DSLR counterpart. Sony did just that with their 35mm f1.4 GM. Sigma also made a mirrorless version of their 35mm f1.4 Art which is lighter than the current Canon equivalent.

Is in not also possible to make an optically superior lens with a wider aperture for the same or less weight?

 

[EOS 4 Life]

I bet the wide aperture ones are all rounded down, so it's likely f/1.299 vs f/1.499. And T stops are more for metering than for estimating DoF, so the listed f number is the useful one for stills people.

As a hybrid shooter, I do not find F-stops terribly useful at all.
I wish every lens had an aperture ring with T stops.
There is no reason that the camera can't show T-stops even if the lens uses F-stops.

 

[neuroanatomist]

Canon typically would have T1.3 and T1.5 respectively not including the RF 85 f/1.2 DS.

Typically? As pointed out above, the EF 35/1.4L II is T1.6-1.7, and the EF 35/2 IS is T2. I guess your definition of typical…isn’t.

 

[AlanF]

Typically? As pointed out above, the EF 35/1.4L II is T1.6-1.7, and the EF 35/2 IS is T2. I guess your definition of typical…isn’t.

According to Bill Claff and the patent, the EF 35/2 IS is f/2.05. So do you think that DxO has got it wrong with it being T2?

 

[neuroanatomist]

According to Bill Claff and the patent, the EF 35/2 IS is f/2.05. So do you think that DxO has got it wrong with it being T2?

Could just be rounding...but DxO is not always correct.

 

[SNJ Ops]

Is in not also possible to make an optically superior lens with a wider aperture for the same or less weight?

It would be an amazing feat to make a 35mm f1.2 that is smaller, lighter and even optically better than Sony’s 35mm f1.4 GM that only weighs 524g.

 

[sanj]

As a hybrid shooter, I do not find F-stops terribly useful at all.
I wish every lens had an aperture ring with T stops.
There is no reason that the camera can't show T-stops even if the lens uses F-stops.

The market that these lenses are made for does not care about T stops. If you want T stop lenses, you have to up your budget.

 

[sanj]

Is in not also possible to make an optically superior lens with a wider aperture for the same or less weight?

As technology changes, it may be possible to reduce it a little. But as Nuro rightfully says "Can't defy physics.".

 

[EricN]

It would be an amazing feat to make a 35mm f1.2 that is smaller, lighter and even optically better than Sony’s 35mm f1.4 GM that only weighs 524g.

Why do you think that? It is only a fraction of a stop wider.

 

[EricN]

As technology changes, it may be possible to reduce it a little. But as Nuro rightfully says "Can't defy physics.".

Please show me which laws of physics this would defy.

 

[Del Paso]

If I recall such x-ray lenses were produced in the 1960s, but why can't they be produced now? It's not too heavy or too expensive because there are 400mm f/2.8 on up to 1200mm prime lenses.

Edit : I meant to say, "... why can't lenses with such wide apertures be produced for photographic uses now?"

They could, but if most aberrations were to be corriged, the weight and the cost of such lenses would certainly be astronomical.
The Zeiss 0,7 was produced for photography, but its optical quality would no longer be considered acceptable, unless as a curiosity.

 

[SNJ Ops]

Why do you think that? It is only a fraction of a stop wider.

You mentioned a 35mm f1.2 that would be smaller, lighter, optically better and 1/3 stop faster than Sony’s 35mm f1.4 GM. To achieve all of that would be a massive achievement and one I don’t think is currently possible but admittedly I am no lens designer. Making such a lens smaller and lighter than Sigma’s 35mm f1.2 Art seems far more plausible.

 

[Del Paso]

You mentioned a 35mm f1.2 that would be smaller, lighter, optically better and 1/3 stop faster than Sony’s 35mm f1.4 GM. To achieve all of that would be a massive achievement and one I don’t think is currently possible but admittedly I am no lens designer. Making such a lens smaller and lighter than Sigma’s 35mm f1.2 Art seems far more plausible.

Possible, but would presuppose the use of extremely expensive special hard to produce glass sorts.

 

[sanj]

Please show me which laws of physics this would defy.

I don't know exactly. But it seems like the lens has to be bigger to let in more light.