Canon 40mm f/2.8 EF STM

[ulf]

Last Update: 03 April 2021 agb/label/spacing

Finalized: Work in progress.

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Canon 40mm f/2.8 EF STM

 

Manufacturer: Canon

Lens Label: CANON LENS EF 40mm 1:2.8 STM

Currently manufactured: No

 

Lens type: Auto focus, Prime, Wide Angle, Pancake lens

Design: 6 elements in 4 groups

Focal length: 40mm

Aperture range: f/2.8 – f/22, electronic control only, 7 blades circular aperture

Magnification range: to 0.18x at 0.3m.

Sensor format/coverage: up to 24 mm x 36 mm

Mount: Canon EF

Flange Focus distance: EF-standard, 44.00mm

Front filter: 52 mm x 0.75 mm

Introduction year: between 2012

S/N of test object: 3261100252

 

Lens review (VIS), on the web: https://www.kenrockw...0mm-stm.htm#rex

Lens info on the web: https://global.canon...duct/ef419.html

 

Image of test object:

Transmittance Summary

Definitions of the parameters below

• Range: The Canon EF 40/2.8 STM lens transmits 1-84% in an increasing slope from 347nm to 400nm.
• T_VISmax (%) = 94%
• T_400nm (%) = 84%
• T_365nm (%) = 40%

• λ_{UV HMvis}(nm) = 368nm
• λ_{UV HM400}(nm) = 366nm
• λ_{UV Zero}(nm) = 347nm
  These three values indicate that the lens is only working for some upper UV-A photography.

Spectral Transmission Graphs

UV-NIR, Canon EF 40/2.8 STM

The transmission measurement accuracy into the end of NIR range is less good due to limitations in the light source.

 

UV, Canon EF 40/2.8 STM

 

UV-Log, Canon EF 40/2.8 STM

Numerical Spectra Data available: Yes

 

General comments about the UV-reach:

tba

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Filters and how to use them on this lens:

 

NOTE: The filter threads are plastic. So you must be very careful when mounting filters. A large filter stack may stress the filter threads.

 

The front filter thread is 52mm standard filter thread.

 

It is also possible to use rear mounted filters, either in lens mount adapters for mirrorless cameras like Sony A-series etc, or placed directly in the camera.

 

An alternative, if space in the camera allows, is to putty-mount a filter directly against the lenses rear surface, that provides a good reference plane for orienting the filter normal to the optic axis.

The rear lens element is not recessed and thus needs a filter mounted in a filter ring to place the filter's glass surface at a safe distance from the rear lens element.

 

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Handling and focussing:

Must be assisted electronically by the camera. Only possible on Canon cameras or with suitable active lens adapters.

Autofocus in UV might work with enough light present. TBD

 

Flare and sun-stars:

TBD

 

Sharpness:

High according to net reviews. For UV ?

 

Lens distortion:

TBD

 

Chromatic Aberration in UV:

TBD

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Image samples:

[JMC]

Ulf, in the section "Filters and how to use them on this lens:The front filter thread is 49mm standard filter thread." it says 49mm filter, but the filter size is 52mm (you had it right further up).

 

Also the link to the Ken Rockwell review goes to Pentax forums for the Novoflex 35mm. The other also goes to something about the Novoflex 35mm.

[Andrea B.]

Editor's Note: I added a warning about the plastic filter threads.

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Proposed simplification of Filters and how to use them on this lens.

 

Front filter:

• The front filter is a (52 mm) standard filter.
  
• OR: The (Zobax 35/3.5) has no front filter threads.
  

Rear filter:

• The rear lens element is recessed enough to permit a putty-mounted rear filter on the lens end assuming there is enough space inside the camera chamber.
  
• OR: The rear lens element is not recessed enough to permit a putty-mounted rear filter.
  

• If a mount adapter or extension tube is being used, then a rear filter can be added directly or internally using step-rings glued in place.

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Comments please??

[ulf]

Editor's Note: I added a warning about the plastic filter threads.

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Proposed simplification of Filters and how to use them on this lens.

 

Front filter:

• The front filter is a (52 mm) standard filter.
  
• OR: The (Zobax 35/3.5) has no front filter threads.
  

Rear filter:

• The rear lens element is recessed enough to permit a putty-mounted rear filter on the lens end assuming there is enough space inside the camera chamber.
  
• OR: The rear lens element is not recessed enough to permit a putty-mounted rear filter.
  

• If a mount adapter or extension tube is being used, then a rear filter can be added directly or internally using step-rings glued in place.

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Comments please??

 

That is OK

 

In general some wide lenses will have problems with dichroic filters and very wide lenses will demand very big front-filters to avoid vignetting, especially with filter stacks.

In some cases you might use a split-stack, placing one filter on the rear side and one at the front. I those cases I would place the BG-filter at the rear, to be able to switch the front filter without exposing the sensor for dust.

Should there be more OR alternatives including these additions?

[Andrea B.]

I'm pretty sure everyone knows (or certainly should know) that wide lenses are prone to vignetting when filtered.

