I'm very interested in macrophotography and I'd like to take photos to the human eye. I have the Canon EOS 80D body and I'm also considering buying the Canon EF 100mm f/2.8L IS USM Macro Lens. I'd like to take images as the one I have linked below. So, my question is whether I could achieve such results with this gear? Is 1:1 magnification enough for this? (Or do i need greater than life size) and what other considerations should I consider for macro photography?
From what I can gather, the average adult human iris diameter is about 12mm, so superimposing that onto your sensor size (about 22mm by 15mm) gives you an idea of what you'll get through a 1:1 lens like the one you mention. Other considerations will include:
getting a subject to hold very still (not just their head, but their eyes) and/or being able to work fast, if you want to have artistic control over the outcome and be able to focus precisely
getting light where you want it, given the small distance between the lens and the subject, and enough of it so that you can work with the small apertures needed for reasonable depth of field, and in such a way that it isn't harmful to the subject
not causing your subject to blink due to TTL pre-flashes, meaning you'll probably want to set the flash power manually. Doing so will also help with the next point:
you'll need to be able to keep the camera and subject from moving AT ALL for the brief time between acquiring desired focus (by whatever means) and when the flash fires (at macro scales, even otherwise imperceptible movement can change the point of focus from the one that you wanted).
The reflection on the left side hints that this photo was taken with a flash fired through a grid (you could use something like this DIY version) from the side. This gives a very focused directional lighting that will bring out the texture. Using flash will allow you to adjust ambient lighting to allow for the amount of pupil dilation you want.
A small LED light stuck on the flash can provide contrasty, but not overly bright, focus-assist lighting. I've actually built LEDs into black straw grids like the one linked to, in which case it also serves as somewhat of a modeling light, so that you can see where the flash is going to hit.
That's what I can think of from a general macro-shooter perspective; someone with more eyeball experience may have more to add.
A 1:1 macro lens such as the EF 100mm f/2.8 IS Macro will get you very close, but might not get you quite all of the way to where you want to be. There's a unique lens that will give you much more room to play with: The Canon MP-E 65mm 1-5x Macro Lens.
This lens is designed to do one thing only and to do it very well: shoot macros. In order to excel at macros, it gives up most of the versatility of more conventional macro lenses. It can shoot only macros and nothing else.
At each magnification setting it only has a single focus distance. At 1X the working distance (the distance between the front of the lens and the subject) is a bit over 100mm. At 5X the working distance is a mere 41mm. The working distances are printed on the lens barrel right next to the magnification markings. The easiest way to focus without changing magnification is to use a focusing rail on a tripod. A focusing rail allows you to slide the camera forward/backwards to move the point of focus with respect to the subject.
Although Canon calls it a 65mm lens it doesn't really have a focal length in the conventional sense at all. Focal length is defined using collimated light at infinity. But the MP-E 65mm 1-5X Macro can't focus at infinity at the register distance for which it is designed. As mentioned above, it can't focus at any distance except the minimum focus distance at each magnification setting. To focus the subject without changing the magnification the entire camera must be moved forward or backward until the desired point on the subject is in focus.
What you do get when set to 1X is a field of view at 1:1 that is equivalent to a 65mm lens focused at a 1:1 reproduction ratio. What you get at 5X is a field of view at a 5:1 reproduction ratio (yes, 5:1 and not 1:5) that would be equivalent to a 325mm lens focused at a 5:1 reproduction ratio if it were possible for a 300mm to extend that far and focus on an object located somewhere between the front of the lens and the sensor!
Another option to increase magnification is to use extension tubes or a teleconverter with a Macro lens or even a non-Macro lens. Just be aware that using extension tubes with a macro lens is a tightrope of sorts: The longer the lens' focal length, the further you need to extend it to get the same increased magnification. With standard extension tube lengths you increase the magnification of longer focal length lenses less than you increase the magnification of shorter focal length lenses. So extension tubes work better for most users with shorter focal length lenses. With a 25mm extension tube the EF-S 60mm f/2.8 Macro has a MM of 1.61X. The EF 100mm f/2.8 IS with a 25mm extension tube increases to 1.39X.
