Welcome to our community

Be a part of something great, join today!

Log in
  • 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 :)

Rainbow striping on image

Mark Deeble

Mark Deeble

Well-known member
Joined
Aug 20, 2010
Messages
188
Reaction score
0
Points
16
Location
Kenya
Website
www.deeblestone.com
Can anyone suggest what might be causing the rainbow striping in this image please? The striping is visible on a number of shots - the more the backlight, the more intense the effect. Sidelight in the same conditions had no visible effect. The camera had been black-shaded before shooting.
Shot backlit in dust-storm Epic Dragon 6K, Optex-Nikon 50-300, 30fps, 180 deg, RC 8:1, Circ POL

https://www.flickr.com/photos/127581889@N04/15424768822/

Edit: R3D https://www.dropbox.com/s/6vy6x29pdxc4x39/A018_C051_1002G1.0000000F.R3D?dl=0
 

Attachments

  • Rainbow striping.jpg
    Rainbow striping.jpg
    17.2 KB · Views: 1
Last edited:
Hi Mark, quick introduction. I'm Joan, a Colombian filmmaker, based in Kenya over the past nine years. I'm very good friends of Simon Trevor (help him out with all his technical issues when possible), but my work really focuses around documentary centred around human issues. I was at the premiere of The Queen of Trees here in Nairobi and was blown away by the beauty of your film (even bought a copy!). I would love to meet you one day, perhaps one day you are transiting in Nairobi, or when I'm in Voi with Simon (actually was shooting a docu on poaching with Robin Dimbeldy couple weeks ago and we saw you Wanted posters).
Right, now straight to the point. I have been a RED Scarelt and now Epic owner for the past three years. I can't really see from the thumbnail the problem you are experiencing as it is very small and it's a jpg, a r3d 1 frame file would be much better. However, I have a feeling that what you are experiencing is CMOS banding or Gate flaring which has been discussed a lot in the DRAGON forum. Are you on a Nikon mount? There has also been some discussion regarding gate flaring with Nikon mounts... Also, are you on OLPF v1 or v2? Also, you mention the camera had been blackshaded, but, have you upgraded the firmware afterwards? With DRAGON it is of paramount importance to blackshade after every and any firmware upgrade. Just as well, blackshading is so much more critical, that it has been stressed repeatedly on the forum that the camera has to reach it's optimal temperature (some people suggest turning the camera on and rolling on a magazine for 10 minutes to allow the camera to warm up evenly and quickly).
(I'm not finding the CMOS thread, will keep on looking)
http://www.reduser.net/forum/showthread.php?119888-Gate-shadow-On-OLPF1-amp-2
http://www.reduser.net/forum/showthread.php?120485-Flare-OLPF-Port-Bushing-for-Dragon
Hope some of this helps!
joan
 
Found a couple of posts related to the CMOS smearing.
http://www.reduser.net/forum/showthread.php?121045-Horizontal-Magenta-CMOS-Lines-Continued/page3
http://www.reduser.net/forum/showth...zontal-smearing&highlight=cmos+dragon+flaring
Also, don't know if you are aware that OLPF system has been updated now and there is a new interchangable system. Some improvements have been made on the old OLPF (previously called v1).
Yup, circular polarizer could play something, but by the description of backlight shots, sounds more like cmos smearing or gate flaring which have been discussed a lot on the forum.
cheers
joan
 
Thanks Joan! - would be great to meet - will PM contact details.
A bit more info on the shots - my Optex-Nikon 50-300 is PL mount, firmware is latest release, I black-shaded at various shutter speeds, 1/50 - 1/300 with camera at operating temp (15 min up to 65 deg). OLPF is v2 ( skin-tone, fixed). I'll try and post a R3D later but am in the bush with a very poor connection :)
I don't think it is gate flare ( I used to see that with the MX, prior to the OLPF bush upgrade). I hope it is the circa. POL but I have never experienced it before with that combo.
The effect is 3 diffuse vertical stripes of colours ( rainbow spectrum - but magenta and green the most obvious) over the entire image.
 
Hi. Can't say I see the CMOS or blackshade related symptoms in this image.
My guess would be an optical source.

Send a file to red and ask, and if you could post a single frame R3D, you could probably get a bit more help.

