Extension Tubes and how to use them.

rivas8409 wrote in post #14978269
So a while back I bought some extenson tubes....without really knowing how/when to use them. I was going through my camera bag just a few minutes ago and I brought them out and started playing with them a bit attached to my 50mm.

My question...does anyone use these? What's they're best application and how do you know which one of the 3 to use? I've got a 36mm, 20mm, and 12 mm that can be used seperately, all together, or any comination of the 3.

They are used to get closer to your subject than the minimum focus distance of your lens would usually allow. You can do this at wide apertures to get shots with very shallow depth of field, or you can use them at small apertures to get psuedo-macro shots. This can also be used in combination with focus stacking to get even more detail in your shot.

I have the Kenko extension tubes and I like to use the 12mm tube with the 50mm f/1.4 at f/1.4 for close up flower shots. I use the 36mm tube with my 70-200, and I almost never use the 20mm tube. These are with the 50mm & 12mm tube:

ejenner wrote in post #14983284
Something like that at 1:1. I'm not sure it's much different than with a macro lens though. For instance with the 100mm macro you loose 2 stops of light at 1:1 magnification (without any tubes).

Unfortunately, while you loose the light, I don't think you gain any DOF - it's not like adding an extender.

You usually need extra light becasue even with a fast prime the DOF is so small at you get very little in focus at large apertures. Even focus stacking would be challenging below f4 at 1:1 magnification. For instance Christopher's first shot above says it was shot at f11 and the eye and most of the body are in focus, but not the nose or leg.

Correct^^^ I shot at F11 and at night time for those and as he pointed out the whole subject isn't in focus. I'm not even sure if stopping down even more then that would do it either.

I haven't tried focus stacking, but I have seen some amazing results with it!

ejenner wrote in post #14983284
Something like that at 1:1. I'm not sure it's much different than with a macro lens though. For instance with the 100mm macro you loose 2 stops of light at 1:1 magnification (without any tubes)...

At 1:1 you loose 2 f-stops - with a lens with pupil magnification =1.
Pupil maginification is thing only macro / micro photographers care about / might know. But in most calculations for normal photographers this pupil factor is = 1 for simplicity.

This 2 stops loose is the same with normal lens and extension tubes and macro lens without tubes - as long as the macro lens don´t use some tricks. On of the tricks is very common: They have internal focussing system (IF) which is like a zoom lens without additional focussing capabilities. For near field focus the focal length is shorter than for infinity! So a 100mm macro lens may have probably 70mm at 1:1.
This may change the real f/stop of the lens too.

I want to add, that normal lenses loose image quality at closer distances with these extension tubes. The lens design is not optimized for that.
For maginifications larger than 1:1 it may be usefull to mount the lens backwards on the extension tube - and loose iris functionaltiy.

vsg28 wrote in post #14979738
I am guessing you have a Kenko set? If so, I would recommend trying out a lens of choice (zoom with IS for instance) by itself on a fixed subject and then adding on the 12mm tube first and so on until you get used to the idea of ridiculous DOF and the need for longer exposures.

Actually I have PROMASTER SPECTRUM 7 tubes. I admit, the DOF is insane. They're going to take some getting used to. I wonder if using them with my 50 1.8 is the best idea. From what I've read on the thread so far I'm assuming a telephoto would be better.

I'm renting a 70-200 2.8 and 24-70 2.8 in a few weeks...I think I'm going to be doing some experimenting with these tubes on those lenses.

ZoneV wrote in post #14984492
At 1:1 you loose 2 f-stops - with a lens with pupil magnification =1.
Pupil maginification is thing only macro / micro photographers care about / might know. But in most calculations for normal photographers this pupil factor is = 1 for simplicity.

This 2 stops loose is the same with normal lens and extension tubes and macro lens without tubes - as long as the macro lens don´t use some tricks. On of the tricks is very common: They have internal focussing system (IF) which is like a zoom lens without additional focussing capabilities. For near field focus the focal length is shorter than for infinity! So a 100mm macro lens may have probably 70mm at 1:1.
This may change the real f/stop of the lens too.

