Cheap Lenses
When I first started taking photos I often wondered why some lenses cost so much more than others. Sure, they were "faster" (had a wider aperture, allowing more light in), but I couldn't see why some were 3x -4x the cost of others (even with similar apertures). It turns out there's many reasons, but there's one that's easy to see in the end result, it's called chromatic aberration.
Chromatic aberration is a type of distortion where the lens fails to focus all colours to the same point on the film / sensor. What you end up with is parts of your picture having halos of colour. See if you can spot it in the first image here (cropped from a larger picture, taken with a Konica Minolta 5D and Minolta 70-300mm 4.5-5.6 D lens):
It's not easy to spot, especially at this size, so here's a zoomed in shot:
See the blue / violet on the bird's shoulder? That's chromatic aberration. The lens has failed to focus the violet light to the same point as all the other colours to make the white (shade of grey in this case) colouring of the bird.
Most lens manufacturers have ways of dealing with this, but it's not cheap. This is where the more expensive lenses come from. In the Minolta (now Sony) range, these normally have the "APO" badge which stands for Apochromatic. This is the name of a method of using multiple lens elements to reduce chromatic aberrations.
If you would like more information, I can suggest the following Wikipedia links. They are very complicated, but all the info you ever wanted is there.
DIY Macro Lens
I have always liked macro photography. Revealing a world of sights that would be otherwise unseen or not thought about is a fascinating process. You can spend a lot of money on a macro setup, and lenses alone can cost you hundreds, or even thousands of dollars. Or, you can use an old-school trick and spend about $20.
The secret to getting a cheap macro setup is in the reversal ring. These are available commercially, but it's easy enough to create your own. My reversal ring (as seen in the picture above, between the two lenses) is a step-up ring glued to a step-down ring. That's all you need. After acquiring or making one, you just need to experiment with different lens combinations to get what you are after.
The setup pictured has a 70-210mm lens @ 210 couple to a 135mm lens. It works great, but the depth of field is extremely shallow, as you can see in this picture. If you leave the aperture wide open (in this case f3.5) on the second lens (the 135mm) you won't get any vignetting, but you will lose a great deal of depth of field. If you adjust it down you will gain depth of field, but it will vignette rather badly.
All in all I had a lot of fun finishing up a roll with some experimentations with this macro setup. I would suggest not bothering to try and hand hold for these shots, a tripod (or in this case just sitting on a table) is a must. You might want to set the timer as well, so you don't shake the camera while pressing the shutter release.
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