What am I losing when using extension tubes instead of a macro lens?

Question

After playing around with macro photography on-the-cheap (read: reversed lens, rev. lens mounted on a straight lens, passive extension tubes), I would like to get further with this. The problems with the techniques I used is that focus is manual and aperture control is problematic at best. This limited my setup to still subjects (read: dead insects) Now, as spring is approaching, I want to be able to shoot live insects. I believe that for this, autofocus and settable aperture will be of great help.

So, one obvious but expensive option is a macro lens (say, EF 100mm Macro) However, I am not really interested in yet another prime lens. An alternative is the electrical extension tubes.

Except for maximum focusing distance, what am I losing when using tubes (coupled with a fine lens, say EF70-200/2.8) instead of a macro lens?

Answer 1

as others have noted you lose light but with extension tubes you gain versatility that is sometimes not available with a EF 100.

I have a EF70-200/2.8 that I use with extension tubes (kenko 12mm, 20mm, 36mm) especially for taking photos of insects. the Minimum Working Distance from the front of the lens to the subject with the lens zoomed to 200mm:

58cm with 12mm extension tube
72cm with 20mm extension tube
86cm with 36mm extension tube

setting the lens to the 70mm position brings your MWD numbers down to the 30cm range

I have the EF 100 macro that I prefer using whenever its expedient but very often the bugs get nervous and skitter away when I get close enough to fill the frame with them. So I use the 70-200 with extension tubes so I can position the lens a couple feet from them and still get very sharp pictures of the bug.

I prefer to not use a flash to take pictures of bugs for a number of reasons consequently another problem with the EF 100 is that when I come in close I often end up blocking the light source or casting a shadow over the subject that changes the dynamic of the picture. By using the extension tubes and the EF 70-200 I can take advantage of a natural light source.

When I do use a flash I use a Canon MR-14EX Macro Ring Lite (I tried a lot of other options and finally bit the bullet) mounted on the EF 100.

as a side note, while purists will sniff disdain, I do stage shots with live bugs - usually what I do is capture several of them the day before and store then in Tupperware in the refrigerator overnight then bring them to the scene I want for a backdrop in a cooler. The cold doesn't kill them but it does slow them down quite a bit so you can stage the shot. Also butterflys are suckers for hummingbird feeder juice made with vodka - they drink some of it then they perch somewhere nearby and move their wings very slowly and don't seem to mind if you get real close to them. Of course if they drink too much and fall over on their side its not a pretty picture.

Answer 2

To give some idea of how things work out, here are a few pictures (all of a US dime, to give an idea of the scale). There are all of the full (APS-C) frame, not cropped, to give an idea of how large an area you get with each. First, a 100 mm macro at 1:1:

Then, the same lens plus 68mm of extension tubes (a bit OOF, but still gives an idea of how much area it takes in):

Then, the 100mm macro 1:1 + a 55 mm macro reversed in front of it (but no extension tubes):

And, 100 mm macro at 1:1 + 55mm macro reversed + 68mm of extension tubes:

Finally, 100 mm macro at 1:1 + 35mm reversed + 68 mm of extension tubes:

As you can see, the reproduction ratio depends on the ratio of the focal lengths -- a longer rear lens or shorter front lens increases magnification.

And as a completely off-topic aside, it's amazing how the same dime transforms from shiny and new to scratched almost to death as you get closer... :-)

Extension tubes do lose quite a lot of light -- and the loss of light is compounded by the fact that especially in the last few shots, the lens is so close to the subject that getting light on the subject becomes quite difficult. A typical ring-light sticks out from the front of the lens too far to use for these, even if you had a way to mount one to a reversed lens. For the last few, I was hand-holding a flash light, almost parallel to the surface to get light into the narrow space between the lens and the subject.

Answer 3

First of all, I think your quest to avoid macro lenses is misguided. The simple fact is, a true macro lens will be sharper, more versatile, and easier to handle than any of the alternatives to that. Either way, however, autofocus when dealing with a small subject and razor thin DoF is pretty much a non-starter, you'll need to get good with manual focus or you will have to deal with the camera hunting for focus.

Anyways, the downsides to the alternatives are:

1) Several stops of light. Extension tubes can cut a lot of light and some times that light is very important, especially dealing with small, and moving, subjects.

2) Sharpness. You're going to put either distance or glass between the lens and the sensor and either of these will impact the overall sharpness of the lens. This may be acceptable, but you should be aware.

