TeleConverters and DOF + Sigma's quality ?

Christian,

I use the Sigma 1,4X with my 100-300mm f/4 HSM and have tested the 2X with the same lens. With the first, I noticed a slight loss of sharpness with apertures greater than f/8 (lens + TC aperture) (100% crop test images). With the second, the image quality definitively suffers even at f/11 or f/16 (lens+TC). Also, with 1,4X TC on, my D100 AF has more difficulty to achieve focus in low light situations.

About DOF, it's an interesting question that I never think about until your post. I will do some testing with a ruler and let you know.

 

Christian, you got email

 

Hi Christian
I have both Sigma TC and the same lens, Rarely is the 1.4 off my 70-200, I love it.
I have only recently had the 2x and it is nice, but man you need a lot of light to use it.
As for DOF, it is about half of what it is without the TC (According to Thom Hogan's website)
These were taken with the 70-200 and the Sigma 2x








I wish I had purchased it a long time ago.

 

With a 2X TC, you do lose 2 stops, the focal length becomes doubled, and the DOF won't change at all. This is because you are now shooting at effectively two more stops down which adds more DOF, just enough to counterbalance the reduction in DOF cause by a longer focal length.

 

Yeah the dragonfly was in flight when I took that picture, it amazed me that it was that sharp. They are so small and with that much lens (that was at 360mm before the 1.5x crop factor) it is hard to even follow them let alone get the lens to lock in focus on them.
I think my favorites from that day were of the sunflowers with the bee's on them taken at 10' away hand held too.

 

Christian,
I have the 70-200 with the 1.4 extender. Works very well. If you check out my airshow pictures in the Planes, Trains, etc. forum they were taken with that combination. I'm very happy with it.

Mike