Working distance of EF 100mm f/2.8L

[RobertCampiin]

I would greatly appreciate it if someone could tell me the working distance to the front of the lens of the 'L' version of the Canon 100mm EF macro lens, i.e. 100mm f/2.8L when at maximum magnification of 1:1.  Unfortunately, various on-line reviews of this lens list its working distance at 1:1 as 13.2 cm, 13.3 cm, 14.0 cm, 14.6 cm, and 14.9 cm.  It turns out, I only have 13.9 cm to work with, so the precise working distance at 1:1 matters.  Yes, I'm aware of the Canon 180mm macro, but its nearly 30-year-old design has lower resolution than the 100mm 'L' that was designed more than a decade later.  Thanks in advance for your help.

[kvbarkley]

Ken Rockwell says 133 mm

https://kenrockwell.com/canon/lenses/100mm-f28-is.htm

[RobertCampiin]

Thanks for that, but the problem is on-line reviews, including Ken Rockwell's, differ from each other.  Because of this, none are to be trusted to be accurate prior to me spending the better part of $1000 to buy the lens.  If someone reading this, who owns this lens, could set it for maximum magnification and measure the distance, I would greatly appreciate it. 

To contribute a measurement of my own to this discussion, I own the older 100mm macro, designed about a decade before the 'L' version.  Setting the camera on the table with a ruler lined up with the end of the lens, it took less than 2 minutes to sneak up on the lens with the lid of a box.  It would focus at 14.8 cm, but not at 14.7 cm, so that's its working distance.  That distance would be great if it were the case for the newer lens, but it's of a different design, for which on-line reviews differ.

[p4pictures · Accepted solution]

Hi Robert,

I have the EF 100mm f/2.8L Macro IS USM lens. The lens does not change its overall external length as it uses an internal focus design. 1:1 magnification is achieved at the minimum focus distance of 30cm. This distance is measured from the film plane on the camera. The flange distance for EF lenses is 44mm. The EF 100mm f/2.8L Macro IS USM lens is 122mm from the front to the lens mount. This added to the 44mm to the sensor means that the distance in front of the lens is 134mm, or 13.4cm. 

I then also carried out your test with a subject in front of the lens, and with the lens at minimum focus the subject was sharp when it was 134mm from the front of the lens.

For my test I used a Canon EOS R6 with Canon EF to EOS R mount adapter, though this only provides the necessary spacing so that EF lenses are 44mm from the sensor when fitted to mirrorless cameras.

[RobertCampiin]

I bought a 100 mm f/2.8L to replace my non-L macro (which will be passed along to on of my granddaughters), and made my own measurements.  When the lens is manually adjusted to the closest focus distance, I measured the distance from the filter mount to the object to be 132 mm, rather than the 134 mm reported by Brian.  Also, if someone needs the very last micron of distance, the lens itself is recessed by 3.1 mm behind the filter mount.  For the non-L lens, I repeated the measurement I reported a few months ago and got the same result; the distance from the filter mount to the object is 148 mm.

[RobertCampiin]

>at minimum focus the subject was sharp when it was 134mm from the front of the lens.

Darn.  That means the lens won't work for my purposes.  Well, at least it saves me ~$1000...

Thanks very much for conducting the actual test.  I sincerely appreciate it. 

[kvbarkley]

Some of this could be sample to sample variation.

You can always rent one to check it out.

Of course, if you can live with 0.95 magnification - or whatever - you can set a longer focal distance.

I don't know about macros, but I doubt that the focal length for any given lens is better than 5% anyway

[RobertCampiin]

>Some of this could be sample to sample variation.

>You can always rent one to check it out.

Renting one wouldn't be a solution. Even if the working distances varied by that much, which is unlikely, and the rental company happened to have a "long" production version, the one I then spent my money to buy easily could be a "short" version.  No, Brian had the correct answer.  Sadly, though, he didn't provide the solution, i.e. the name of an aftermarket macro lens having 140+mm working distance and at least the lp/mm resolution of the Canon 2.8L.  

[spencerselvidge]

Stumbled onto this forum post looking for similar info. Are you looking for less than 13.9cm or more than 13.9cm? I am unclear. 

I need >152mm or 5.9in (of minimum working distance) to achieve 1:1 reproduction on a full frame camera for an automatic slide scanning machine I built out of a Kodak Carousel projector. Works great but I need a longer Min. Working Distance (MWD) unless I want to do some serious and irreversible Dremel damage to the front of the projector. 

Of course as you pointed out there are discrepancies on various websites. This site incorrectly does the math for the MWD on the 100mm L , claiming 5.9inches is 146mm when it is actually 149.86mm. But I personally know 5.9" is still not close to the 1:1 on that lens. So I am inclined to believe the "Accepted Solution" above as accurate. If it fits your use care, you are good to go. I would be confident. Also, many camera shops would let you test on the spot and should carry this lens in stock. Camera and lens makers are notorious for rounding their numbers. You can verify here by choosing scenario 3 of 3 on any lens (on the top right), though its very, very technical. This site uses the lenses actual measurements rather than the claimed values: https://www.photonstophotos.net/GeneralTopics/Lenses/OpticalBench/OpticalBench.htm#Data/US007864451_... 

If you are looking for < 13.9cm MWD, the Sigma 70mm Macro ART is an INCREDIBLE value. It's MWD is 82.25mm. I use it for all my 1:1 needs except my special use case of the projector. Dollar for dollar (<$500) it blows away the competition and still has autofocus: https://www.closeuphotography.com/1x-test-2020/2019/12/13/1x-magnification-test-2020 

If looking for > 13.9cm MWD, the Sigma 150mm Macro may work well. This one has a MWD of 186mm. It is the one I am getting for my Kodak "scanner" needs:
https://www.the-digital-picture.com/Reviews/Sigma-150mm-f-2.8-EX-DG-OS-HSM-Macro-Lens-Review.aspx

My EF 100mm L is nice but leaves me with a lot of unused sensor on my R5 in my case.  The closest I can get it before the front plastic hits the Kodak machine is 5.9" which cuts off a lot of the sensor. Thought I use the sharpest, center part of the lens at about 1.35:1 - AKA 0.73x reproduction - I lose a lot of potential resolution getting only 33MP instead of 45MP. Though I don't know where the lens is most optimized for sharpness, I suspect it is not at 1:1... though it is a specialized lens to get there. 

[Tronhard]

Hi Spenser and welcome:
Please, to avoid confusion between two posts for similar but quite different and detailed issues, please start your own thread, so we won't get mixed up with whom we are engaging.