EOS-M: 22mm f/2.0 STM lens - what is the REAL focal length?

[Marco Nero]

I have a question on the Canon 22mm f/2.0 STM lens that nobody else seems to have an answer for:

I automatically assumed that the 22mm designation of this lens means it's a 22mm when fitted native to an EOS-M camera. This lens is designated an M-Series STM lens (as opposed to the EF and EF-S lenses - which are both cropped when added to an APS-C camera).

DPreview lists the focal length for this lens at 20mm, not 22mm. See for yourself:

http://www.dpreview.com/products/canon/lenses/canon_m_22_2/specification


But online sellers are claiming this lens has a 35.2mm focal length (equivalent 35mm). This means they are treating this lens as a 1.6x crop.

What gives?

 

[Howard S]

Marco Nero wrote:

I have a question on the Canon 22mm f/2.0 STM lens that nobody else seems to have an answer for:

I automatically assumed that the 22mm designation of this lens means it's a 22mm when fitted native to an EOS-M camera. This lens is designated an M-Series STM lens (as opposed to the EF and EF-S lenses - which are both cropped when added to an APS-C camera).

DPreview lists the focal length for this lens at 20mm, not 22mm. See for yourself:

http://www.dpreview.com/products/canon/lenses/canon_m_22_2/specification

But online sellers are claiming this lens has a 35.2mm focal length (equivalent 35mm). This means they are treating this lens as a 1.6x crop.

What gives?

 

[Marco Nero]

Howard S wrote:

It is 22mm and is used on a "1.6x crop" sensor so gives the same view as 35mm on "full frame"

The thing is, closeup portraits and pictures taken with this 22mm lens on the EOS-M show considerable barrel distortion typical of a 22mm lens, not a 35mm lens. I was also under the assumption that the 1.6x crop applies to the us of EF and EF-S lenses on this camera because the native EOS-M lens sits much, much closer to the sensor. Since ONLY the EF-M lenses can only be used on the new M-Mount, WHY would Canon not simply label the lens "35mm" or something like that?

Doesn't make a whole of of sense to me why they wouldn't simply call it a 35mm lens since it's never going to be used on another camera where the aperture and focal length might produce different results.

Looks like a wider than 35mm lens to me - perhaps it's the proximity to the subject?

Another 22mm lens shot that looks much more like a wider-than-35mm lens




--
Regards,

Marco Nero.
www.pbase.com/nero_design

 

[Howard S]

did you follow my link?

 

[Marco Nero]

Have a look at this link and scroll down for some shots taken with the 22mm f/2.0 STM EF-M lens:

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www.photigy.com

Looks pretty wide to me. Very much like a 22mm focal length.

--
Regards,

Marco Nero.
www.pbase.com/nero_design

 

[Marco Nero]

Howard S wrote:

did you follow my link?

Sorry... missed the link.

Just took a look now and it says that the lens produces a cropped image. But the samples I'm seeing online don't resemble 35mm... they look much wider. And even DPreview lists this lens at 20mm. I'm not sure that the results match the specs. Is it possible an error was made because I've caught them out with mistakes before and they've retracted them as soon as they were verified.




--

Regards,
Marco Nero.
www.pbase.com/nero_design

 

[Howard S]

Trust me, I have the lens and also 20mm and 35mm on the 5D2 and it's 22mm giving the same view as 35mm on FF

 

[Lemming51]

Marco Nero wrote:

Have a look at this link and scroll down for some shots taken with the 22mm f/2.0 STM EF-M lens:

http://www.photigy.com/canon-eos-m-ongoing-review-first-impressions-and-sample-photos/

The lens is 22mm focal length. The 20mm stat in the dpreview is a typo. The lens focal length is a function only of the lens elements, it has nothing to do with whether it is EF, EF-S, EF-M, or any other mount or system.

The Von Maur pic below is not exceptionally wide. It looks like what I'd expect with the specified 63 deg diagonal AoV, same as a 35mm lens gives on 'full frame'. There is NO apparent barrel distortion in that pic. The columns on either side of the frame are straight, as is the line of tiles at bottom and the wall above the Von Maur lettering. What you're perceiving as barrel distortion is that the store opening is not flat, it is curved.

Similar with the close-up of the cosmetics. There is only perspective distortion in this pic, due to the close focus and not any lens fault.

Looks pretty wide to me. Very much like a 22mm focal length.

--
Unapologetic Canon Apologist

 

[Marco Nero]

Howard S wrote:

Trust me, I have the lens and also 20mm and 35mm on the 5D2 and it's 22mm giving the same view as 35mm on FF

That's exactly what I wanted to hear. Thanks for the comparison that you noted with your own equipment. I also see from the poster below that DPreview has a typo on their page for this lens.

