Absence of something wider than 18mm on crop sensors

[Aldherrian]

Been exploring crop sensors for a bit now and only recently, I decided to give a try on the older Efs15-85 having realized that I didn't use so much the reach part of my 18-135.

And I wanted to try out this 15-18mm range to get an idea of what it would look like with a more traditional 24mm on a full frame camera.

In my use case, I was a bit surprised at how wide 15mm actually is and that it almost nullified the need for a dedicated UWA lens.

I ended up thinking about why it was the only lens on Canon crop systems to achieve that 15mm at the wide end, a field of view that seemed really like a staple to me on full frame cameras.

Attempting to look up a bit, I discovered that there actually were a lot of 28mm-X on older EF lenses through the ages. I would not have bet on it given the number of 24-X zooms on mirrorless systems and the compromises around the development of a recent 28-70mm to achieve a better aperture.

I was curious to ask here to some much more well versed in optics history what made this 24mm range something that normal on full frame in recent times but didn't on crops sensors

All thoughts appreciated

 

[neuroanatomist]

The EOS M system launched with an 18-55mm kit zoom, but Canon subsequently replaced that with a 15-45mm kit zoom providing the 24mm equivalent FoV.

But so far, there is no RF-S equivalent. Perhaps one reason is to get people who want the wider FoV to purchase a second lens, that certainly makes sense from a business point of view.

 

[docsmith]

It may not be exactly what you are looking for, but here is a geek blog article by Roger Cicala, aka "Uncle Rog" on the development of wide angle lenses, and includes some discussion of other lens designs.

 

[Aldherrian]

The EOS M system launched with an 18-55mm kit zoom, but Canon subsequently replaced that with a 15-45mm kit zoom providing the 24mm equivalent FoV.

But so far, there is no RF-S equivalent. Perhaps one reason is to get people who want the wider FoV to purchase a second lens, that certainly makes sense from a business point of view.

Totally forgot the EF-M system indeed ! (as Canon did too, if I may say so)
The range was more constricted but it's interesting than having done such a lens for the M system, they chose (at least so far) to not do it for the RFS cameras. Maybe Canon has data telling them the cost is not worth it considering public interest and retail price of such a lens

It may not be exactly what you are looking for, but here is a geek blog article by Roger Cicala, aka "Uncle Rog" on the development of wide angle lenses, and includes some discussion of other lens designs.

It's still in topic as it underlines the complexity on extending the wide end of a lens and it was a very instructive read.
If I make some practical guesses on my general understanding of it, it would mean than lenses on crops systems being generally smaller (considering one of the appeal of crop system is keeping it small) it makes it more and more difficult to reach a good wide end lens considering complexity and space needed to achieve decent image quality. Where in full frame camera, the user is easier to convince to get a bigger lens with wider end and great IQ.

But it probably all boils down to the idea that Canon considers it's too much of a pain/cost versus public interest and acceptable price.

 

[docsmith]

But it probably all boils down to the idea that Canon considers it's too much of a pain/cost versus public interest and acceptable price.

Canon does make the RFs 10-18. They also make the RF 15-30 in addition to EFm and EFs lenses already mentioned. So they do have lenses that are designed for crop sensors or well suited for crop sensors wider than 18 mm.

I think the fundamental designs change. One design works well for a give range but as you stretch that range, the IQ suffers if not falls apart entirely.

Quick comparison, but look at the design differences between the RF 10-20 and EF 24-70 II


EF 24-70 II


Some elements look a little familiar, but the UWA lenses are bending light much more than a general purpose zoom. Look at that front and rear elements, the degree of curvature. Whether FF or crop, less than 18 mm is very close to the sensor, the light is bent more severely in order to spread it out over the image circle compared to large focal lengths.

So, I think that is the issue. UWA focal lengths are very close to the image sensor they require a design that bends light more.

 

[Aldherrian]

You're right in the fact that there are UWA lenses for Canon crop systems both from Canon itself and third-parties with the latest additions of both Sigma and Tamron. The RF15-35 is a little stretch as it's a UWA lens meant for FF that translates in a very wide/semi general purpose lens on crop system (with a price range well above regular crop options but one can't have everything)

My question was more meant at the wide end of a general purpose lens than a dedicated UWA which is more lenient in accomodating all that's needed for quality in a reasonable space.

As demonstrated by your post, the optical design on UWA-only lenses are much more efficient on getting distortion under control whereas standard zooms leaning on WA/UWA territory can't do as much.

I talked about Canon but even looking at other manufacturers, there are very few general zooms meant for crop systems claiming a wide end with a field of view that actually compares to what a standard zoom can deliver on full frame. Either lacking IQ or getting real pricey, getting in the price range of some L lenses. Also makes it apparent that those zoom can exist but are difficult to achieve to bring a significant edge over more common 28mm equivalent wide end.
Not taking price entirely into account, I would guess it means that multiple lens manufacturers considered that getting a crop standard zoom to 15/16mm wide end would take the price too high for the target audience of a crop system in the first place

 

[AJ]

I ended up thinking about why it was the only lens on Canon crop systems to achieve that 15mm at the wide end, a field of view that seemed really like a staple to me on full frame cameras.

EF-S 15-85 was a popular lens. It was a decent performer and covered a very useful range. A lot of people (on the net anyways) were hoping for an update to this lens, a mk2 version, but that never materialized.
On the M side, there was the 15-45 as Neuro points out, but this lens has a much more limited zoom range, limiting its utility for many.
I don't recall there being any Sigma 15-something zooms for APSC?