originally posted as a discussion in a Flickr Group "4/3rds Adapters: Legacy Lenses on Four Thirds DSLR Bodies"
Sometimes the biggest aperture value written on the lens does not necessarily mean that the lens you have is faster or slower than the other with a different widest aperture. Not only the aperture but also, the coatings, number of elements etc. affect the amount of light reaching the detector.
I don’t know why but probably because of curiosity I have done a speed test with the Legacy Lenses that I have. I admire my Konica Hexanons more.
The process is simple.
1- Keep the lightning and the position of the camera (in this case E420) constant.
2- Change the aperture
3- Keep the exposure meter reading at 0.0eV by changing the shutter speed.
4- Record the shutter speed with the corresponding aperture
5- Normalize the speeds.
I have included 40/1.8 Konica AR in to this category. The focal lengths are between 40 and 58mm.
I don’t have any other 1.4 lens to compare with Mamiya Sekor 55/1.4. So what I can say is that it really is fast. (faster? slower?)
x- At 1.8 Konica AR 50/1.8 is 25% faster that Olympus OM 50/1.8. Mamiya, Konica 40mm and Olympus have same speeds.
x- At 2.8 where the lenses are becoming sharper 40/1.8 K/AR, 50/1.7 K/AR and Helios are at the same speed. Then follows the others.
The test includes 3 lenses; Vivitar 28/2.5 AR, Olympus 24/2.8 OM and JCPenny 28-80/3.5 OM zoom lens kept at 28mm. The speeds are normalized with the same way that was done for the primes. So all speeds are comparable with each other. (Meaning all the graphs shown here are consistent with each other)
The lenses have almost identical speeds. At 4.0 where the lenses are sharp the JCPenny lacks speed compared to the others.
The champion of "The Longers" is Vivitar 135/2.8.
Hope this helps,
Thanks, it was fun