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Fli, Fla, Flare


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#1 lars

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Posted 15 July 2003 - 05:38 AM

Hi Gurus :unsure:,

I read about the flare issues related to the sigma lenses in some threads.
Now i tried it myself with our brand new sigma 28-300mm f3.5-6.3 DL
Aspherical IF Hyperzoom. I just gave it a try in the sunset to check if this
is a problem with all sigma lenses and not only with the wide angle ones.

here you can see some results, which are at least for me a bit disappointing :(

Posted Image
Posted Image

I mean i haven't expected flares which are not round at all as you can see it
in the first picture on the left side.

here is a nice one but it has this odd green flare on the left side:

Posted Image

So my question is if anybody knows how to control the flare effect
a bit, apart from not shooting into the light ;)

Looking at the exif data i guessed that the aperture might control the
size of the rings? But its just guessing?


ciao Lars
Lars Kirchhoff [<a href='http://www.digideep.com' target='_blank'>http://www.digideep....m</a>]<br>Nikon Canon 10D / Jonah Housing / 2 subtronic alpha pro strobes

#2 diverhead.com

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Posted 16 July 2003 - 01:32 AM

Ditto that. Any suggestions from the pros would be great/super/wonderful.

Posted Image

#3 pakclu

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Posted 18 July 2003 - 11:39 PM

As a new user of the sigma 14mm and raw converter, I got what I believe to be flare on the following image. At first, Ididn't know that it was a lens issue and thought that it was my begginners touch with the raw converter. After reading the preceeding posts, I know otherwise. Was my flare caused by the placement of my flash units? Is there anything else that can be done to prevent this or post processs it out?
Stupid me... I can't figure out how to add the image to my post (what a neophyte) Any direction to a how to section would be most appreciated.

#4 lars

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Posted 19 July 2003 - 03:55 AM

hi pakclu,

lens flares are created by directly shooting into a light source. As long as the flash unit isn't
in front of the lens it isn't the source for any flare effect B)

There are two different types of flares. The first which causes the rings or circles and the other
which produces the streaks around the light source.

As far as I could figure out the lens flare depends on the combination of the following things:

1. the angle of the light source to the camera
2. the number of optical elements in the lens
3. the number of aperture blades
4. the material of the optical elements of the lens
5. the cleaness of the lens
(6. the aperture)

1. The cause of the lens flare is that some parts of the light are reflected at the edge of the
optical elements of the lens instead of going through it. These reflections create new light
sources. Every element between the light source and the film or ccd can cause reflections
and can so create new light sources which than result in flares.

2. With the number of the lens elements the number of flare rings or circles within the picture
will grow as well. This means a zoom lens will create much more flare rings then a normal lens.

3. The streaks around the lights source are depending on the number of aperture blades used
in the lens. As the area where two blades are more reflective then others this will create
additional light sources forming the strikes. As you can see on my last image the sigma lens
uses 8 aperture blades resulting in 8 strikes. You can only see the lower one, but can easily
imagine, that the lower one can be mirrored. The upper one can hardly be seen because the
sky is too bright.

4. The material of the elements is important as well. Different glasses causes different reflections.
This is the reasons why the lenses are different in price i guess :unsure:. Zeiss for examples produced
a glass with a coating which almost reduced all reflections on the lens parts. This where then
used from the nasa to take pictures from the sun.

5. If you have dirt on the lens this produces reflections as well which then can cause some flare.

So my conclusion is if you want to prevent the flare dont shoot into a light source. If you still want
to capture the light source try to shoot with a big aperture number e.g. 20. this reduce the light
going the the lense and there reduce the number of reflections. But i can't prove this so far. If anybody
has any ideas about this, I would like to hear it.

After reading some about the flare effect I still wonder how this bubble flare could be created on
my first image. Normally the flare are circles and not these. I do not know how to describe this
correctly but look at the left bottom of the image.

ciao Lars
Lars Kirchhoff [<a href='http://www.digideep.com' target='_blank'>http://www.digideep....m</a>]<br>Nikon Canon 10D / Jonah Housing / 2 subtronic alpha pro strobes

#5 pakclu

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Posted 19 July 2003 - 06:55 AM

Hi Lars
Thanks for the flare info.
Can you direct me to a place where I can learn how to add images to my posts? I haven't found any place in the wetpixel site that explains this?
thanx
peter

#6 lars

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Posted 19 July 2003 - 07:06 AM

Hi Peter,

I do not know any links where this is explained ;), but it's not that hard :unsure:.

The only thing you need is some webspace where you can put your image.
Then you can use the [img] button and enter the url of the picture and the
image will be included in the text.

In my case I put my images on my webspace at the university server and
then linked to it with the img button.

I didn't tried the upload function for attachments so far. I guess then you
only get a download link in your text instead that the picture is displayed.

/lars
Lars Kirchhoff [<a href='http://www.digideep.com' target='_blank'>http://www.digideep....m</a>]<br>Nikon Canon 10D / Jonah Housing / 2 subtronic alpha pro strobes

#7 james

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Posted 20 July 2003 - 08:27 PM

Digital cameras (except for the 1Ds and the 14n) shoot through the center of the lens only. So you can do this:

Posted Image

to reduce flare. It helps a lot.

HTH
James
Canon 1DsMkIII - Seacam Housing
Dual Ikelite Strobes
Photo site - www.reefpix.org

#8 diverhead.com

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Posted 03 August 2003 - 10:46 PM

Is this lens flare, bad strobe placement, or both? This is the only/first photo with my Sigma 15mm with strange results. Using large dome port for my Sea and Sea housing. Was thinking my strobes were too far forward, but I'm not entirely sure because of the pattern of the artifacts. Either way, it would be cool to know exactly what it was as to be able to prevent it in the future. What do you think?

Posted Image

#9 lars

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Posted 04 August 2003 - 02:01 AM

to me it seems that the dome port is too big for your lens, means the distance from the lens to the dome glas is too large. this raises the reflection inside the dome, which you can see at the top and the bottom of the picture. Eventually this has caused this "squared" flare effect as well. I'm not to sure about this. but I dont think that this has something to do with the strobe placement. How far was your body?

/lars
Lars Kirchhoff [<a href='http://www.digideep.com' target='_blank'>http://www.digideep....m</a>]<br>Nikon Canon 10D / Jonah Housing / 2 subtronic alpha pro strobes

#10 james

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Posted 07 August 2003 - 04:57 AM

What you are seeing is the built in lens hood on the Sigma 15mm lens.

My guess is that stray light is getting into the port to cause the reflection. Does your dome port have a shade on it? Is the back of the dome (the flat part) black? It should be. All should be 'blacked out' except for the front of the dome.

Cheers
James
Canon 1DsMkIII - Seacam Housing
Dual Ikelite Strobes
Photo site - www.reefpix.org