I got this idea from my Flickr friend Jim. I’ve played with this idea in the past but didn’t have the right combination of lenses to really make it work. Seems the kit lens on my Pentax K10D and my 20 year old Pentax-A 50mm f/1.7 make a pretty super duper super macro lens.

The trick is to shoot through a second lens, thus dramatically shortening the minimum focus distance of the combined lenses. This works best with a medium focal length primary lens (attached to the camera) and a fast secondary lens held (typically backwards) in front of the primary lens.

In this case, the 49mm diameter front element on the 50mm fits perfectly inside the 52mm diameter of the 18-55mm Pentax kit lens. I found that I had to zoom the kit lens all the way out to 55mm to eliminate vignetting. I tried reversing the set-up but the 18-55’s  smaller maximum aperture resulted in vignetting at all focal lengths (hence the need for a fast secondary lens). For the shot above I simply switched the camera into manual focus, dialed in a handful of positive exposure compensation and got up close on a bulb on our Christmas tree:

Depth of field is essentially non-existent- as is typically the case with all macro lenses. Changing the focus of ether lens had very little effect on the focal distance to the subject. To achieve focus you have to simply move the camera back and forth while composing through the viewfinder. The problem is that with such a micro thin slice of DOF any movement will throw off your composition. I ended up dialing up the ISO to 800 so that I could get a decently fast shutter speed (around 1/100 sec) and taking a bunch of hand held shots to get a couple of winners. Use of a tripod would have certainly helped, though holding the secondary lens in position while composing the shot on a tripod might be tricky.

A couple of additional shots taken with this set-up:

My understanding is that you can get similar results by simply reverse mounting certain types of lenses. There are accessories available to do this. Also, I think you may be able to use a threaded step-up adapter ring to attach the two lenses like in my set-up. The $20 screw-on close-up lens adapters (the kind that look like filters) IMO are pretty worthless unless you buy very nice quality ones but you might as well put that cash towards a dedicated macro lens.

The most popular macro accessories (besides a dedicated macro lens, of course) are extension tubes. Again, the price of entry here comes close to a decent dedicated macro lens (or zoom lens with macro capibility). There are cheaper alternatives and quality is less important if you are OK with losing auto focus and communication with your lens. I got some very nice results with my old Canon 5D and 85mm f/1.8 + 12mm Canon extension tube:

Keep in mind that all of these options will limit your focus distance to macro applications. A dedicated macro lens typically will be able to focus to infinity, making it usable as a regular lens in addition to a macro. However, if you have a couple of the right kind of lenses laying around and you want to take some close-up shots, now you know how. Thanks, Jim!

UPDATE:

Playing around a bit more with this set-up and I got these shots:

It also occurred to me that one of the reasons my set-up works so well is that my old manual focus 50mm lens has an aperture ring. This means I can crank it open to f/1.7 to get a clear shot through. More modern lenses often lack an aperture ring and default to the smallest aperture when removed from the camera body. If this happens to you, look for the aperture lever on the inside face of the lens and try sliding the aperture open to get a clear view through your secondary lens.