Extension tubes or Macro lens?

[remco-jan.woldhuis]

Hi,

 

What are the benefits of a "real" macro lens (I am thinking of the Tamrom 90mm or Sigma

55mm) compared to a Nikkor 50mm/1.8 AF with extension tubes?

 

Of course, a macro lens is easier to use because you don't have the hassle of mounting the

extension tubes, but how do these options compare optically?

 

Remco Jan Woldhuis

[work-page]

Here are some considerations:

 

At 1:1 magnification with tubes, you'll need 50mm extension total which translates to a 2 stop light loss.

 

The effective aperture is not correctly reported to the camera in case of tubes.

 

A macro lens focusses from infinity downto 1:1 continously. With tubes at 1:1 you'll find that the amount you can adjust focus by turning the focus ring is almost none.

 

Macro lenses are designed to be used close-up, an ordinary 50mm excels at longer distances (for instance 10ft/3m).

[timarmes]

Extensions tubes are a lot cheaper.

 

If you're working in a controlled environment, the many off the disadvantages of extension tubes listed above are less likely to cause a problem:

 

If you're using a digital SLR, then you'll see immediately if the exposure was right and you can then correct it manually.

 

You have plenty of time to adjust the camera position to get the focus that you want.

 

Optically speaking, the results will be as good as the lens. There isn't and degradation.

 

So, while a macro lens is definitely better, if you're just wanting to experiment a little for a low cost then getting some extenstion tubes could be a good solution.

[tristanlaing]

What can you actually get with extension tubes? Don't you get vignetting? I have a 50mm F1.4 (and 1.8), what kind of macro capability can I get from tubes?

[vivek iyer]

Tristan, No vignetting with extension tubes and a 50mm lens. You need to get the ones from Kenko to have metring correspondence from an AF lens. The image will be softer with tubes.

 

Remco, There is light loss with macro lenses also when you go higher in magnification (exception 70-180mm af-d micronikkor). A macro lens is better for the sake of convenience and better image quality.

[lex_jenkins]

Extension tubes are only as good as the lenses mounted on 'em. True macro lenses are designed to minimize field curvature at close range. Not many non-macro lenses can produce particularly good flat field results at minimum focus.

 

(Field curvature produces the illusion of the subject ballooning out toward the center of the photo. It's not the same thing as barrel distortion, which affects only the edges of the image. Barrel distortion can be handled by simply cropping the edges. It's impossible to eliminate the effects of obvious field curvature other than using digital processing.)

 

The best macro lenses are optimized for close focusing, usually 3 feet or less. But it depends on the focal length. The advantage to a 200mm macro lens over a 55mm macro is that the longer lens delivers the same magnification at longer range. Very handy if you'd prefer to fill the frame with a photo of that scorpion from 5 feet rather than 1.5 feet.

 

On the other hand, not many macro lenses are ideal for use as all purpose lenses because they tend to deliver inferior results at or near infinity focus. Some are better than others. Some are pretty lame. Part of the problem is that macro lenses are geared to make fine focusing easy at close range while compromising fine focusing ease toward infinity - with my older AI'd 55/3.5 Micro-Nikkor 75% of the available rotation is dedicated to the range from 1:10 to 1:2 magnification. From 2.5 feet to infinity is crammed into the remaining 25%. While cramming near to far focus into a short throw on a wide angle is no problem, it's a hassle when trying to focus between 15 feet to infinity with a 55mm lens when there's no more than 1/4" of rotation available.

 

Personally, if I didn't have a real macro lens I'd rather use good quality close up diopters than extension tubes. Extension tubes always involve some loss of effective lens speed. Close up diopters don't.

 

And since not many photographers who want to shoot objects up close really need to completely eliminate field curvature, close up diopters are ideal for the slowish zooms that typically come with SLR "kits". Using a variable aperture f/3.5-4.5 zoom with an extension tube is torture. Few AF SLRs can autofocus well with effective minimum apertures of f/5.6 or slower, which is what happens when an extension tube is used with a slow lens. So close up diopters are a much better option for many photographers on a budget.

 

I've often used Olympus brand close up diopters on my 75-150/4 Zuiko zoom with my OM-1. When photographing flowers, bugs - the usual macro fodder - the results are just as good as when I use my 50/3.5 Zuiko Macro or 55/3.5 Micro-Nikkor.

 

But if you plan to photograph documents, bugs on a brick wall, etc., there's no substitute for a flat field macro lens.

 

There are also other issues involved, including the way macro lenses are corrected so that all colors focus at the same point when used up close. Other lenses may be well corrected enough for use within their intended ranges, but will show color flaws (chromatic aberrations) when forced into macrophotography.