In any case, my experience says that if macro is something you really want to shoot, then you need to go to a proper lens, designed for this. Everything else is simply going to be a step on a path and will cost you more in the end.

Answer 4

Especially on internal-focus designs, you'll often run into problems with field curvature and longitudinal chromatic aberrations. (Every lens is slightly different, you'd need to test.)

The field curvature may be no big deal -- it depends on the type of subject you want to shoot. With round or organically-shaped things, it's usually not a problem, but if you're the type who insists on photographing his stamp collection (I actually knew somebody like that) it can be hell trying to find a focus point that will allow DoF to bring the subject into focus.

LCAs, though, can be truly annoying. Again, if your lens doesn't show much bad behaviour, go ahead and use it.

While I've been typing this, I've seen two answers come in to warn about the dangers of light loss. Again, don't worry about it -- it isn't unique to tubes. Any time you focus very closely, you are increasing the effective length of the lens, so you are also decreasing the effective aperture. At 1:1 magnification, you lose two full stops. That's a fact of life, and it doesn't matter whether you focused in that closely using tubes or using a macro lens. If you can meter through the lens, it's all taken care of for you. If you are metering manually, you'll need to compensate by the appropriate amount regardless of the setup you use. (Diopters are a special case, but they're also the worst way to go about it.)

Using a macro lens makes your life easier, and you know that a good macro lens is going to perform well at macro distances. The field is flat, and the CA behaviour has been tuned to give good performance at long rear focus distances. And if the cost of the EF 100 is a turn-off, take a look at the Tamron SP 90 f/2.8 -- it's a magnificent lens at every distance from infinity to 1:1, and it's less than half the price of the Canon.

Answer 5

Just to add one thing to already posted answers: If you are going to do a really serious macro photography then you can not only forget about autofocus but in fact you can forget about manual focus as well.

You will hate autofocus because it will introduce delay and your shutter will fire too late. Also it will never focus on exactly what you want. Sometimes it will miss your insect and focus on the background, sometimes it will go like crazy back and forth and your insect will be long gone before the shutter fires. Sometimes you will get focus on the flower that the insect is sitting on instead of the insect itself which may look fine on the camera display but you will be disappointed when you see it on a large screen.

The only reliable way to make sure that the focus is right is to set it manually more or less how you want it - which is usually as close as it gets - and then to move your camera to the right distance from the subject without even touching the settings of your lens. It's easier to move yourself 2 millimeters that to turn the focus ring on your lens by 0.1 mm or something like that while standing perfectly still.

For example in those photos of a colored pencil notice how the depth of field is in different places on the pencil but I didn't do it with changing anything on the lens but by moving the whole camera closer to the pencil:

I used a Helios 44-2 lens on some long macro rings that resulted with a paper-thin DOF that you can actually see on the last picture where the pencil wooden texture is in focus. This is not a typical setup that you will usually use for shooting insects but you would be able to make an interesting portrait of an insect with sharp head and blurred body to which no autofocus could go even close.

My advise for shooting such pictures with moving insects would be to set your lens how you want and not touch it, position yourself in a way that your subject is in focus, lean a little bit backwards and start slowly mowing forward while shooting as fast as you can. That is when you shoot live nature where insects are moving and flowers are leaning on the wind. You need to be patient but the result will be stunning.

Good luck.

Answer 6

I just got extension tubes, so here's the skinny.

...what am I losing when using tubes...?

A very considerable amount of light! Increasing that distance from the end of the lens to the sensor can cut your light several stops. Combined with the fact that you'll usually shoot stopped down - expect to need to increase your ISO considerably.

The fact the macro's are usually considered very very sharp, although I believe that 70-200mm 2.8 is supposed to be quite sharp.

The ultra low distortion typical of many macros.

I wouldn't worry too much about the bokeh since the DOF will still be quite limited.

Coupled on my 50mm, a full 60mm'ish extension tube results in a DOF of about a couple inches in front of the lens. On my 70-300, its probably around 2-3 feet in front of the lens to about a foot in front of the lens.

Answer 7

You'll also loose some light with extension tubes. Not to mention you'll loose the cool bokeh of the 100mm lens. Also, zoom lenses will do strange things with extension tubes, zooming out will dramatically change the focus, for instance. Also, from the experience of @rfusca, I understand that the range can be quite limited, maybe only a few inches, depending on the lens.

Still, the electrical connected ones can be a step somewhere between, and are much better than the screw on lenses that exist.