Extension tubes with 50mm and 100mm

swag72

swag72

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Tried my extension tubes on both my nifty fifty and my 100mm macro. As a true ludite, I would have expected that the extension tubes on the 100mm would have resulted in a far closer image than those on my 50mm.

In short, it didn't. Why? There are some of you out there getting fab images with your tubes, I am sure you will be able to help with this.

I would ask "Am I doing anything wrong?" but what can possiby go wrong?;)
 
set your macro lens at 1:1 and take a picture of a ruler you should see approx 16mm stick your tubes on and do the same you should see around 8mm 2:1, do the same with the 50mm and see what you can see.

Remember set the lens to 1:1 and focus by moving the camera not the focus ring / autofocus as this will alter the magnification.
 
Paul,

They look the same :eek:- Is this right? Surely not!

100mm macro got in about 40mm and then with the extension tubes this went down to 16mm. The 50mm was taking in the whole set square on its own, then with the extension tubes also went to 16mm.
 
swag72 said:
Tried my extension tubes on both my nifty fifty and my 100mm macro. As a true ludite, I would have expected that the extension tubes on the 100mm would have resulted in a far closer image than those on my 50mm.

In short, it didn't. Why? ;)
Click to expand...

If you'd added twice the tube length to the 100mm than you did to the 50mm then you'd have seen about the same increase in magnification. The extension required to increase the magnification is directly related to the original focal length of the lens.

Clead as mud eh?

Bob
 
if its a true macro 1:1 (which lens have you got ?) you should see approx 16mm without any tubes.

1_1.jpg



if its only 1:2 you will see approx 32mm..
 
Added the same tubes to both Bob - The whole damn lot!!!

I've got the Canon 100mm macro - so are you saying that without the tubes I should see 16mm?
 
Have you got the limiter switched on ?

'A focusing limiter which limits the magnification to 0.25x is built-in.'
 
Dogfish_magnet said:
Have you got the limiter switched on ?

'A focusing limiter which limits the magnification to 0.25x is built-in.'
Click to expand...

Errrrm - don't know - Lets see.

I've got the Focusing distance range set at 0.31m - infinity. I can't see anything about a limiter, either on the lens or in the manual.
 
Yes.

:eek: That's increased in price since I bought it!! Better investment than stocks and shares!! Note to self, photography saves you money!!!
 
I did yes. Although I have been known to use it in AF!! To take the pics of the ruler, I set it to MF as I didn't have my tripod to ensure I was the same distance away for the shot.
 
:thinking: If you set the lens (100mm macro) / camera to MF and the the focusing scale is set at 0.31 and you move the camera to get the ruler in focus you should get 16mm - dont change the focus ring. give it a go and post the results
 
Dogfish_magnet said:
:thinking: If you set the lens (100mm macro) / camera to MF and the the focusing scale is set at 0.31 and you move the camera to get the ruler in focus you should get 16mm - dont change the focus ring. give it a go and post the results
Click to expand...

This isn't actually correct. I'm guessing that you've worked it out using the angle of view for 100mm. Lens focal length is specified when focussed to infinity and focussing closer will reduce the focal length....quite considerably in the case of a macro lens which has very close focus ability. A 100mm macro lens is probably down to around 75-80mm when at its minimum focus distance and hence the horizontal angle is larger. The viewfinder coverage will trim a little of the scale off but 20-22mm at 300mm distance would be closer to reality.

Bob
 
Gawd you lot like to make things complicated. If the macro lens is focused at 1:1 then the ruler should show the same width as the sensor, 22.5mm for a 1.6x crop if memory serves.
 
pxl8 said:
Gawd you lot like to make things complicated. If the macro lens is focused at 1:1 then the ruler should show the same width as the sensor, 22.5mm for a 1.6x crop if memory serves.
Click to expand...

Or approx 16mm top to bottom as in post 5....But that statement wont help the OP who is getting 40mm
 
Canon Bob said:
This isn't actually correct. I'm guessing that you've worked it out using the angle of view for 100mm. Lens focal length is specified when focussed to infinity and focussing closer will reduce the focal length....quite considerably in the case of a macro lens which has very close focus ability. A 100mm macro lens is probably down to around 75-80mm when at its minimum focus distance and hence the horizontal angle is larger. The viewfinder coverage will trim a little of the scale off but 20-22mm at 300mm distance would be closer to reality.

Bob
Click to expand...

No i looked at the canon website who state 0.31m / 1ft. (film plane to subject) closest focusing distance and as 1:1 is achieved at the closest focusing distance and at 1:1 the image will be the same as the sensor size i assumed it to be correct. also as the photo in post 5 was with a 105 macro at 1:1 the 100mm will show the same at 1:1 as focal lenght will not affect image size at 1:1 - only sensor size
 
pxl8 said:
Gawd you lot like to make things complicated. If the macro lens is focused at 1:1 then the ruler should show the same width as the sensor, 22.5mm for a 1.6x crop if memory serves.
Click to expand...
:) It's not complicated as you say...it's simply the sensor size. I was trying to figure out where the 16mm had come from and did a bit of reverse maths to guess what had initiated it.

Bob
 
Paul and Bob,

Thank you for your time and help on this one. Public humiliation ...................Read the effing manual!! I NOW understand how this lens works. :nuts:
 
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