Double Catch-lights: A Problem?

[Arthur Morris]

When photographing hummingbirds at a six-flash set-up I have no problem removing the extra catch lights and leaving only one. I often photograph birds around water. As I usually work with the sun behind me, I often wind up with two catch-lights in the bird's eye, one from the sun, and one from the sun's reflection off the water.

Do you have a general policy in such cases, or do you decide on a case by case basis on whether to remove one of the catch lights. (The upper catch light is the one from the sun.). Many folks do not realize that the two catch-lights are entirely natural.

The juvie Western Sandpiper here is an example. You can see the original post here (http://www.birdphotographers.net/forums/showthread.php/87918-No-Bears-at-Hallo-Bay...).

[Roger Clark]

Good morning Artie,

Because it is natural, I would not remove it.

I have observed double catchlights in birds not in the water, and in those cases the double catchlight must be is due to reflections in the eye, for example one off the cornea at the surface, and one off the lens in the eye. The double catchlight depends on phase angle.

I would bet most of the time a catchlight from a reflection off of the water would be more diffuse and stretched out up an down from the wave action unless the water is really smooth. In your image, the water has a lot of ripples, so I bet the 2 catchlights are due to eye lens and cornea reflections, and the phase angle was about 20 degrees. I would not remove a catchlight.

Nice image too.

Roger

[Arthur Morris]

Thanks for commenting Roger. If you are correct then why do I notice double catch-lights almost exclusively when there is water between me and the subject? If they were due to cornea reflections as you surmise would they not occur in most of my sunlit images?

[Roger Clark]

Thanks for commenting Roger. If you are correct then why do I notice double catch-lights almost exclusively when there is water between me and the subject? If they were due to cornea reflections as you surmise would they not occur in most of my sunlit images?

Artie,
I looked through a number of my bird images and find double catchlight often. However, it depends on several factors, including phase angle, head angle, and the structure of the bird's eyes. Some birds where I thougnt the double catchlight would show, it does not, on other birds it was faint but there. I have a cormorant phase angle sequence I took last spring in Florida at the Venice Rookery where the cormorant was on the west side of the pond, next to the shore and double catchlights in the eyes in most of my images taken over a large range of phase angles. There was no water for a reflection off the water at the low sun. So check your cormorant images.

The main reflection is from the surface of the eye: the cornea. The second reflection must be from the lens inside the eye.

Roger

edit--I wrote anhinga but meant cormorant (weird how that works--or doesn't)--so corrected it.

[Arthur Morris]

Thanks Roger. For now I will stick with my belief that significant second catch-lights are caused by the sun's reflection off of water :)

[Desmond Chan]

[quote] As I usually work with the sun behind me, I often wind up with two catch-lights in the bird's eye, one from the sun, and one from the sun's reflection off the water...

Sounds like it's something natural and could be visible with the naked eyes by any spectator present. So, what is the reasoning behind "correcting" them then? It seems to me it's totally all right not to do anything to them while doing otherwise would be against the nature...especally when those highlights usually appear teeny tiny in a photo that hardly anyone would notice their presence. No? :S3:

[Roger Clark]

Here are some recent BPN images showing double catchlight:

Black-headed Grosbeakhttp://www.birdphotographers.net/forums/showthread.php/87125

Red-bellied Ploverhttp://www.birdphotographers.net/forums/showthread.php/87581

Wilson Ploverhttp://www.birdphotographers.net/forums/showthread.php/87983

Vulturehttp://www.birdphotographers.net/forums/showthread.php/88149

and Artie's own
Katmai Puffinshttp://www.birdphotographers.net/forums/showthread.php/88139

Roger

[John Chardine]

I have never seen a double-catchlight caused by anything but flash usage or a low sun reflecting off water. I don't like the result in the former and would remove. The latter is totally natural and so it stays always.

[Roger Clark]

All,

The eye is made up of 2 optical elements, cornea and lens, giving 4 optical surfaces. There are 4 reflections from the 4 optical surfaces. The front cornea element has the cornea-air interface so has the highest index of refraction difference and the largest reflection. The other 3 optical surfaces are surrounded by the liquid in the eye so the index of refraction difference is small, leading to a usually small reflection intensity.

