Here's a really nice article that walks through an example of image equivalence:


If you're purchasing a mixture of gear, or if you're purchasing gear and want to recreate what someone else has done with different gear, or if you're in the field with different formats and attempting to achieve the same effect then this is good stuff to know.

If you have one camera and you're doing your own thing, keep calm and carry on...

Bob Howland said:

I find that the concept of equivalence is not at all useful. When taking an image with an R7 and a Sigma 18-50, I don't calculate the equivalent FF focal length and DOF. I just zoom the lens and use the DOF of the lens that I'm using and it works. One consequence is that I shoot wide open or nearly so most of the time.

I don't think that equivalence of DOF is how most people think. Equivalence seems to be an attempt of a small group of posters to say that other posters are incorrect and must be enlightened. My background is in psychology and economics so, for good or ill, that's how I see the world.

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I agree in the sense of practice in the field: it's not too useful unless you're shooting each format side by side and need to synchronize effect. I only tend to use one or the other (my own camera is FF at this point, but my kiddo has an 80D) — but even then, it's almost like speaking different languages: unless you need to switch mid-sentance, you're thinking and doing in language A or language B but not a mix. You simply figure out what lenses achieve on your format and run with it.

Bob Howland said:

I find that the concept of equivalence is not at all useful.

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Ok. The fact that you personally don’t find it useful does not mean the concept is inaccurate, nor does it mean it’s not applicable to photography. It is both.

Bob Howland said:

When taking an image with an R7 and a Sigma 18-50, I don't calculate the equivalent FF focal length and DOF.

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Of course not, that’s not the point of equivalence. If you were considering replacing that R7 with a full frame or m4/3 camera, the concept of equivalence could help you decide which lens you should buy to enable you to keep taking pictures like the ones you currently take.

Bob Howland said:

I don't think that equivalence of DOF is how most people think.

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I'm not sure if you are just being stubborn, or you remain utterly confused about the concept (willfully, because you haven't read the links previously posted, or because you've read them and remain unable to understand the concept). It's not about "FoV equivalence' or 'DoF equivalence' or 'noise equivalence' – it's about image equivalence. FoV, DoF and noise are all characteristics of an image… and they are all affected by sensor size.

As above, the concept doesn't matter when you have a camera in your hand and you're out taking pictures. You're going to frame your shot how you want and pick your aperture for the DoF you want.

Bob Howland said:

Equivalence seems to be an attempt of a small group of posters to say that other posters are incorrect and must be enlightened. My background is in psychology and economics so, for good or ill, that's how I see the world.

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So in your world view, incorrect statements should not be challenged or corrected? Or if they are, no explanation should be provided?

Sensor size has no effect on images, and ignorance is bliss. Mmmmmkay.

dwkdnvr said:

Thinking more about the 15-70/4, I find it somewhat interesting that it's not quite a direct head-to-head competitor to either of the Sigma normal zooms, but that the Tamron 17-70 IS which IS a bit more of a direct competitor never appeared for RF-S. Makes me wonder whether Canon did actively prevent Tamron from offering that lens in RF-S mount.

I still wish this would have L-grade construction, but it seems far more likely that it'll be on the level of the budget FF STM lenses.

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The absence of the 17-70 does indeed make more sense now, that was Tamron’s only mirrorless APS-C lens that didn’t directly compete against a superior Sigma alternative on RF mount, and one that would’ve been popular with the RF-S bodies lacking IBIS (4/5 currently).

If the construction isn’t L caliber, I hope it’s at least along the lines of the RF 28-70 f/2.8.

Bob Howland said:

I find that the concept of equivalence is not at all useful.

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It is really important when comparing cameras with non-standard image sensor sizes.
It was really just intended for focal lengths.
The arguments start to come in when we apply depth of field.
Depth of field is not always important.
In fact, sometimes having more in focus can be an advantage.

Thinking more about the 15-70/4, I find it somewhat interesting that it's not quite a direct head-to-head competitor to either of the Sigma normal zooms, but that the Tamron 17-70 IS which IS a bit more of a direct competitor never appeared for RF-S. Makes me wonder whether Canon did actively prevent Tamron from offering that lens in RF-S mount.

I still wish this would have L-grade construction, but it seems far more likely that it'll be on the level of the budget FF STM lenses.

