Red problem !

[Ryan Avery]

Originally Posted by Mike Stevens

Piotr:

A double threaded version is hard to find - in fact of the B+W I don't think it exists, so this is what I did. I have a 77 to 100 step-up ring with a 95mm thread inside, to which I clamp my Cavision matte box (see my threads on that for interest). Inside this step-up ring I have a 95 to 77 step-down ring that holds the 77mm IR/UV filter on the inside so that the IR/UV filter is in fact in "backwards." This allows the use of the 77mm filter behind a matte box and is a lot cheaper than using the 100mm filter which is about $500 or wasteing a matte box slot. This arrangement works fine and there is no vignetting at any focal length by reversing the filter so it is as close as possible to the camera.

Mike

Mike,

Your solution seems to be a great option for EX1 users. For RED users it doesn't work because of the thread size. This is why we made the mattebox option as well which full explaination is in my previous post.

Thanks for the good idea and solution for a EX users.

Ryan Avery
Schneider Optics

[Piotr Wozniacki]

Dear Ryan,

Thanks for your answers; however, sticking to the EX1 and Letus 35mm adapter applications, which filter I'd be better off: the existing 486, or the existing 489 one?

[Ryan Avery]

Originally Posted by Piotr Wozniacki

Dear Ryan,

Thanks for your answers; however, sticking to the EX1 and Letus 35mm adapter applications, which filter I'd be better off: the existing 486, or the existing 489 one?

Based on the discussions here and my knowledge of both filters, I would think that the 486 would be the better choice. I do not have direct experience with the set up you are talking about but from a science aspect the 486 is the proper filter.

Ryan Avery
Schneider Optics

[Piotr Wozniacki]

Originally Posted by Ryan Avery

Based on the discussions here and my knowledge of both filters, I would think that the 486 would be the better choice. I do not have direct experience with the set up you are talking about but from a science aspect the 486 is the proper filter.

Ryan Avery
Schneider Optics

Thanks again Brian,

The specifics of the setup I mean is that with the 35mm adapter like the Letus, the 486 filter would be "closed" between the camera lens and the achromat lens of the said adapter. Reflected IR could bounce within this space (of course being partially absorbed), but wouldn't they contaminate the picture?

Conversely, with the 489 filter the IR would be absorbed by the filter, hence theoretically less reason for concern...

Is this theory right?

[Sean Donnelly]

Piotr, earlier in this thread I suggested that perhaps that isn't so much of a concern. I still maintain that it doesn't really matter what happens to the IR light reflected by the 486, as long as it doesn't pass though to the sensor. It's not going to contaminate the image, and it's also not going to cook your Letus :)

[Piotr Wozniacki]

Originally Posted by Sean Donnelly

Piotr, earlier in this thread I suggested that perhaps that isn't so much of a concern. I still maintain that it doesn't really matter what happens to the IR light reflected by the 486, as long as it doesn't pass though to the sensor. It's not going to contaminate the image, and it's also not going to cook your Letus :)

Sean,

Considering that even without the Letus I am getting the green tint in the picture extremities (because of the angle of incidence of the light), the multiple reflections of the IR could increase this effect.

On the other hand, with LEX the camera is zoomed in to some Z78, which should help avoiding this...

Unless the multiple reflections will cause considerable amount of IR to reach the lens at the "wrong" angle also in the middle, and this possibility is the reason for my concern!

Since I need to make up my mind which double-threaded filter model to pick, I'd be grateful for some more authoritative answer.

[Mike Stevens]

Serena asked me does the 486 IR/UV work. It does - big time.

I just came back from three days in the desert (that was hot this trip) and I compared the 486 vs. the standard UV/Haze. The green foliage that looks brown with the UV/Haze is correctly green with the 486.

The 486 did mute the reds a tad and so I compensated with a matrix shift of G-R=15 and that seemed to work for me.

Mike

[Leonard Levy]

This thread mystifies me. Is there any consensus about the green vignetting that Piotr documented?

The pictures he posted were extreme, far worse than any red problem I've seen, but it doesn't seem like anyone else has seen it, or if they have they aren't concerned.

I could live with an overall green cast that's correctable, but the vignetting was unacceptable to me.

Are you other guys with the filter having any of this problem at wide angle or anywhere else? Is there any consensus about when you will or won't have the problem. Other images would be appreciated. Thanks

Lenny Levy

[Steven Thomas]

Yes, I'm wondering the same thing. Does the 486 IR/UV have the green cast issue on the edges?

