The Sleeping Giant's Sea Lion

by Jakub

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As far as I understand all three options help you do macro photography but are their other reasons for having the three different items? I figured reversal rings and extension tubes were just for the low cost but with additional more expensive features being added to the two options it seems there may be certain situations for each type? What are their biggest differences and advantages over each other?

  • Are there situations where you would have one over the other?
  • Do all three options have the same "wafer thin" depth of field?
  • Do they all suffer from the same light loss?
  • Do any of them affect your photos more negatively than the others?
  • Can I achieve the same magnification with rings and tubes that I can with proper lenses?
  • Would you ever combine these options together or would there be no need for that?

I ask because I recently bought a cheap extension tube and reversal ring and I'm trying to get a better overall understanding of each. I tend to use the extension tube a lot more, because I can put it on my 70-200 and have a workable distance between subject and lens.

This photo was taken with 49mm of extension tube on the 70-200 I believe which may be greater than 1:1. Would it be sharper with a macro lens?

Herd of Shells Larger Version on 500px

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possible duplicate of What am I losing when using extension tubes instead of a macro lens? –  mattdm Jan 10 '12 at 18:34
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Well, I don't think it's a duplicate. A lot of what I asked is covered but it's not the same question. But, I tried to search, to make sure this wasn't already covered and that question never came up. The search on this site is very unhelpful. –  Vian Esterhuizen Jan 10 '12 at 19:54
    
i agree with the crappy search when trying to research whether a similar question has been posted before. As for the extension tubes; one word of cation; do not get the cheap ones. I decided to try it out and my lens almost fell off the tube. Other then that the macro effect was pretty nice. –  Jakub Jan 10 '12 at 20:00
    
Can you make the title of this into a question? I think that really helps focus the question and the answers you get, and can help clarify why this isn't a duplicate. –  mattdm Jan 10 '12 at 20:02

2 Answers 2

up vote 5 down vote accepted

Depth of Field

Reversing a lens will produce a very shallow DOF. You may also get distortion and vignetting and have difficulty focusing, as you can only focus at a very narrow range of distances. From memory extension tubes have less DOF than a macro lens, but I am not certain of that.

Light Loss

You will lose 1-2 stops of light using extension tubes. You can argue that macro lenses at 1:1 lose some light (mine reduces from f/2.8 to f/3.5). I don't know about the loss of light with reversed lenses, but it would would seem clear that the light gathering ability of the lens would be reduced when reversed, given that the aperture opening tends to be quite a bit smaller than the front of the lens.

Magnification

You can achieve 1:1 with extension tubes with say roughly 50mm of tubes and a 50mm prime lens. Reversing a lens you can get greater than 1:1.

Quality and Ease of Use

You will lose sharpness in reversing a lens or using extension tubes. You may lose metering and AF capability with a reversed lens (and some tubes), although some reversing rings and extension tubes have metering capability.

An important difference to me is that macro lenses can focus from their min distance to infinity (other two options have a narrow range of focus ability, so the camera and subject must be a certain distance apart). So once you reverse your lens or put on some extension tubes, you will be locking in a certain magnification and subject-camera distance, where a macro lens you can move closer or further away from your subject to compose the shot.

Reversing a lens, or sticking it at the end of some extension tubes, you are not using the lens for what it was originally designed and optimised for, so you wont get the same performance as a dedicated macro lens.

But both options do a good job considering the relatively low cost.

Re: your new question about using them together. Yes, you can use an extension tube or teleconverter with a macro lens to increase magnification, or to give you more working distance for the same magnification. With more working distance and the same magnification, because you are focusing at a greater distance, you should end up with more DOF as well.

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Why would you loose sharpness with tubes? There are no optical elements in the tube. –  Sridhar Iyer Jan 10 '12 at 22:12
    
Macro lenses are optimised to be sharpest at closest focus - designed to be at their best when used for their intended purpose. Non-macro lenses tend to be optimised to be sharpest at infinity, and when put at the end of a tube, they (most anyway) cannot be focused at infinity. And the image circle they project will be enlarged and so I would expect less resolution than a macro lens. –  MikeW Jan 10 '12 at 23:20
    
Depth of field depends on the magnification, not on the method used to achieve that magnification, so reversing a lens is no different to extension tubes or a dedicated macro lens in this respect. –  Matt Grum Nov 21 '13 at 13:54

I disagree with some of the things MikeW said. No matter what is between the subject and the sensor (or film), there will be light loss relative to what you would otherwise expect by considering only the f-stop. This is basic physics.