Click said:

Lovely! I really like the firs one.

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Thanks, Click! I prefer it also. The second was obviously for the snowy contrast.

Click said:

The first one is really beautiful. Well done!

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Thanks, Click! These things are so fun to watch. You'd literally think they were a hummingbird the way they move. Wings beat super fast, too.

neuroanatomist said:

Oh, I think it is. They made one of the elements an aspherical, but it's still the same basic 6-element, 5-group, double Gauss design. In fact, Canon states, "The RF50mm F1.8 STM features an enhanced version of the highly praised optical configuration employed by the EF 50mm f/1.8 STM..."

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Lumping 6 element 5 group lenses together rather overlooks the subtlety of optical formulas.
Here are both the EF 50/1.8 & RF 50/1.8 ( latter on the right.)

The EF 50/1.8 is a classic double gauze planar design.
Here is the block diagram of the 1964 Canonet 45mm f/1.7 rangefinder lens

Both the Canonet 45mm lens and the RF 50mm f/1.8 have a very similar optical formula, and is a cross between a double gauze and a Zeiss Biometar formula. The modern update on the RF lens replaces the fifth simple element of the Canonet with an aspherical, and makes the doublet a curved mating, possibly achromatic, to improve performance and probably because with modern manufacturing techniques it's not now prohibitively expensive to do, whereas in the '60s it would have added a lot of cost to the lens.
I presume that Canon went down this optical route as the Canonet formula was already created for a rangefinder flange distance, although I note that in the RF 50/1.8 the rear element is quite a way off the sensor.
This is why I say that if the RF lens is a 'reshuffle' of anything, it is the 1964 Canonet lens, not the classic 'planar' of the EF 50/1.8.

DPReview have spoken with Canon at CP+, shortened quote from the last paragraphs:

Pressing further on the possibility of more broadly opening the RF mount to licensees: "So we will carefully watch and listen to the customers' feedback and make the strategic decision."

So it appears that it is not entirely up to Sigma to decide on FF AF RF lenses.

See: https://www.dpreview.com/interviews/5615138412/canon-cpplus-interview-2026

The first one is really beautiful. Well done!

Very nice shots, I especially like the first one.

Lovely! I really like the first one.

neuroanatomist said:

No idea, but I'd expect that if the new 400mm and 600mm lenses have an integrated, switchable 1.4x TC (there were patents published on those about a year ago) then they'll go up in cost a bit over the current versions. Maybe $1K or $2K more?

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Like any new lens, this will make it more expensive. If it adds a feature that's not found in other lenses, or is extremely rare, the price immediately skyrockets. I'd guess they'll add $3,000-4,000.I'd be happy to use the version with even just the 1.4.

Ron888 said:

Right or wrong it's how almost everyone thinks.Just go with it

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I find that the concept of equivalence is not at all useful. When taking an image with an R7 and a Sigma 18-50, I don't calculate the equivalent FF focal length and DOF. I just zoom the lens and use the DOF of the lens that I'm using and it works. One consequence is that I shoot wide open or nearly so most of the time.

I don't think that equivalence of DOF is how most people think. Equivalence seems to be an attempt of a small group of posters to say that other posters are incorrect and must be enlightened. My background is in psychology and economics so, for good or ill, that's how I see the world.

homebodyMacro2 said:

Given the identical front end size requirement, do you figure getting to 600mm adds more cost than the 2x (instead of 3x) zoom factor reduces it? Honestly, unless some magic happens, I'm not really in the market for this one either

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Probably not, unfortunately.

R52+RF600/4, Ardea cinerea, I don't know what's wrong with her fingers...

Bob Howland said:

It's not f/6.3. It's a 15-70 f/4 lens with the DOF of a 15-70 f/4 lens, regardless of the size of sensor. The only reason the DOF changes is when people move forward or back or change the focal length to maintain the same FOV. I'm rather interested in this lens but I already own the 18-50 Sigma and I highly value small size and especially light weight.

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Right or wrong it's how almost everyone thinks.Just go with it

neuroanatomist said:

It's technically possible to have a focal reducer that maintains the same lens mount and flange focal distance - there is a 0.7x focal reducer for PL to PL. Of course, technically possible ≠ easy...that optic is 20 cm long, has 13 elements, rotates the image 180° and costs $5500. But it will give you 0.7x the focal length and an extra stop of light with a FF lens and an S35 sensor (or an S35 lens and an S16 sensor).

