Canon 28-135 IS USM as macro lens?

[slejhamer]

I have read, on this forum and others, that the Canon 28-135mm IS lens is good at close-up (macro) imaging.

However it is not a "macro" lens per se, and based on the spec sheet has a closest focusing distance of 0.5 meters, or roughly 1.6'. By comparison, the Canon 50mm f2.5 macro lens can focus at slightly less than half that distance.

My main question is this: is the 28-135mm lens able to focus at 0.5 meters throughout the focal length range, or does that spec apply only at the widest angle? (The spec sheets only list the distance, not the distance at Xmm.)

Also, perspective differences aside, if the 28-135mm lens could (theoretically or otherwise) focus at 0.5 meters in the 100mm position, would that be more-or-less the same as using a 50mm lens from half that distance?

And finally, what are the pros/cons of an extension tube vs. a good quality close-up diopter? (I already know about light loss with the tube vs. flare/distortion possibilities with the added glass, but what else, if anything?)

I should point out that macros are a once-in-a-while thing for me, so I don't really want to invest in a dedicated macro lens but wouldn't mind a couple of less-expensive accessories to achieve closer focusing.

TIA,

[pwagner]

Using the 28-135 with a close up screw on dioptor instead of using extension tubes or switching to a dedicated lens means that you will take the lens on and off the camera body fewer times. For me, the reduced risk of getting your sensor dirty is worth the loss in image quality when I'm out in the field.

[slejhamer]

Good point, pwagner. Given the frequency of complaints about dust on the sensor, I think I will pick up a Canon 500D (+2 diopter), the only one available in 72mm ring size.

But I'd still like to know (anyone?): does the minimum focusing distance apply throughout the range of a zoom lens, or only at full wide?

[toddb]

I just got the 500D for my 28-135mm UMS IS. Here is a shot I took this weekend:

http://www.toddburke.net/post/fly.jpg

You can be just as close, if not closer, when you are zoomed all the way to 135mm. I measured 6 inches from where it focused from the end of the lens.

[slejhamer]

Toddb: Thanks for the response and sample pic. I wasn't sure if the 500D's +2 strength would be enough, but now I'm sure that it will be more than I need! Also, thanks for the comment on focusing distance - very helpful.

Cheers,

[plato]

I haven't used my 28-135 lens for macros for some time, but I'm pretty sure you need to be at 135mm to get the minimum 0.5m focusing distance. I find that it's just about adequate for occasional macros, though no where near the quality of a dedicated macro lens. The 5.6 aperture at 135mm also means that you can't really blur out the background. Hope this helps.

[toddb]

I claim to be no expert...but, for taking that fly shot above I had these settings:

500D
Focal Length: 135mm
ISO: 400
Av: 9.5
Tv: 1/350

Even at this smaller aperture, I still can't get all of this fly in focus (just happened to be the best of the bunch is why I displayed it). As I under stand after reading allot of stuff online is that the closer you are, the smaller the DOF plane is for the same given aperture value. So a 5.6 is already too big of an opening to make the shot worth while. Just my observations...again I don't claim to know what I'm talking about.

[slejhamer]

toddb wrote:
As I under stand after reading allot of stuff online is that the closer you are, the smaller the DOF plane is for the same given aperture value. So a 5.6 is already too big of an opening to make the shot worth while. Just my observations...again I don't claim to know what I'm talking about.

You are correct; the distance to subject makes a big difference in depth of field. Also, the diopter exaggerates the effect, reducing DOF even further.

With my G1 and +4 (or stronger) diopter, I had to stop down to at least 5.6 to get adequate DOF in extreme close-ups. (On those tiny sensor P&S digicams, f5.6 is more like f28 on a 35mm.)