The additional light loss relative to f-stop is 1/(1 + M)^2, where M is the magnification from the real subject to its size on the focal plane. When taking a picture of a mountain or something, M is a very small number 1/1.000001 is still basically 1, so you don't notice the effect. However, at 1:1 we have 1/(1+1)^2 = 1/4, or 2 f-stops down. Real macro lenses may hide this effect by adjusting the aperture.

You don't lose more light because you flipped a lens around. You do lose light because you're probably magnifying more than unity else you wouldn't have flipped the lens around in the first place, so you're down 2 f-stops or more depending on actual magnification. Flipped lenses work because the lens was designed to focus close on the camera end and far on the subject end. With greater than 1x magnification, the lens will be closer to the subject than the film plane, so flipping it around uses it closer to how it was designed.

Depth of field is again due to physics. It's a function of the f-stop and magnification. Dedicated macro lenses live by the same laws of physics and can't make this go away. What they can do is have unusually high f-stops to allow for larger depth of field if you have the light to otherwise support using the high f-stop. Eventually diffraction effects get you (another basic physics issue), so even for dedicated macro lenses there is no point going further. For example, my Nikon 60mm macro lens stops down to f/64. That's about where diffraction effects start making the picture look a bit less sharp, so they stopped there. I have to think about using f/64 to consider whether the extra depth of field is worth the loss in sharpness. If the lens had f/91, I'd probably not use it anyway.

One effect to consider for extension tubes in particular is center haze. It happens because the light rays from the subject are less parallel than the widest angle difference the lens was designed for. Basically, when subject light comes in from a wide angle, the effective aperture is not constant accross the image. This is part of the same issue why DX lenses don't work with FX frame sizes. In case you think this is just a academic argument, here is a good example of this phenomenon:

Notice the white haze in the middle of the picture. This was a decent 135mm lens at f/8 with extension tubes. At f/8, it's not a diffraction issue and I've seen this at wider f-stops too. Some of this is also due to light bouncing off the inside of the extension tubes. Yes they rings and a flat black coating, but just looking thru them with your eyes you can see some reflection off the inside walls. This is a inherent problem with extension tubes.

Since the magnification was still less than 1 (I'm guessing maybe 1/3), flipping the lens around wouldn't have yielded anything useful, and I don't have such a adapter anyway. I don't blame the 135mm lens, since this was well beyond a geometry is was designed to operate at. This is actually a very nice and sharp lens when used as intended.

Here is a shot at about 1:1 magnification with a real macro lens:

Notice how the brightness appears pretty even over the whole frame. The macro lens is a Nikon 60mm at f/32. I've tried various lenses with extension tubes and not gotten something that even and without distorion effects in the corners.

Here are two pictures that illustrate the diffraction effect at very small apertures. This is the native pixels of a small region in the center of the previous image:

That was at f/32 as I said above. Here is the same shot at f/64:

There is a little motion blur (it was hand held at 1/15 second although my hand was resting on the ground), but that's not most of why it looks less sharp. You can see the aperture is smaller because the depth of field is greater as can be seen by comparing the backgrounds. It's not a focusing error either. From the whole picture I can see that this little fruiting body was about in the middle of the focused region.

So in conclusion, you can get useful shots with any of the three methods as long as you know the limitations of your setup and are willing to deal with them. However, dedicated macro lenses have some technical advantages that make them more convenient and allow higher quality pictures in some cases. They cost more, but extension tubes that carry all the special electrical signals and mechanical actions between the camera and lens aren't cheap either. Getting all that with a reverser is even harder, which makes them even more expensive if they do all that. Compare that to the price of a decent macro lens and the latter may not seem all that expensive for what you get after all.

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+1. Thanks for the detailed answer. I especially like that you have example photos. The central haze is a good thing to know about. –  Vian Esterhuizen Jan 11 '12 at 2:39
    
Great answer, Olin. Helps clarifying some points for the similar question I asked here: photo.stackexchange.com/questions/9169/… –  ysap Apr 4 '12 at 2:23
    
+1 for sample photos alongwith the points –  kmonsoor Nov 21 '13 at 16:31
    
Got some extension tubes today and remembered reading this about center haze. Sure enough got massive haze! I'm going to try lining the inside of the tubes with something less reflective. –  rfusca Apr 9 at 23:15
    
For anybody reading this: Take a cardboard tube (the inside of a toilet paper roll is perfect) and cut it to length to fit your extension tubes. Pop it in and it completely clears up the haze. –  rfusca Apr 10 at 4:20

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