First attempt with linear filter grating.

[Andrea B.]

EDIT: 26 Mar 2018. The original images were replaced with 180° flips in order to place the longer wavelengths on the right, shorter on the left.

---

 

Gear: D610 + UV-Nikkor 105/4.5 + LaLa Diff Grate @1000 lines/mm + UV-Pass Filter

 

Note: I was not keeping the camera/lens in a fixed position while fumbling around learning how to shoot these spectra. Sorry 'bout that! Thus the spectra are not the same size. Still, you can see that the patterns are repeated.

 

BaaderU, two examples

^{Converted in Photo Ninja using a D610 color profile and a BaaderU white balance preset.}

The spectrum patterns and false colours are repeatable.

 

 

Schott U-340 (4.00mm) Unfiltered, three examples

^{Converted in Photo Ninja using a D610 color profile and a U-340x400 white balance preset.}

If unfiltered, this thick U-340 passes a little IR, but not much. Again the patterns are repeatable. You can see that the U-340x400 spectrum is slightly different in the middle from the preceding BaaderU version.

 

 

BaaderU, two raw composites

^{Demosaic, gamma 2.2 curve, autoscale to 16-bit in Raw Digger.}

Of course, the actual raw colors recorded prior to any white balance step are the most interesting thing to me. Again the raw spectral patterns are repeatable. It is much more apparent (to my eye anyway) that the BaaderU spectral pattern is different from the U-340x400 pattern when looking at these raw false colours.

Sunset

 

 

Schott U-340 (4.00mm), three raw composites

^{Demosaic, gamma 2.2 curve, autoscale to 16-bit in Raw Digger.}

No exposure adjustments were made in these raws, so you can see that the first one is a bit overexposed. There is much less purple on the left here than the BaaderU.

Sunrise

[Cadmium]

Well done. I kind of expected a bit of turquoise blue on the green end (given the range of the UV-Nikkor), but this points out the cutoff point of the Baader U, 320nm, right about where turquoise blue would start to show up.

Given a lower band U filter, it still might not look turquoise, if the filter cuts off higher UV-A, which the lower band U filters I have seen seem to do. Just a guess, but my test of a 330WB80

shows much more obvious 325nm transmission than the Baader U, and that is only using the Kuri 35mm which cuts to zero T around 320/325nm, and shows no turquoise, but also removes a bit of the upper UV-A range.

 

Hoya U-340 4mm:

In order to suppress all red/IR with your U-340 4mm you would need to stack it with at least S8612 0.75mm, or even 1mm,

otherwise you get a Red/IR leak of about 0.5% mixed in with those shots, which is above the danger zone of 1E-03.

I would think the red/IR leak might show up off to the side on the blue side of the grating shot.

[Andrea B.]

EDIT: 26 Mar 2018. The original images were replaced with 180° flips in order to place the longer wavelengths on the right, shorter on the left.

---

 

 

There's this nifty little trick you can do in Photo Ninja. In the Color Enhancement tool, turn off all colours by moving Saturation slider to -50. Then turn each color back on one-by-one by moving Saturation slider back to some value between 0-50. I usually use at least Sat +20 for this to heighten the color. Using these settings, let's look at what colours make up these photos. Not scientific, but fun.

 

 

BaaderU with white balance.

^{See remarks above about the PN conversion.}

Remember that each converter app will perform white balance slightly differently so relying on a white balanced photo to tell you something about transmission might be not be quite the way to go. I prefer looking at the raw composites (or maybe separate channels, which I haven't done here.)

There were no results from turning on the Red, Orange or Cyan patches.

From top to bottom: Magenta, Blue, Yellow, Green.

Yes, I know the magenta looks blue, but that's what I got for the Magenta patch. Seems that violet wavelengths land mostly in the blue channel?

 

 

U-340x4.00 with white balance.

^{See remarks above about the PN conversion.}

There were no results from turning on the Red or Orange patches.

There was only a faint tinge when the Cyan patch (last foto) was turned on.

From top to bottom: Magenta, Blue, Yellow, Green, Cyan (just a trace).

