# How to know your ratio using extension tube?

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#### Del_CtrlnoAlt

##### Senior Member
Anybody know how 2 calculate the ratio if i use extension tubes?

now i have a 13mm, 21mm, 31mm no autofocus set, & another 25mm kenko autofocus.

problem is i dunno what magnification if i combine all to use together...

den the most funny thing i tried is using with a 28-75, totally cannot use... wonder why... with all together, i can still focus with a 75-300 at 75mm range.

the cam i using is Dynax 7D, so is the 1.5crop a factor for the magnification as well?

#### ortega

##### Moderator
Staff member
Take a referance photo of a ruler scale and measure.
Simple solution to a difficult question.

Just shoot it!

#### ortega

##### Moderator
Staff member
Another unit of measure is

Cool, Way cool and blow me away. ha ha

#### eawtan

##### Senior Member
Checkout : http://xoomer.virgilio.it/ripolini/Introduction to closeup.htm#Extension

Del_CtrlnoAlt said:
Anybody know how 2 calculate the ratio if i use extension tubes?

now i have a 13mm, 21mm, 31mm no autofocus set, & another 25mm kenko autofocus.

problem is i dunno what magnification if i combine all to use together...

den the most funny thing i tried is using with a 28-75, totally cannot use... wonder why... with all together, i can still focus with a 75-300 at 75mm range.

the cam i using is Dynax 7D, so is the 1.5crop a factor for the magnification as well?

#### megaweb

##### Moderator
Staff member
for non-macro lens,
if focal length of ext tube = focal length of lens should give 1:1
meaning if 2x 25mm ext tubes mount with 50mm lens should have 1:1 magnification

however if focal length of ext tube > focal length of lens, you cannot focus the lens ..

#### Del_CtrlnoAlt

##### Senior Member
thanks eawtan! but its very very cheem... will try to calculate...

btw megaweb, whats the diff between using a 50mm lens & 100mm lens & 200mm lens?

since previously to get 1:1 is for a 35mm, so now with my 1.5x crop, how to factor into the 1:1?

#### megaweb

##### Moderator
Staff member
Del_CtrlnoAlt said:
btw megaweb, whats the diff between using a 50mm lens & 100mm lens & 200mm lens?
I guess there is formula to calcuate the magnification but too chim for me ...

Different lens have different focusing range. Longer focal length + ext tube can give longer focusing distance. You can see Canon EOS Closeup Lens and Extension Tube Information.

Del_CtrlnoAlt said:
since previously to get 1:1 is for a 35mm, so now with my 1.5x crop, how to factor into the 1:1?
should be 1.5:1

#### Guncon

##### New Member
not so sure about non-nikon extension tubes, but for nikon ones, the instruction manual that comes with the tube has a table indicating its effect on each nikon lens (magnification ratio). anyone who owns a PK-11A/12/13 can verify?

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