Thursday, December 10, 2009

Working with Macro Tubes

Something that has come up recently on Fred Miranda.com... Shooting Macro via... extension tubes.

While there are many "macro" (or Micro if you're a Nikon shooter) lenses out there, very few are actually Macro lenses. That is... Lenses capable of shooting at minimum focusing distances of less than a foot or so, and are able to produce images that are 1:1. What is 1:1?

1:1 is where the area you are shooting, equals the size of the image on the sensor or
meaning the image on the film is the same size as the object being photographed (wiki).

As far as I'm concerned, there's 2 ways to go about doing Macro. One is getting a macro lens. The other is getting a decent lens and attaching it to extension tubes.

Most of the big manufacturers make a 1:1 lens in some way or another. Canon has their 100mm 2.8 Macro. Sigma produces a 105mm 2.8 Macro. Tamron has a 90mm macro 2.8. Nikon has... something. I dunno. Don't really care. :P

Canon also has a 50mm Macro and a 60mm macro, but I don't know much about them except that the 50mm needs the life size converter to do 1:1, and the 60mm is in the EF-S mount, which I have vowed to stay away from in the future (except unless a 10-22 falls into my lap). There's also the MP-E 65mm, but that's a whole new bag of tricks, as it goes above and beyond 1:1 (it can do 5:1)

While I can't tell you much about those lenses more than I already have, I can tell you that Macro Tubes have their pros and cons. If you go for a true 1:1 lens, you can still use a macro tube and potentially gain better than 1:1.

1) Minimum Focusing Distance (MFD) can drop (heavily) in some lenses, it reduces it so much that you pretty much touch the subject

2) If you buy cheap-o tubes, you have no Aperture confirmation. You'll get 00 on your display. Auto-settings tend not to work well. However, if you go with Kenko or Canon's EF25, you do retain Aperture confirmation, as they have connectors to maintain the camera's ability to talk to the lens.

2a) If you have cheapie tubes that have no aperture confirmation you have to work with your lens while wide open or, you have to attempt enforcing stop-down through a bit of a physically complicated method:
Step 1 - Put your lens on the body
Step 2 - Choose the F stop you want (keep in mind, DOF is narrower with tubes)
Step 3 - Hold the DOF preview button and remove the lens.

Step 4 - Attach lens to macro tube and then lens+tube to Camera
As mentioned, Depth of Field (DOF) decreases as you add tubes, so if you're aiming to get a macro shot with a lot of detail, you need to drop the aperture (F/10-16 works for me). But if you want a small amount of detail to show through, go wide-open.

Sharpness sometimes isn't much of a problem with macro tubes if the lens you're using is already razor sharp to begin with. I wrote all of this info once before, and they were asking about using tubes in conjuction with either the 24-70 or 70-300 (both by Canon). As i stated then, it won't be much of a problem with the 24-70 because of how sharp it is, but the 70-300 (assuming it's not the DO or an L) will only yield okay-ish results - post processing will be needed on lower-end lenses.

3) Lighting is extremely important... if you're not out and about in full sun, get yourself a macro ring if you can, otherwise, you'll have to play with off-camera flashing, and that can be frustrating if you're learning macro at the same time. at least... it was for me. *shrugs*

An alternative to macro-ring flashing is off-camera flashing with a diffuser, or if you want to do Macro in a "studio" environment, then build (or buy) yourself a lightbox. I did, and one of these days I'll get around to sharing the method and materials required.

Now, there are two other options that Canon has made available. They are the 250D and 500D filters. They provides a little more magnification to your lens, but at a heavy cost and only come in a limited amount of filter sizes.


Now, understanding how to get true macro, we need to understand what's going on with a macro tube. First and foremost, I have never been able to achieve 1:1, at least, not to my knowledge. I may have incidently and not realized it but that's not the point here. What the point is, trying to understand where you stand with your macro tubes and current stock of lenses. Thanks to Pixel Perfect at FredMiranda.com, I have this nice little formula.

Magnification = extension length divided by lens length or
m' = e/L
So, if you have an extension of 25mm and a lens of 80mm, your magnification will be 0.3125x.
With 55mm or extension and a 70mm lens, you get 0.78x. Which I'm thinking equals to 1:1.24, meaning that i'm close, but not quite. Remember that MP-E lens i mentioned? It gets up to 5:1 (aka 5x magnification). Because I'm at 1.24, I am shooting stuff that is 1.24x smaller than the full frame. Confused yet? good... because so am I.

-edit- This next part is thanks to Kakomu

The easiest way to figure this out is to photograph a ruler so that you have a measurement of the width of your shot. Compare that to the size of your sensor: Voila, magnification ratio.

For instance. Let's say you have a 50mm lens on 30mm of extension tubes. You point it at a ruler and measure X mm from the left frame to the right. Then, you go to the manufacturer's website, and find that your sensor is Y mm wide. Your Macro ratio is, thus, 1 : (X/Y).

Example: the measurement on the picture is 40mm and the sensor size is 20mm. Thus, the ratio is 1 : (40/20) = 1:2. The object, therefore, is half as large, on the sensor, as it is in real life.

It's also important to note that where the lens is focused makes a big difference. I typically try to focus the lens at Infinity and just move back and forth. I hear all the time that lenses perform best when you focus to infinity compared to the MFD. Then again, the MFD of a lens on a macro tube doesn't seem to make a colossal difference, so I don't even worry about it.

Also, longer lenses on extension tubes can produce some excellent results too. You won't easily get 1:1 macro shots like you would with a 50mm lens or shorter, but you can take pictures of things up close and have greater subject isolation. Flowers and other small objects benefit greatly from this approach, in my opinion.


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