Macro Lens working distances

[jeremy_craig]

Partly in confusion regarding another poster's query a few down from

here (regarding merits of 50mm vs. 100mm macro lens):

 

I'm confused a bit on relative merits of a 100mm Macro vs. 50mm Macro.

 

Using the Canon lens line-up as that's what I had some info on, their

usa.canon website indicates that 1:1 working distance on 100mm lens is

5.9". This somewhat makes sense since lens is about 4.75" long and

minium focus distance is 12"... but not exactly.

 

The 50mm "working distance" isn't listed, but the minimum focus

distance is indicated as being 9" -- given that lens is 2.5" length,

wouldn't working distance be 6.5" (or more than the 100mm)?? Also

mentioned is fact that if you use the lifesize converter, it INCREASES

working distance.

 

And the 180mm Macro L lens has min focus of 18.84", but given lens

length is 7.375, effective does this give you 11.5" working distance?

[tom_montemarano]

Is the lens length in each case, the length when the lens is fully extended for close focusing?

 

Tom

[jim_strutz]

I don't know the answers in detail, but I believe minimum focusing distance is from the film plane. So you have to subtract the lens length, and also the lens mount to film plane distance as well, to find the "working distance." Your calculations seem to be missing that last part.

[jeremy_craig]

Jim, I'm sure you're right on that point... although I'd guess safe to say that the lensmount-to-film distance is a constant no matter what lens is mounted, no?

 

Basic gist of what I'm getting at is that I've seen lots and lots of posts really advising folks to get 100mm macros instead of 50mm for the "extra working distance". Trying to find out how much is really gained (maybe less than 1 inch -- is it worth it)?

 

Also, just from pictures mind you, but a lenshood for a 100mm lens looks quite a bit longer than a lenshood for 50mm. some more food for thought.

[richard_oleson]

the 100mm working distance is for 1:1 magnification, and the 50mm would be for 1:2. at 1:1 on 100mm, the nominal lens-subject distance should be about 8"... so 5.9" actual clearance to the subject sounds reasonable since the lens has a deep integral hood in the barrel. at 1:2 on the 50mm, the nominal lens-subject distance is about 9"... working distance would be a little less than that for the same reasons as above, perhaps 7 to 7.5". at 1:1, the 50mm of course would be much closer, working distance would only be about 2-3" depending on the barrel design.

 

i'm not familiar with the 180, but i'd guess at a 18.8" minimum focus you'd probably have a working distance of about 15 inches.

 

rick :)=

[jon_crayg]

Sounds good, Except that Canon's lens info site anyway, says that the 1:1 "lifesize" converter for the 50mm macro INCREASES working distance -- not the reverse... so I guess I'm still confused or unclear of what the advantages are of say a 100mm Macro over a 50mm Macro -- given at least in Canon's line that the former is about twice the cost of the latter.

[jimstrutz]

I've never used one, but isn't the lifesize converter really just a dedicated TC & closeup combo? If so, maybe the 50mm macro is being bumped to an 70mm or 80mm macro.

 

I have the cheap Vivitar 100mm f/3.5 macro and it uses a dedicated closeup lens to make it go to 1:1. Of course, that really makes the lens the equivilent of 75mm, or some such thing. So the effect is just the opposite of the Canon lifesize converter.

[johnlund]

I can confirm that the working distance of the 100mm USM macro is just under 6" at life-size. I read elsewhere in these forums that the 180mm yields about 10" at 1:1. I didn't find data on the 50mm (at 1:2).

 

As noted earlier in this thread, the one element you left out of your equation was the distance from the rear of the lens to the sensor plane, which I estimate to be 42mm. (Does anyone have authoritative data on this?) Here are the results of my working distance calculations: 50mm=4.9", 100mm=5.9", 180mm=9.9".

 

I'd like to know more about the life-size converter's side effects, including a specific working distance. IMO its $200 price tag makes it less attractive than buying a 100mm in the first place.

 

Speaking of relative merits, I've read that the 100mm uses internal extension to achieve magnification -- some say to the equivalent of a 70mm macro lens. I've never seen any hard data on the matter, but I get a loss of about 1.6 stops when dialing from infinity focus to life-size. Can anyone tell me if the 180mm does something similar?

[richard_oleson]

The only kind of "1:1 adapter" that would increase working distance would be a teleconverter... in this case, you'd get 1:1 at the same distance where the lens alone gave you 1:2, so for any given magnification you do get more working distance than you got without the converter. i do this often because it's a lot handier than the extension tube and the close distances that come with it. i don't know of any advantage this would give over a 100mm 1:1 macro lens though, unless you have applications that need the 50mm perspective.

 

as for light loss, i think you'd generally expect to lose about 2 stops at 1:1 due to lens extension, so the loss through a converter isn't too much worse.....

 

:)=