 

I agree we should add something about dichroic filters. Would please suggest the proper terminology for that suggestion? I've never been sure what the dichroic discoloration is called.

[ulf]

I'm pretty sure everyone knows (or certainly should know) that wide lenses are prone to vignetting when filtered.

Absolutely, I just wanted to add an idea of a possible solution, not having both filters of a stack in the front thread.

 

I agree we should add something about dichroic filters. Would please suggest the proper terminology for that suggestion? I've never been sure what the dichroic discoloration is called.

 

A seed of the cause of the problem is something like this:

 

The filtering effect of Dichroic filters depend on the angle the light is passing though the filter.

Many dichroic filters including the Baader U are made for astronomy and designed for light passing at a normal angle, (close to 90°) to the Filter's surface.

 

When the angle deviates from 90°, the cutting wavelengths shift.

At some angle the this shift becomes too disturbing creating too much of a discolouration in the images corners.

 

Wide angle lenses are most prone to this problem with their wide FOV, but lenses with a small rear lens element and short back-flange distance might also see this problem.

[Andrea B.]

Well, yes, I know what causes it, but I was not sure what it is called. "Dichroic discoloration" is the terminology it seems.

[Stefano]

According to Wikipedia, this lens has been discontinued in March 2021: https://www.google.com/url?sa=t&source=web&rct=j&url=https://en.m.wikipedia.org/wiki/Canon_EF_40mm_lens&ved=2ahUKEwi2oKTtyqv1AhVQhv0HHRCiCBEQFnoECD4QAQ&usg=AOvVaw3YuuSrGeu6b0ACPpXE8nY4

 

If Canon will make a new version, I hope that it will have the same or comparable UV reach. Metal filter threads would be a nice improvement too.

[Doug A]

@Stefano guessing Canon will not replace this lens. They have been discontinuing DSLR lenses and pivoting to their mirrorless platform. They might bring it out for the the new mount. 

 

Thanks,

Doug A

[ulf]

Updated the Manufacturing status to the new status, No. (2022)

 

Thanks Stefano for the reminder.

[Avalon]

This is fairly new lens, what makes it better at UV? Please test Sony E-mount lens too.

[ulf]

33 minutes ago, Avalon said:

This is fairly new lens, what makes it better at UV? Please test Sony E-mount lens too.

Thin lens elements made of glass types that happens to have reasonably low UV-blocking makes it better at UV.

Not designed for that. It just happened to be so.

 

This is one of the few modern lenses known to be reasonably good for UV.

 

Sorry, but I have no use for Sony E-mount lenses for the moment. 

The lenses I have measured and published here are mostly known to be acceptable for UV.

After buying my UV-Nikkor and several Canon-TS lenses I do not want to spend more money buying even more lenses.

I already have too many lenses in my collection that I never will use.

 

If you want to buy me an E-mount lens I can measure it. ;-)

 

[Stefano]

4 hours ago, ulf said:

After buying my UV-Nikkor and several Canon-TS lenses I do not want to spend more money buying even more lenses.

So you got one too. I hope you like it. Who knows, maybe I will buy one too, far into the future, if I ever will.

 

I cannot afford one, and I honestly can't justify the price, just like I won't spend 10,000 € for a SWIR sensor, even if I could afford it.

 

Even if this lens is really sharp, corrects chromatic aberration, and is built vith very tight tolerances, I don't know if the price is justified, or if it's high also because it's a niche item.

 

For just a little more (8,000 €), you can buy a Nikon Z 58mm f/0.95 S Noct lens. It has 17 elements in 10 groups, including 3 aspherical elements, and it's sharp in the center and corners straight from f/0.95. Its sharpness is an incredibile achievement at that aperture. Stopping down is only needed to increase depth of field, and here it is said that past f/4 diffraction is already softening the image. The UV-Nikkor has only 6 elements in 6 groups, all spherical as far as I know.

 

This said, it's still a really nice lens, and I really wish you enjoy it. This wasn't a critic, just a personal thought.

[Stefano]

As for the Canon 40 mm pancake, I have one and it's a nice little lens. It has enough UV transmission to produce false yellows and lavenders, although not as saturated as those from a Soligor 35 mm f/3.5 lens, and it also works well in IR. I wish there were more currently manufactured lenses like it.

[moondigger]

Ulf, you mention owning some Canon TS lenses. Are these usable for UV imaging? I own a couple myself, which I have used quite a bit for landscapes (in the visible spectrum). But I haven't seen any indication elsewhere that they might be good for UV imaging.

[lukaszgryglicki]

I have Canon TS-E 17/4 - I use it on Fuji GFX - I cannot tell anything about UV transmittance because it is not possible to put filters on its huge front element.

 

[ulf]

Do a search for "tilt" in the forum search function. Select "This Forum"
You will find that there are a few topics about TS-lenses and UV.

 

When posting further about that, please create a new topic or continue in one of those better suited topics.

It is very easy to do.

Then the discussion and valuable findings will be much easier to find later.

 

This topic is about the Canon 40mm f/2.8 EF STM that have no relation at all to TS Lenses.