 

The best close up diopters are designed as doublets - two elements cemented together - to minimize chromatic aberrations. While not perfect, it works well enough for most purposes. The most important factor is to start with a good lens.

[joseph_wisniewski]

Remco - I'm not sure anyone really answered your questions...

 

If you compare your 50mm f1.8 on a Kenko extension tube (so your metering will work) to a Tamron 90mm or Sigma 55mm macro, you'll notice two things.

 

The "working distance" on the 50mm f1.8 will really annoy you. If you extend your 50mm f1.8 by 50mm (the 36mm + 12mm tubes from the Kenko set) you'll reach 1:1 magnification, and the front of your lens will be just 58mm from the subject, because of the deeply recessed front element of the 50mm f1.8, and because it's a short lens. If your subject is alive, being 2 inches away will scare it away. If the subject isn't alive, it's hard to approach within 2 inches and not cast a big honking chadow of lens and camera on the subject. The working distance for the 90mm Tamrom (an excellent lens) is about 125mm at 1:1, so you'll scare the subject less, and you're over twice as far away, which makes lighting a lot easier. The Sigma 55mm also has an edge over the extended Nikon 50mm in this area, because it's a little longer and not as deeply recessed.

 

And overall image quality will be higher on the "real" macro lenses. Even in the center of the image, the extended 50 won't be as sharp as a nacro, and it won't have as much contrast. The corners of the image will be noticibly soft. This isn't much of a problem if you're shooting flowers or bugs (those pics really don't emphasize the corners) but it's death if you're shooting postage stamps, watches, anything flat and frame-filling.

 

What are you shooting?

[joseph_wisniewski]

Peter - you got pretty much everything right. Remco is new at this stuff, so I'll add (for his benefit) that when you say "The effective aperture is not correctly reported to the camera in case of tubes" that this is primarily important when you are using a light meter, instead of the camera's TTL metering. In that case, you have to do calculations (or read charts) to find the "bellows factor" of the extended lens and look up the adjusted aperture.

 

Tim - "Optically speaking, the results will be as good as the lens. There isn't and degradation". You're movign the lens very far away away from the focus distance it was designed to work at. So, of course, there is degradation. Massive degradation. Curvature of field destroys sharpness. All aberrations and distortions increase. It's fun to play with, and may even result in sellable pictures, if the subject is something like a flower, that doesn't need high contrast or sharp corners, but normally a conventional lens on extension tubes is just for having a little fun, it's not a serious tool.

 

Lex - barrel distortion (the most common first order kind) does affect the image all the way from center to edge, the effect increases with distance from the center of the image. You can have a big curvature of field problem in a lens with zero barrel distortion. The lines will be straight all the way across the image, they just won't be sharp at the corners because the "field" (the plane of focus) has curved away from the subject in the periphery of the image. And you can have a lens with massive barrel distortion with a totally flat field. The Nikon OP fisheye (remember that) has a flat field, and the massive barrel distortion of a fisheye.

 

And closeup diopters do result in a loss of speed. I don't know where the myth that they don't started.

[vivek iyer]

Joe is exactly right about distortion and field curvatures. The famed 55mm f/3.5 micronikkor (>100 lp/mm resolution for 1/10X) has a distortion of +0.5% (in comparison, the old 135mm f/5.6 El Nikkor has a distortion of +0.025%).

 

One of the problems using a lens like 50mm f/1.8 with ext. tubes is the increased amount of spherical aberration which is diminished when the lens is stopped down well.

[vivek iyer]

"And closeup diopters do result in a loss of speed. I don't know where the myth that they don't started."

 

Thanks again for pointing this, Joe. Surprising to find that even film veterans like Lex seem to forget the "filter factors". Except in very special circumstances (these optical attachments are rare, extremely expensive and very bulky), diopters do affect the lens speed.

[craig_bridge]

Start with a true macro lens! Ease of use, focus/magnification range, flat focus field, and working distance are all important factors. A 90mm has more working distance (front of lens to subject) than a 50mm to 60mm.

 

Stacking Kenko AF extension tubes usually results in an unwanted tilt. The weight of a lens (or body) hanging off multiple joints causes each to droop slightly.

 

Extension tubes are better suited to decreasing the minimum focus distance of a zoom or long tele or to increase the magnification of a macro lens than for attempting to convert a prime into a macro lens.

[hayward]

I've tried reversing, diopters, and extension tubes, but a macro lens beat 'em all hands down for me in ease-of-use.

[joseph_wisniewski]

Craig, good point.

 

Aside from the droop, stacked Kenkos tend to get intermittant in their connection with camera and lens, so some very strange things happen. Metering shuts down, or sometimes the camera locks up and you have to power on and off.