IR Chrome and "Aliexpress Aerochrome filter"

[Marc del Piro]

I have been away for a long time since the publication of the IR Chrome DIY Chinese version. After playing around with colour glass filters in IR photography for a while, I am coming back to set this new post about IR Chrome and the "Aliexpress Aerochrome filter". Nantong Foric Optical Glass Factory is making a pinch with it. Since they published it, more than 100 filters have been sold at my acknowledgement.

 

So I think now that some Instagrammers call it IR Chrome as if it was the original, or some even say Kolari is buying it from Aliexpress, I think it deserves a bit more insight investigation and explanation of why both filters are similar, but not the same in technical aspects. Even though for the sake of photography, they give the same results if meaningful postprocessing is done, as demonstrated previously in my post: "Kolarivision IR Chrome DIY Chinese version".

 

CONSTRUCTION

 

First of all, both filters are made of two glasses. Kolari Vision states on its webpage that the IR Chrome filter is made of "Fused Glass", which is "Thicker than other filters", and it is "AR coated". This is basically because they are using either two different filters, which are cemented/fused. Or it could be one single glass layered in two or more pigments, coatings or materials that produce this filter with the properties I will show later on. I once tried to unscrew the filter from the ring, but I couldn't.

 

Secondly, we have the QB19 + Heat absorbing (GRBx). This filter, as I exposed in my previous post, "Kolarivision IR Chrome DIY Chinese Version", is made of two different glasses of 1mm each (1:1). They are not fused or cemented, so if the ring save is unscrewed, both filters can be separated, and the factory does not offer AR coatings. Even though my tests brought me to use a 2mm QB19 + 1mm GRB3 (2:1) this past few months, this setup comes at the expense of using a filter cap, of course, but one cannot have everything in life, can I?

 

In conclusion, we can see that both filters resemble each other in certain aspects and that Kolarivision could not create a new filter without using a traditional technique: probably mixing a Heat Absorption Glass + a Blue Filter.

 

FILTER COLOR AND APPEARANCE

 

Filters look different from side to side. Let's take a look at them. From left to right: QB19 + GRB3 2:1; Kolari IR Chrome; QB19 + 1:1.

 

 

 

 

 

At first glance, the 2:1 is darker than the other filters. Since the 1:1 looks similar to the Kolari IR Chrome, I decided to check what a ViS camera sees through them. The following images are taken with a Fujifilm X-T30, with a 15-45mm at f8 and ISO 1000. Images are taken on the same white paper as the picture above. Images are equally cropped to match the centre and avoid vignetting. WB was set to 5500ºK (as the white paper in the photo above gave me exactly 5500ºK as a WB in Lightroom). The green-magenta balance was set to 0. Finally, sharpening was set to 0 and noise reduction maximized to 100 to produce a flat colour image. Finally, histograms were equalized so the first point of light matched the same point in the histogram in each image.

 

The resulting images are the following:

 

QB19 + GRB3 2:1

 

Kolari Vision IR Chrome

 

QB19 + GRB3 1:1

 

The last filter is the one that produces the softer blue tone. Vegetation tends to appear duller in the 1:1 version of the QB19. This is because the amount of IR and red light entering the filter is not well compensated by the blue/green tone of the filter. The histogram shows a bit less amount of red light passing by the filter, but the reds are more towards the lights (right), which means middle tones will have more reds overall than in the other two filters. If you want to see the histograms, please download the images and check them in Photoshop, Lightroom or any other software of your choice.

 

Please note this is just a ViS light test, which we'll come back to later in this post.

 

WAVELENGTHS

 

First, I must ask for forgiveness from those most scientific, scrupulous, and meticulous members of this forum. I did some tests, but they were not high-grade professional tests. I could access a test room in a local university, and the equipment was a bit old (it runs with Win95 ). Anyway, it helped me a lot in understanding the behaviour of the filters: their similarities, differences and why the final results after postprocessing are quite similar and to be honest, indistinguishable.

 

The following graphs have some noise that we could not suppress due to the nature of the sensor and the source of light we used.

 

To obtain the transmittance values, a Red Tide USB650 sensor from Ocean View and a halogen light were used. The sensor was balanced to set all received values to 100% and the filters were set between the light source and the sensor. The resulting results were processed in an Excel document to produce the graphs of each filter.

 

The graphs contain a lot of noise from 350 to 370. Those values were deleted for the sake of this presentation since they present no useful information due to the noise.

