Image circle of DT lenses on FF cameras

[mike2008]

Hi,

I started a thread over on dpr asking at what focal length (if any) the image circle stops being visible when you use a DT zoom lens on a FF camera. Someone mentioned that DK had tested the CZ1680 and found that it's image circle was aps-c sized at all focal lengths. I searched here and on dpr but found nothing, can you confirm this and show me the post?

Also, if anyone has any more info on this it'd be great. I'm really just trying to find out how bad the image circle problem is when using the 30mm sigma and 18-250 sony on a FF camera.

Thanks

[David Kilpatrick]

Yes, I've checked the 16-80 (not much use), 16-105 (does actually cover full frame at 105mm only), 18-250 (always a circle). You could get a decent square crop from the 16-xx lenses. The thread you are looking for is in the comments to the Alpha 900 Anti-Shake and 100 per cent viewfinder post.

David

[ianmiddy]

Follow-up to Davids - FWIW the Kit 18-70 seems ok from about 24mm [but maybe a bit more to be safe] on the Film 5...

[oh...and fairly sure when I checked the Sig 10-20 it's always a circle]

IDM

[mike2008]

Thanks for the quick (and useful!) response. My mail kicked off some rather unuseful responses over on dpr but it looks like something useful will come out in the end. I am disappointed in the 18-250 results; perhaps I was overly optimistic after hearing that the 18-70 actually works well after 24mm on FF, I figured maybe the same would follow on the sal18250. Shame that. Have you got any photos of the image circle on FF?

It'd be very interesting indeed to have more info on this. Makes a big difference in lens selection if you know a lens is really ONLY DT or just for part of the range.

Hope Sony don't try to force cropped mode on the user in the A900.

[harveyzone]

[oh...and fairly sure when I checked the Sig 10-20 it's always a circle]

Yep - Sigma 10-20mm definitely doesn't work well on FF (apologies for the poor images and lack of details - I just took a few snaps on the end of a film and forgot that I couldn't check the Exif details later )...

10mm:


Roughly 15mm:


20mm:

[ianmiddy]

The Sony 11-18 looks pretty good 14mm. I can deal with 14, that's pretty darn wide still...

That's one thing that annoys me after I went for the Sig rather than the Tamron [which then got cheaper] - against Davids advice, lol !

IDM

[Vidgamer]

It would be neat if the FF camera had a "DT crop" mode for those times when you wanted to use one of your other lenses. (I read that a competitive camera does that.) I suppose there's not a huge incentive for Sony to do that, but it'd be nice. You could always crop in pp anyway. Wouldn't take full advantage of your new FF camera, but it's not like you'd be worse off than an A350.

[bakubo]

See an old DK post about the Sigma 10-20mm and Tamron/KM 11-18mm on full-frame:

http://forums.dpreview.com/forums/read. ... e=16163076

Then this further post that says the 11-18mm at certain focal lengths pretty much covers full-frame:

http://forums.dpreview.com/forums/read. ... e=16190431

[01af]

The Sony 11-18 looks pretty good by 14 mm. I think I can deal with 14, that's pretty darn wide still ...

14 mm on 35-mm full-frame actually is even wider than 11 mm on APS-C.

However, at 14 mm you'll get slightly darkened corners ... which for some subjects may go un-noticed. When cropping the farthest left and right from the frame, the vignetting is gone. You'll get a perfect image at 14 mm on, say, 24 × 32 mm format. You'll get perfect illumination and geometry on 35-mm full-frame from 16 mm on---which leaves you with a 16-18 mm 1:5.6 zoom lens. This is not exactly stunning for a zoom but still pretty useful as a full-frame super-wide-angle lens. At 16 mm, the angle of view on 35-mm format is the same as at 11 mm on APS-C format.

With the AF-DT 18-70 mm 1:3.5-5.6 (D) it's a similar story. On 35-mm full-frame, it starts getting useful from 24 mm on and perfect (well, within its own limits) from 27 - 28 mm on. Again, at 28 mm the angle of view on 35-mm format is the same as at 18 mm on APS-C format.

The SAL 16-80 Z and the SAL 18-250 should be perfect on 35-mm format from 24 mm or 28 mm on, respectively. If they aren't then it's because the barrel is designed in a way that mechanically prevents the image circle from getting wider at longer focal lengths. This is good and bad both---bad: they cannot be used on full-frame bodies; good: less internal flare and scattered light on APS-C format.

-- Olaf