UV hotspot issue with angles near sun

[Andy Perrin]

I am having a bit of a problem shooting images at angles that are close to the sun. The angle is forced on me by the subject matter, which is 'ghost ads' on walls of buildings. To shoot the advertisements, I have to use a moderately wide angle lens (35mm Noflexar) and due to the time of year, time of day when I have available for shooting, and placement of the buildings in question, I have only a narrow angle to shoot in, which happens to be close to the sun. This is resulting in some kind of green hotspot. I am not using a lens hood, which is my next step, but I'm not sure that will do it, as the problem seems to be coming from the sun being too close to the optical axis? Is there anything that can be done about this sort of issue?

 

Sample:

filter: 2mm UG11 + 1.75mm S8612

Novoflex Noflexar/3.5

F16 20" iso100

 

P.S. This ad is fascinating, as it's actually a palimpsest of several ads over each other, which become visible in different wavelengths. There will be a writeup at some point.

[enricosavazzi]

I don't have a tried-and-tested solution, only a short list of things to try.

 

- Use a longer and narrower lens shade. In particular, the clear rear diameter of the lens shade at its attachment to the filter (or front of the lens) needs to be only about 22-25 mm with a 35 mm f/3.5 lens on Micro 4/3. It may need to be slightly wider on larger sensors, but I would be surprised if it must be wider than about 36 mm. The clear diameter at the front of the lens shade also depends on the sensor size. You can restrict this opening with step-down adapter rings screwed into the front of the lens shade. Both the front and the rear openings of the lens shade must be just as wide as necessary to avoid vignetting. The lens shade should be as long as practical.

 

- If the front lens element of the lens is very recessed (which I think is the case in the Noflexar), use a different lens where you can attach a lens shade close to the front element of the lens, or if possible build a lens shade that fits within the recess (e.g. by stacking step-up rings and empty filter rings and attaching a small 25 mm or 28 mm filter at the bottom). A recessed front lens element forces you to use a lens shade with a wide clear rear opening, which is what you should avoid.

 

- Move the filter to the rear of the objective. If the flare is somehow related to the angle of incidence of light on the filter, it will be less of a problem in this position. If it is a lens problem, moving the filter will not solve the problem.

[dabateman]

Enrico has listed the obvious solutions, try adding a lens shade, which should work or use a different lens.

The only thing I wanted to add was, have it listed in a priority for photography. Then on your next day off, federal holiday or weekend if you get it off. Go and photograh it at the best time based on light.

There are many phone apps designed for landscape photography that indicate time and placement of the sun. Petapixels even had article on them recently. Use this to predict the best time and then on next day off, photograph at that moment.

[nfoto]

Another useful option is to use a small paper or similar held well off the lens and blocking the sun rays from striking across the lens front.

[Cadmium]

Yeah, or just stick your hand out there, however, hot spots can happen without any sun on the lens, but a hood should be used.

[Andy Perrin]

I did actually try waving my hand around without seeing much effect, although it might just have been in the wrong place. The sun was pretty diffuse that day (and the previous time I got this problem) so it was hard to see exactly where the rays were coming from, although the general direction was clear enough.

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Thank you all, Enrico and dabateman particularly!

[OlDoinyo]

Given the color, the hotspot might be out of band (e.g. IR.) The wngle dependence also suggests something of the sort.

[Andy Perrin]

OlDoinyo, that thought occurred to me, and I actually took two photos, one with 1.5mm S8612 and the other with 1.75mm S8612, and did not see any change. Personally I think 1.75mm S8612 ought to be pretty good blocking? This is from Cadmium also, so no dodgy filter worries.

[Andrea B.]

I've seen those odd green flares also sometimes caused by a light leak. (Why green? I don't know.)

Try covering these areas: LCD, both top and back. Viewfinder if not EVF. Try wrapping a cloth around the lens mount area. And on the Noflexar try wrapping the lens. You can accomplish this it would seem (now that I've listed it all) by just putting some kind of drape over the camera/lens -- like in the olden days!!

 

Also, is there a building across from this one you want to shoot? Perhaps you can get permission to shoot from a window which is up a couple of stories? Might change the angle enough to prevent flare?

