Defective 50mm prime lens?

[maxforwardspeed]

I just picked up this 50mm F1.8 STM and have been noticing some strange artifacts when shooting with the aperture fully open. Since this is my first "fast" lens, it could simply be that I don't fully understand how they normally work and what to expect. Here are a couple of sample photos, both of which were taken with the aperture at 1.8, fully open. In short, I notice a haze or glow that seems to come from the brightest highlights in the image. The picture of the rose was taken in broad daylight while the other was during the evening. The rose seems to have a haze or glow around it while the bubble maker's LED lights produce the same glow in low light conditions. I've read extensively on flare/ghost abnormalities, but I'm not so sure that this is the same thing. I should mention that the camera body is the Canon Rebel XSi, and I don't have any lens filters on either. Is this to be expected? Or do I simply have a bad lens copy? Thanks.










Notice the glow around the LED near the end of the bubble maker

 

[Steve Balcombe]

It's common for large aperture lenses - even very expensive ones - to show some form of chromatic aberration or colour fringing in areas of high contrast. That's what you are seeing here.

Notice how in both cases the problem is around areas which are burnt out? The rose is heavily over exposed and you should have used exposure compensation, or partial metering, or whatever technique you prefer to get a correct exposure. That might have removed the problem, my guess is it would. In the other shot the exposure for the main scene is good but the very bright light from the toy has inevitably burnt out - not much you can do about that.

If you are rescuing a shot which has already gone wrong, Photoshop and Lightroom do a pretty good job of correcting chromatic aberrations and colour fringing, especially if you are converting from RAW.

 

[hotdog321]

Part of the problem is that these are overexposed--the flower in particular is easily 2-3 stops overexposed.

The overexposure is making the flare worse. That, and shooting a fast lens wide open in the sun just asking for optical issues. Optically this lens is fine, nothing to write home about, but it needs to be used with care to see the maximum benefit.

--
photojournalist
http://craighartley.zenfolio.com/

 

[bronxbombers4]

You need a more APO design to fight off purple/green glow and to get better contrast and not get so much hazing near wide open when shooting under intense broad daylight.

It's normal for that lens.

Over-exposing can make the issue seem ever worse.

 

[Desert Rose]

Bronx may be right, but I'd start with proper exposure as the others have suggested. The biggest issues with those pics are blown highlights. That happens a lot with flowers as they're often brighter than their background. You can try rolling back the highlights in post but you can only go so far with that and it isn't usually nearly as satisfactory as a properly exposed image.

 

[J A C S]

Apart from the overexposure, the 50/1.8 II had similar problems, worse than a typical fast lens. From what I have seen, the STM is not much different. The crop format makes it worse.

 

[maxforwardspeed]

It's common for large aperture lenses - even very expensive ones - to show some form of chromatic aberration or colour fringing in areas of high contrast. That's what you are seeing here.

Notice how in both cases the problem is around areas which are burnt out? The rose is heavily over exposed and you should have used exposure compensation, or partial metering, or whatever technique you prefer to get a correct exposure. That might have removed the problem, my guess is it would. In the other shot the exposure for the main scene is good but the very bright light from the toy has inevitably burnt out - not much you can do about that.

If you are rescuing a shot which has already gone wrong, Photoshop and Lightroom do a pretty good job of correcting chromatic aberrations and colour fringing, especially if you are converting from RAW.