It might not be possible to accomplish that in a TC-sized optic, though the 'boost' would not need to anywhere near a full stop because the light loss from an extension tube (along with the magnification benefit) decreases with increasing focal length.

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The 180 rotation makes sense. that would indicate that the adapter created an intermediate focal plane and supports what my friend told me. I guess you could create yet another focal plane and rotate the image back for only $12k .

neuroanatomist said:

No idea, but I'd expect that if the new 400mm and 600mm lenses have an integrated, switchable 1.4x TC (there were patents published on those about a year ago) then they'll go up in cost a bit over the current versions. Maybe $1K or $2K more? The 1.4x TC is selling for $600...

Even if the 300-600/5.6L is not a rumor, while it will likely be cheaper than the 400/2.8 and 600/4, it won't be 'cheap'. Likely a bit north of the RF 100-300/2.8, so figure on the order of $11.5-12.5K.

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Yeah, the integrated TC would seemingly add a bit to it. Definitely would make for some steep prices

It does seem like a 300-600 f/5.6L should be in the ballpark of the 100-300L unless some magic happens. Given the identical front end size requirement, do you figure getting to 600mm adds more cost than the 2x (instead of 3x) zoom factor reduces it? Honestly, unless some magic happens, I'm not really in the market for this one either

Okay, today a White-lined Sphinx moth (aka hummingbird moth) visited my garden! Getting lots of visitors lately.

Saturday we had some crocuses appearing.

Today we had some yellow ones appearing, but not opening. I guess they wanted to stay warm...

Dragon said:

A friend of mine who worked for Canon for many years once pointed out to me that the reason no one made the equivalent of a Metabones Speed Booster for EF-to EF is that focal reducers do not extend the focal plane like extenders do so they can only be made to fit inside the existing back focus distance of a lens. Hence, we have focal reducers that replace the EF to M and EF to R adapters, but no focal reducers for EF to EF or R to R.

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It's technically possible to have a focal reducer that maintains the same lens mount and flange focal distance - there is a 0.7x focal reducer for PL to PL. Of course, technically possible ≠ easy...that optic is 20 cm long, has 13 elements, rotates the image 180° and costs $5500. But it will give you 0.7x the focal length and an extra stop of light with a FF lens and an S35 sensor (or an S35 lens and an S16 sensor).

It might not be possible to accomplish that in a TC-sized optic, though the 'boost' would not need to anywhere near a full stop because the light loss from an extension tube (along with the magnification benefit) decreases with increasing focal length.

neuroanatomist said:

That hypothetical 1x-1.4x TC would require reducing optics for the 1x setting, a completely different set of optics than the extender optics that would need to flip in when the 1.4x elements flip out. Same thing as the magical unicorn 1x-1.4x-2x TC that people have been dreaming about after someone misinterpreted a Canon patent for something completely different that happened to have 1-1.5-2x markings on the diagram.

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Not sure that even reducing optics would solve the problem. A friend of mine who worked for Canon for many years once pointed out to me that the reason no one made the equivalent of a Metabones Speed Booster for EF-to EF is that focal reducers do not extend the focal plane like extenders do so they can only be made to fit inside the existing back focus distance of a lens. Hence, we have focal reducers that replace the EF to M and EF to R adapters, but no focal reducers for EF to EF or R to R.

homebodyMacro2 said:

Do we expect these potential 400mm and 600mm big whites to be comparable in cost to their predecessors? I wish I were in that market... sigh. I feel there's a fair chance this 300-600L zoom is perhaps destined to remain a rumor lol.

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No idea, but I'd expect that if the new 400mm and 600mm lenses have an integrated, switchable 1.4x TC (there were patents published on those about a year ago) then they'll go up in cost a bit over the current versions. Maybe $1K or $2K more? The 1.4x TC is selling for $600...

Even if the 300-600/5.6L is not a rumor, while it will likely be cheaper than the 400/2.8 and 600/4, it won't be 'cheap'. Likely a bit north of the RF 100-300/2.8, so figure on the order of $11.5-12.5K.