 

If the wideness of the lens is the problem, then maybe shoot with longer focal length and stitch together several shots to cover what you need. (Yes, more work I know.)

[Andy Perrin]

Andrea, a light leak is a strong contender here. I know I have at least one that I've never managed to completely nail down the location of. I THINK it's actually at the place where the camera strap is attached to? Anyway, I did try covering that area with no result, but just with my hand shading it, not full aluminum foil or something.

 

In this case, the building is about an hour away from me so it's not a fast round trip, and it's in a fairly bad neighborhood too, so I'm unwilling to spend much more time shooting than strictly necessary to get the job done. (If I met the owner of the building across from this one, I might get a pair of cement shoes for asking...it's that kind of neighborhood.) My plan would be to try to duplicate the circumstances near home and fix the problem here if possible, then redo the shoot at some point.

 

Image stitching is out because I need near perfect alignment with the images from the other filters (IR, vis, etc.) for the ICA program to function.

[Cadmium]

Green or yellow... who knows, but either can be found in the UV-A shots with a Baader from time to time, all quite within band, and if visual yellow, then that would not be suppressed by S8612, but by the UG11, so if the UG11 isn't good, then... ?

But I think you just have a common hot spot, just the light/lens(?), so use a hood, and it will probably;y go away, and you may be sharper shots doing that also.

Never heard of a UV hot spot problem with Noflexar however.

 

[Andy Perrin]

Cadmium, I've never seen a UV hot spot problem with the Noflexar either, until I shot this close to the sun. Anyway, I got loads of stuff to try from the above comments, so will experiment some more.

[Cadmium]

Well, here is a UG11 2mm + S8612 1.5mm graph, and even it looks good to me.

Frankly, I would use U-360 2mm myself, I think it has better blue cutoff than UG1, but UG11 is good and has even better blue cutoff.

[Andrea B.]

Andrea, a light leak is a strong contender here. I know I have at least one that I've never managed to completely nail down the location of. I THINK it's actually at the place where the camera strap is attached to?

 

Try taping it over perhaps? I forgot to mention also the hotshoe as a leak area maybe? Not sure on that one. Go to Bed Bath and Beyond and get a nice thick, dark bath towel to use as a drape. That's all I can think of that would be inexpensive!!! It has worked for me in the past. I'm sure there is some kind of light-blocking cloth available from a photographer's supply house but that would not be usable later after a shower. :D

[Andy Perrin]

Hot shoe is long since taped-over with electrical tape. In fact every year my camera gets more bits of tape! It leaks like a tea strainer.

 

For temporary use, aluminum foil has worked for me in the past. The problem with the possible light leak at the camera strap connector is that the strap itself keeps pulling the tape off.

[Cadmium]

Enrico is a smart guy, so start with a hood before you wrap the thing in electrical tape...

 

And as tape goes, electrical tape get goopie gunkie stuff all over everything, I know... I have used it also,

so what are other people using for tape, because I would like to find some that doesn't leave goop like electrical tape.

 

The towel idea is good too. You can pretty much wrap the whole camera and lens up.

[Andrea B.]

So, Andy, carry some tape and tape up the strap connector just before shooting. I forget which camera you are using. Which one is it that you suspect of leaking?

 

Here's a suggestion for less desireable areas of Boston. Wear a fluorescent safety vest, hard hat and a pair of workboots. Ma sez, "Srsly, do this!". Also useful to let a hammer dangle from the work pants tool loop.

 

I was thinking of getting some safety vests printed up with UltravioletPhotography.com. Bjørn Birna always always made me wear a safety vest when shooting within a mile of any traffic. And of course out in the fields or woods one needs to be visible in case of hunters. Fluor safety vests also let park rangers and the like know that you are photographing for a serious purpose. (lol, we hope....in some Arizona nat parks, rangers are not convinced by anything and investigate you thoroughly. Always have ID on you.)

 

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Cadmium: ...so what are other people using for tape, because I would like to find some that doesn't leave goop like electrical tape.

 

Steve that is a totally good question!! Worthy of a separate topic. Which I will now go create. :D

 

Go here to discuss tape.

LINK: What kind of tape for taping up camera light leaks (and other stuff)

 

 

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