What to purchase for magnification?

[FeatherMonkey]

Using a Sigma 105mm f2.8 EX DG macro os on a canon 600d/rebel t3i curious what would be the best choice tubes or close up filters.

 

[480sparky41 41]

Tubes. And ones with mechanical & electrical connections to maintain communication between the body & lens.

 

[FeatherMonkey]

Thanks Sparky had a feeling tubes might be best.

 

[Gary A.]

The problem with tubes is while you're not encroaching on the existing IQ of the lens by layering optics onto the lens designed to alter the focus ... you are significantly diminishing the amount of light hitting the sensor. So have your tripod ready.

Conversely with close-up filters, the amount of light available to the sensor is unaffected, but now you have a layer(s) of optical changing glass on the front of the lens which may not be of the same quality as the lens. Even if the close-up filters were of similar quality as the lens ... you still have a layer of optical changing glass screwed into the front of your macro. But I have seen some wonderful images captured with high end close-up filters ... like a Raynox.

Both have advantages and disadvantages ... tubes will get you closer but light falloff is significant and the setup can be expansive. Close-up filters minimize light falloff but may also affect IQ.

 

[Dao]

http://www.bobatkins.com/photography/eosfaq/closeup2.htm

 

[TCampbell]

If you want the best possible quality, use extension tubes rather than close-up filters.

The problem with close-up "filters" (diopters) is that they're single element magnifiers. An excellent example to understand how they work is to look at a simple magnifying glass.

If you hold a magnifying glass over a sheet of newspaper (black & white print), you'll notice that at the right distance, you can focus the text in the "center" of the glass. But if you move your eye over near the edges of the glass, you'll notice the image quality degrades and you're even seeing color bleed from the edges of the print (even though the print is black & white only). The color comes from the fact that the paper is white and is reflecting broad spectrum light which combines to form "white". The blue light bends more strongly as it passes through the lens than the green... which also bends a bit more strongly than the red. This creates "color fringing" (chromatic aberration or "CA" for short) and you see color bleed. It would be as though you separated a single photograph of the newspaper into a "red" color channel copy, a "green" color channel copy, and a "blue" color channel copy. Then shrink the "blue" image by 2%, shrink the "green" image by 1%, and leave the "red" image alone... and try to recombine them to create one single image again. You can align the text at the very center of the image, but the text at the edges will not converge to a sharp image.

BTW, you can fix "CA" in software -- well... somewhat. Just as I mentioned that the CA is an effect which is "as if" you separated the color channels and shrunk each color channel by a fractionally different percentage than the next, you could do exactly that with software... in reverse. Separate the color channels and fractionally enlarge the blue by perhaps 2%, green by perhaps 1% and leave the red alone. Many editors have CA correction and this is exactly what it does (without you having to deal with channels... just slide the adjustment until the colors converge and you're done.) I say "somewhat" because there's not just ONE wavelength of "blue" light entering your camera lens... all wavelengths technically disperse just fractionally... but once it lands on the sensor the camera only records it as "blue" (it looses all information about what constituent wavelengths were really present.) That means you have fractionally "soft" blue, green, and red channels.

The diopters in close-up filters aren't nearly as thick or curved as a traditional magnifying glass, but they do degrade around the edges.

Canon makes a few special close-up filters that are more expensive -- these are 2-element diopters. They're basically stacking the elements to create an achromatic doublet. The first element is convex glass, but the second element (the one nearer to the lens-facing side of the filter) is concave on the front and nearly flat on the back. The front element is convex glass and it's job is to magnify the image -- but it creates dispersion (CA). The second element does not magnify -- it's job is to attempt to reverse some of the effects of CA. It does not do a perfect job... but it's a lot better than nothing at all (a triple-element would be even better, but nobody makes those. At one point I found ONE other vendor that made dual-element close-up filters and now I can no longer find them. I think Canon might be the only company that makes the 2-element filter.) Canon makes the 250D and 500D versions. Each are designed to handle a DIFFERENT range of focal lengths. According to the notes in the B&H Photo description of the product, the 250D is intended for use on lenses in the 30-135mm range; the 500D is for the 70-300mm range. They only make them in a 52mm and 58mm thread diameter size. Notice they're not available in the more common 77mm size or 82mm size more common on high-end lenses.

Extension tubes, on the other hand, don't have glass in them... at all. That means there are no negative effects of dispersion (no "CA"). The device is extremely simple... imagine having a video projector... and a video projection screen. If you move the projector farther away from the screen, the image on the screen gets larger. Simple. You do have to adjust focus because -- just as with the video projector -- once you change the distance the image will no longer be accurately focused. There are several implications. (1) the distance indicators on your lens barrel are no longer correct (e.g. if you focus the lens carefully to and the lens barrel indicates the lens is focused to precisely 3'... the subject isn't really going to be 3' away -- it'll be close than that.); (2) an effect of moving the lens farther from the imaging plane is that the entire "range" of focus for your lens is shifted closer and as a consequence the lens cannot focus to "infinity" with the extension tube in place; (3) the lens CAN focus to subjects which are nearer to the camera than previously possible with that lens; (4) the camera's auto-focus may no longer function correctly when using the viewfinder to focus and you should manually focus the lens (or switch to liveview). Chances are, that if you're doing extreme macro photography, then you're probably going to be using a tripod and resorting to focus-stacking and that means manually focusing the lens anyway.

The advantage of the extension tube is the obvious notion that since there is no glass, there is no optical degradation of the image caused by the extension tube. But as you are magnifying the image from your lens, you are RELYING on the detail resolving capabilities of the lens. Use a poor lens and magnify the image means you see more flaws. Use a high quality lens and it can withstand the scrutiny of close-inspection of the detail.

There are other choices as extreme macro lenses (the Canon MP-E 65mm lens) or use of macro-bellows (think of them as "variable length extension tubes").