I had no clue that a teleconverter would allow crop lenses to be used on full frame.
Don, you could always use your 18-70 kit lens past 20mm. ;)
Peter, I was surprised to hear that about the 17-35, I thought I had seen lots of good reports of that lens, but maybe they were all in reference to crop sensors.
Originally Posted by laydros
Oh, it is a neat trick, but the image degradation is a bit more than I am willing to tolerate. Happily with the 14mm f/2.8 and the 17-35mm f/2.8-4 ... I am able to shoot around it without a problem and much brighter.
The 10-20mm f/4-5.6 DC does shoot much sharper w/o a T/C, do not be uncertain about that. It is a great lens, once it is re-tuned by the factory. OOTB it can be kind of tricky, because of QC-issues with SIGMA lenses.
The weird part of the 10-20 mounted on the Full Frame is that even at its longest (20mm), there is still a vignette around the image. Of course, all that can be easily solved by setting the menu selection to APS-C Capture Mode to "ON", but it instantly becomes an effective 15-30mm lens and the images are 11.3 MP. It does maintain its sharpness, though. A mixed blessing, I suppose.
For the 1mm of extra width ... by using the T/C, it just is not worth the image quality and light sacrifice. That's just my take on it ... everyone is entitled to their own.
Don, it was worth the experiment. A teleconverter always degrades the image but usually not so much with a 1.4x; I was surprised how much degradation there was.
Jason, the TC enlarges the image circle so yes, a 1.4x enlarges the crop lens image circle to just over that of the FF lens so vignetting shouldn't be a problem unless the lens already suffers from it and of course, poor edge/corner performance will be exacerbated.
As for my comments about the 17-35mm, I'm perhaps being hypercritical and I suppose I could have a less than optimal example. It doesn't mean I think the lens is all bad, on the contrary when you take the price into account, just that you need to take its failings into consideration when setting up a shot.
Maybe Don will post some centre/corners shots from his A850/17-35mm combo.
My only experience with crop lenses on FF until recently was the Sony 18-70 on a Minolta film body. It turned out that there were no black corners once you got a little longer (maybe 24mm or so?) However I was surprised when I tried my Tamron 17-50, because at all focal lengths there was a major black circle around the image.
Originally Posted by DonSchap
Jason, you probably already know but ....
The Image Circle projected from the lens Pupil more than covers the sensor which is why the Vignetting on the FF is not as bad as you might expect, however, the quality of the "overspill" is pretty bad as the distortion and loss of detail get exponentially worse.
One of the things that was really bothered me is the corruption that the filters have on the focusing systems. I have a Calumet (Hoya) UV filter for protection for my CZ 135mm f/1.8
If I shoot through it, close-up ... focus is pretty similar to what it is w/o it ... but the focus gets noticeably "hosed" (<- this is a professional photographic term for bad optical response) with it at around ten feet. W/O it, the focus is "spot-on" at 10-feet. So, you decide, but I already have. I have ordered a Tiffen Ultra-CLEAR ø77, as suggested by B&H Video customer support, which is supposed to introduce no ill-optical effects.
Obviously, the price of perfection is going up. I need to do more testing in this area ... with other filter makes, but it is opening up another very non-happy observation. I also punched in for a B+W Kaesemann Polarizing ø77 filter to add a filter ring to the front. My current low profile (slim) is fine on a UWA, but kind of sucks on the front of the longer focal lengths, as it lacks the front filter ring threads for utility and the lens cap.
So don't use a protecting (tech. term for degrading) filter.
The only filters I use are Polarising and ND and then rarely.
I figure it is worth a try. I will know immediately after putting it on if it distorts the image, as I check it through its range. I do not want to leave the 135's 1st element exposed to ... "Mother Nature." Just too much cost and time involved in my, now, warranty-less lens to take the chance.
In 40 years, I have yet to suffer impact damage to the front element of a lens.
Having now tempted fate, I await with resignation.....
Do you typically use a lens hood?
Originally Posted by Peekayoh