Using extension tubes with a 1:1 macro lens?

[FocusDave]

Question is pretty basic: is there any reason not to use extension tubes on a lens that is already a 1:1 macro lens? There's a lot of discussion on buying extension tubes vs. buying a dedicated macro lens, but I'm asking about doing both. I have a 50mm Sigma macro lens, but we want to get even closer. Is there any reason using extension tubes on the lens wouldn't just provide even further magnification?

 

[unpopular]

other than teh risk that your lens may burst into flames. no.

 

[FocusDave]

Oh boy, burst into flames, that can't be good. I guess that means I shouldn't risk using the Sigma and instead get a 200mm f/2.8 to use with the extension tubes, huh?

 

[jwbryson1]

other than teh risk that your lens may burst into flames. no.

WTF does that mean?

What about using the Kenko extension tubes with the Tokina 100mm f/2.8? What's wrong with that?

 

[unpopular]

Totally. The macrofluid is very flammable at these kind of magnifications!

 

[Josh66]

other than teh risk that your lens may burst into flames. no.

WTF does that mean?

The results might be too much for the lens to handle...


See if you can get the focus close enough to take a picture of the front element.

 

[Overread19 7]

Ok ok lets not go too insane here shall we?

First up lets look at the rough maths for extension tubes and what you get with them. For extension tubes the maths for magnification is:

(length of the extension tubes in mm - divided by - focal length of the lens in mm ) + base magnification of the lens = magnification : 1

For example a 100mm macro lens at its closest focusing point (ie magnification of 1:1) and adding 50mm of extension tubes would be:

(50/100)+1 = magnification :1
which gievs
0.5+1 = 1.5:1 magnification

Those are rough numbers since the actual focal length of most macro lenses at 1:1 focusing distances is a little shorter than stated and since you'll likely have a different value for the extension tubes (eg 65mm). However, as you can see, it does give you a decent boost to the magnification possible with the lens.

You will, of course, lose working distance and also lose infinity focus when using the extension tubes (as on any lens). If you start adding extreme lengths of extension tubes you can run the risk that the setup becomes very forward heavy and very difficult to use in the field. In addition (though this tends to be an issue with shorter focal length lenses, unless you start adding extreme lengths of extension tubes) adding extension tubes can run the risk of moving the focusing point so close that it actually ends up inside the lens - by which point the lens can never focus. But its unlikely to happen with a 100mm lens and you are more likely to see it a problem on 40mm or shorter focal length lenses.


Personally for smaller gains in magnification I prefer to use a teleconverter; a 1.4TC gives you almost no loss of optical quality (esp if you're taking your macro photos at smaller apertures) and also lets you retain the full working distance and infinity focus. It gives you what you'd expect as well - 1.4 times the magnification or 1.4:1 on a regular 1:1 macro lens.

 

[FocusDave]

These would be used in a studio with plenty of lighting and on a very sturdy tripod. Not sure if you guys have ever heard of iFixit, but that's the company I work for. Occasionally we want to get really close to stuff, which is why we have the Sigma 50mm macro. We used to have a Sigma 105mm f/2.8, but it ran away, causing me to be very sad.

How much better are the Kenko tubes compared to Vivitar and Zeikos that they are so much more expensive? We use manual focus for everything, so that's not a big deal at all.

 

[jwbryson1]

Totally. The macrofluid is very flammable at these kind of magnifications!

:er:

 

[cgipson1]

The Kenkos are probably the highest quality tubes you can buy today for a reasonable price. The others are cheap copies of the Kenkos.. and yes, you get what you pay for! lol! With a 50mm macro lens that has an extremely small close focusing distance to start with... you will be hurting badly with tubes on it. It can be done.. but your lighting will have to be spot on, as the lens will be so close to the subject that it will be shadowed.

You also lose a signicant amount of DOF when adding tubes.. so depending on what you are shooting, that may be an issue.

You would be better off at straight 1:1 and doing some cropping, IMO.

 

[Overread19 7]

FocusDave Kenko extension tubes pretty much set a good standard for build quality and features. The most important feature being that they have the metal contacts. These are important since, whilst you won't be using AF you will be using the aperture blades in the lens. Ultra cheap extension tubes will lack these metal contacts and thus you wont' have any normal aperture control available. There are some other 3rd party tubes in the same line as Kenko - generally I'd say if they've got the metal contacts they should be good enough - though I've no idea on build quality (but tripod work with a 105mm macro shouldn't be too much strain upon them).