2011/3/3 Eric Weir <eew...@bellsouth.net>: > Thanks for posting this, Jostein. Impressed with the frugality of his > "kit" as well as the insects. I'd like to know more about the tubes > and a reversed lens setup, but as I'm not going to be attempting > to emulate him soon -- it would be in still photography -- I'll hold > my questions for now.
Then I'll take the risk of providing a preemptive answer. :-) I'm not the most skilled insect photographer on the list, but the technique is essentially similar to what I use for snow crystals. Toine Kuiper can probably explain this better for the context of insects, but here goes. The extension tubes are pretty straight forward. When you extend the distance between the lens and the focal plane, you also shorten the close-focus distance of the lens. Thus you get more magnification. With extension tubes you get a rigid system with a few fixed extension alternatives. With a bellows, you can choose exactly the extension you want, but with a more flimsy construction. The total magnification you get depends on both the lens used and the amount of extension. For example (rough approximation): A 50mm lens with 50mm extension will give you 1:1 A 25mm lens with 50mm extension will give you 2:1 A 50mm lens with 100mm extension will give you 2:1 A 25mm lens with 100mm extension will give you 4:1 4:1 means the subject will be rendered in 4x life size on the chip. Unfortunately, a non-macro lens is designed so that the plane of focus is actually an arc. The effect is negligable for normal photography, but in the macro range it becomes a problem. In contrast, the rear side of the lens is designed to render focus in a plane. So if reversing the lens, you can achieve a plane of focus where your subject is. With enough extension, the curved focal plane towards the pixel chip is not a problem. For reversing the lens you need a particular adapter, with a K-mount bayonet (the lens part) on one side and a filter thread on the other. Like this one: http://www.bhphotovideo.com/c/product/82191-REG/General_Brand_AV49PS_Reverse_Adapter_Pentax_Universal.html The main challenge with working a setup like his, is that you're on full manual. There's no aperture coupling, so you have to stop down the lens manually. Also, there's no P-TTL. You need to set the flash for manual, and figure out the right combination of flash output and aperture for yourself. Add a diffuser like his, and you are basically down to trial and error to get it right. But once you do, you can use the same setup every time, and concentrate on your motifs. Which is good because as as the guy says, it requires a lot of patience. :-) And do take a look at Toine's webpages. He's pretty darn good. :-) http://www.repiuk.nl/index.php/component/content/article/104-bugs Jostein -- http://www.alunfoto.no/galleri/ http://alunfoto.blogspot.com -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
