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10-26-2010, 05:45 PM   #1
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Weird Flaring off compact fluoro lights

I was outside after dark tonight with an -A 1.4 50mm at f2 1/60th playing with fill flash on the front of the house, getting ready for Halloween night.
I was horrified to see the most awful flaring off the compact fluoro lights on the house entry way.

https://www.pentaxforums.com/forums/members/wombat2go-albums-wombatspics-pict...ngprob3818.jpg

(Hope this link works, it is my first try)

I recently purchased (based on price) quite a large number of filters called Kokonor HQ UV 49 mm with the idea of leaving new, clean filters permanently on my -M and -A collection .

Some tests:
Take the filter off the lens : Flaring disappears completely.

Put an ancient worn and dusty Hoya UV(0) japan filter on : Flaring is very much reduced, slightly visible against black.

Put the Kokonor back on, switch off the compact fluoro lights , switch on fill flash : no flaring visible.

Put the Kokonor back on, switch on the compact fluoro lights , switch off fill flash : no flaring visible.

The flaring only occurs when the Kokonor is on and the flash is on and the compact fluoros are on. I suppose it will take an optics person to explain it .
Any comments will be appreciated.

best regards to all

10-26-2010, 07:22 PM   #2
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Ever lens interface (glass to air or air to glass) makes a reflection of any light entering or leaving the glass. This light bounces around in the lens. If there is a lot of light and it is even across the photo it just may look like a veil (haze) is across the lens. This is veil flare. A lens hood may help keep light from out side the scene from getting in the lens. If the light is very bright and the reflection lands on a dark spot on the photos you get lens flare (bright spot). To help reduce this manufacturers use coatings on the lenses. This can’t always stop this but it can greatly reduce it. Some filter manufacturers also uses coatings on the more expensive filters. Even with the coatings on the filters because they are flat (not curved like most lenses) they are still more susceptible to flare. This is why most photographers say with night shots to leave the filter off unless you really need it for some reason. Some say leave them off for all shots but especially for night shots. If you use a flash you can brighten up the whole scene and this can make the flares less noticeable. Change the angle just a little and the flares can come or go. Drag the shutter or not and the flares can come or go. Change the aperture and they can come or go.

The photo you posted looks like a textbook example of flare from the filter. Ever spot has a light on the other side of the lens right thru the center of the lens. As the angle, aperture, ISO and shutter speed can effect how the flare will look unless you keep all of the variables exact the same it is hard to say precisely why for a given photo the flare is there and not in the next. This is why so many say to just take the filter off as it is to hard to predict.

DAZ

Last edited by DAZ; 10-26-2010 at 08:58 PM.
10-26-2010, 08:13 PM   #3
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Agree with Daz. Great explanation. Get rid of the filters.
10-27-2010, 12:53 AM   #4
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Amazing, but true, that the most critical glass/air interface seems to be at the filter, rather than all those deep within the lens itself. Actually, I think what you're seeing is reflections from the lens front element being in turn reflected from the filter back into the lens.

The effect will be minimised by use of the highest quality multicoating on the lens front element and the filter itself. An interesting survey of several popular UV filters can be found here, and makes very interesting reading:

UV filters test - Introduction - Lenstip.com

The problem is by far at its most acute in night situations - I 'd venture to say that with quality multicoating you won't really have much of a problem in "normal" situations. For that reason, maybe the best solution is to use a quality UV filter to protect your lens, but to take it off when you recognise a problematic scene (that's what I do nowadays).

Regarding the intermittent nature of the effects you're experiencing, don't forget that some fluorescent lights will flicker at perhaps twice the mains frequency (some much higher), and that therefore you may experience variability in the brightness that the camera captures. (It may not appear variable on the photo, because the highlights are well and truly "blown", but as far as the flare is concerned, this could be varying a great deal!)

10-27-2010, 03:00 AM   #5
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All well explained and agreed, I have to make some remarks, too ,.-)

AFAIK the green blobs come from those highlights being reflected by the sensor itself back onto one of the lens surfaces or the filter. That is why they are always axially symmetric.

It might have to do with the light source's color temp and afaik all these blobs are of green color (night scenario). No explanation here really.

