Iridium filter

[GaryR]

Found a bit of a buzz on FB about the Kolarivision Iridium filter. It looks like a RGB tri-band filter, designed to enhance pure red, green and blue colors. No UV sensitivity, but it might be useful for false color.

 

https://www.danwampler.com/blog/2023/11/Iridium-filter?fbclid=IwAR32sHXYs9IDG4_Qrm_FsueFwRJFW5609ro3NGtmU2tDtyZTXEdswor4_T8

https://kolarivision.com/what-is-iridium-filter/

 

[Wayne Harridge]

It would be interesting to look at the spectral response for the filter.  I would have liked to see comparison shots with & without the filter.  I doubt that using the iridium filter combined with an IR pass filter has much effect.

 

 

[colinbm]

@Wayne Harridge https://kolarivision.com/what-is-iridium-filter/

[Wayne Harridge]

19 hours ago, colinbm said:

@Wayne Harridge https://kolarivision.com/what-is-iridium-filter/

Thanks Colin, that article shows the spectral response and has a few comparison shots which is helpful.  So it seems the filter passes plenty of IR so if you add (for example) a 720nm IR pass filter on a FS camera the iridium filter will have little effect as the 720nm will pass very little of the "manipulated" visible part of the spectrum.

 

[DKoch]

these types of RGB separation filters that remove the " crossover" wavelengths to increase saturation  have existed for decades...As a cinematographer , we would have died to get our hands on something like this is the Photochemical Epoch of feature filmmaking! We were pure photochemical from acquisition, through post , colour grading and finally printing of course. All we could really control was density and colour balance.

  When Digital Intermediates became the norm for theatrical features, one then had amazing control in the colour grade when going from film to digital.

So, a filter like the Kolari Vision can be easily replicated in digital image manipulation now; highly tuned selective colour saturation boosting is quite easy; if one use the LAB colour space , the results are even crazier!

 

I own numerous different versions of this type of filter from the 90's and early 2000s; a peculiar thing: they are super impressive to the human eye when you look through them; less impressive results on imagers.I suspect that Wayne Harridge is correct that it wouldn't have much effect ...

[lukaszgryglicki]

Well I don't see any filter that I can screw-in onto lens (no 52mm/77mm screw-in threaded versions) - only the sensor cover glasses - I would give it a try if I could buy it as a "normal" lens filter...

 

[Kai]

Inspired by this "Iridium" filter, I took two photos of two microscopy slides stuck together. As a light source I once used a flashlight with a fluorescent tube and the other time a large LED lamp. The light from fluorescent tubes is less soft.
The images reflect the visual impression. In fluorescent light (tube with three phosphors) you can see the interference fringes much more clearly than in LED light (and visually in sunlight). The color differentiation with LED light is much better.
Result:
With just a few, narrow-band lines, you can achieve in this case more contrast and stronger colors at the price of poorer color reproduction.

[ulf]

This is an interesting phenomenon caused by constructive and destructive interference due to the short distance between the two glass surfaces.

The principle is often used for flatness analysis with an optical flat reference.

This is normally done with a rather monochrome light source like a low pressure sodium lamp with dominantly yellow light.

 

As you demonstrate here a more continuous  light source as the white LED-lamp a smearing effect hides most of the interference bands.

 

I assume that you are not linking this interference directly to the "Iridium" filter's colour enhancing effect from a technical point of view, or am I missing something here?

I am sure the CRI is very bad for the florescent flash light giving bad colour reproduction when used as a light source.

 

Interestingly the "Iridium" filter is supposed to improve images by limiting parts of the spectrum reaching the camera's sensor.

This filter is quite advanced.

 

Historically there has been other types of "enhancing" filters, often based on different diodynium type of filter glass.

Some years ago I collected such enhancing filters to examine with my spectrometer.

They were marketed as Red Enhancer, Blue Enhancer...

 

The same type of glass has also bee used to improve astro photos as some of the glass types block the yellow sodium light quite well and could then limit the light pollution from cities and street lights. When shifting to LED illumination that use is gradually lost.

 

Another area for such filters is to block the bright yellow flame you get when flame heating glass during glass blowing. The flames become yellow due to the sodium content in the glass material and there are special goggles that can help visibility.

 

[lukaszgryglicki]

Is there any such filter available as a threaded filter to be screwed on the lens? I cannot find it - I can only see sensor cover glasses options.

 

[ulf]

15 minutes ago, lukaszgryglicki said:

Is there any such filter available as a threaded filter to be screwed on the lens? I cannot find it - I can only see sensor cover glasses options.

 

If you are asking about the older types here is an example:

https://www.ebay.com/itm/184141810248

Search for enhancer filter on eBay to find more

 

[lukaszgryglicki]

Right, I saw those enhancers (various types). -I was specifically referring to this Iridium one - Kolari even answered to my question on email that they don't offer lens filters for this.