Best
G
 
Now that I've seen the image properly and download the r3d file, yes, does not seem cmos related, does look like optical. You mentioned you have noticed this in this type of light conditions. Have you had similar results without the circ pol or have you always had it on when this has presented itself?
 
Thanks Joan - I have filed a support ticket. I have gone back through recent material and also noticed it on other shots from previous days (not backlit - and just high natural light).
 
That looks optical, like stacking ND with circular POLA. because it is a new sensor and the IR tendencies are different you might need to go with another brand of circular POLA or variable ND. The flare probably has something to do with it as well.

Or it could be the circular pola, lens, combo (lens coating, pola, different OLPF) could contribute to these kinds of effects.

What PL glass was it?

Battistella
 
Mark.

Just a way out suggestion for a long-shot try. I am assuming an optical not electronic cause and that you may be well and truly distant from product support. If you are using mattebox filters 4x4 or larger, maybe try painting the frosted edges of the filter glasses with black felt tip marker and round the shiny face edges where they slip into the mattebox slides just in case something is coming off the smooth surfaces of the mattebox slide frames themselves and illuminating the frosted edge surfaces.

Maybe mask off the filter mattbox port to just outside of your widest lens view with a blackened paper or cereal-packet cardboard insert, maybe one for each lens field-of-view if the longer lenses are more prone to show the artifact.

Also maybe cut a piece of softly folded blackened paper with a sensor port cut in it and lay this in the space in the camera body behind the mount so that the horizontal "steps" in front of the sensor are covered over by a smooth taper.

Maybe cut a blackened rectangular "frame" exit pupil aperture to go on the rear of each lens like some lenses have fitted to mask some internal reflections.

These may all be red herring suggestions. If the colourations are vertically banded, then it may be a sensor issue. If they are horizontally banded then it might be an optical fault.


Does the artifact move around the image if you dutch or roll the camera whilst remaining on subject or only change in intensity whilst the image moves?
 
I'm also wondering if it is some internal reflections between the lens and the filter. I had some of those internal reflections going on yesterday on some stuff, but it was related to filter distance from the front element. Even with minimal space, at certain angles I was getting reflects. But none of it was sensor related.

If you loos the filter, do you see it?

Battistella
 
Thanks guys - I am away from the camera but will test when I get back, if I can recreate conditions where I see it again. Lens was an Optex converted Nikon 50-300 f 4.5 to universal mount ( mounted PL in this case) which I use for a lot of wildlife work. Polariser was a Hasselblad 95mm circa polariser. I should have tested more at the time, but I had waited days for the action and it lasted less than a minute - so was rushing around trying to cover the action rather than analyse the problem. I'll try different filters, windowing, camera orientations etc early next week and report back.
(It may well have an internal reflection component as I had to change out the lens shade I normally use as it was vignetting at 6K coverage)
 
I am torn between the notion that there is something electronic going on versus something related to the polariser and the sensor.

This is a useless comment but here it goes anyway as it will only take 15 seconds or so to try the suggestion.

During your examination of the camera, perhaps remove the lens to look at the sensor itself, through the polariser filter itself held up to your eye and rotating. You might need to view from different angles to side of optical axis and maybe move the light source behind you relative to the camera by swivelling the camera a little.

If there is an apparent faint banding pattern reproduced on the surface of the sensor, perhaps remove the special OLPF if you can safely do so without introducing dust, or swap with another different OPLF to see if the pattern is reproduced.

OPLFs are made specifically for a pixel pitch but it may just be that the pixel count for a given dimension is slightly different to that which the OLPF is tuned for. This is real witchdoctory on my part which has no basis in science whatever so please do not pay it any but fleeting notice.

If the issue is not electronic in origin, then there might be potential for features pixel pitch related, to interact to produce a faint repetitive pattern.


The actual pixel count per measured unit across the sensor.

The pitch of the printed bayer pattern of coloured masks being not quite coincident with the pixel pitch creating a moire not cancelled out entirely by the sensor calibration process.

The OLPF frequency cut off point.


The trouble with dangerous armchair theorists like me is that dead-ends and red herrings most often abound to create distraction. However if this is an issue which is not quite solved then it might stimulate another direction of thought by tech people who really know their stuff.


Who knows? When this program goes to air, please let us know here and via Facebook. Attenborough must surely wish that this tech was around when he did his best work or that he should enjoy agile health for another few years to work with the new gear.
 
You must log in or register to reply here.
Back
Top