 

Shown in the image above are the QB19 + GRB3 in both versions. As shown by the graph, the 2mm QB19 cuts more R and NIR light than the 1mm. At around 770 they both equalize, producing the same falling line due to the GRB3 properties. Note also how the 1mm has a bit more green than the 2mm. This fact produces the difference in the images presented before in this article. The 1mm gives a richer tonal towards G, hence producing a more turquoise image.

 

Following, the IR Chrome graph is presented: 

 

 

I will leave interpretations of this last graph to the community of this forum.

In the next graph we can see the comparison of the three of them:

 

 

IR Chrome allows more visible light to pass through compared to two other filters. However, it blocks a lot of the infrared (IR) light. The graphs explain why images taken with QB19 at 1mm look less vibrant than those with IR Chrome. Even though QB19 at 1mm permits slightly more green light, it doesn't make up for the excessive R and NIR.

 

Conversely, QB19 at 2mm addresses this issue by blocking more red light than IR Chrome and allowing more near-infrared light, resulting in richer red foliage. The extra NIR in addition to the deeper blue hue of the filter, can create magenta vegetation in specific situations. But there are drawbacks: sometimes, the images may appear too cold, and the filter is too large to fit a cap on it.

 

In summary, while IR Chrome lets in more visible light, QB19 at 2mm compensates for the red light and enhances certain colours, albeit occasionally creating a colder image and being cap-unfriendly.

 

It is also expected that IR Chrome creates fewer hotspots than the other two filters, but this is going to come at some moment in the future. This post has gotten long enough already.

 

CONCLUSION

 

Anybody interested in IR photography who wants to produce red/orange foliage straight out of the camera can benefit from any of the filters. I consider IR Chrome to be well-built and useful in many different kinds of situations. It's better balanced, but as a result, the sky looks more turquoise and the vegetation looks orangeish. At the same time, it's much more expensive.

 

The Chinese "Aliexepress" version can fulfil the necessities of 99% of the users, and for the price of one IR Chrome, you can supply all your lenses with filters. Kolari Vision indeed has the new Clip-in magnetic filter, but they don't fit some lenses, and it's 200$ nonetheless! Sent to my door in Barcelona it would get up to 300$. No way I want to afford it.

Whatever filter you are going to use, may you all have a nice day of IR shooting!

[Andrea B.]

Mark, thank you for this analysis of the Kolari IR Chrome and the two QB19 + GRB3 stacks. 

 

First, I must ask for forgiveness from those most scientific, scrupulous, and meticulous members of this forum. I did some tests, but they were not high-grade professional tests.

 

You are forgiven.  While the measurements might have their flaws, the results are still useful for comparisons between the IR Chrome and the two stacks. Your observations that the QB19 x 1mm stack is less vibrant than the IR Chrome and that the QB19 x 2mm gives richer red foliage are certainly correlated to the graphical displays.

 

I looked up what the closest Schott stack would be. The heat absorber GRB3 matches (more or less) Schott KG3. But the QB19 does not have a Schott equivalent. Probably the Schott BG38 is the closest match?

 

I agree that the Kolari IR Chrome must be a cemented stack. There is a benefit to that - no "air gap" to induce detail-destroying veiling-like flare in some lighting conditions. Also with any uncoated blue-green glass, we have to be ever vigilant about preventing oxidation. The IR Chrome with its AR coating will probably last longer than any uncoated glass. But as you have pointed out, for the price of one IR Chrome....several replacement QB stacks can be made!! 

[Marc del Piro]

On 12/15/2023 at 10:43 AM, Andrea B. said:

I looked up what the closest Schott stack would be. The heat absorber GRB3 matches (more or less) Schott KG3. But the QB19 does not have a Schott equivalent. Probably the Schott BG38 is the closest match?

I've checked many brands but found no similar filter to the QB19. Schott BG38 has too much red light passing through, it won't work like the QB19.

 

On 12/15/2023 at 10:43 AM, Andrea B. said:

There is a benefit to that - no "air gap" to induce detail-destroying veiling-like flare in some lighting conditions. Also with any uncoated blue-green glass, we have to be ever vigilant about preventing oxidation. The IR Chrome with its AR coating will probably last longer than any uncoated glass.

I've been checking around the forum about oxidation occurring in optical filters. If I am not wrong, the main factor to fight against is humidity. In that sense, there are affordable products for nanocoating glass. Nanocoating should prevent moisture from reaching the filter and would make it last longer. I've never tried, so it's just a guess, but I think image quality should not be affected by nanocoating filters. On the other hand, I've found some AR sheets that could be applied to the filters, but they present just 2-3H scratch resistance. That means the process of cleaning filters would probably damage the sheet, thus, nano-coating is mandatory in this case. And again, just a guess, it might protect the layer from being easily scratched.