I am wondering why the OP states that it only happened with the flash on. Might have to do with my green color theory, as the flash would have shifted the color temp.

Best, Georg
PS: Here's a nice thread about provoked reflections of all sorts. Not a lens fault per se but an attribute .-)
10-27-2010, 03:49 AM   #6
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QuoteOriginally posted by georgweb Quote
I am wondering why the OP states that it only happened with the flash on. Might have to do with my green color theory, as the flash would have shifted the color temp.
The camera would be setting a different aperture and shutter speed also. Could be that the flare only becomes obvious with a smaller aperture. No EXIF provided so we can't tell but that shot does not look like f2 as stated in OP.
10-27-2010, 04:26 AM   #7
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Thanks very much for the explanations and links. I will read about filters and try to get some that are low reflective because I don't use lenses without filters on.
I am thinking that the compact fluoro must be highly reflective when it is on, and not when it is off.
The flash was an old AF160 that i modified its sensor to chop faster than normal for fill flash with exposures in range 1/90 to 1/30. The flash duration would be about quarter of normal.
The camara was istds in manual and iso 400 1/60 and the -A lens was set by aperture ring to one stop off wide open (f2).
10-27-2010, 08:19 AM   #8
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Out of curiosity, what color were the compact bulbs? I use the yellow "bug light" ones outside. There are other colors on the market including blue, green, black as well. Plus, there are different temperature ranges for all of the white ones as well. That said, before trying to get a filter, I would try setting the camera to fluorescent light in those situations and see if that helps.

10-27-2010, 10:19 AM   #9
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6500 K which is a peak about 5500 angstrom and I see that the turquoise to apple green of my flares is 5000 to 6500 Angstrom. The old AF16 flash is 5800 K.
Yes, Blue, the camera was on AWB and tonight I will try different WB. This is fun but i don't know what the neighbors think of it.
10-27-2010, 12:13 PM   #10
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Oh-Oh, it IS the UV filter. Too bad I bought a whole batch of them.
I just took these 3 shots looking toward the sun
I don't think the brand K is fit for purpose, I will see what the vendor thinks.
Pentax_A 1.4 50 mm with no filter
PentaxA NoFilter - wombat2go's Album: LensFilterCompare - PentaxForums.com
Old Hoya UV(0)
Hoya UV 0 - wombat2go's Album: LensFilterCompare - PentaxForums.com
Kokonor HQ UV
Kokonor HQ UV - wombat2go's Album: LensFilterCompare - PentaxForums.com
10-27-2010, 01:37 PM   #11
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Filterhouse.com has offered a refund so I will change to their Hoya UV(0) filters
10-27-2010, 11:04 PM   #12
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QuoteOriginally posted by wombat2go Quote
Filterhouse.com has offered a refund so I will change to their Hoya UV(0) filters
That's really good news! I think the multicoating on the inner surface of the filter (especially) is really important (make sure you get the HMC multicoated filters!).

By the way, I reckon the green colouring of the flares will be due to the Pentax SMC multicoating on the surface of the lens's front element. The Kokonor filter appears to be a good job of reflecting the reflections from the front element back into the lens! (That's just my speculation, of course.)
10-28-2010, 06:24 AM   #13
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Yes m42man you are spot on I think.
What i found after testing some different brands (about 6 brands) with a CFL on an adverse angle is that
Kokonor HQ UV types had the worst flaring of all
But
Kokonor UltraQ UV Guard MC slim had the least flaring of all,
Better than the older Hoyas I have here which were 2nd best of all.

UltraQ are very thin about 2mm and i guess MC means multicoat

I tested with SMC Pentax 2 50mm wide open (52 mm filter thread)
and SMC -A 1.4 50mm set at f2 (49mm filter thread)
For my purposes, i can leave the UltraQ filters on lenses permanently.
Its curious that the good ones are listed at same or lower cost than the bad ones.
I went ahead and ordered some UltraQ and some Hoya UV(0)
10-28-2010, 11:31 PM   #14
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Interesting info regarding the Kokonor UltraQ UV Guard MC slim - I shall look out for them. And glad to see that you've got your filter problem finally sorted!
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