p.1 #1 · Why do crop lenses usually start at 18mm?
I've always wondered why most APS-C standard zoom lenses seem to start at 18mm (29mm equiv), while full frame lenses start at 24mm. (The one notable exception was the old EF-S 15-85mm, which was a great all around lens.)
Is there some underlying technical reason for this, or just product strategy to drive people to full frame?
The R10 + RF-S 18-150mm would be the perfect light travel kit if if started at 15mm. The next best option is the R8 + RF 24-240mm, which is much heavier.
p.1 #2 · Why do crop lenses usually start at 18mm?
The Canon sensors are sub-subminiature for starters, e.g, R7 is only 22.3x14.8 mm instead of 24x16 mm.
We still use the Nikkor 16-80 DX and there was a 15-85 Canon EFs also.
p.1 #5 · Why do crop lenses usually start at 18mm?
I think they do this to create a "Jack of all trades, master of none" type lens. Anything other than a standard kit lens will be extra money you have to spend. I recently purchased an R7 body and a Tamron 11-20mm f2.8 which (ironically) equates to a near 18-32mm field of view.
Years ago when I shot with Nikon DX gear, I had the Nikon 17-55mm f2.8 DX. With my Canon 7dmk2 (which I still have), I use a Canon EF-S 17-55mm f2.8 USM. Despite being built specifically for crop sensors, neither of these lenses were truly wide enough for me.
p.1 #6 · Why do crop lenses usually start at 18mm?
My guess, no it´s neither fact nor alt fact , is that more lens elements are needed to bend a wider image angle into a retro focus design with acceptable shortcomings. 18mm is a limit. Wider would be more expensive and would not fit the kit lens idea of a "cheap" camera.
With the much shorter flange focal distance of the RF this limit should be pushed back to much wider designs. And yes, I do like the RF-S 10-18 STM. And, Canon, a very nice and fresh, small RF-S 15-85 would be a winner!
p.1 #7 · Why do crop lenses usually start at 18mm?
Just to clarify my point: I’m fully aware that Canon makes wider APS-C lenses (like the 10-18mm). My question is why do their APS-C “standard” zooms always seem to start at 18mm, while full frames start at 24mm (15mm equivalent)? I would love to have a small/light single lens travel kit, but 18mm is not wide enough. The RF-s 18-150mm would be perfect if it started at 15mm.
p.1 #8 · Why do crop lenses usually start at 18mm?
I figure it's because the the RF-S 18mm- zooms are less expensive, period. The R-series APS-C options are relatively new, and they represent the low end of the product range. In order to build a low-end userbase, the products have to be inexpensive. Later, when the R-series APS-C userbase has become established (if ever), then Canon will introduce the more expensive RF-S lenses.
p.1 #9 · Why do crop lenses usually start at 18mm?
I just think it's a missed opportunity by Canon. As smart phone cameras have gotten so good, I find myself struggling to justify taking my R10 with multiple lenses on vacation. A small, light 15-150mm lens would really fit the bill. Even a 15-85mm would be great. I just don't understand why 3 extra mm would add so much to the cost.
My current intermediate compromise is my G5X Mark II, which has a 24-120mm F1.8-2.8 lens. It's an amazing little camera, but it's like 6 years old and lacks the great AF or the R10.
p.1 #10 · Why do crop lenses usually start at 18mm?
Kmccarthy wrote:
Just to clarify my point: I’m fully aware that Canon makes wider APS-C lenses (like the 10-18mm). My question is why do their APS-C “standard” zooms always seem to start at 18mm, while full frames start at 24mm (15mm equivalent)? I would love to have a small/light single lens travel kit, but 18mm is not wide enough. The RF-s 18-150mm would be perfect if it started at 15mm.
As I read the first set of responses, it crossed my mind that you were thinking of the so-called “kit lenses” often sold as starter lenses with the less expensive APS-C cameras. And it is true that a whole lot of those do start at 18mm at the wide end. (This has been true of other manufacturers of kits lenses, too.)
I don’t have the answer, but I’m inclined to think that a few of the posts are on the right track. That extra 2mm to get to the 16mm wide end that some of the more expensive lenses for Canon and other brand’s APS-C cameras entails takes some added engineering and costs. And it is related to that to point out that slightly less capable starter lenses do leave open the door for later purchases — lenses with a slightly larger focal length range and perhaps a larger, fixed aperture.
