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]

>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.