On Wed, 7 Sep 2005, Tom Reese wrote:
have you ever used this Teleconverter?
Have you some comments?
In my experience, it doesn't work well with long lenses because it has a
limited focusing range. The instructions are to set the lens at infinity
then allow the teleconverter to do the focusing. With telephoto lenses, this
only works when the subject is at or near infinity. When the subject is
closer, the lens has to be focused closer too. The teleconverter will then
fine tune the focusing.
I think the TC was designed with long lenses in mind. What the manual
says is that if you move away from infinity, the combo will likely
vignette, but that's a physical limitation (is my guess). My other
guess is that the limited focusing range is a trade-off with the
multiplication (and thus the loss of light, and the minimum
maximum-aperture of lenses usable with it).
Other points:
- The maximum aperture you will get is 2.8, irrespective of the
maximum aperture of the lens you attach. So, with the 50/1.4 you get
a 2.8 combo, just like with the 1.7 (that's more like 2.9, but you
get the drift) and the same is true for the 1.2.
- The 50/1.4 and the 50/1.2 are not recommended for macro work with the
extender, for reasons of flatness of focus, as discussed at the list
in another thread. The cheap-as-chips but lovely 1.7 is a better fit
perhaps.
- Theoretically, the minimum maximum-aperture of lenses you can use it
with is 2.8; this tallies up with the theoretical limit on AF lenses
of 5.6. In practice I think people get away with slower lenses.
- http://www.pentaximaging.com/files/manual/SMC_PENTAX-F_AF_ADAPTER_1[1].7X.pdf
- I love it.
Kostas