In a way, the 18mm wide end is ever so slightly more of an issue on Canon APS-C cameras compared ot other brands. Canon uses a slightly smaller (as EB-1 points out) version of APS-C that is effectively a 1.6x crop compared to full frame, while others (Canon, Fujifilm, Nikon) us a slighlty larger 1.5x crop sensor size. IN simple terms, that means that 18mm doesn’t seem as wide on the Canon cameras as it does on the others.
(In angle-of-view eras, 18mm on the 1.6x cropped sensors is roughly equivalent to about 29mm on full frame. 18mm on 1.5x cropped sensors is equivalent to 27mm. Both are close to the “classic” 28mm focal length.
Aug 14, 2025 at 09:39 AM
AmbientMike Offline • • • • • • [X]
p.1 #11 · Why do crop lenses usually start at 18mm?
Kmccarthy wrote:
I've always wondered why APS-C standard zoom lenses always seem to start at 18mm (29mm equiv), while full frame lenses start at 24mm. (The one notable exception was the old EF 15-85mm, which was a great all around lens.)
Is there some underlying technical reason for this, or just product strategy to drive people to full frame?
The R10 + RF-S 18-150mm would be the perfect light travel kit if if started at 15mm. The next best option is the R8 + RF 24-240mm, which is much heavier.
24-240 apparently requires computational imaging at 24mm, seems quite a bit harder to start at 24mm. 28-300 much more common than 24mm to tele
Even the 24-105 didn't have a great reputation. Good enough reputation, not noted to be super sharp. In contrast the 28-70 II had a good reputation even though relatively inexpensive and non L
28-85 or 28-90 used to be pretty popular, 18-55 pretty close. 18-150 more or less 28-200 on ff, more common than 24mm to even 135mm. Aapparently 24mm is harder since its much wider
p.1 #12 · Why do crop lenses usually start at 18mm?
AmbientMike wrote:
24-240 apparently requires computational imaging at 24mm, seems quite a bit harder to start at 24mm. 28-300 much more common than 24mm to tele
Even the 24-105 didn't have a great reputation. Good enough reputation, not noted to be super sharp. In contrast the 28-70 II had a good reputation even though relatively inexpensive and non L
28-85 or 28-90 used to be pretty popular, 18-55 pretty close. 18-150 more or less 28-200 on ff, more common than 24mm to even 135mm. Aapparently 24mm is harder since its much wider
It sounds like the hard part is in making a wide-to-tele zoom wider. Whereas making an ultrawide-to-wide zoom wider isn't as difficult. So for cost, and likely size and weight, reasons, it's better to keep the cheaper zooms from getting too wide, then make a separate lens for the ultrawide duties.
p.1 #13 · Why do crop lenses usually start at 18mm?
I'm going expose my age by reminiscing when in the FF, Film days 50mm was a Normal lens, 35mm was Wide Angle, and 28mm was "Super" Wide angle, and anything wider than that was Fisheye.
p.1 #14 · Why do crop lenses usually start at 18mm?
It's mostly about cost. General-use kit lenses are designed for a modest price range, small size, and popular zoom range. An extra stop or couple of millimeters wider will greatly increase both the size and cost. If you have the cash, you can skip the kit lens and buy something wider and faster. I used the EF-S 17-55 2.8 IS USM for a decade during the DSLR era, and the extra millimeter and stop were greatly appreciated. It's really dated now—soft at 17mm and prone to flare—and awkwardly huge with an adapter. I rarely remove my RF 100-400 from my R7, but when I do, the RF 14-35 4L IS USM makes a nice kit lens substitute on the R7.
p.1 #15 · Why do crop lenses usually start at 18mm?
Sy Sez wrote:
I'm going expose my age by reminiscing when in the FF, Film days 50mm was a Normal lens, 35mm was Wide Angle, and 28mm was "Super" Wide angle, and anything wider than that was Fisheye.
Yeah my dad's kit from the 70's & 80's when I was a kid consisted of 28, 50, and 135 lenses and a flash, all from K-Mart. We're really spoiled today.
p.1 #16 · Why do crop lenses usually start at 18mm?
Sy Sez wrote:
I'm going expose my age by reminiscing when in the FF, Film days 50mm was a Normal lens, 35mm was Wide Angle, and 28mm was "Super" Wide angle, and anything wider than that was Fisheye.
In the 70s a 24mm was also a wideangle. The 24/2.8s were reasonably priced and not out of the ordinary. 20 or 21 mm was more of a superwide. I had a 28/2 Nikkor which was considered fast as was the 35/1.4.
Back to OP, I think that the expectation for a "normal zoom" is that is covers at least 28mm if not 24mm angle of view at the short end. A "super-wide zoom" like a 12-24 or 10-18, etc. on APS-C is different.
