100-400 and extension

[jeff_nolten]

I have both a 100-400 and 500D. While the 500D is nice for some applications, the maximum working

distance of ~18" is often too close. So my question is what length of extension, 12 or 24 mm, would bring

the 100-400's minimum focus distance down to about 24" (at 400 mm) and then what would the

maximum working distance be? A typical use for this setup would be chasing butterflies around rather

than true macro work. I could buy the full Kenko set of tubes but if a 12 or 24 would do, I could save

some money.

 

Thanks for your help.

[mark_chappell]

<I>... what length of extension, 12 or 24 mm, would bring the 100-400's minimum focus

distance down to about 24" (at 400 mm) and then what would the maximum working

distance be? </i><P>

 

I think you are going to have to experiment with this to be sure, but probably<B> a lot

</b> more than 24 (25?) mm of tubes will be necessary. I'd estimate that the

reproduction

ratio at 24 inches would be roughly 1:2 (1/2 life size). Since the reproduction ratio of a

simple (non- internally focusing) lens is about equal to extension/focal length, you would

need 200 mm of tubes to take a plain-vanilla 400 mm lens to 1:2 purely by extension.<P>

 

With a real-life 100-400 you would need less than 200 mm of extension, given that (a) its

'native' focus ability gets to about 1:5 and (b) the lens is not really 400 mm at closest

focus (more like 360 mm or so, due to internal focus mechanisms). Nevertheless, you'll

need much more than 24 (or even 36) mm of extension to do what you want to do.<P>

 

Somewhere on the web is Julian Locke's lens calculator, which may give you a more exact

answer, but I can't find the URL.<P>

 

FWIW, I often use extension tubes with my 100-400, but for tight closeups I usually rely

on the 500D. To approach the same magnification with a 25 mm tube I have to zoom

back to ~ 150-200 mm or so -- with an extension tube, the magnification increases as

focal length decreases, the opposite of what you get with the 500D.

[eosdoc]

<a href=

http://ca.geocities.com/lokejul/jlcalc.htm

>http://ca.geocities.com/lokejul/jlcalc.htm</a><BR>

<a href=

http://eosdoc.com/manuals?q=100-400LIS

>http://eosdoc.com/manuals?q=100-400LIS</a>

[mark_chappell]

Loke.... Locke..... <B><I>THAT'S</b></i> why I couldn't find it!

[jeff_nolten]

Well thanks for the info. The lens calculator helps a lot! I've book marked it and will

certainly use it again.

 

Looks like I need to buy the kenko set. The 36 mm on the 100-400 gives me a 4.7' - 15'

range and with the 500D I get 1' and 1.4X magnification. With the 70-200, the 20 mm

gives me a 3'-11.5' range and with the 500D 1' and .87 X magnification. Interestingly, on

the 100-400 the whole extension doen't get me much more just as you said.

 

Thanks again and cheers -Jeff