thanks for the information. i will have to think about this whole subject of teleconverters for a while. you see, today, i just got myself an A* 400 f2.8 too and it's not quite long enough for birding even on the *istD, so i am resigned to having to use a teleconverter on it quite a lot of the time. i have the A1.4X-L and A2X-L converters too and i find them to be quite sharp, but at 40-60 ft distances, the DOF is so low wide open that it's hard to be precisely on focus without some back and forth. that means time, and that means lost pictures. i guess that is where the AF converter is best. manually get focus close and let the camera do the rest.
i also have the pair of current Sigma AF 1.4X and 2X converters and i find that they lose some contrast and sharpness over the Pentax Ls, and have frequent strange bokeh on top of that. i have been thinking about the 1.7X AF converter because the AF still functions somewhat but i was wondering about quality. i did do some chromatic abberation tests with the A2X-L converter mounted and the combination did very well. no visible abberation on the *istD images out to the corners. what do you use for a support when shooting with the 400 f2.8? right now, i have a Wimberley head on a Gitzo 1325, but it's hard to stalk a bird. instead, i pick a position and edge up a bit, but that is about all. is a big monopod good enough for this? incidentally, i mounted my *istD on an A* 1200 f8 this morning and tried to take a picture under complete overcast. my Gitzo 1325 with the Wimberley head is just not adequate to support the lens steadily. i could have tried holding and bracing more than i did, but i didn't think it was a good use of my time. this is a lens where if you can't shoot at 1/1000s or faster, you'll just get vibration blurs most of the time. i can see this lens being used on a tripod with an automatic adjusting monopod/ball head on the camera at all times. Herb.... ----- Original Message ----- From: "Mark Cassino" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Sunday, April 11, 2004 12:52 PM Subject: Re: PAW- Bird and Moon Shots > Hi Herb - > > I mostly use the 1.7x teleconverter because it's a good TC on the 400mm > f2.8. The AF capability is really minimal - it is enough to ge tthe final > snap into focus, but otherwise has very limited range on a lens that > long. I also have the 1.4x-L and 2x-L. In my tests, the 1.4x-L showed no > discernable drop in quality when compared to the 400mm alone. But, I found > the 560mm focal length to be too short for a lot of birding. The 2x-L > showed a slight loss in contrast and sharpness is tests, but in practice I > get very few sharp images whenI use it, which I attribute to poor technique > (I must not be holding the rig steady enough.) I also find that the 2x-L > can produce a horrible bokeh in some situations. I haven not formally > tested the 1.7x. It's ironic, because my initial subjective reaction to it > was quite negative. I almost sold it but decided to take it out for a > final test run and found that I was wrong - it seems to be optically quite > good.