EBH
Aug 14, 2025 at 03:10 PM
AmbientMike Offline • • • • • • [X]
p.1 #17 · Why do crop lenses usually start at 18mm?
Mike_5D wrote:
Yeah my dad's kit from the 70's & 80's when I was a kid consisted of 28, 50, and 135 lenses and a flash, all from K-Mart. We're really spoiled today.
Some friends' dad had 35, 50, & 135, I think the 50/1.4 & m42 body Sears branded! I had a Focal (Kmart) lens hand-me-down, early on
Aug 14, 2025 at 04:26 PM
AmbientMike Offline • • • • • • [X]
p.1 #18 · Why do crop lenses usually start at 18mm?
Mike_5D wrote:
It sounds like the hard part is in making a wide-to-tele zoom wider. Whereas making an ultrawide-to-wide zoom wider isn't as difficult. So for cost, and likely size and weight, reasons, it's better to keep the cheaper zooms from getting too wide, then make a separate lens for the ultrawide duties.
Tamron made a 28-300 , rather than 24-200, so yeah i agree, the wide end seems harder
In theory I need uwa <24mm ff equivalent, so 28mm ff equivalent is good for me. Used to use 21, 35, 50 very happily. Although I've been bad about carrying my uwa zoom recently
p.1 #19 · Why do crop lenses usually start at 18mm?
I've been using a 24-105 on my FF 5 series since the original so I'm kinda spoiled at having 24 wide without swapping lenses. Fortunately my now 7 year old G1X Mk III has a 15-45 mm lens on the same sensor as the 80D. In its youth it was ridiculed for its slow f2.8-5.6 aperture range but which now doesn't sound to bad compared to most RF-S lenses. The IQ is at least as good as the 15-85 on an 80D. I had to have the clock battery replaced earlier this year which Canon performed for free (CPS).
I have to say I really like the 18-150 and Sigma 18-50 lenses on my R7. I also have both 10-18s which are easy to carry and swapping isn't bad if there's no rush. I'm really impressed with all the RF and RF-S lenses which have improved as much as the RF bodies. Still, my trusty G always goes as 2nd body.
p.1 #20 · Why do crop lenses usually start at 18mm?
Here is a good answer from ChatGPT. The very last sentence seems to be the bottom line.
1. Back Focal Distance vs. Mirror Box
Most APS-C DSLRs (Canon EF-S, Nikon F-DX, Sony A-mount) inherited the same mirror box size as their full-frame counterparts.
• To design a wide-angle lens, the rear element must sit closer to the sensor.
• But the mirror physically blocks how far back you can go.
• Getting much wider than ~18 mm on APS-C in a cheap kit zoom means resorting to very strong retrofocus designs (extra lens groups to push the rear nodal point forward). That increases size, cost, and aberrations.
⸻
2. Aberration & Distortion Control
As you go wider:
• Distortion (especially barrel distortion) skyrockets.
• Field curvature and chromatic aberration become harder to tame.
• For APS-C, 18 mm (≈29 mm equiv.) is the compromise: still wide enough for general use, but avoids the extreme design challenges of, say, 15–16 mm as a standard zoom starting point.
You can make a 16–50 mm APS-C zoom (and some exist, like Sony’s 16–50 OSS or Pentax 16–50 f/2.8), but they’re optically trickier and often more expensive or with more compromises (soft corners, distortion that must be corrected in software).
⸻
3. Image Circle Efficiency
A lens has to project an image circle large enough to cover the sensor.
• At 18 mm, designers can keep the image circle just large enough for APS-C while minimizing wasted glass and weight.
• Going wider forces either:
a) more glass diameter (heavier, pricier), or
b) strong optical corrections (more complex designs).
⸻
4. Historical Inheritance
The very first APS-C kit zooms (Canon 18–55, Nikon 18–70) weren’t “arbitrarily” chosen — they were about the widest focal length you could practically design for a small, inexpensive kit lens that still worked with the DSLR mirror box geometry. Once that standard was set, it stuck.
⸻
✅ So the physical sweet spot comes from:
• Mirror box depth (can’t put the rear element close enough for much wider without exotic retrofocus).
• Manageable distortion/aberrations at ~18 mm.
• Smaller glass/image circle efficiency.
That’s why APS-C zooms usually bottom out at ~18 mm, while full-frame “standard” zooms start at 24 mm — which is about the same design difficulty level relative to their format.
, is that more lens elements are needed to bend a wider image angle into a retro focus design with acceptable shortcomings. 18mm is a limit. Wider would be more expensive and would not fit the kit lens idea of a "cheap" camera.