Strong flare "effects" in polluted environment


aladab

Link Posted 02/02/2010 - 18:59
hello,

I'm in Cairo at the moment, and the other night I was out taking photos...when I noticed a luminous spot in one of the photos (mosque courtyard, lit background - spotlights on top of columnade). I probably wouldn't have noticed it if it hadn't been in the wrong place, that is, above the colunmade, in the sky.

After trying to take a number of photos against the same and other lit backgrounds (same angle of shooting), I noticed the following:

a) whenver a spot-light or a street-light is in the picture, if the light they radiate is strong enough, the spot-light or street-light replicate itself somewhwere above its location. Usually it looks as if there were a bulb hanging from the sky. I never got more than one of these luminous spots, but they're all surrounded by halo;

b) elsewhere in the picture, the glow surrounding other (less strong) sources of light is perfectly noticeable (and looks quite annoying). I'm comparing this with night photos taken in London, where the flare is on the contrary hardly noticeable;

c) if I remove the UV protection filter, the glow at b) (or flare) becomes less noticeable. Also the lumninous spots at a) are much less visible (though still present);

d) if I use a "blue" filter, the glow at b) (or flare) disappears. The luminous spots at a) are almost gone but still slightly visible.

Cairo is extremely polluted. There's a lot of dust in the air, and probably my sensor is already covered in it. Nights are really dark here, and this seems to make any street-light look much more luminous than it would in London, for instance.

I also seem to recall reading somewhere that dust in the air can reflect light in night photography and increase the flare, but I don't know if this is really the case.

Do you know the issue, is all this happening simply because my sensor is dirty, or might there be some other reason? Any advice you could give me, also regarding home-cleaning the sensor (if that's a good idea at all), and/or trying to avoid flare? I tried using a hood, by the way, but it doesn't really make much of the difference. I also tried out different lenses, but the result in terms of flare and luminous spots is the same.

Thanks.

aladab

Link Posted 02/02/2010 - 19:01
I've forgotten to add that I have only limited access to internet, so might not be able to post any photo by way of example.

aladab

Link Posted 02/02/2010 - 19:18
...also forgotten to mention that I'm using a Pentax K20D

iceblinker

Link Posted 02/02/2010 - 19:21
A dirty sensor results in dark spots or marks at small apertures, not luminous ones.

I think you are getting flare from the lens and filter. A hood may help to some extent, but you can't always avoid it.

I would ditch the filter.
~Pete

aladab

Link Posted 02/02/2010 - 19:25
thanks iceblinker

I'll do as you say re: the filter. The lenses I'm using are:

- (all SMC-A) 28/2.8, 50/1.7, and 135/2.8.

They never game me flare problems (not to this extent anyway) in night photography in London. Do you think it's got to do with the environment?

iceblinker

Link Posted 02/02/2010 - 19:59
I think dusty air can intensify the overall glow or washed-out type of flare, but not the individual highlight type (luminous spots and patterns).

Perhaps it's simply because the lights are stronger than you are used to in London?

I'm not sure. Let's see what other readers think.....
~Pete
Last Edited by iceblinker on 02/02/2010 - 20:01

johnriley

Link Posted 02/02/2010 - 21:00
If you could post an example it would be very helpful.
Best regards, John

gartmore

Link Posted 03/02/2010 - 08:58
"whenver a spot-light or a street-light is in the picture, if the light they radiate is strong enough, the spot-light or street-light replicate itself somewhwere above its location. Usually it looks as if there were a bulb hanging from the sky. I never got more than one of these luminous spots, but they're all surrounded by halo"

What you are experiencing is ghost imaging caused by light reflecting off the lens surface onto the back of your UV filter. Interestingly Pentax used to make Ghostless UV filters to prevent this. They do appear on Ebay from time to time but only in 49mm thread.

Using the UV filter is your problem.
Ken
“We must avoid however, snapping away, shooting quickly and without thought, overloading ourselves with unnecessary images that clutter our memory and diminish the clarity of the whole.” - Henri Cartier-Bresson -

iceblinker

Link Posted 03/02/2010 - 10:30
Aladab says the lumninous spots are still present without the filter, though less visible. So there is a certain amount of flare or ghosting with the lens as well as the filter.
~Pete

amoringello

Link Posted 03/02/2010 - 11:17
If it is lens flare, the light will generally show as a reflection in the inverted/backwards location -- as if you flipped the image over a line drawn from one corner to the other. i.e... say a bright spot light is in the upper left, the lens flare will be in the lower right. If they dots match up in this method, you can pretty much bet it is just lens flare.

Not much you can do with some lenses. Try to change your viewing angle if possible. Block out the light, etc... I was pretty disappointed with the DA* 50-135 in that most any bright light will cause a significant doppleganger hanging around regardless of how close or far from center they might be. Makes photos of a city skyline ,for example, a complete waste of time.
Last Edited by amoringello on 03/02/2010 - 11:19

aladab

Link Posted 06/02/2010 - 11:51
thanks for all your comments - i'll try to find good connection and post a couple of photos. The ghost imaging theory seems to make a lot of sense. i'll try and look out for those filters. i'll also try to experiment different ways to block out light reflection and post the result as soon as i can.
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