FOV for RF 100mm F/2.8L Macro IS USM macro

[MarkNot2]

Hello: Could you please provide information on the field of view, if objective RF100 mm f/2.8L macro (on EOS R6) is placed 50 cm above the in-focus specimen to be pictured? The official answer to that question is "is 23°10" but I very much would appreciate specifications such horizontal x vertical (in cm or inch). Thanks you!

[AtticusLake]

Hi,

The field of view of a lens is normally quoted as an angle, because then the distance doesn't matter.  But the field of view also depends on your sensor size, because that determines how much of the lens' image you are actually capturing.  For that lens, on a full-frame camera, the field of view is about 20° wide by almost 14° high.  I have no idea what "is 23°10" is - unless that's the diagonal?

Anyway, good news, what you're looking for - the actual size of the subject at a given distance - is easier.   If we define the following:

• S - sensor size
• F - lens focal length
• D - distance from camera to subject

then the size of your subject is just

• D * S / F

For size, use the horizontal size of your sensor (36mm for you) to get the horizontal size of the subject; use the vertical size of your sensor (24mm for you) to get the vertical size of the subject.  Make sure your units are consistent - if your focal length is in mm (it is) then everything needs to be in mm.  You can convert to inches when you're done.

So, your 100mm lens, on a full frame sensor, 500mm from the subject, the subject size ("field of view" as a dimension) will be 180mm wide by 120 mm high.  About 7.0 by 4.7 inches.

If that's too big, bear in mind that lens can focus a lot closer.

[MarkNot2]

Thanks a lot!

"23°10" (an answer provided by Canon through communication with provider) also sounded to me like "42". What you wrote makes sense. The problem was that we also got the recommendation of 95 cm (required distance for a 9 cm specimen) and that would have been climbing a ladder for each of the many we document. Thanks.

[AtticusLake]

Glad to help!  Yeah, 95cm for a 9cm target is way off for a 100mm lens.  I just tried it on my camera and that's nowhere near.

BTW I'm not sure where that distance is measured from - which will start to matter if you get close.  It seems to be some point within the lens but I'm not sure where.  Maybe someone who knows optics better can help.

[MarkNot2]

I understand that it is the crossed-through circle on the heighth of the position of the flash-light on top of the body, from where the minimal distance is measured, at least this is the case with an older 77d and a 60 mm macro-lense. A similar crossed-through circle is also drawn on the R6 body. The minimum distance is not what is required at my side, but 9 cm diam petridishes with fungal cultures. For doing so, I am sure that I will come back with many questions that relate to colour reproduction. Thanks again!

[AtticusLake]

The crossed-through circle marks the position of the sensor.  I'm not sure that applies to the macro focus distance - but I could be wrong.

[FloridaDrafter]

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@AtticusLake wrote:

The crossed-through circle marks the position of the sensor.  I'm not sure that applies to the macro focus distance - but I could be wrong.

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Hello, Atticus.

It is indeed measured from the sensor.

Newton

[AtticusLake]

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@FloridaDrafter wrote:

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It is indeed measured from the sensor.

Yeah, that's what I would have guessed, and of course that's what you would use for focus distance.  But for field of view, the numbers don't seem to work out.  I get the calculated field of view when I measure from about half-way down my lens.  The entrance pupil, perhaps?

[FloridaDrafter]

Thanks, Atticus!

Honestly, due to the way I shoot macro (my subjects), I've never thought about FOV. Typically, I start at MFD or in the case of hand holding, as close as I can get.

Newton