Which extension tube for macro for my Nikon D610 with sig 105mm macro

[glennb]

Hi all Im wanting some extension tubes for my macro Sigma 105mm with Nikon D610. I was thinking Kenko from HK on ebay for $150ish which gives me 12 20 36mm. Anyone recommend anything else?
Cheers
Glenn

[basketballfreak6]

i went with kenko, build is nice, maintains all electronic functions, great bargain as you get 3 tubes, problem free with my old 60D and my current 5D3

and kenko air is the same as nikon/canon air, if you get what i mean

[ameerat42]

Glenn. I am just wondering why you would want to put extension tubes on that lens.
It has a reproduction ratio of 1:1. To even get NEAR double that magnification you're going to probably need all the tubes stacked.
What will happen to your DOF? - Not to mention exposure value.

What sort of magnification are you trying to get with the setup? I found some articles about this and macro in general:
http://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm

One point it says is that extension tubes don't give much magnification with telephoto lenses (they mean compared to standard and wider lenses).

This article gives you the formula for calculating magnification of a lens plus extension tubes:
http://www.dummies.com/how-to/content/choose-the-right-size-extension-tube.html
which I quoted below:

Additional magnification = Extension tube’s length in millimeters divided by the focal length of a lens

For the 105mm lens - OK, what, around f=130mm when closest focused???
Say: Additional mag = 130 / 68 (all tubes stacked) = 1.9 (approx)

Well, I searched on "focal length with extension tubes". There are heaps other refs.
Am.

[glennb]

Thanks guys. Am, really appreciate that info and the links I will look into it a bit more. I was hoping to be able to get that bit closer to insects so I can reduce the amount of cropping and thought it would be good for when I stack images, get the most detail I can.
Cheers


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