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Macro Exercise


Prominent Member
Santa brought me a new macro lens (Canon 100mm F2.8). I decided to compare it with my Sigma 70-300APO (that calls itself 'macro' but isn't quite) for image size at closest focusing point.
I also added a full set of extension tubes to the Canon macro just to see how much closer I could get.

I used a five pence coin as it's a clearly understandable size.
Although done to satisfy my own curiosity, it may be of some interest here.....

Sigma 70-300APO

Canon 100mm F2.8

Canon 100mm F2.8 & 3 stacked extension tubes


Established Member
Very interesting Colin, have you tried the extension tubes with the Sigma lens?


Prominent Member
Here's the Sigma with tubes:


I see that the top of the coin is in focus but the bottom isn't. There was no discernable angle between subject plane and lens plane but I know from setting up the earlier shots the DoF was barely a fraction of 1mm with the tubes on.....and that's at F11 :eek:
Tricky stuff.
Now I see why Allie C needs to do his focus stacking!


Established Member
Are you going to have a go at stacking then Colin?


Established Member
Those are great comparison shots. I really must think about getting into macro in the near future.

Thanks for taking the time to show the differences in the set-ups.


Prominent Member
Good comparison Colin.
The shot from the macro lens with the extension tubes has incredible detail!
Did you use manual or auto focus for these?

BTW. The more extension tubes you use, the shorter the DOF becomes.


Prominent Member
@Tomato1: I mistakenly assumed that my DoF calculator would apply but quickly learnt just how wafer thin it was - especially on the Canon 100 with tubes attached. To avoid touching either the subject or the camera (either of which, however delicate, could throw out the focus), I used the remote liveview feature to focus the lens from a nearby PC. It gives incredibly fine control - far beyond anything my clumsy fingers could achieve via the lens itself
BTW - any idea how to calculate DOF with extension tubes??

@Lightpainter: No immediate plans to try focus stacking.....just a better understanding of why it's needed at this scale.


Prominent Member
I was forgetting about remote live view... that's the perfect feature to have for this sort of thing with a tripod setup.

I don't know how to calculate depth of field with an extension tube, but I've never found it to be more than a few mm even with a focal length of 24mm when (only) using the 12mm tube. It means that choosing your focal point is really important.

The thing to remember is the bigger the extension tube (or combination of tubes), the closer the lens will focus and the bigger the subject will appear but the DOF will be shallower.
Also, with a shorter focal length the lens will focus closer.
I normally go with the 20mm tube on my 24-105 and use the zoom to focus, while leaving the lens switched to MF.

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