Using wide apertures in natural light

Mister Vain

I love my new Sigma 50mm lens. However I noticed my photos are sometimes soft when shooting at wide apertures. It's ok when I'm using flash so I'm guessing its down to camera shake or else the shutter speed is too low. If I'm shooting portraits outside in natural light, I usually shoot in Aperture Priority mode and put the ISO in auto. Would I be better off using Manual mode and dialing in the shutter speed myself?

DaireQuinlan

Mister Vain wrote: »

I love my new Sigma 50mm lens. However I noticed my photos are sometimes soft when shooting at wide apertures. It's ok when I'm using flash so I'm guessing its down to camera shake or else the shutter speed is too low. If I'm shooting portraits outside in natural light, I usually shoot in Aperture Priority mode and put the ISO in auto. Would I be better off using Manual mode and dialing in the shutter speed myself?

By 'wide apertures' do you mean, say, f/1.4 ? Probably just focusing issues. Have you any examples ? Do you notice that the focal point is noticeably behind or in front of your intended point of focus? If you mean small apertures i.e. f/16 or something then yes, likely your shutter speed is too low, check it. If you dial in the shutter speed yourself to make it faster than the metered speed then you'll likely end up with an underexposed shot (though I have no idea what auto iso does in the manual case) so you'll have to open up the aperture a bit to balance it out.

magicbastarder

if you don't see the issue at small apertures, i'd suspect focusing issues as DQ mentions - a problem at wide apertures which are not occurring at narrow ones would rule out camera shake (as you'd expect the opposite of what you're seeing); and possibly suggest that the greater depth of field at narrow apertures is hiding a focusing issue.
however, it not occurring with flash would contradict that...

Mister Vain

DaireQuinlan wrote: »

By 'wide apertures' do you mean, say, f/1.4 ? Probably just focusing issues. Have you any examples ? Do you notice that the focal point is noticeably behind or in front of your intended point of focus? If you mean small apertures i.e. f/16 or something then yes, likely your shutter speed is too low, check it. If you dial in the shutter speed yourself to make it faster than the metered speed then you'll likely end up with an underexposed shot (though I have no idea what auto iso does in the manual case) so you'll have to open up the aperture a bit to balance it out.

Yeah basically bigger apertures to get a shallower depth of field. My focal points seem to be ok. No obvious signs of front or back focusing, just an overall softness which is more pronounced at wider apertures. I don't think exposure would be a problem as the ISO will likely increase to compensate for the faster shutter speed. I guess I'll just try shooting in manual the next time. I'm relatively new to prime lenses so I probably just need more practice.

magicbastarder

lenses will perform at their best optically somewhere in the middle range of apertures - often around f8 - but if you're seeing excess softness it could be a lens issue. though again, that wouldn't explain the flash discrepancy.
what sort of shutter speeds are you getting?

Mister Vain

Yeah when I use off camera flash the images are always tack sharp. I assume the flash is freezing any motion. It could be camera shake or my subject moving that's causing the problem when shooting in natural light.

ED E

Mister Vain wrote: »

Yeah when I use off camera flash the images are always tack sharp. I assume the flash is freezing any motion. It could be camera shake or my subject moving that's causing the problem when shooting in natural light.

If you're wide open on a 50 then your shutter should be really fast if its bright. Are you talking 11AM or 5PM here?

Check your exif for the bad shots, is it over 1/200?

Mister Vain

ED E wrote: »

If you're wide open on a 50 then your shutter should be really fast if its bright. Are you talking 11AM or 5PM here?

Check your exif for the bad shots, is it over 1/200?

The time I shoot at varies. Usually late morning or early afternoon. I had a look at some of the soft photos. They seem to be between 1/125 - 1/250, all taken in Aperture Priority.

ED E

1/125 would be a little susceptible. Not terrible if you've a large body with two hands on but more in shakier situations.

Use M, go up one ISO stop and don't go slow.

Winter light can be deceiving, our eyes are really really good at compensating.

TheQuietFella

What aperture setting are you using?

Iancar29

For the 50mm sigma (standard) lens heres the MTF data for each f stop. As you can see it performs best at smaller apertures, as do nearly all lenses.


I would echo ED E , go manual mode. Learn how to compensate fully for each scene.