07-22-2010, 02:25 PM
I have two similar macro lenses. Mamiya 120/4 and Canon 100/2.8 IS. Both go from infinity to 1:1 and FL are very similar (and BTW, so is IQ). There are, of course differences. The Mamiya gets very long when you go from infinity (125mm) to 1:1 (205mm) while the Canon has a constant (125mm) length thanks to IF design. And of course, the Mamiya does not offer AF or IS.
I knew all that before but what surprised me is that there is a very big difference WRT light loss. I mounted my camera (7D) on a tripod and pointed it to an evenly lit (daylight) wall which was about 2m away. I also set it to spot metering from the center, just to be on the safe side. I used Av and kept ISO and all other parameters were not changed as I wanted that the only difference in shutter speed will be from the lenses themselves. I then mounted both lenses (the Canon was set to MF and IS off, just to be on the safe side) and set them to infinity and 1:1 and half-clicked the shutter release button in order to activate the light meter. The Canon was checked at f/4 (to equalize things as much as possible) and wide open.
To say that I was amazed would be an understatement.
Mamiya (wide open) at infinity - 1/250. Mamiya (wide open) at 1:1 - 1/20. A whopping 3.5 stops of light loss.
Canon (f/4) at infinity - 1/125. Canon (f/4) at 1:1 - 1/45. A much more moderate 1.5 stops of light loss.
Canon (wide open) at infinity - 1/250. Canon (wide open) at 1:1 - 1/90. Same light loss as above. Not very surprising.
Other conclusions: At 1:1 the Canon enters twice as much light to the camera. At infinity it enters half.
From http://www.cambridgeincolour.com/tutoria...lenses.htm I know that light loss should be about two stops but none seem to be there. The Canon is slightly better but the Mamiya is far worse. The other differences also puzzles me.
Thus my question is simple: Why do they differ so much?
TIA.
I knew all that before but what surprised me is that there is a very big difference WRT light loss. I mounted my camera (7D) on a tripod and pointed it to an evenly lit (daylight) wall which was about 2m away. I also set it to spot metering from the center, just to be on the safe side. I used Av and kept ISO and all other parameters were not changed as I wanted that the only difference in shutter speed will be from the lenses themselves. I then mounted both lenses (the Canon was set to MF and IS off, just to be on the safe side) and set them to infinity and 1:1 and half-clicked the shutter release button in order to activate the light meter. The Canon was checked at f/4 (to equalize things as much as possible) and wide open.
To say that I was amazed would be an understatement.
Mamiya (wide open) at infinity - 1/250. Mamiya (wide open) at 1:1 - 1/20. A whopping 3.5 stops of light loss.
Canon (f/4) at infinity - 1/125. Canon (f/4) at 1:1 - 1/45. A much more moderate 1.5 stops of light loss.
Canon (wide open) at infinity - 1/250. Canon (wide open) at 1:1 - 1/90. Same light loss as above. Not very surprising.
Other conclusions: At 1:1 the Canon enters twice as much light to the camera. At infinity it enters half.
From http://www.cambridgeincolour.com/tutoria...lenses.htm I know that light loss should be about two stops but none seem to be there. The Canon is slightly better but the Mamiya is far worse. The other differences also puzzles me.
Thus my question is simple: Why do they differ so much?
TIA.