[pacerr]

No doubt the TC's added 'glass' will have some measurable effect on comparitive image quality. I accept that and choose not to evaluate the use of a TC solely on the basis of absolute IQ alone.

I consider a TC to be something that changes the geometry of the scene -- the perspective lines/vanishing points -- rather than simply a 'magnifier'. It changes where I may (or have to?) stand to frame a given scene as I want...the edge of a cliff, a blind, a river bank, in flight...whenever unable to "zoom with your feet" or swap out lens FLs.

Changes in practicable exposure values when using a TC will also affect (may degrade, or sometimes even enhance?) 'bokeh', shutter-speed, DoF, etc.

Unfortunately CSA's shots didn't include enough background to make my points -- perhaps this comparison will serve to illustrate my concept - shot with different FL effect aside from magnification -- although this was shot primarily to maintain subject size:



Some personal thoughts: A TC will...

- have many different effects through out the FL range of a zoom lens.

- change the shooting location / perspective points of any scene

- possibly be the only way to frame a scene from a given or desired position

- best be used ONLY with the BEST lens at hand to frame the scene as desired (I had an Adaptall SP 180 mm plus Pz-AF 1.4x TC that outperformed any other equivalent lens option available to me between 150 - 300 mm - I do miss it! - until I acquired the DA*300. So, you may ask, do I shoot the 300 with a TC? Yes, when the situation warrants it for best effect.)

I look for the best overall result rather than simply the arguably best IQ after PP even if that comes with a slight degradation in absolute comparative IQ. If I'm pleased with the final result why measurebate over an alternate choice-not-made?

[normhead]

One thing I think is relative to the topic is, is using the TC the same as just using a longer lens. After all if my DA*200 can resolve all needed detail in an images, a 300mm lens isn't going to be any better, it just crops off more of the surrounding FoV, To my mind there's practically no difference between asking if you need longer lens, like the DA*300 ƒ4 or would be better off with the FA*200 with the 1.4. My perspective being that adding a TC to a lens is no different than using a longer lens with a stop narrower minimum aperture. The DA*200 2.8 with the TC is 280mm, ƒ4. The is also 300 ƒ4 is also. The obvious advantage of the DA*200 is 200 2.8 which there is no way the 300 can match. But can the 200 2.8 with 1.4 match the 300 ƒ4? Possibly...especially since I suspect it focus breathes less than the 300.

IQ is debatable what isn't is that any lens used with a TC has two, or in the case of my DA*200, 4 confiurations, it's 200 alone, 280 ƒ4 with the 1.4 TC, 340 ƒ4.5 with the 1.7 TC or 476 with stacked TCs. Four configurations with one lens and two very small TCs. If the weakness of primes is flexibility, TCs go a long way to overcome that. But my personal preference is TCs on 2.8 glass. My experience with ƒ4 glass isn't as positive. every piece if 2,8 glass I own, 50 macro, 70 macro, 90 macro, 100 macro, 200 and 300. It's still functional on the DA*60-250 but not as snappy.

[csa]

Norm, thanks for the link; a really great explanation!

Mike, no problem!