Wednesday, 11 January 2017

reflection vs refraction

One of the terms you may have come across at while photographing water are terms reflection and refraction. Reflection refers to whatever picture/object reflects off the surface of the waterdrop, where refraction is the image inside the drop, which is being refracted by lens-like properties of water.

Water and liquid droplets are in fact tiny, natural fisheye lenses and it is this property that allows us to capture all kinds of images inside them, and the more tiny the subject inside the droplet is, the more narrow will our field of focus be, resulting in more surrounding areas being out of focus, which is called “bokeh”.

Equally interesting is the droplet surface and indeed many droplet photographs aim to capture the outside primarily.

One of the things that usually don’t happen is that you will manage to perfectly focus on the outside and the inside at the same time. In fact, when focusing on the image refracted inside, you are moving the focus away from the surface, and as our focal distances are very tiny, that results in blurring of one or the other. So, except in vary rare circumstances of using extremely small f-stops like f45, if we aim to capture the image inside the drop, the outline and whatever the drop is placed on will largely be out of focus, with only a small line of focal area, whereas if we focus on the outside of the drop, the inside will be more blurry.

It’s also worth mentioning that liquid droplets are not perfect optically and in nature, it is not possible to capture the image inside it as perfectly sharp. Due to properties of liquids, their composition and impurities, all images captured inside the droplets are slightly soft.

Also, all refracted images are subject to distortion due to fisheye-like properties of droplets.

Various pieces of software and techniques such as focus stacking (insert link) which aim to overcome some of the shortfalls of the cameras as well as human vision, by using multiple frames and computer programs to compile a final macro image. These programs will stack usually 7 or 8 images such that in the final mage, the inside and outside of the drop as well as whatever the drop is placed on is all sharp at the same time.

Macro Fun by Rick Reiff

This technique is most often used if shooting at extremely high magnifications, such as subjects of 1-2 mm or smaller, with lenses such a MPe65, but it can be used to achieve perfect sharpness along different focal planes regardless of the lens.

Personally, I feel strongly that if used, focus-stacking should be clearly declared in the artist’s statement (such as it is in the picture above), because otherwise we may unwittingly be putting unrealistic expectations on natural (single frame) macros. To draw an analogy with people who had plastic surgery -they are still people and in no way inferior just because they had their appearance cosmetically altered, but if this is undisclosed, it will put unrealistic expectations on people who do not want to go in that direction because they may, in comparison, be viewed as “less perfect”. Certainly this will have most effect on young people, beginners or everyone unfamiliar with the subject (as you can imagine, a surgeon is a lot less likely to believe certain proportions on a model are natural than perhaps a young teenager who does not have the benefit of life experience and technical knowledge).

Metaphors aside, it is important to understand the physics of water and be familiar with all the available techniques available in macro as well as extreme macro photography. I’ve had heated discussions with several insect photographers who use focus stacking all the time, without declaring it because in more technical circles this knowledge is assumed. They were convinced that non-focus stacked droplet refractions are technically and visually “inferior” because they have much more shallow depth of field. Also, they felt very strongly that focus-stacking isn’t a photomanipulation, because it is necessary at extremely high magnification.

So, a happy medium that I achieved in my mind was to accept focus-stacking as simply a piece of equipment used in extreme macro (magnification 2:1 and higher), but to see it as photomanipulation (which needs to be declared) when shooting droplet refractions at less than 2:1.

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