I recently got my Tamron 150-600mm and I'm loving it. Tamron has shown that it is possible to build a pretty decent 150-600mm f/6.3 zoom at an affordable price. This has some interesting implications.
It is often thought that with long and fast lenses, the amount of glass needed is a big factor in the price hike. If I am correct, a 600mm f/6.3 must have a front element with a diameter of at least 95.24mm. The Tamron is just about there, with a 95mm filter thread. This could explain how sharpness grows considerably when stopping down to f/8, as if the size of the front element was barely enough to achieve the FL/aperture combination desired.
I would like to share an observation. A 500mm f/5.6 would have a front element with a diameter of at least 89.28mm. This makes the use of a 95mm filter thread much more advantageous. In other words, it should be possible to build a 500/5.6 with more or less the same glass as for a 600/6.3 - thus around the same price. If you consider that building a shorter prime should be easier than building a longer zoom, a 500/5.6 at around 1100 EUR/USD is both technically feasible and promising IQ-wise. The Big Ron (or Tamrosaurus, or Tankron) gets really sharp at f/8; trading 100mm of focal length for a full stop of light (without losing IQ) could be worthwhile in many situations. For reference, the Canon 400/5.6 L takes 77mm filters having a front element of at least 71.43mm and the IQ is still good although it's an old lens.
Thoughts?
It is often thought that with long and fast lenses, the amount of glass needed is a big factor in the price hike. If I am correct, a 600mm f/6.3 must have a front element with a diameter of at least 95.24mm. The Tamron is just about there, with a 95mm filter thread. This could explain how sharpness grows considerably when stopping down to f/8, as if the size of the front element was barely enough to achieve the FL/aperture combination desired.
I would like to share an observation. A 500mm f/5.6 would have a front element with a diameter of at least 89.28mm. This makes the use of a 95mm filter thread much more advantageous. In other words, it should be possible to build a 500/5.6 with more or less the same glass as for a 600/6.3 - thus around the same price. If you consider that building a shorter prime should be easier than building a longer zoom, a 500/5.6 at around 1100 EUR/USD is both technically feasible and promising IQ-wise. The Big Ron (or Tamrosaurus, or Tankron) gets really sharp at f/8; trading 100mm of focal length for a full stop of light (without losing IQ) could be worthwhile in many situations. For reference, the Canon 400/5.6 L takes 77mm filters having a front element of at least 71.43mm and the IQ is still good although it's an old lens.
Thoughts?