 

[lukaszgryglicki]

Looks like MIDOpt have some interesting dual bandpass and tripple bandpass filters available - they can be ordered with standard M52-M82 threads - I've contacted them for quotes for few of them.

 

[DKoch]

On 12/7/2023 at 11:42 AM, lukaszgryglicki said:

Right, I saw those enhancers (various types). -I was specifically referring to this Iridium one - Kolari even answered to my question on email that they don't offer lens filters for this.

 

 

Filters like the Kolari Iridium are thin film filters ; they don't work by simple absorption so they are sensitive to the angles that the light rays pass through them...the wider the lens, the more the corners of the frame are filtered differently!!! Putting them in front of the imager will help somewhat, but depending on the lens design , there may still be lots of "uneven" filtering across the frame. Lenses that are very tele centric on the image/sensor side work best; these tend to be more modern lenses...

  The Didymium glass style  Enhancers first entered photography in the  early 80s and we used the Tiffen Enhancer quite a lot with colour negative films way back then.This is the most famous one of the type Ulf mentions...they work by absorption so there are no effects due to focal length or light angles....Singh Ray made "red" , "Green"  and "blue" enhancers, but when you study their transmission curves, they are all the same didymium /rare earth mixture with dyes added to change their characteristics. These filters are notable in that they have very steep "walls" on their peaks and valleys, but are not thin film filters.Youcan still buy "Enhancer" filters in all sorts of sizes I believe.In motion picture we use a lot of Tiffen filters and they made the Enhancer all the way up to 6.6 x 6.6 INCHES! 

[DKoch]

here's crude transmission curves of the three different types of Enhancers made by Singh Ray they really are just variations on the same didymium rare earth ("RED") filter, with dyes added to pop the greens or blues..;

[DKoch]

here is a "Omega XB-19"  thin film Enhancer filter from the late 90s . Mine is only 40.5 mm round ; i use it in front  of the film or sensor.Same concept as Iridium in that it removes the "crossover" wavelengths between the R G B curves....again, this was something that was generally more impressive to the human eye than to the sensor..

[DKoch]

On 12/7/2023 at 1:14 PM, lukaszgryglicki said:

Looks like MIDOpt have some interesting dual bandpass and tripple bandpass filters available - they can be ordered with standard M52-M82 threads - I've contacted them for quotes for few of them.

 

 

there are a LOT of really interesting double, triple and quadruple band filters out there! However, remember that they are all thin film filter$ and will be small and work best with telecentric  light paths and will need to be in front of sensor and never in front of lens...Omega Optical is worth a look!

[DKoch]

here is a comparison of no filter with the Omega XB-19 filter shown above

[lukaszgryglicki]

Hmm but they sell threaded filters like M52 to M82 - so, obviously, they can be used on the lens - so the question is - will they be usable?

The price is also a killer (they've sent me quotes) M82 tripple-band is almost 1080 EUR, double bands are 637 EUR - they didn't sent M52 quotes yet.

 

[DKoch]

the top image is the filtered one; bottom is no filter reference...shot on a Panasonic Lumix

[DKoch]

11 minutes ago, lukaszgryglicki said:

Hmm but they sell threaded filters like M52 to M82 - so, obviously, they can be used on the lens - so the question is - will they be usable?

The price is also a killer (they've sent me quotes) M82 tripple-band is almost 1080 EUR, double bands are 637 EUR - they didn't sent M52 quotes yet.

 

 sure, but on their title page they describe their  "Machine Vision filters".... machine vision uses very special ultra telecentric lenses! So these type of filters would work in any diameter with those type of specialized lenses ; all the light rays go through the filter perfectly parallel, a condition that few normal pictorial lenses do.Here is an example of a custom made narrow RGB triband filter that I had made by Omega, the same people who made the other XB-18 shown above... same focal length, but there is something even more critical about the need for telecentric rays through this filter! See how the colour is different across the frame ! These images all had the filter out front, but using a long lens

[lukaszgryglicki]

OK, thanks for the info.

[Andy Perrin]

If you use a long enough lens it’s not too bad, depending on the filter. I’ve used the dual band DB850 from MidOpt for ages with my 80mm EL-Nikkor lens and never noticed any problems. Obviously the filter DKoch is showing must be more sensitive. 

[DKoch]

On 12/9/2023 at 11:44 AM, Andy Perrin said:

If you use a long enough lens it’s not too bad, depending on the filter. I’ve used the dual band DB850 from MidOpt for ages with my 80mm EL-Nikkor lens and never noticed any problems. Obviously the filter DKoch is showing must be more sensitive. 

that makes sense Andy. The narrowband RGB filter I had made has very narrow tolerance for angle on incidence through it for some reason... when you look through it by eye, it's immediately visible!