Strange Lens Flare

[doug_brightwell1]

I'm curious about a lens flare I recently experienced, and would

appreciate any thoughts.

 

I was shooting a building exterior at late dusk, almost full

nighttime. There was a light pole illuminating a sidewalk... one of

those common, totally diffuse plastic spheres that are about the

size of a beach ball. Definitely not a point source light.

 

6008i. 40mm Super Angulon. No filter on the lens.

 

If I framed the image so that the light was well inside the frame,

no flare. If I framed the image to keep the light well outside the

frame, again no flare. But if I framed the image so that the light

was just barely out of frame, I got noticeable flare against the

almost black background.

 

What's going on? Why would I see flare in the viewing screen

only when the light is just barely out of frame, but not when it's

well inside or outside the frame? Do lenses just flare more

noticeably at certain angles relative to light sources?

 

Or, is it possible that the lamp was actually in the shot to a very

small degree, but since the viewing screen does not show a full

100%, perhaps I wasn't seeing it. If so, what would that mean?

 

Is it possible to get flare purely from the way a hotspot is

projected onto the viewing screen, without it showing up on the

film?

 

Thanks,

Doug

[edward_s_carmick]

Isn't this diffraction. I quote from the Oxford English Dictionary

"The breaking up of a beam of light into transverse series of dark and light bands of coloured spectra by the edge of an opaque body or a narrow aperature: an analogous phenomenon with other waves; the spreading of waves of any kind by the edge of an obstacle."

Ed Carmick

[michael_chick1]

Perhaps I can be of some assistance. Here's a little experiment which might make this "flare-thing" seem less threatening. (Try this without people around you. ahem..:) put your index finger very close to your eye; but just so that you can still see over your finger (if your are wearing glasses, then let the finger touch the glass itself). Now, look at a distant object (anything more than 6 feet is OK in this demo). Do you see a "halo-like" thing around your finger? That is exactly what happens when you have a light source very close to the edge of the lens. Wanna make it look deliberate?? try some diffusion material/vaseline/soft-focus filter. "LONG LIVE FLARE!!"

 

PS. e-mail me if you have more questions

oh, by the way, the wider the lens, the more likelyhood of flare.

[Rob F.]

I don't think the effect you describe is too unusual. Some lenses, perhaps many, seem vulnerable to flare with a light source positioned as you describe. I think that light entering at such an oblique angle becomes scattered, probably by reflection from the edges of the elements and by less than perfectly blackened lens mount parts, both of which come into play for light entering at this angle. An even more off-axis source is less a problem since the lens hood cuts it off. I think it might help to use a rectangular lens hood, the deepest one possible without vignetting, such as a bellows type hood.

[kornelius_j._fleischer]

Did you get the effect on film, too? Or in the viewfinder only?

[Bill C]

Hi Doug. More than likely this is actually camera body flare. Here's what happens. If you put the lamp image actually into the frame (onto film), all is fine. But if you move the lamp image slightly OFF the film, where does it go? Answer: it is projected onto the side wall of the camera; this is probably the source of your flare.

 

You might think that the baffles and black inside should stop it, but remember, this is a very bright spot compared to the rest of the image. The ideal way to protect against it would be to use a lens hood that will prevent an image from being projected anywhere inside of the camera except right on the film. However, such a hood would sometimes vignette the image slightly. Now you can understand the point of those adjustable bellows with drop in black frames (what I always call a compendium hood) on the front of cameras used by movie studios!

[doug_brightwell1]

Kornelius... I never shot a frame with the flare in it, unfortunately.

Would have been a good idea for troubleshooting purposes.

 

Bill... I was hoping a reflection off the interior of the camera body

wasn't the reason, but what you say makes sense..

 

Thanks for the comments...

[victor_randin]

It is possible to watch a similar effect of flare with a LF or MF view camera when an image of a source of a light is just barely out of frame. A flare is noticeable when using a ground glass on a film gate (on a Hassie for example)and watching an image of lamp placed on the edge of the frame. In such a case the flare is out of a frame or between frames when shooting a 120 or 135 film as well. I suggest that the flare is the reflection from the edge of film gate. The lens doesn�t matter. You are right, Doug, that the viewing screen does not show a full 100% of a frame, and you couldn�t see it, but if the screen would be a little more than a frame, you could.

[victor_randin]

The last comment concerning a screen is right for view camera only, not for SLR.

[randy_shafer]

Just because light sources don't register in the viewfinder doesn't mean they aren't striking the front element of the lens. Any light source striking the front element can and probably will cause flare. You didn't mention using a lens shade, and wide angle lenses tend to have rounded front elements that can pick up light sources from far outside their field of view. It is always good practice to use a compendium or fitted lens shade or a flag or gobo to shield the lens from any light source.