Originally posted by Barry Pearson So far, inconclusive. Some cases are worse, some appear to be better. I'm not sure how to predict!
Today I photographed a plane in flight with the 28-105mm + Pentax 1.4x converter. It was simply a test which I expected to fail, but it didn't!
Assuming this way daytime, there would have been plenty of light, so not that unexpected.
Quote: Yesterday I photographed a statue with the same combination. I thought it should be an easy success. But it failed.
How did it fail ? Bad focus ? Or acquired focus, but bad quality image ?
Quote: I think the problem is that the lenses I was trying the converter on, (28-105mm and 150-450mm), are naturally f/5.6 at the long end, which becomes problematic once the converter is on. If there is low light, the combination is pushed into noise or shake. Some failures were on a tripod with a slow shutter speed, and a 2-second self-timer which switches off SR. But something managed to shake the camera during the slow exposure.
Yes, low-light really and high f/stop throws the teleconverter off too.
If the issue is just focus, for a static subject and tripod, you can use manual focus and live view with focus peaking. That is what I did in my tests.
Depending on which tripod you have, 2-second self timer may not be enough. When I was doing my tests on tripod with the highest focal length + TC (ie. 420mm equivalent), just changing aperture with the dial, it took a long time for the image to stabilize in live view. Much longer than 5 seconds. And I used wireless remote control rather than self-timer. I waited about 3-4 seconds, plus the 3 seconds delay with wireless remote drive mode. At that point, the image was fully stable.
This won't help me much in the field, though, as I normally don't carry a tripod with me. A tripod weighs more, takes more space, and more time to setup the camera on it and shoot. I use the tripod mostly at home. So, the teleconverter won't really be all that helpful at long focal length. If it only works at smaller focal lengths, then it is just not as useful, and won't help with getting a FF superzoom replacement, no matter which lens is attached (D FA 28-105mm zoom, or APS-C superzoom).
---------- Post added 07-07-18 at 02:58 PM ----------
Originally posted by mikesbike Something to consider as well- the crop mode does give a larger image in the frame, but not actual magnification, while the addition of a TC does provide additional magnification. But then come the downsides of the additional glass, and yet slower aperture (even higher ISO). I think a better test would be no TC and the Sigma 18-300mm lens at 300mm in FF mode, and at 200mm in crop mode, even though the FF 300mm would still have greater actual magnification. That still would not address the matter of the lens's wider aperture, and thus potentially lower ISO, capabilities at 200mm vs 300mm in dealing with lower light situations.
IMO, using higher ISO is OK on a body like the K-1 II which has very good sensor performance.
As far as the Sigma at 200mm in crop mode without TC, I did test that here :
Using the Sigma 18-300 in FF mode without TC produces very significant vignetting. I will do a few test shots now to show just how much.
Edit: those test shots are here. Just meant to show the vignetting. I shot in FF mode and square (1:1) modes, at various focal lengths - 18mm, 80mm, 135mm, 200mm, 300mm.
https://imgur.com/a/nQy9SFP
As you can see, there is significant vignetting in all of them, even in square mode. Unless you are looking for a circular image, without a TC, the Sigma 18-300 lens really doesn't fill much more than the APS-C portion of the sensor. And really, you can't expect it to, as it is an APS-C lens.
With the Tamron 1.4x TC, it fills most of the FF sensor area (not all), but you pretty much lose AF at longer focal lengths.
Last edited by madbrain; 07-07-2018 at 03:10 PM.