Macro Magnification with 500mm lens

[David Stephens]

I'm using my EF 500mm f/4L IS on my 7D with the EF 1.4x TC and the EF 25mm ET for bugs and close birds. I'm very pleased with the DOF and ease of working distances and wondering what my magnification potential is. It looks like it's close to 1-to-1 when the subject gets in close.

My question is, what is the maximum magnification of this rig? 1.6-crop sensor body, 500mm lens, 1.4x TC and 25mm extension tube. I know, I could shoot some test shots and measure a 4x6 print, but I'm hoping that someone here knows.

Thanks,

[Alfred Forns]

Hi David I'm sure Roger or Arash will give the exact magnification but with one tube don't think its close to one to one ? ... don't forget to take more tubes and stack :)

[David Stephens]

Hi David I'm sure Roger or Arash will give the exact magnification but with one tube don't think its close to one to one ? ... don't forget to take more tubes and stack :)

Yes, I'm ordering another as I "speak."

[David Stephens]

Not exactly a 4x6, but close. I think that the B'bee is approximately lifesize, maybe a little more. This is from around 15', uncropped, so I think there's more magnification available. (The ET wasn't needed here, but it was on because he was moving around close to me). No critique please, I'm just posting this for informational purposes.

What do you think Alfred?

[Roger Clark]

The 500 plus extension tube was discussed recently in thread:
http://www.birdphotographers.net/for...ight=extension

The magnification, M, is b/a (b and a in the above thread. For the 500mm + 1.4x and 25mm extension tube = 0.2x, or 1/5th full size. (Crop factor has nothing to do with magnification.)

Roger

[David Stephens]

Hi Roger. My understanding of the standard for measuring magnification is what percentage is the subject in an uncropped 4"x 6" compared to the subject's actual size. Is my understanding wrong? If so, what is the measure, expressed in a measured image?

In my example, the bumble bee looks somewhere around life sized, maybe slightly more or slightly less, but close. It's certainly NOT 1/5th full size. The calculated number is so far from what I'm seeing that I think that I'm either not understanding the concept or the calculation is flawed.

[Roger Clark]

David,

Magnification of a camera lens is defined as the size of the subject in the focal plane relative to life size. What you are measuring is the size on the print. That is also a valid measurement, but a different one. In the case of a 4x6 inch print, relative to an APS-C sensor, you had to enlarge the image by 4 inches/0.62 inches, or 6.5 times. So if the bee was life size on a 4-inch high print, it would have been 1/6.5 = 0.15x in the focal plane. That is pretty close to the value I gave for 0.2x for the 500 mm + 1.4x TC plus extension tube at closest focus distance.

Roger

[David Stephens]

So, "life sized" is referring to what we get if we had film the same size as our sensors and made contact prints, right? That definition is, understandably, a relic from a largly bygone era. No wonder there's so much confusion.

I kind of like the definition of "life size" where it's actually related to something that we use for viewing an image, like a 4"x6" print. I don't know where that idea came from, but it makes lots of sense to me. That truly is "macro performance" level and makes more sense than touting minimum focus distance as the measure of macro performance. How large the image is on the sensor has lost a lot of relevance, at least in my mind.

[Roger Clark]

So, "life sized" is referring to what we get if we had film the same size as our sensors and made contact prints, right? That definition is, understandably, a relic from a largly bygone era. No wonder there's so much confusion.

Life size refers to the size in the focal plane. It is independent of film or sensor and this definition of the magnification of an optical system has been in use long before film.

I kind of like the definition of "life size" where it's actually related to something that we use for viewing an image, like a 4"x6" print. I don't know where that idea came from, but it makes lots of sense to me. That truly is "macro performance" level and makes more sense than touting minimum focus distance as the measure of macro performance. How large the image is on the sensor has lost a lot of relevance, at least in my mind.

One could equally argue that 4x6-inch prints are old and that many people don't print anymore so it does not apply. Then the rest of the world could argue it should be "A" size paper, etc. If one includes enlargement one could then argue that a telephoto lens is not actually 500 mm, but 8,000 mm because one makes 16x24-inch prints from an APS-C digital camera. Then for the same size print, different cameras produce different "magnifications" with the same lens. It is a slippery slope.

And then when someone posts an image on a web site, what is the magnification; is it still defined relative to a 4x6 inch print?

So by trying to redefine macro to include the print, and a 4x6-inch print in particular, makes the situation much more complex in my opinion.

The optical definition of magnification has withstood the test of time, whether before film or digital, whether large format film, or P&S fingernail sized digital sensor.

But it is equally valid to specify the equivalent magnification of a subject on a particular output, whether print or screen, whatever size that may be. Just don't confuse that with the original in camera magnification by the lens, nor confuse it with some reference to 4x6-inch prints. Just like lens focal length. which is now more confusing than ever. We have "35mm equivalent focal lengths" from crop factor. This has led to so many misconceptions in modern photography, that in my opinion is the most confusing and most often incorrectly described subject in photography, surpassing depth of field. If we now redefine things to include enlargement, today will seem simple compared to the confusion that will come next. -- Just my opinion.;)

Roger

[David Stephens]

All good stuff Roger, but magnification is tied up in the same confusing mix as "35mm-equivalent." Latching onto 35mm as an equivalency size is every bit as arbitrary as a 4"x6" print. It was comparing DSLRs to SLRs and forgetting that there were other SLR formats. 35mm was merely the most commonly used at the time of the transition to digital.

The optical definition of magnification probably has its photographic roots in glass plates that were not typically enlarged. "Life sized" on the plate was "life sized" on the print.

I've read a lot lately about "what is macro" and it's very, very rare for discussion of "life sized" or "1-to-1" or ".2-to-1" to mention anything about "at the sensor."

Anyway, I now clearly understand the measure and the confusion surrounding it and I'll do my best to not add to the confusion.

Thanks for your valuable input Roger.

[Roger Clark]

I've read a lot lately about "what is macro" and it's very, very rare for discussion of "life sized" or "1-to-1" or ".2-to-1" to mention anything about "at the sensor."

David,
This is not surprising. The internet is a two edged sword. It allows a lot of information to be transfered. Unfortunately, it also allows a lot of misinformation to be transferred. And sometimes that misinformation gets perverted and misused so often it becomes the norm. Sometimes as truthiness (now an official new word; word of the year 2006), and sometimes as a torquing of the meaning of a word so that language must evolve to accept the new meaning (e.g. prime lens).

Crop factor telephoto reach (truthiness)

http://www.merriam-webster.com/info/06words.htm

;););)

Roger

[David Stephens]

My truthiness is beyond repute.

Thanks Roger