 

 

 

BaaderU raw composite.

^{See remarks above about the Raw Digger export.}

The raw colours of course do not include Blue, Green or Cyan.

From top to bottom: Magenta, Red, Orange, Yellow.

^{Looks like I oversaturated the Red.}

 

 

 

U-340x4.00 raw composite.

^{See remarks above about the Raw Digger export.}

The reduced false colour spectrum for the U-340x400 is quite evident when looked at using this patch-by-patch method. This filter peaks to the left of the BaaderU and is not passing as much between 380-400nm, the region typically recorded as as raw magenta (false blue-violet/blue). The BaaderU passes much more of that as evidenced by the Magenta bar in the preceding set.

Again, no raw Blue, Green or Cyan. And also no raw Magenta.

From top to bottom: Red, Orange, Yellow.

[Andrea B.]

I kind of expected a bit of turquoise blue on the green end (given the range of the UV-Nikkor), but this points out the cutoff point of the Baader U, 320nm, right about where turquoise blue would start to show up.

 

Right. We learn nothing about the lens here - only about the filter on the lens. The UV-Nikkor transmits 70% flat between 220 - 900nm. And works beyond those endpoints, but I don't know the rates outside that region. It's not "supposed" to be an IR lens but I've used it successfully with the Schott RG1000x2.00.

[Andy Perrin]

Neat, Andrea! I like the idea of turning on the colors one by one.

 

To paraphrase Dorothy Parker, "why is it no one's sent me yet/ one perfect UV-Nikkor, do you suppose?/ It's always just my luck to get/ one perfect rose."

[Cadmium]

Here is a comparison of the U-340 (1mm, 2mm and 4mm), Baader U, and U-360 (2mm).

The Baader U transmits more upper UV-A range than the U-340 4mm does, thus the Baader U would show more purple (especially using the same white balance).

The U-340 4mm has a transmission center in a lower range than the Baader U, it removes practically all of the UV purple range, and centers on the UV green range,

and indeed it seems like there is more and longer green in your U-340 4mm RAW diffraction than in your Baader U RAW diffraction.

[Cadmium]

Andrea, Do you have a 330WB80 filter?

Given that your UV-Nikkor + U-340 4mm filter together transmit below 300nm, I might anticipate seeing some turquoise on the green edge of the U-340 4mm diffraction shots.

However, I don't see any turquoise in your shot.

It would not necessarily have to be what I am calling 'turquoise', but some color of green/blue that can be differentiated from the common 330nm~340nm green color that we are seeing in your examples.

 

Also, minor point, just nitpicky, but it might be nice to turn the colors around the other direction so they correspond to typical graphs and charts for the UV/V/IR spectrum.

320nm/green being on the left, 400nm/blue being on the right.

[Cadmium]

This may or may not relate, but years back I made a test using the 330WB80 filter, comparing two shots of the sky.

Shot #1 was using the Kuri 35mm (cut-off 320/325nm, about the same as the Baader U).

Shot #2 was using a pinhole (no lens, no cutoff).

The 330WB80 transmits below the cutoff of the Kuri 35mm, and below the cutoff of the Baader U.

The same white balance is used for both examples, and the pinhole shot looks more green and maybe more turquoise.

There is a combination of factors with the difference in color here, not just the cutoff point, but also the transmission curve/slope of the Kuri.

This test leads me to think that without the restriction of the transmission depth of the lens, the white balance shifts toward more turquoise/green content using a filter that transmits lower than the 320nm cutoff of the lens.

Also to note: the below test was done with a D7000 full spectrum camera. I have no idea how different the Bayer array is between camera models,

however I suspect that there may be some differences which would change UV false color results and expectations between different camera models. I have never tried this test with any other camera model.

Here is the old test:

[Alaun]

Some thoughts:

The grating picture “sorts” the light according to wavelength. So each position along the “rainbow”-pictures reflects a specific wavelength.