 

[KCampbell]

It doesn't matter how large the sensor is on which the lens projects its image, the focal length is the focal length is the focal length.

If the lens is designed so that it can produce a large image circle without distortion or vignetting then it's possible to have a wide angle of view/field of view, which is what happens with a 22mm focal length lens on a full frame sensor. The same focal length designed for a much smaller sensor only has to produce an acceptable image circle of a smaller diameter, because the sensor is smaller, and consequently that smaller sensor sees a narrower angle of view - it's "cropping" only a portion of the center of the image circle.

Lenses are specified in terms of focal length because it's a physical characteristic of the lens optical design. The 35mm full frame equivalent is often quoted because that's just familiar to people - which is why you'll see it quoted even on fixed lens compacts with tiny sensors.

Kevin

 

[leoskats]

I have a question on the Canon 22mm f/2.0 STM lens that nobody else seems to have an answer for:

I automatically assumed that the 22mm designation of this lens means it's a 22mm when fitted native to an EOS-M camera. This lens is designated an M-Series STM lens (as opposed to the EF and EF-S lenses - which are both cropped when added to an APS-C camera).

DPreview lists the focal length for this lens at 20mm, not 22mm. See for yourself:

http://www.dpreview.com/products/canon/lenses/canon_m_22_2/specification

But online sellers are claiming this lens has a 35.2mm focal length (equivalent 35mm). This means they are treating this lens as a 1.6x crop.

What gives?

--
Regards,
Marco Nero.
www.pbase.com/nero_design

Hey. Guys what’s the difference between a 35.2mm and a 35mm focal length? Is it different? is it the same?

 

[Sittatunga]

I have a question on the Canon 22mm f/2.0 STM lens that nobody else seems to have an answer for:

I automatically assumed that the 22mm designation of this lens means it's a 22mm when fitted native to an EOS-M camera. This lens is designated an M-Series STM lens (as opposed to the EF and EF-S lenses - which are both cropped when added to an APS-C camera).

DPreview lists the focal length for this lens at 20mm, not 22mm. See for yourself:

http://www.dpreview.com/products/canon/lenses/canon_m_22_2/specification

But online sellers are claiming this lens has a 35.2mm focal length (equivalent 35mm). This means they are treating this lens as a 1.6x crop.

What gives?

--
Regards,
Marco Nero.
www.pbase.com/nero_design

Hey. Guys what’s the difference between a 35.2mm and a 35mm focal length? Is it different? is it the same?

Less than 0.6% difference. Near enough for a country job.

If you're going to be really precise the crop factor is 36/22.2 or 1.621621 recurring, assuming the full frame is exactly 36x24mm (full frame sensors usually aren't precisely that size). You would have to measure the focal length at infinity and several other focus points as internal focussing lenses focus at least partly by changing their focal lengths, sometimes quite considerably. Bear in mind that a 5% tolerance on the stated focal length is normally considered quite acceptable. As I said, it's near enough the same.

 

[leoskats]

I have a question on the Canon 22mm f/2.0 STM lens that nobody else seems to have an answer for:

I automatically assumed that the 22mm designation of this lens means it's a 22mm when fitted native to an EOS-M camera. This lens is designated an M-Series STM lens (as opposed to the EF and EF-S lenses - which are both cropped when added to an APS-C camera).

DPreview lists the focal length for this lens at 20mm, not 22mm. See for yourself:

http://www.dpreview.com/products/canon/lenses/canon_m_22_2/specification

But online sellers are claiming this lens has a 35.2mm focal length (equivalent 35mm). This means they are treating this lens as a 1.6x crop.

What gives?

 

[brightcolours]

I have a question on the Canon 22mm f/2.0 STM lens that nobody else seems to have an answer for:

I automatically assumed that the 22mm designation of this lens means it's a 22mm when fitted native to an EOS-M camera. This lens is designated an M-Series STM lens (as opposed to the EF and EF-S lenses - which are both cropped when added to an APS-C camera).

DPreview lists the focal length for this lens at 20mm, not 22mm. See for yourself:

http://www.dpreview.com/products/canon/lenses/canon_m_22_2/specification

But online sellers are claiming this lens has a 35.2mm focal length (equivalent 35mm). This means they are treating this lens as a 1.6x crop.

What gives?

 

[ffabrici]

Mounted on an EOS-M camera, the 22mm f/2.0 has the same field of view as a 35mm FF lens mounted on a FF camera.

The lens focal lengths are approximate and if you study the detailed lens tests a 70-200mm zoom could for example be 72-197mm in specific measures. We don't even know if the 22mm is 21.5mm or 22.4mm, so please don't worry about those tiny details.

