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Central Length in Reverse Lens Macro Method

Macro, Landscapes and Seascapes are usually my favorite genres in photography, yet as I don’t travel much, We tend to shoot more macro within my backyard. Last time, I published an article on high magnification macro photography on a tight budget , where I pointed out the truth that I use the reverse lens method in order to achieve high magnification macro photos. The technique really works great in case you give it a try and the good news is that you do not require expensive gear to yield gorgeous macro shots – a cheap package lens will do wonders!

But have you ever considered why reverse-mounting a lens on your camera body makes it act like the macro lens? Actually, the truth at the rear of it is that flipping a zoom lens around by itself doesn’t automatically indicate converting it to a macro zoom lens. Basically, reverse mounting a zoom lens moves the lens farther far from the camera, giving it the ability to concentrate at closer distances, which has a comparable effect as using a set of expansion tubes. Both ends of the zoom lens are not made equally. For an perfect lens, flipping it would make simply no difference. However , in real lens, real compromises have to be made. The rear part of the lens is typically designed in order that it will project the image on an even plane close to the lens. This allows for many optimizations in the lens design. Because the front part of the lens is meant to pay attention to more distant objects, different optimizations can be made there. Simply put, the lens is normally made to take specific field-of-view and project it on to a sensor, which is relatively smaller when compared to the entire scene. Hence, simply by reverse mounting a lens on your camera body, you are simply having the opposite projection by taking a small picture and projecting it much larger.

Focal Size

With the reverse zoom lens macro technique, focal length will probably behave in a different manner. Whilst in the case of a real macro zoom lens you need a longer focal length to improve the effective focal length, therefore enabling you to focus progressively closer, while using the reverse lens technique, zooming within triggers the opposite reaction: it decreases the effective focal length out of your lens to the sensor. This means that the shorter focal length in the invert lens technique would result in higher magnification, allowing you to focus much nearer to your subject, while a longer central length would result in reduced magnifying. To explain this more clearly, I got captured a couple of macro shots from different focal lengths:

From the above shots, you can observe how focal length acts within an opposite manner to magnification within our reverse lens macro setup (focal length is inversely proportional towards the magnification).

But perhaps you have noticed something strange in the over pictures? As my focal size decreases, resulting in greater magnification, our image gradually gets darker plus darker, despite the fact that I shot every images at exactly the same exposure configurations. Why is that? The reason behind it, would be that the lens’ effective f-stop increases, which includes an increase in depth-of-field, resulting in more dark images. I will talk about this in more detail in my next article and for right now, I hope you found the above details useful!

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