I want to add, that normal lenses loose image quality at closer distances with these extension tubes. The lens design is not optimized for that.
For maginifications larger than 1:1 it may be usefull to mount the lens backwards on the extension tube - and loose iris functionaltiy.

thanks for the clarification. I am still not understanding completely... 1:1...so for a lens that is a fixed f/1.4... that means it's 1:1.4....so the 2 stops of light should increases by a factor of 1.4 also, right? so more like 2.8 stops of light (which I'm not sure what that actually converts to). The whole aperture scale is confusing to me... I'm pretty sure you don't just add 1.4 and 2.8 together to get f/4.2 (essentially 4.2 when shooting at 1.4). Or am I right? Thanks

Mark-B wrote in post #14983377
They are used to get closer to your subject than the minimum focus distance of your lens would usually allow. You can do this at wide apertures to get shots with very shallow depth of field, or you can use them at small apertures to get psuedo-macro shots. This can also be used in combination with focus stacking to get even more detail in your shot.

I have the Kenko extension tubes and I like to use the 12mm tube with the 50mm f/1.4 at f/1.4 for close up flower shots. I use the 36mm tube with my 70-200, and I almost never use the 20mm tube. These are with the 50mm & 12mm tube:

I feel like i've seen more sharp examples of the use of the kenko tubes.. I'll try to find the one I saw recently that drew me more to them. The 4th image is the only one that is kinda satisfyingly in focus in my opinion, but even this one a little more contrast/clarity may have helped to convince me more that it was in focus...could be just my eyes. Perhaps a function of the lens that you used as well?

by the way, Mark-B - I like your watermark It's classy and clean.

hyogen wrote in post #14987393
thanks for the clarification. I am still not understanding completely... 1:1...so for a lens that is a fixed f/1.4... that means it's 1:1.4....so the 2 stops of light should increases by a factor of 1.4 also, right? so more like 2.8 stops of light (which I'm not sure what that actually converts to). The whole aperture scale is confusing to me... I'm pretty sure you don't just add 1.4 and 2.8 together to get f/4.2 (essentially 4.2 when shooting at 1.4). Or am I right? Thanks


I feel like i've seen more sharp examples of the use of the kenko tubes.. I'll try to find the one I saw recently that drew me more to them. The 4th image is the only one that is kinda satisfyingly in focus in my opinion, but even this one a little more contrast/clarity may have helped to convince me more that it was in focus...could be just my eyes. Perhaps a function of the lens that you used as well?

It's not your eyes, but I think this was how he wanted to photos to come out. Just guessing.

고맙소 ^^

Sure thing, but like I said I'm just guessing.

hyogen wrote in post #14987393
thanks for the clarification. I am still not understanding completely... 1:1...so for a lens that is a fixed f/1.4... that means it's 1:1.4....so the 2 stops of light should increases by a factor of 1.4 also, right? so more like 2.8 stops of light (which I'm not sure what that actually converts to)...

First we probably need to be clear that magnification and f-stop are different things.
1:1 magnification tells us that the image on the sensor is from same size as the object in real life. A 10mm bug (parallel to sensor plane) is 10mm long on the sensor. And much bigger on the monitor afterwards.

The f-stop 1:1.4 of f/1.4 is the ratio focal length / entrance pupil.
The effective f-stop (we search for) is the ratio image distance / entrance pupil.
At infinity both f-stops are the same, cause image distance = focal length.

At 1:1 you add to a simple lens an extension tube / bellows / helicoid-extension in the length of its focal length. So the image distance is 2x focal length.
And effective f-stop is for a wideopen f/1.4 lens f/2.8.

The 2 f-stops you loose are a factor of 2. One f-stop would be an factor of 1.414 (square root from 2).
Or you memorize the full f-stop series:
1.0 - 1.4 - 2.0 - 2.8 - 4.0 - 5.6 - 8.0 - 11 - 16 - 22 - 32 - 45 - 64 - 90

Hope this helps!