November 26, 2014, 04:31:12 AM

### Author Topic: extention tube calculations? help needed.  (Read 1108 times)

• Rebel T5i
• Posts: 120
##### extention tube calculations? help needed.
« on: April 27, 2013, 05:58:57 AM »
hi, i bought a set of extention tubes for my macro work.

i need someone who can to explain to me how to calulate the new MFD and magnification.

for example when i put a 25mm extention tube on my 90mm macro that has 29cm MFD and 1:1 magnification... what is the new MFD and magnification?

or what if i put a 31mm extention tube on my 70-200mm f4.

is there maybe a good website that explains how to calculate this?

#### canon rumors FORUM

##### extention tube calculations? help needed.
« on: April 27, 2013, 05:58:57 AM »

#### J.R.

• 1D X
• Posts: 1515
##### Re: extention tube calculations? help needed.
« Reply #1 on: April 27, 2013, 08:13:34 AM »
5D3, 6D, 600D, RX100
16-35L, 24-70L II, 70-200L II, 100-400L, 50L, 85L II, 135L, 24TSE, 40, 100 macro, 18-55 II, 55-250 II, 600RT x 4
I come here to learn something new, not to learn how bad my gear is - I know that already ;-)!

#### TW

• PowerShot G1 X II
• Posts: 55
##### Re: extention tube calculations? help needed.
« Reply #2 on: April 27, 2013, 08:25:36 AM »
Simply divide the amount of extension by the focal length pf the lens. 25mm ext/ 50mm lens = 1/2x, or 50% magnification. Also, just take a pic of a ruler and do the math!
35+ years of Canon gear...good grief! Still have 2 FTb cameras in working order, too!

#### Canon-F1

• Guest
##### Re: extention tube calculations? help needed.
« Reply #3 on: April 27, 2013, 08:55:25 AM »
Also, just take a pic of a ruler and do the math!

yeah why not invent the wheel again.

sure much easier to do that for a dozend lenses * 3 extention tubes then searching a formular.

Quote
http://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm

+1

was going to post that.
« Last Edit: April 27, 2013, 09:00:28 AM by Canon-F1 »

#### canon rumors FORUM

##### Re: extention tube calculations? help needed.
« Reply #3 on: April 27, 2013, 08:55:25 AM »