Color change on Zomei 850

[GaryR]

After switching from a Hoya R72 to a Zomei 850nm, I've noticed that images have a blue-ish cast. That never happens when switching from the R72 to any of my B+W IR filters. Re-setting the CWB, gets rid of the blue cast, so I can't complain, considering the cost of these filters.

 

Another interesting anomaly about the Zomei is when you set the CWB, then remove the filter, foliage turns vivid yellow, with a cyan-green sky.

 

Test shot with Zomei 850 (CWB to Hoya R72)

 

CWB set to Zomei 850

 

CWB set to Zomei 850

 

Same shot as above, with Zomei filter removed

 

All shots: fs-Sony a7R + 75mm El Nikkor

[ulf]

After switching from a Hoya R72 to a Zomei 850nm, I've noticed that images have a blue-ish cast. That never happens when switching from the R72 to any of my B+W IR filters. Re-setting the CWB, gets rid of the blue cast, so I can't complain, considering the cost of these filters.

 

Another interesting anomaly about the Zomei is when you set the CWB, then remove the filter, foliage turns vivid yellow, with a cyan-green sky.

The difference in colour casts is normal and typical for different types of IR filters, when using the same WB.

 

I see it all the time in the preview thumbnails from the camera.

I never bother to WB in the camera as I switch between many filters and only shoot RAW.

Then I can do a more selective WB on a selected area of the image.

 

The cast depends of the cutoff wavelength and the sensitivity variations of the RGB-channels in the camera.

There is no universal WB for IR filters and each type need its own WB.

An incorrect WB can give such strange colours you have in the last image.

 

I would be surprised if there wasn't a similar cast with the B+W 093, with a CWB from a R72 .

Do you have the B+W 093 IR filter?

It is rather close to the Zomei 850nm filter as it is made with the Schott RG 830.

 

There is nothing strange with the Zomei IR filters in general.

They have the typical transmission curves similar to the Schott's and Hoya's longpass filter glass types.

https://www.schott.c...jun-2017-en.pdf

The difference in filtering characteristics is not significantly different as far as I can see or measure.

 

The Zomei filters are an example of Chinese good quality products with a very reasonable price.

The polishing of the glass and quality of the metal rings are flawless.

The only thing I do not like is the plastic box the filter is stored in.

 

Naturally the quality of the B+W filters are higher, especially their filter rings made of brass are superb.

I have several B+W filters, but none of their IR-types. B+W is otherwise my preferred brand.

 

I have the full collection of Zomei IR-filters, marked 680nm, 720nm, 760nm, 850nm and 950nm, and have examined their transmission curves with my spectrometer.

The first four have the steep cut on like RG715 or RG850, while the Zomei 950nm behave more like a RG1000 with a less steep slope.

[GaryR]

Thanks for your response Ulf.

 

My B+W 093 is MIA, and is why I switched to the Zomei 850.

 

I do have a B+W 092 that I've tested with the Hoya R72. Aside from the color saturation difference, between a 695nm (092) and 720nm (R72) filter, no CWB adjustment is needed when switching these filters. It was the same with the 093, as I remember.

 

The color shift isn't an issue, but just surprised that it even exists.

 

Very glad to hear you mention about the quality of Zomei filters. If my 093 doesn't turn up soon, I'll order some smaller size Zomei filters, to fit my El-Nikkor lenses. The Zomei 950nm sounds interesting indeed!

[Andrea B.]

The Zomei filters are an example of Chinese good quality products with a very reasonable price.

 

Ulf, this is good to know. Thanks! We should update the Filter Sticky to point out this particular given that you have assessed its quality.

 

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Gary, against what did you make the custom WB in the images above? I was guess that CWB was made "against the scene", as we often do with IR-pass filters.

[ulf]

Thanks for your response Ulf.

 

The Zomei 950nm sounds interesting indeed!

 

I stopped using the Zomei 950nm for landscape as I could not see any difference in landscape images.

There might still be some difference in making water darker, that I never tried or found.

 

The huge difference is exposure time. The 950nm need much mor exposure time.

The colours are monochrome with both filters.

[Andy Perrin]

There might still be some difference in making water darker, that I never tried or found.

 

The near infrared water absorption peak is between 950 and 1030nm, with the max at 976nm:

Refractive indices of water and ice in the 0.65- to 2.5-μm spectral range, Linhong Kou, Daniel Labrie, and Petr Chylek. Applied Optics Vol. 32, Issue 19, pp. 3531-3540 (1993)

Plotting and data processing by Andy Perrin.

[GaryR]

The Zomei filters are an example of Chinese good quality products with a very reasonable price.

 

Ulf, this is good to know. Thanks! We should update the Filter Sticky to point out this particular given that you have assessed its quality.

 

*********

 

Gary, against what did you make the custom WB in the images above? I was guess that CWB was made "against the scene", as we often do with IR-pass filters.

 

For these images, I used my driveway in full sun, as the target. Not much difference when I use a gray card, so I use whatever is available.

