[ARA]

Apologies if I've put this in the wrong area, but can anyone help ?

Is this Pentax-DA converter fully compatible with the Sigma 50-500 F4-6.3 APO EX DG ?

Thanks in advance.

Alex

[Paul the Sunman]

Only on APS-C. It will badly vignette on a full frame sensor. You will also lose a stop of speed, so be prepared for a very dark image in the viewfinder at 500 mm, and possibly poor AF. Others may have tried it and can advise more authoritatively.

[jatrax]

I think there are two questions here:
Is it physically compatible? I've never tried so I cannot say for sure. I do know that some Sigma lenses do not work with some Sigma TC's. My concern would be whether the glass elements might physically come into contact.

Is it usable? As already noted it will vignette badly on FF but should be fine on APS-C. And you lose a full stop of light so that you are trying to focus at f/9 which I am not sure will even work or at least not reliably. The other factor is you then trying to stabilize a 700mm lens. That is not going to be easy.

Rear converters are intended to work with fast glass like the 300mm f/4 not with slow consumer superzooms. That doesn't mean they cannot work, just that your results might not be any better than just cropping an image from just the lens.

[Sakura]

Only on APS-C. It will badly vignette on a full frame sensor. You will also lose a stop of speed, so be prepared for a very dark image in the viewfinder at 500 mm, and possibly poor AF. Others may have tried it and can advise more authoritatively.

I recently tested just for the fun of it tha DA 1.4 rear converter with the DA 50-200 (that was the kit lens with the K7 i still own). And to my surprise, the vignetting wasn't as extreme as i expected over the full range of the lens.It looks even rather usable and vignetting fixable.

But i won't use it instead of my FF modded DA *60-250 or my D FA 150-450

[clackers]

Hi Ara,

I actually own and use the HD converter on my K-1 frequently.

Vignetting is least when the subject is close, greatest at infinity.

Here's a shot with the FA*300 f4.5.

In wildlife, you're always cropping so vignette is irrelevant. For sports, the framing is important because the players get close and get further away, you would have go work out how much you could cut out or simply lift the slider to remove in Lightroom.

I will say you are maximising your image quality by going with this converter rather than the older full frame ones you might see on eBay or whatever. I have a 2x Sigma somewhere and it's despicable! And it's WR (not that your lens is).

If you have a crop body, not a K-1, then we need not even have this discussion

[DWS1]

I think when using it on full frame the amount vignetting will vary among different lenses and apertures.