Originally posted by jpzk Hi Scott.
So what that means is that the camera will set the real lens focal length but in reality, we are shooting at 1.4X 300mm = 420mm. (for the Tamron 1.4x "normal" TC).
Wouldn't that cause some out of focus problems? I did some shooting with the DA*300 plus the 1.4X TC and that produced less "keepers" than I expected.
The 1.7X AF adapter use requires input of the focal length, in this case that would be 500mm (closest to the 510mm real total focal length).
As long as it is a fairly contrasty day - good light and contrasty subject - I find the results quite similar to using the 1.4X TC = less keepers again.
Some people use it differently:
they turn the camera SR off, turn the camera off, install the lens/1.7x AF adapter, turn the camera on, and at that point there is no "request" to input the focal length.
I tried that. I found that the shots were not as sharp as when I had to input the focal length "as per requested" by the camera.
Anyway, that is sometimes confusing as to what is the best method to use. I guess whatever works best is what one should use.
JP
Hi Jacques,
What I do is to use the closest FL that I can for the SR. In the case of a 300 + 1.7x AFA, it would be 500mm. With the pass through AF TCs, you have no choice, and must use the unmagnified FL recognized by the camera body. Hopefully, you can compensate for the less effective SR by stepping up your long lens handholding technique. SR only augments long lens technique -- it does not replace it.
Lower percentage of keepers with a TC is usually dismissed to image degradation by the TC, but when good quality TCs are used with premium lenses this is, IMO, something of a bad rap (except maybe in the case of most 2x or greater TCs). Most users will try a few shots, and assume that the problem is the TC, but (again IMO) the problem is more likely a combination of testing procedure and technique. Another reason many have dismissed TCs is that they try them with less than optimal lenses, then assume that the TC is at fault when all it has done is magnify the limitations of the lens used. My usual comments on TCs apply only to use with premium lenses. . . but I digress. . .
Consider this -- most shooters, when "testing" a new TC, will take some shots with the bare lens, then install the TC and take their comparison shots at the same settings, using similar technique if handholding. This stacks the test against the TC from a number of standpoints. Handholding a 500mm lens is considerably more demanding of technique than using a 300mm, and while I seem to be able to shoot at 300mm pretty casually, I have to really concentrate on technique at 500mm. And then there's the light loss caused by the TC's magnification. To keep things kinda fair, you'd have to bump the ISO up an appropriate number of stops plus increase shutter speed by a factor equal to the TC magnification (as is indicated by the 1/FL "rule") -- even with SR -- Finally, you have to disregard any image degradation caused by increased noise at higher ISO -- it's really not that easy to do this test fairly. . .
A good alternative is to do the test indoors with flash to eliminate technique faults as much as possible. Try this, and I think you'll be impressed. The point is to determine the true image quality potential of the lens/TC combination, then knowing this, the challenge is to step up your technique to equal the gear's potential in real life situations.
Scott