Re: Extension tubes, etc

John Taylor [The Banshee] (rphjt@minyos.xx.rmit.OZ.AU)
Fri, 22 Jan 93 20:52:59 +0000

>> 1)Macro lenses---very expensive
>> 2)close-up lenses (as discussed here) cheap but they *do* suffer distortion
>> 3)A "reversing ring" ad J. Del Col mentioned.
>> 4)Extension tubes---these are cheap and also my favorite way to get
>> close-up or even macrophotos. For macro work you should combine
>> these extension tubes with a reversing ring for best images.
>
>I've tried 1 & 2 above.
>
>My problem has always been getting good depth of field. About the only
>way to get everything sharp in, say, a rosetted drosera is the boring
>top-down shot with the lens axis perpendicular to the plane of the
>rosette.
>
>Bright light helps a lot since you can use a high f-stop, but it is
>still a hassle since the lens usually shades the subject.

You really do have to use as high an f-stop as possible (whilst avoiding the
diffraction, etc problems that Barry has mentioned) to get reasonable depth-of-
field. A DOF preview button/lever on your SLR camera is a *great* help for
checking your shots before shooting them. Lens shadow is only a problem for
me when you use extreme magnification (which usually means very short lens to
object distances) or awkward sun positions. Artificial light helps here (but
watch you don't hit the lens directly...)

>Another item I'd really like to get is an enhancement of #4 in Barry's
>list: A bellows system. Unlike a fixed extension tube, a bellows is
>continuously adjustable so that you can get any magnification you want.

At 4 to 5 times the price of a typical 3-tube set... You can get slight mag.
variation using a fixed f-length lens by using the focus setting - it acts
like a zoom lens when you use extension tubes. A zoom lens gives you coarse
and fine zooming using the zoom and focus rings respectively. (However, it
is normally best to set the focus ring at infinity - it may/should help your
depth of field).

I recently bought a set of extension tubes for my camera, and just like my
flash, I haven't used them at all yet! I've had some problems with my zoom
lens causing "shadowing" of the image (the lens axis seems wrong or the moving
sections of the lens are loose?) - I'll have to borrow my parents 50mm fixed
lens (I have always used a standard 50mm lens + tubes for macro photos in the
past with fairly good results).

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| John Taylor [The Banshee] | Royal Melbourne Institute of Technology |
| rphjt@minyos.xx.rmit.oz.au | Department of Applied Physics |
| MOKING IS A HEALTH HAZARD. | Melbourne, Victoria, AUSTRALIA |
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