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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

A strainge magenta fx

N

Nicos Ambatzis

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Today shooting with the Red MX (24fps, ISO 800, Day light, 18mm lens +ND 9) in a sunshine day, there was in the center of the frame an octagonal more or less light magenta spot shown more to dark areas (black dress). I try everything possible but with no better results. Any idea how can I correct it. What may be wrong? Your help will be very much appreciated. Thanks in advance.
 
Someone may have a better answer, but it may be IR pollution/caused by the ND. What kind of ND are you using? I had a similar effect using a Schneider ND1.5 and solved it by swapping for a .6 and stopping down
 
Have you tried blackshading calibration with the body cap on? Also, be sure to balance those ND's with IR filters or it could possibly be giving you something off... do you have a still of this black dress? .r3d trim from REDCINE-X?
 
It's IR pollution of the blacks, caused by using heavy NDs. The solution is to drop a hot mirror in front of your ND or use IRNDs. The MX sensor is prone to it, but it's a well understood problem. Have a search on here and you'll find a load of threads explaining it in detail.
 
agreed on the IR pollution. You start seeing IR pollution when using a .9 ND, plus you might be stopped down a bit and thats why you are seeing it in the center in an octagonal shape. Thats the actual opening of the iris that your seeing. Agreed on the HOT MIRROR, with the EPIC / Scarlets I think those do the best job of blocking and keeping colors close to neutral.
 
I don't think its an IR problem if You are using a superspeed 18mm. Its a very pronounced effect with the wide angles of that group since they were not designed having a flat glass in the path to the film
plane ( now the sensor). Try to shoot below f5.6 by lowering ISO to 320, go to ND 12 and shorten the exposure time to maybe a 60th.
 
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Thank you very much to all of you. You have been so helpful. I tried the IRND and the situation improved. Now I will try the hot mirror. Thanks again.
 
Chad Cooper said:
Someone may have a better answer, but it may be IR pollution/caused by the ND. What kind of ND are you using? I had a similar effect using a Schneider ND1.5 and solved it by swapping for a .6 and stopping down
Click to expand...

yup, the Schneider NDs screwed me first time I used them over .6 without an IR filter. Turned all my footage pink and was barley able to bring it back to neutral. learned the hard way from that mistake!
 
I don't think its IR pollution...I had a similar problem with some old Pancro's..Bare lens not ND or anything,,,The ND may make it more obvious but it would happen to me with no ND.... Usually the 18mm or wider lenses would give me a lens flair that was purple or magenta the shape of the iris.. went away when I didn't focus so close and changed the way the light was entering the lens.. Really ruined a few shots but learned to work around it with those lenses.
If you can repeat the effect try opening and closing the iris and see if the spot gets bigger and smaller as you open and close down..
 
I've had a similar experience when using Schneider NDs, try the auto white balance with the filter on, works for me.
 
IR Pollution. can also happen if you are shooting something "hot"... like a candle or a fire. Basically anything that's putting out alot of IR. Hot Mirror helps to cut down
 
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