Short focal length macro lens design?

Started May 21, 2009 | Discussions thread
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SteB
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Short focal length macro lens design?
May 21, 2009

As someone who tends to specialise in macro photography there is one area of macro lens design that I find quite irksome on the shorter focal length macro lenses. At or close to their minimum focus distance there is not a great deal of working distance with shorter focal length macro lenses. The recessed front element of a lot of these lenses is fine at slightly lower magnifications, but a pain close-up. Not only is there the issue of shading (not just with natural light, but with insects it causes them to move away) but the end of the lens constantly gets in the way and fouls nearby vegetation. Especially for insects and other small invertebrates this is a big problem. You simply can't get at lots of them because the end of the lens is too big and if the end of the lens so much as touches anything connected to what the insect is resting on, it immediately flees. Also it prevents you from getting a low enough angle on something resting on a flat surface.

So I got to thinking about what purpose that big end bit of the lens and the filter thread serves in this type of lens. Often the front element is quite small and the lens diagram appears to indicate that there are no optical part that needs all this surrounding structure. Although I do realise that sometimes the extending inner tubes need to be housed somewhere. However, I think a lot of these macro lenses are simply designed like this out of convention i.e. because that is what lenses look like.

From a usability point of view though it would be much better if the end of the lens was more cone shaped with the surrounding part to the front element being as narrow in diameter as possible. If it was still thought necessary to have a conventional recessed end to the lens for longer distances it would be quite easy to have a removable end that screws/bayonets on and off. I got the idea after seeing some special macro lenses used by wildlife movie/videographers which look like a long tube (I did find out what these lenses were but I've forgotten the name/link - but they are ultra expensive, normally hired, and no longer produced). This design allows them to get much lower angles. Anyone who photographs insects etc. a lot will know how important it is to get as low as possible with many shots and even a small change in angle makes the difference between a mediocre shot and one with real visual impact.

So I'd like to ask those with an interest in this sort of thing, or who are knowledgeable about lens design - about whether this sort of lens could or should be made. In other words have lens designers just stuck to the current design out of convention, or is there some reason for the great big surround to the small elements on the front of these shorter focal length macro lenses.

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