Tuesday, September 22, 2009

Stacking teleconverters

One of the biggest challenges in photographing and videographing small songbirds is getting close enough to "fill the frame" before the shy little creatures fly off. Ever alert to stalking predators, the photographer frequently needs to set up in a blind and wait patiently near a feeding site in the hopes that an unwary subject will venture close to allow a decently close shot.

Another tactic is go heavy on telephoto glass, where 300 - 400 mm is the bare minimum lens required to get a sufficiently detailed image of a small bird. To that end, I stacked two Canon teleconverters, 1.4 and 2.0, onto my Canon 100-400 L telephoto zoom. The advantage is obvious in that the effective focal length on my 5D Mark 2 dslr totals out to 1120 mm -- certainly capable of giving me some decent working distance from a nervous songbird. However, there are some formidable downsides to this stacking arrangement:

1. loss of light: a full 3 stops of light are lost with this arrangement, rendering maximum aperture from the normal f5.6 of the 100-400 lens at full 400 extension down to f13 maximum aperture with the stacked teleconverters. Not too much of a problem at high noon in bright sunlight, but huge in the dimmer light of sunrise or heavy overcast (sometime both!). When shooting video with the 5D2 the only options are to reduce the frame exposure to its minimum 1/30 sec and increase ISO radically to boost light sensitivity to the sensor. Fortunately, the 5D2 works wonderfully in low light situations which may well defeat other smaller-sensored vidcams.

2. camera shake: always magnified with telephoto and macro lenses, the high 1120mm focal length (= zoom of 22.4x) is brutal when showing camera vibrations. A solid tripod/video head is the only answer here. Even very slight camera movement is distracting and detracts from the subject material.

3. manual focus: any lens with a maximum aperture greater than f5.6 will not have auto focus on the Canon 5D2. Even at the relatively closed aperture of f13, the Depth of Field of this lens combination to a subject 10 meters away will be a scant 7 cm -- which feels razor thin when trying to manually adjust focus on a flitting target! Again, patience is key as well as a fine touch on the focus adustment wayyyyy out in front of you!!

This is short 2 minute clip shot a few days ago of a mated pair of Northern Cardinals shot in the early morning from my deck at the side of my house. The light was dim, but the electronic "noise" isn't too bad at such a high ISO (6400):


No comments:

Post a Comment