I found a black widow spider in a plant pot today

White crowned sparrow sitting on blackberry branch.

As a wildlife photographer I love long lenses.  The word "long" here describes a lens which is telephoto in nature, but even that doesn't do it justice.  Just as wide angle lenses have more extreme values and are called "ultra-wides", telephotos also have their ample cousins.  Dubbed "super-telephoto" lenses, these allow the wildlife enthusiast to render the small and distant into something substantial.

What is considered a super-telephoto?  This would depend on who you talk to, but I consider something in the 400 mm range a good beginning.  The problem with giving any one mm value is that it means different things on different cameras.  I have an 80 - 400 mm lens, a favourite, that I use on an APS-C sensor camera.  However, that is not its effective focal length, as cameras with this size sensor have a crop factor of 1.5, or in Canon's case, 1.6.

Think of a projected image on a screen.  Let's say the screen is 4 feet high by 6 feet wide and the projection fills it from edge to edge.  This is analogous to a full frame camera which has no crop factor.  The 80 - 400 mm lens I mentioned produces the expected level of magnification.  Switching over to an APS-C sensor camera, we bring the crop factor into play.  For our screen analogy it means making the screen physically smaller but having the projector at the same place.  You see less of the image on the screen.  In essence, the image has been magnified.  The 400 mm lens now behaves like a 600 mm (400 x 1.5 = 600). 

I would not consider the 400 mm much of a super-zoom on a full frame camera, but at 600 mm it makes a substantive impact.  The photograph above was taken with my 150 - 600 mm lens extended at the full 600 mm.  On the APS-C sensor camera that is equivalent to a 900 mm lens on a full frame camera.  If I compared it to a pair of binoculars, it would have a magnification of 18x.  This explains why I can be 30 feet from my quarry and still get a good photograph of it.  There is also some cropping going on and a little sharpening, but you can't argue with the results.

Although I value long lenses, there is a reverse relationship between focal length and depth of field.  Longer mm values have progressively less depth of field.  There is also a proportional relationship with shutter speed and wight/length in that longer lenses are bigger and need higher shutter speeds to produce a quality image.  Throw cost into the mix and you have a recipe which says that you can only go so big before the size, cost, shutter speed, and depth of field aspects become untenable.

I find my 600 mm lens quite adequate for my needs, as long as I can use it on a crop sensor camera.  I have been happy with many of the images I have been able to capture with it.

Thanks for reading.  www.ericspix.com  Eric Svendsen