The 22mm f/2.0 is a fantastic lens btw.

 

[brightcolours]

Mounted on an EOS-M camera, the 22mm f/2.0 has the same field of view as a 35mm FF lens mounted on a FF camera.

The lens focal lengths are approximate and if you study the detailed lens tests a 70-200mm zoom could for example be 72-197mm in specific measures.

How was that measured, and what distance was focussed on?

We don't even know if the 22mm is 21.5mm or 22.4mm, so please don't worry about those tiny details.

The 22mm f/2.0 is a fantastic lens btw.

 

[rrccad]

I have a question on the Canon 22mm f/2.0 STM lens that nobody else seems to have an answer for:

I automatically assumed that the 22mm designation of this lens means it's a 22mm when fitted native to an EOS-M camera. This lens is designated an M-Series STM lens (as opposed to the EF and EF-S lenses - which are both cropped when added to an APS-C camera).

the real focal length is 22mm. it's a 22mm lens.

however if you look at the Field of view from a 35mm full frame camera equivalent, it gives you the same field of view as a 35mm lens.

 

[ffabrici]

The focal length is always specified at infinite focus distance. Many lenses suffers from FL breathing which means that the FL shortens at MFD.

From TheDigitalPicture:

Some have asked if the 100-400 L II's focal length is really 400mm on the upper end. This is a fair question because it seems that manufacturers sometimes take the liberty of rounding off/up the specified focal length numbers in zoom lenses. In this case, the lens set to 400mm frames a test chart from 42.86' (13.063m) while two of Canon's prime 400mm lenses (the 400 f/2.8L II and 400 f/5.6L) frame the chart at 44.87' (13.675m) and 44.54' (13.576m) respectively. If I take the average of those two comparables, I get 44.70' (13.625m) (using the metric numbers for calculating). Using that number, the 100-400 II's max focal length seems more like 383mm or just slightly wider. Especially with distortion potentially effecting this calculation, that number is close enough to 400mm that few will care about any actual difference. Canon has claimed to be within 5% of the specified focal length number, adding credance to the calculated figure's possibility.

 

[Sittatunga]

The focal length is always specified at infinite focus distance. Many lenses suffers from FL breathing which means that the FL shortens at MFD.

Actually if a lens doesn't breathe (alter its field of view) when focussing it definitely changes its focal length to focus.

The simple thin-lens formula is 1/u + 1/v = 1/f where f is the focal length, u is the object distance and v is the image distance. The angle of view is determined by v, the distance to the sensor, which is always greater than f unless u is infinity. Just to complicate extension tube calculations, camera lens focussing scales are calibrated from the image plane so the scale actually shows (u+v).

From TheDigitalPicture:

Some have asked if the 100-400 L II's focal length is really 400mm on the upper end. This is a fair question because it seems that manufacturers sometimes take the liberty of rounding off/up the specified focal length numbers in zoom lenses. In this case, the lens set to 400mm frames a test chart from 42.86' (13.063m) while two of Canon's prime 400mm lenses (the 400 f/2.8L II and 400 f/5.6L) frame the chart at 44.87' (13.675m) and 44.54' (13.576m) respectively. If I take the average of those two comparables, I get 44.70' (13.625m) (using the metric numbers for calculating). Using that number, the 100-400 II's max focal length seems more like 383mm or just slightly wider. Especially with distortion potentially effecting this calculation, that number is close enough to 400mm that few will care about any actual difference. Canon has claimed to be within 5% of the specified focal length number, adding credance to the calculated figure's possibility.

 

[brightcolours]

The focal length is always specified at infinite focus distance. Many lenses suffers from FL breathing which means that the FL shortens at MFD.

No, focus breathing does not mean the FL changes. It means that the FOV either widens or narrows when you go through the focus range.

When the focal length remains the same, you will see a narrowing FOV towards MFD.

From TheDigitalPicture:

Some have asked if the 100-400 L II's focal length is really 400mm on the upper end. This is a fair question because it seems that manufacturers sometimes take the liberty of rounding off/up the specified focal length numbers in zoom lenses. In this case, the lens set to 400mm frames a test chart from 42.86' (13.063m) while two of Canon's prime 400mm lenses (the 400 f/2.8L II and 400 f/5.6L) frame the chart at 44.87' (13.675m) and 44.54' (13.576m) respectively. If I take the average of those two comparables, I get 44.70' (13.625m) (using the metric numbers for calculating). Using that number, the 100-400 II's max focal length seems more like 383mm or just slightly wider. Especially with distortion potentially effecting this calculation, that number is close enough to 400mm that few will care about any actual difference. Canon has claimed to be within 5% of the specified focal length number, adding credance to the calculated figure's possibility.