TC Confusion

Hi all,
Has anyone ever experienced a bad tele converter I appreciate they denegrate an image somewhat, but is it possible to have a duff one. Mine is a Sigma 1.4x APO DG.....
I took some test shots this morning and the TC showed as WAY softer than the bare lens ( A Sigma 300mm F2.8 ). I deleted those pics so I can't show you I tried to test the set-up again just now, and for some reason they seemed equal now
I tested on a tripod, mirror lock up and with a remote cable and the subject had good contrast..... I just wanted to know has anyone had a TC spoil an image to the point of being unuseable
Thanks

Out of curiosity do the same test set-up and use your 100-400L at 400 and f8.0 LV 5X or 10X, IS OFF, tripod mounted, 2sec. delay timer, Manual focus, AV mode, on a high contrast subject from say around 30 ft. and do a 100% crop.

Regards,

Thanks Silverfox1,
I actually did include my 100-400 in the test and it kicked both images into the dustbin..... But, then my 1-4 is a super sharp version..... I did use AV, images were at F8 and I did use a remote and mirror lock up to omit vibration on a tripod. I will repeat the test tomorrow in better light and post the results. I was about 20 feet from my target which was a small white garden picture, against a cedar red fence.....
Cheers

Dont forget to turn the IS & OS OFF when testing.

How long have you had this Sigma TC ?

I have a Sigma EX 1.4x APO DG teleconverter and it works quite well. However since it magnifies the image projecting onto the sensor, it magnifies your lens's flaws, and camera and subject motion even if it had no aberrations of its own. The image quality will get worse but using a teleconverter should yield results that are a bit better than cropping the image without a teleconverter for the same print size.

You have very high resolution cameras so this will show the faults even more when viewed at 1:1. F/8 is wide open with a TC on the 100-400 where it is weakest too. Try some at f/11 to f/16 where the lens is performing better. If the image is still much worse, then maybe the TC has a problem.

Wait at least 5 seconds for mirror up vibrations to dampen before triggering the shutter.

F/16 will show diffraction beginning to creep in.

20 feet is actually pretty close at 560 mm (400 x 1.4). Lens should do well enough, but 50 feet or 100 feet or infinity would be better, given what the lens is designed for.

Ok,
I've taken some test pics this morning. They were bare lens comparisons. The first pic is at F2.8, the second is at F8. Tripod mounted, mirror lock up and a 10 sec timer were the conditions they were taken under. There is a HUGE difference in IQ, not what I was expecting.....

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The next two were with a 1.4x TC added. The same test conditions were used. Wide open at F4 first and stepped down to F8 for the second shot. I was blameing my TC but the lens looks like it could be the fault here.....

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