Sigma 17-50mm f2.8 OS with 1.4x TC to make 24-70mm f4 OS?

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Scottelly
Scottelly Veteran Member • Posts: 9,033
Sigma 17-50mm f2.8 OS with 1.4x TC to make 24-70mm f4 OS?

I wonder if anyone has tried this, and if so what the results might have been. I know, it's probably a bad idea, but I'm considering getting a 1.4x TC and possibly even a 2x TC, because I want to shoot longer photos with my lenses, and I'd rather not carry so many lenses. I have a 70mm f2.8 EX Macro, and a 1.4x TC would make that into about 100mm f4, right? That might be good, as long as the 1.4x TC doesn't ruin my image quality. It would make a 135mm f5.6 if I use a 2x TC (actually 140mm), and I figure that might make a good portrait lens for shooting at f8, which is what I normally do when shooting close-up face shots, to increase the depth of field. I want to shoot the moon, and right now I have a 70-300mm lens. I figure I'll be shooting at f11, but that's a lot better than using a telescope or paying some exorbitant amount of money for a 600mm lens . . . or even a 500mm f4 OS Sport lens and cropping . . . though I do realize the image quality probably won't be as good . . . probably not anywhere near as good . . . but then I'll be a few thousand dollars richer too, right? Maybe I can stack a bunch of photos and improve my image quality a bit with the low-end set-up . . . just until I can afford something that costs more than a tele-converter.

I have been considering a long mirror lens for shooting the moon and long distance wildlife, but I thought I might try a couple of tele-converters first. One of my lenses is a 17-50, and I wonder how it might work out with a 1.4x or 2x teleconverter on it, since it's a really sharp f2.8 lens with OS. I figure it might perform pretty well as a 34-100mm f5.6, especially since I'd be shooting most things at f8 anyway, to increase my depth of field and improve the detail captured in the photos.

I did read this, which makes sense to me: "Since it’s only projecting a smaller central part of the original lens, vignetting is actually reduced when using an extender. Unfortunately, all of the flaws in the original lens become magnified so this means that chromatic aberrations become more apparent, the image becomes softer and there is a reduction in contrast. A 2x extender will therefore always deliver a softer image because it is magnifying the flaws by 2x instead of 1.4x. The actual optical quality of the extender itself doesn’t have as big a part to play in this whole thing as most people would imagine."

https://shuttermuse.com/ultimate-guide-to-extenders-teleconverters/

Anyone got any thoughts?

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Scott Barton Kennelly
http://www.bigprintphotos.com

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