[GaryR]

I stopped using the Zomei 950nm for landscape as I could not see any difference in landscape images.

There might still be some difference in making water darker, that I never tried or found.

 

The huge difference is exposure time. The 950nm need much mor exposure time.

The colours are monochrome with both filters.

 

Aside from crisp white foliage, I really like high contrast, black skies and clouds. So far, I find the 850 is a nice filter to work with, but for the small cost, I've just ordered a 950 to compare the difference. I would also guess that veins, just below the skin, would be more prominent with the 950.

[GaryR]

The near infrared water absorption peak is between 950 and 1030nm, with the max at 976nm:

Refractive indices of water and ice in the 0.65- to 2.5-μm spectral range, Linhong Kou, Daniel Labrie, and Petr Chylek. Applied Optics Vol. 32, Issue 19, pp. 3531-3540 (1993)

Plotting and data processing by Andy Perrin.

 

Interesting info Andy. Thanks for posting!

[dabateman]

I would think the different color cast is due to different degrees of visible blocking.

Ulf, can you share your spectra of these IR filters.

My R1000 filter had the following spectra, which I now believe to be a counterfeit based on our Hoya R72 discussion and I can't remember where I bought this from. You can clearly see a dip between 400nm and 500nm which would creat a blue cast.

[ulf]

I would think the different color cast is due to different degrees of visible blocking.

Ulf, can you share your spectra of these IR filters.

My R1000 filter had the following spectra, which I now believe to be a counterfeit based on our Hoya R72 discussion and I can't remember where I bought this from. You can clearly see a dip between 400nm and 500nm which would creat a blue cast.

I agree, that is the reason.

My measurements of the Zomei filters is lost somewhere.

I can't find them and think the files wasn't that well named.

 

I will eventually do new measurements and present the results in a properly structured way.

 

I'm working on how to best format such filter-information topics and would like to get that formar right first

The Zomei filters can be the some of the first to test the concept.

[Andrea B.]

For these images, I used my driveway in full sun, as the target. Not much difference when I use a gray card, so I use whatever is available.

 

This is fairly standard practice for white balancing IR - using a driveway or street whether asphalt or cement. It does not provide a "perfect" white balance, but for IR we are not always looking for that. I'm not anyway! Just trying to get some interesting false IR colours.

 

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The differences in IR-pass filters are not big once you get past 830 nm, methinks. The skies gradually darker but not enough so that it is startling.

 

Somewhere I have an IR false colour chart. I'm going to go look for that. It illustrates the point at which you see the changeover.

Found the chart. The discussion was here: Schott IR Filters: 15 Views of the White-balanced Color Checker Card

 

You can see that there is a change around 780/830 nm. The converted camera begins to record more in the blue channel and drops the green altogether. Interesting to see the Bayer dyes at work here.

[Andy Perrin]

Andrea, I agree if you are restricting this to long pass filters past 830nm. If you use bandpass filters, there is a potential (which seems to be mostly unused so far) to bracket the NIR water absorption bump at 975nm, which might make some unique monochrome images in subjects containing water. I’m trying to obtain a narrow bandpass to investigate this soon.

[GaryR]

Andrea, I convert everything >700nm to bw, so color white balance isn't that critical for me. I could probably work with blue-ish cast of the Zomei filter and get the same results, but the in-camera CWB just looks better when composing a shot.

 

Your chart shows a huge color difference between the RG715 and RG850, and very little between the RG850 and RG1000. I'll have to wait and see if the contrast and general blackness of sky and water is worth the increased exposure time on the Zomei 950.

 

Here's another, showing the tonal qualities of the Zomei 850. (fs-Sony a7R+75mm El Nikkor)

[Andrea B.]

Gary: ....but the in-camera CWB just looks better when composing a shot.

 

Yes! Makes getting a good exposure so much easier in IR.

 

Those sunflowers are very cool!

 

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Andy: If you use bandpass filters, there is a potential (which seems to be mostly unused so far) to bracket the NIR water absorption bump at 975nm, which might make some unique monochrome images in subjects containing water.

 

Very interesting to learn about that 975 nm bump! Thanks.

I'll tryout the MaxMax IR bandpass filters on that. It will take me a while to get posted though.

[Andy Perrin]

Andrea, take a look at the picture of the bump I posted above in post 6! That will give some guidance in picking a filter.

[Andrea B.]

The MaxMax "red" IR-bandpass filter peaks just before 950 nm. But it will still catch 976 nm with longer exposure perhaps? The "green" MaxMax IR-bandpass filters flat-tops between 825-850 nm and is quite damped down past 950 nm but not to a large OD. There's a bumplet around 980 or so. Still one might expect some small difference between the two? It's not looking like I will be able to go to the shore today. Can I test against a glass of water?

 

https://maxmax.com/BP_Color_Series.htm

[Andy Perrin]

You might see a difference in the water but to really see it, you have to match the bump peak or the part of the passband outside the bump will wash it out. I’m going to see if I can exactly filter at the bump soon.

[Andrea B.]

ok, thanks for the details!