Kenko Extension Tubes Question

windoze

i have a sigma 150 macro. my primitive understanding is that you have to be at least 38 cm away from your subject. does that apply only for AF or can you get closer if you want to use manual? when i add a kenko extension tube
( say 12mm ) what does that allow me actually to do, eg. can i now get closer than 38 cm? if im not being clear let me phrase it this way "when i put the tube on the cam, can i now break the 38 cm barrier"?


troy

ziggy53

Troy,


My experience with a Pentax macro lens and extension tubes:

The extension tubes will let you get closer, but distortion in the corners will also increase. At some point you will get better restults using a reversing ring adapter so that the lens works in the opposite direction. A macro lens designed for bellows use is also OK for extension tubes use.

Another interesting technique is to combine two lenses to give extreme macro and even micro distances.

Ane excellent article that covers the popular techniques is:

http://www.nikonlinks.com/unklbil/macro_adapter.htm

ziggy53

windoze

Ziggy, thanx!!

Now why would reversing a lens be better? Why didnt they make it that way in the 1st place if it lets you get closer???



troy

ziggy53 wrote:

Troy,


My experience with a Pentax macro lens and extension tubes:

The extension tubes will let you get closer, but distortion in the corners will also increase. At some point you will get better restults using a reversing ring adapter so that the lens works in the opposite direction. A macro lens designed for bellows use is also OK for extension tubes use.

Another interesting technique is to combine two lenses to give extreme macro and even micro distances.

Ane excellent article that covers the popular techniques is:

http://www.nikonlinks.com/unklbil/macro_adapter.htm

ziggy53

ziggy53

windoze wrote:

Ziggy, thanx!!

Now why would reversing a lens be better? Why didnt they make it that way in the 1st place if it lets you get closer???



troy

Remember that most lenses are designed to be used asymetrically, that is, they are normally used close to the film-plane (imaging-plane) and give greater distance to subject. At extreme magnifications, more than 1:1, reversing the lens puts the asymetry to your benefit, at the expense of working distance.

Macro designs tend to be more symmetrical, but can still benefit from reversing, usually!

ziggy53