Diagonal lens flare with street lights

ziggo · Dec 31, 2011

Hello,

After not visiting this forum for a long time I recently bought a Canon 550D with a Sigma DC OS 18-50 f2.8-4.5 HSM lens. I'm now trying out my camera and noticed that when I shoot evening/night shots with street lights in them a diagonal, quite disturbing flare appears. This happens when I use a wide aperture of around 2.8. When I move up to f16 and f22 the street lamps become star like light sources and the whole flare problem is gone. Sometimes I don't want those star like figures and hence I use a big aperture giving these flares (yellow street lights in the posted picture). Could somebody please tell me how to avoid these flares (not by increasing the f-number, as that gives side-effects) or just tell me that it is impossible and that my lens is not up to this sort of stuff (then I would stop looking for a solution). I thank you all in advance for any helpful tips. Photo is taken at ISO800, f2.8, 18mm, 1/10s shutter speed.

Rephargotohp · Dec 31, 2011

First off , if you are using a UV filter, take it off it will lessen flare.

The other side of it is, Flare is a natural thing that happens with Point source lights, We don't see a lot of it with our eyes because our eyes have a much wider Dynamic Range than our cameras. If you were to look at the sun (DO NOT LOOK AT THE SUN) midday you would not see a distinct ball you would See a large amount of flare.

The more over exposed the point source lights are the larger the flare. So you could under expose this scene until you just get the bulbs in the street lights. Unfortunately that will turn the rest of your scene VERY dark, You could shoot earlier in the evening and then if you underexposed the image it may not be too bad.

Honestly, I see nothing wrong with the flare you have, in fact f you eliminated it I think it would look less natural, I would celebrate it rather than try to hide it. But, That's me

Buckster · Dec 31, 2011

Looks to me like you just need a careful lens cleaning. And if it's wearing a filter, remove it. Do those things, try again, and get back to us on results.

ziggo · Jan 4, 2012

I don't have any filters on my lens, so that was not the problem. After wiping the front part of the lens with a soft cloth I took another picture and it shows no flare anymore with the same light sources. The lightning conditions are slightly different and the shot is taken at ISO800 f3.2, 18mm and 1/13, but I think the situation is comparable to the initial shot. I really didn't think of such a simple solution, sorry. Thank you for the help!

GnipGnop · Jan 4, 2012

The flare is coming from the large aperture you are using. The amount of blades in the aperture affects the shape of the star bursts the light produces as well.

The only way around it, as I see it, is to shoot earlier, underexpose, or shoot two photos (one being underexposed) and carefully merge the two in PS.

480sparky · Jan 4, 2012

Clean your lens better.

ziggo · Jan 4, 2012

GnipGnop thank you for the explanation, but as I mentioned in my first post I want to avoid the "side-effects" (the star-like lights). Hence I want to stay with a large aperture. After cleaning my lens the flare was gone (see latter picture).

480sparky; do you mean that the latter pictures stills shows artifacts that are caused by smudges on the lens? If so, could you point them out for me please? In my opinion the last picture I posted is quite ok (regarding the picture quality, not aestheticly speaking)

Buckster · Jan 4, 2012

ziggo said:
I don't have any filters on my lens, so that was not the problem. After wiping the front part of the lens with a soft cloth I took another picture and it shows no flare anymore with the same light sources. The lightning conditions are slightly different and the shot is taken at ISO800 f3.2, 18mm and 1/13, but I think the situation is comparable to the initial shot. I really didn't think of such a simple solution, sorry. Thank you for the help!

Glad that worked out for you, and you're very welcome. Always glad to help if I can. :thumbup:

480sparky · Jan 4, 2012

ziggo said:
.......480sparky; do you mean that the latter pictures stills shows artifacts that are caused by smudges on the lens? If so, could you point them out for me please? In my opinion the last picture I posted is quite ok (regarding the picture quality, not aestheticly speaking)

Never said the second image had any. What you have in the first image is a smear of some sort of the leans. That acts as a bunch of little prisms, and tends to splay out the light reflection in a 90° angle to the smear.

I'll go out on a limb...... you don't wear glasses.

DiskoJoe · Jan 5, 2012

3.2 is a bit wide for night shooting and landscape. I would say go with f8. You should get a nice balance and still no significant flaring.

DiskoJoe · Jan 5, 2012

I shot this at f8

Disko/Broadfoot by DiskoJoe, on Flickr

ziggo · Jan 5, 2012

Ok, thank you for the tip. Your picture looks very nice. I see on Flickr that you were using a 25 second exposure. As I was just taking a walk through town I had no tri-pod with me and I was shooting hand held, hence a smaller aperture was not a real option.

DiskoJoe · Jan 5, 2012

ziggo said:
Ok, thank you for the tip. Your picture looks very nice. I see on Flickr that you were using a 25 second exposure. As I was just taking a walk through town I had no tri-pod with me and I was shooting hand held, hence a smaller aperture was not a real option.

ahhh, that makes sense. A tripod is very necessary for night shots. I hate lugging mine around but it is a necessary evil. Now in situations such as yours a nice sturdy flat surface like a bench or trashcan top could double as a tripod in a pinch.

DiskoJoe · Apr 26, 2012

ziggo said:
I don't have any filters on my lens, so that was not the problem. After wiping the front part of the lens with a soft cloth I took another picture and it shows no flare anymore with the same light sources. The lightning conditions are slightly different and the shot is taken at ISO800 f3.2, 18mm and 1/13, but I think the situation is comparable to the initial shot. I really didn't think of such a simple solution, sorry. Thank you for the help!

Clean glass makes all the difference. Make sure to keep you a micro fiber cloth in your camera bag.

KmH · Apr 26, 2012

GnipGnop said:
The flare is coming from the large aperture you are using. The amount of blades in the aperture affects the shape of the star bursts the light produces as well.

f/2 is a large aperture. f/11 and f/16 is a small apertures. f/2 is a much larger number than f/11 is, because those numbers are fractions. The f is equal to the focal length of the lens being used.
So a 50 mm lens set to f/2 has a lens aperture that is 50mm / 2 = 25 mm wide. At f/11 the 50 mm lens aperture is 50 / 11 = 4.5 mm wide.

The number of aperture blades determine how many spikes there will be if the aperture used is in fact small enough to cause diffraction spikes (star burst). Typically, inexpensive lenses have 5 aperture blades, while high quality lenses typically have 9 aperture blades.

A diagonal spike like in the OPs photo is likely not caused by the aperture blades.