CANON EF12: Come closer!
Written: Aug 11 '04 (Updated Aug 12 '04)
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Product Rating:
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Pros: magnification gain, EF12-II updated for EF-S mounts
Cons: very limited working distance, wide-angle limited to 18mm, little effect on telefoto lenses.
The Bottom Line: A cheap way to gain extreme magnification especially with wide-angle macro lenses.
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| theuerkorn's Full Review: Canon Extension Tube Ef 12 |
SLR cameras have at least one undeniable advantage: They allow to exchange lenses and provide more flexibility than any point-and-shoot camera ever could. However, buying a wide range of lenses sure doesn't come cheap, not to mention the space needed in your travel gear.
I entered SLR photography little more than 8 years ago and recently switched to digital. Staying with the same manufacturer (Canon) allows to reuse 'old' lenses but mine were especially lacking in extreme close-up capabilities. (This feature is often called Macro.)
So my choices were:
- Close-up filter (lens that mounts to the lens)
- Extension Tube (between lens and body)
- High magnification macro lens ($$$)
1. Extension Tube Introduction
2. Lens Test
2.1. Camera Settings
2.2. Canon EF-S 18-55mm
2.3. Sigma 70-300mm APO
3. Conclusion
4. Picture Links
Extension Tube Introduction
After trying the closeup filter with marginal results, my next attempt was an extension tube and since I am using the Canon Digital Rebel my choice was the EF12-II. The 'II' refers to a recent revision of the standard EF12 to make it compatible to the digital lens mount EF-S as found in the EF-S 18-55mm lens that's included with the Digital Rebel Kit. (Note: The standard EF12 Extension Tube is not compatible with the EF-S mount.) Other differences are subtile and don't go far beyond the added markers for the offset key for the EF-S series. Otherwise both models are interchangeable and especially with view to EF mounts practically identical.
There is a myth of added o-rings for improved sealing floating around, but that's not more than a myth since (a) there are no o-rings and (b) the claimed seal doesn't help anything if camera and lens aren't weatherproof. However, the EF12-II extension tube fits without noticable play into the EF mount and has a very solid feel to it.
The extension tube fits between the camera body and any lens with an EF or EF-S mount. The axial offset increases the projected picture size (on film or sensor) and therefor magnification. Main side effects indluce reduced working distance and limited focus range. Magnification is measured as the size with which the opbject is projected onto the imaging plane of the camera (sensor or film). Hence, if you read magnification of 0.5, that means an actual object with the size of 1 (inch or mm) will cast an image with half that size onto the imaging plane 0.5 (inch or mm). While this sounds like a reduction, keep in mind that the image then will be enlarged for the photo.
So let's look into the real-life gain provided by the EF12-II extension tube (which includes the EF12). I am going to use the following different lenses as they may represent most applications. (Besides if someone wants to sponsor one of those 'IS' lenses, I will be happy to included that as well. ;-)
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Test Lenses:
- Camera Settings
- Canon EF-S 18-55mm 3.5f-5.6f, Macro
- Sigma 70-300mm Super II APO, 3.5f-5.6f, Macro 0.95m
Common camera settings:
Camera: Canon Digital Rebel Kit
I tried to keep main parameters identical (as possible) in order to achieve comparable results. For that reason the Aperture has been set to f10.0 (which happens to be close to the sharpest setting for most common lenses). The use of a tripod and the mirror-lockup function eliminate camera shake.
Focus is somewhat hard to obtain as autofocus is not recommended and the extremely shallow depth of focus makes it hard to find that sweet spot. Autofocus still worked surprisingly well but required to double-ckeck every picture and eventually re-take about 30%.
Camera: Canon Digital Rebel
Shooting Mode: Program AE
Av (Aperture Value): 10.0
Metering Mode: Evaluative
Exposure Compensation: 0
ISO Speed: 100
Mirror Lockup: Enabled
Image Size: 3072x2048
Image Quality: RAW
Flash: Off
White Balance: Custom
AF Mode: Manual Focus
Contrast: Normal
Sharpness: Normal
Color saturation: Normal
Color tone: Normal
Color Space: Adobe RGB
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Canon EF-S 18-55mm & EF 12 II
Despite the macro function of this lens, magnification is decent but nothing to brag about at 0.28. With a minimum working distance of 280mm, especially tiny objects are hard to capture in full size (regarding the imaging sensor). Since the 280mm are already very close to gain of a 3 closeup lens, little is gained from adding this filter-type lens to this lens.
Using the EF 12 II extension tube, however, boosts magnification significantly and now at 0.68 (per manufacturer specs), it allows to approach the object up to 130mm. Eyeballing results, the true magnification indeed was right around 0.7. All detail is very well retained and distortion due to the 'out-of-focal-plane' mounting of the lens is virtually non-existent.
Note: The depth of focus is very shallow and this basically works with flat objects only if there is no blur of out-of-plane detail allowed or desired.
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Sigma 70-300mm SuperII APO & EF12-II
Sigma's zoom lens sports good quality (APO lens elements) and a large zoom range. Somewhat unusual for a zoom like that is the macro function which is admitedly somewhat inconvenient, but allows a magnification of 0.5 at a working distance of 950mm. While these are the factory specs, I was able to get as close as 700 mm and reach a magnification of somewhere around 0.6.
Given that diopter lenses (a.k.a. close-up lens) are seldom optimized for a specific lens, the B W 3 model failed almost completely with the Sigma lens. Magnification of more than 1.0 is great, but it was impossible to obtain a sharp focus and the result looked more like a built-in softening filter.
Using the EF12-II extension tube, (unfounded) expectations were high. However, the manufacturer points out that the greatest effect is achieved with wide-angle lenses, and improvements at the other 'end' of the spectrum would be less dramatic. Well they are and despite shortening the working distance to 600 mmm, the new max. magnification turned out to be about 0.67.
Again, it was virtually impossible to tell any quality degradation related to the extension tube, but the gain was rather minimal too. This may be a case for the EF25-II extension tube.
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Conclusion
The $80 investment in an extension tube like the EF12-II may be worth it if extreme magnification while retaining best quality is desired and specific macrolenses are out of reach. Other than price, there is no reason to purchase the older EF12 model, as the EF12-II is required to use EF-S lenses. This is mostly relevant for APS sized sensors or film.
I found the use of an extension tube extremely easy while retaining amazing imaging quality which I was unable to get with close-up filters. Focussing can be an issue as that happens at the widest aperture and that results in extremely shallow depth of focus
Unfortunately it works only for closeup and does not function as a tele-extender since the planar offset causes the lens to be unable to focus at a greater distance. (Would have been nice though.)
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Picture Links
Excellent detail:
- Full resolution details (insets 100%)
[783kB] - http://vault.designpreference.com/lens_compare.jpg
- Low resolution details (Scaled to 50%)
[234kB] - http://vault.designpreference.com/lens_compare_small.jpg
Magnification / Field of view:
- Pictures scaled to 10%
[240kB] - http://vault.designpreference.com/field_of_view.jpg
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Recommended:
Yes
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