What is the Advantage of a macro lens compared to a macro tube? [duplicate]

Question

I want to do some macro photography (plants, insects...) additionally to my landscape photography and now I am looking if it is more useful to just buy a macro tube to convert my existing lenses (a 18-140mm, a 70-210 mm and a 150-600mm) for my Nikon D7200 to macro lenses or just buy some extra macro lenses. I am not planning to do a awful lot of macro photography but I want to expand my possibilities.

My concern is that it would be cheaper just to buy a macro tube to adapt the lenses but for that I would loose a lot of sharpness and functionality of the lenses like the autofocus and the Image stabilization.

Are there any other Advantages than this to a special Macro lens compared to just a macro tube with a lens?

Did anyone has some suggestions for good macro tubes which don't cost me a arm and a leg and allow at least autofocus and f-stop capabilities?

Answer 1

I also first used extension tubes before going for macro lenses (of which I now have 3, so you might have an idea the direction I am about to go....).

I didn't have the problems you mention with autofocus or aperture not functioning. However I had a lot of issues, in that it was incredibly difficult to get the focus where I wanted. The very slightest movement with the (longer) lens I was using with the extension tubes would move the focus point. I found this even with a tripod (which is also horribly difficult to get to the right spot, for the composition one wants), as a tiny breeze might move that leaf.... As the depth of field is small in macro photography, this can make a huge difference. And one misses rather a lot of insects which have meanwhile moved on to another resting spot....

The other problem I had, was that the long lens I had cut out a lot of light, increasing the problem with depth of field and also limiting shutter speeds. I have to admit as someone who grew up with analogue, I don't rush to shoot in daylight at enormously high ISO speeds. (And there is always some kind of noise issue, so I personally don't see high ISO as a great solution.)

Macro lenses are not always expensive. I've got two I bought secondhand which work well, neither of which cost a lot more than my set of extension tubes.

Answer 2

Are there any other Advantages than this to a special Macro lens compared to just a macro tube with a lens?

There can be and usually are.

Most macro lenses are highly corrected for field curvature. The point of correcting for field curvature is to give the lens as flat a field of focus as possible. If one is using a macro lens for reproduction work of flat works of art or documents, for instance, this is an important feature. Many other lenses do not have as flat a field of focus. Some lenses, even very expensive ones, intentionally do not even attempt to fully correct for field curvature.

Only pinhole cameras and theoretical 'zero thickness' lenses have a perfectly flat field of focus. Every other simple single element lens starts out with a field of focus that is a portion of a sphere. As corrective elements are added for various aberrations including field curvature, eventually the field of focus of a highly corrected lens can resemble a lasagna noodle: It's basically almost flat, but there are undulations across the field.

Non-macro lense designers usually also attempt to render as flat a field of focus as is practical for the lens in question. Part of how much is practical for a specific lens is the target price of the lens. Lower priced zoom lenses are usually more concerned with price and other image quality characteristics than they are with a very flat field of focus that can be very expensive to do, particularly across the various focal length ranges of zoom lenses.

But there are also reasons why uncorrected or undercorrected field curvature can actually be desirable in a lens. The main one is that such lenses can demonstrate very smooth out of focus areas, sometimes referred to as 'smooth bokeh'. Lenses that highly correct field curvature tend to have 'busy' or even 'harsh' bokeh.

If you are going to use extension tubes for macro work and desire uniformity of sharpness and focus distance across the entire frame, it's usually best to begin with a fairly well corrected prime lens (a lens with a single focal length) rather than with a zoom lens.

Another consideration regarding extension tubes is that their effect with regards to overall magnification is based on the ratio of the tube's length to the lens' focal length. A 25mm extension tube will increase magnification by a much larger ratio for a wide angle lens than for a telephoto lens. For example, a 25mm extension tube will double (+100%) the effective distance between the optical center of a 25mm lens and the imaging sensor. That same 25mm extension tube will only increase the effective lens to sensor distance of a 250mm lens by 10%.

For more about how a lens designed for macro work might different from a lens of the same focal length designed for portrait work, please see: Why is the Tamron 90mm 2.8 marketed as Macro and not as a "portrait" lens?

Answer 3

• The macro lens being a fixed-length lens(*), is usually sharper (less compromises to make)
• It doesn't "eat light" like a tube
• But mostly with a true macro lens you still have the ability to focus far away. With a tube, your lens becomes myopic: it can focus closer, but it cannot focus beyond a couple of feet. And this also applies to your viewfinder: you cannot look for your subject in the viewfinder and then get closer, you have to be already very close to see it. Not a much of a problem if you shoot still objects in a studio, a real nuisance if you shoot handheld, and even worse if that includes moving objects like insects. With a macro lens you can start far away, and get closer: to shoot an insect, you start taking a few shots at a distance, and then get closer while taking more shots until you or the insect gets scared/bored. At the end you have the closest shots that the insect allows. With a tube, you have to estimate the distance, get close enough, and hope that the insect doesn't escape/move while you aim. You need a lot of luck.

A macro lens is also an incredibly sharp lens in your bag, that can be used for non-macro uses: portrait, short fast tele for indoor sports... (if you have a 100mm or more)

(*) even if their focus system is actually more like a zoom, I heard.