I want to buy one, but I'm also confused on if its problems might out weight the IR contamination fix.

[Piotr Wozniacki]

Guys, the green cast at the extremities is due to IR light angle of incidence, and even Ryan Avery of Schneider Optics confirmed it's unavoidable with those screw-on, circular filters - so I guess you cannot avoid it completely.

As I said: in natural light, this is not a problem at all (even indoors).

It's most pronounced with incandescent / tungsten (warm) lighting, as my pics posted earlier show (they were deliberately chosen from the worst part of my recording, though).

With LED light it's not visible (have done some tests recently, but only in the mixed natural light at dusk, and some LED lamps - see the grabs attached); unfortunately couldn't wait for the sunset at that particular location, so cannot be sure how it works with LED light on its own. One of the grabs shows the scenery in natural light at dusk; the other with LEDs switched on (taken within just a couple of seconds time). As you can see, there is virtually no green cast even in the corners (even though I was at the widest in the right grab).

[Bob Grant]

Interesting tests by Adam Wilt:

http://provideocoalition.com/index.p...lter_tests/P0/

This is not the first such tests I've read of, interestingly all camera seem to have these issues to varying degrees. The other not public tests found that cameras such as the Varicam can need an external IR cut filter.

[Piotr Wozniacki]

Thanks Bob for the link - what Adam is showing as the adverse effects of the 486 on EX1 at full wide, is nothing compared to the ugly cast in my grabs posted here earlier!

As I said - all depends on many variables, but having a filter like this handy is a must with the EX1.

[Mike Stevens]

Originally Posted by Leonard Levy

This thread mystifies me. Is there any consensus about the green vignetting that Piotr documented?

The pictures he posted were extreme, far worse than any red problem I've seen, but it doesn't seem like anyone else has seen it, or if they have they aren't concerned.

I could live with an overall green cast that's correctable, but the vignetting was unacceptable to me.

Are you other guys with the filter having any of this problem at wide angle or anywhere else? Is there any consensus about when you will or won't have the problem. Other images would be appreciated. Thanks

Lenny Levy

The green casts and vignetting have nothing to do with the 486 filter. Piotr has something else going on or the filter is bad or is mounted wrong. As I said, the only down side is a slight muting of the reds that I somewhat corrected with a green to Red +15 in the matrix.

[Piotr Wozniacki]

Originally Posted by Mike Stevens

The green casts and vignetting have nothing to do with the 486 filter. Piotr has something else going on or the filter is bad or is mounted wrong. As I said, the only down side is a slight muting of the reds that I somewhat corrected with a green to Red +15 in the matrix.

C'mon, Mike. While I picked those ugly pics on purpose, the green cast is a fact, confirmed by the filter manufacturer.

In 90% of my shooting scenarios, it's a non-issue at all - so it's possible you have just never noticed it. Especialy that - afaik - yours is not directly on the lense, is it? By increasing the distance (e.g. mounting it in the matte box), you're avoiding the critical incidence angle.

[Ryan Avery]

Originally Posted by Piotr Wozniacki

Thanks again Brian,

The specifics of the setup I mean is that with the 35mm adapter like the Letus, the 486 filter would be "closed" between the camera lens and the achromat lens of the said adapter. Reflected IR could bounce within this space (of course being partially absorbed), but wouldn't they contaminate the picture?

Conversely, with the 489 filter the IR would be absorbed by the filter, hence theoretically less reason for concern...

Is this theory right?

The 486 and 489 alter IR light differently. The 489 will absorb the IR light but only affects this end of the spectrum. The 486 reflects the IR light within the layers of the filter and therefore also controls the UV contamination which will affect blue and green casts to your image. The sensitivity of digital sensors to UV light is much less than the IR light. Therefore a 489 should be relatively as effective as the 486 but for the fact that UV sensitivity still exists with digital sensors and this could be what you are getting with your lens set up.

In mounting the filter, the sequence is very important. A 486 filter reflects the light and there for should be used in the front of all elements. If you are mounting the 486 internally then the issues you state could be happening. The 489 is a better application for internal use such as the situation you state. It is better to have no UV filtration in the 489 and aviod the internal reflection problems.

In short, for this application only, use the 489 internally OR put the 486 in front of the 35mm lens.

Ryan Avery
Schneider Optics