In some circumstances, depending on the eye structure, phase angle, head angle, and how overexposed the main catchlight is, the other reflections can become visible. One only other reflection, off the front of the lens, has similar convex curvature, so when a second reflection is seen, it is usually only this one. (I'm ignoring the reflection from water with does occur and can appear similar in intensity to the main catchlight if the water is smooth.)

If one stretches low phase angle images of a subjects eyes you can sometimes show the secondary reflection if it is not seen with the normal exposure. I've attached an image of Abdim's stork taken in Ngorongoro crater beside the road with no water around. In the unstretched image (this is an out of camera jpeg with an unsharp mask applied) the secondary reflection is faintly seen and it is brought out in the stretched image. I've seen double catchlight reflections due to water, and from the lens in the eye on birds and animals. Also sometimes seen (and not to be confused with a lens reflection) is the light focused on the back of the retina.

Roger

[John Chardine]

Interesting Roger. Never seen this specific effect but in the stretched version below I can see another faint light area above the faint catchlight, and it reminds me a little of "steel-eye"- which I have seen!

[James Shadle]

I always leave the double catch light when it is caused by a water reflection.

[Kaustubh Deshpande]

I always remove the second catchight :-) I feel the eye looks sharper that way...especially if the catchlights are close to each other and the bird is small in the frame.

[Kaustubh Deshpande]

a couple of images to illustrate what I was saying above

99406

99407

[Arthur Morris]

Roger, With all due respect, the 2nd catchlight in the images in Pane 9 is so faint as to not warrant consideration. I stand by my original statement that "I often wind up with two catch-lights in the bird's eye, one from the sun, and one from the sun's reflection off the water." Furthermore, I followed up on the Black-headed Grosbeak image that you linked to in Pane 7; the poster checked the EXIF and found as I suspected that flash was used for that image. Without a doubt it was the flash that caused the second reflection.

I almost always leave both catchlights where the second one is caused by the sun's reflection off the water. I can however, see Indranil's point when the two catchlights are very close together.

Would love to hear from more folks as to what they do with double catchlights that are caused by water.

[Kaustubh Deshpande]

Artie, In my examples, do you agree that the eye appears slightly sharper with removal of catchlights? at least to my eyes, it does. Did you mean to say my name instead of Indranil :-)

[Roger Clark]

Roger, With all due respect, ...r.

Artie,

Check this out. These are crops from out of camera jpegs taken at the Venice Rookery for a series explaining phase angle. Images 8899-8912 were taken in the same position from 6:36 to 6:38 pm April 17 on the western side of the lake at a phase angle of 60 degrees. Image 8864 was taken at 6:26 pm at a phase angle of 15 degrees. For the 60 degrees phase angle, the sun was off to the right. The bird was on a log at the shoreline and there was only a tiny bit of water directly below the bird and the shore was about where the word sun in for the lower left frame, and the bird's feet were about 1.5 bird heights above the water. The sun was so low at this point there was no sun on the water below the bird because of the bank.

The images show that with small movements of the head, the second reflection moves in all directions. In the 8899-8912 series, the phase angle is large enough that there is usually great separation between the two reflections so the second reflection is close to the edge of the eye. If the reflection were due to a reflection from water of another external source, the two reflections would always be in the same orientation with respect to the sources. Note 8912 shows a very close double reflection. Note too that 8902 shows 3 reflections in different directions.

At lower phase angles, the double reflections tend to be closer together. Image 8864, at 15 degrees phase,shows 4 reflections, one from each optical surface in the eye.

Roger

[Arthur Morris]

Artie, In my examples, do you agree that the eye appears slightly sharper with removal of catchlights? at least to my eyes, it does. Did you mean to say my name instead of Indranil :-)

Sorry KD! It was a combination of a brain lapse and laziness on my part. And I agree that that image looks better with a single catchlight.

[Arthur Morris]

Roger, I fully understand that the phase angle (which I do not understand) and the structure of the eye can cause additional catchlights. I do however still stand by my previous statements: such catchlights are so tiny that in most but not all cases they can be left or disregarded and that in addition, large second catchlights are often caused by the sun's reflection off of water.

[Daniel Cadieux]

For me it is like James and Artie...if the second catchlight is obviously caused by water it usually stays (I've removed some before for the same reason as KD and that is almost always when it is located within the pupil), if not, out it goes.

[Jim Fenton]

I agree that if it's there naturally and not due to flash being used, it stays unless it really obnoxious.