The unmodified RAW values coming from the pixels behind the filters of the three Bayer-Colours would give a relative transmission for the specific wavelength. For every wavelength you get a reading from the red, green and blue pixels in that area. I think it does not matter, what color you later on calculate from these readings with a specific white balance setting. These relative values for a given wavelength should be constant for a specific sensor. It might be a way to compare different sensors, how much the different filters leak UV-Light in areas of the spectrum (using same light and lens and UV-Filter)?

After applying a gamma curve, you loose the linear relationship between the signals of the sensor, so a comparison of the signals to get the relative transmission is no longer possible.

 

When you can add light from known laser sources with known wavelength, you can also calibrate your spectrum (try your laser pointers).

[JMC]

All very cool. Thanks for sharing.

 

Steve, with regards to your comment;

 

"Andrea, Do you have a 330WB80 filter? Given that your UV-Nikkor + U-340 4mm filter together transmit below 300nm, I might anticipate seeing some turquoise on the green edge of the U-340 4mm diffraction shots.

However, I don't see any turquoise in your shot."

 

The camera sensitivity is going to be extremely low at 300nm, either from the Bayer filter absorbing the light, or just the sensitivity of the sensor dropping at the low wavelengths. With my monochrome camera, by the time I get down to 300nm, it is basically insensitive. Yes, it does have Schott WG280 over the sensor, but the sensitivity drops gradually and continually as the wavelength decreases from 480nm, so I don't think the Schott WG280 is the limiting feature here.

 

Andrea, sorry, I may have missed it, but what is the light source? If it's sunlight, then that will be changing across the range you have here, with virtually nothing below 320nm. Try using your UV torch, to fix a wavelength point - being a single wavelength, or at least a very narrow range, it should allow you to set one position on the grating.

[Andrea B.]

Thanks, everyone, for the input. :D

This is a new experiment for me, so I'm feeling my way.

 

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Steve: Do you have a 330WB80 filter?

 

For 330, I have the 1.5mm thick Hoya U-330 filter and the 1.5mm UG5. Don't know the bandwidths for those.

 

---

Werner: After applying a gamma curve, you lose the linear relationship between the signals of the sensor, so a comparison of the signals to get the relative transmission is no longer possible.

I think it does not matter, what color you later on calculate from these readings with a specific white balance setting. These relative values for a given wavelength should be constant for a specific sensor.

 

The raw photo cannot be seen unless the midtones are raised! I'll try to make some histograms of the spectral band to see what those show.

Yes, that's certainly true abut the wb for a given sensor (and lens+filter combination). But we always enjoy comparing across brands in these tests, so I will continue to use the raw composite in addition to the wb versions.

 

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Jonathan: Andrea, sorry, I may have missed it, but what is the light source?

[also]......using your UV torch, to try and fix a wavelength point.

 

The sun. To get the spectral band you have to aim the lens at about a 45° angle from the sun.

And, yes, I will test with the 365 UV-Led. (Assuming I can corral the cats and get them out of the room.)

 

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Cadmium: Also, minor point, just nitpicky, but it might be nice to turn the colors around the other direction so they correspond to typical graphs and charts for the UV/V/IR spectrum.

 

oh la! Yes, I see the need. :D Will do.

 

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I will try this experiment with the UV-Nikkor on the Lumix GH1, the Sony A7R and the Pentax K5 to see what I get.

Have to wait until we get sunlight back. Seems to have gone missing again. All the winter weather has been crammed into March where I live. Too weird!

 

For 4 camera brand/models try the Linear Grating experiment.

Camera: D610, A7R, GH1, K5. All converted to full spectrum.

Filter: BaaderU

Filter: Lala Linear Grate 1000 lines/mm

Lens: UV-Nikkor 105/4.5 set to f/4.5

ISO: Use base ISO for each camera to get the least noisy colors.

Illumination: Sun. 365 Nichia UV-Led.

(May have to order adapters? Need Sony-Nikon, m4/3-Nikon, M42-Nikon.)

[Cadmium]

A small correction. I said a 'pinhole' was used for the 'no lens shot', but I remember now that it was just a filter mounted directly on the camera with no lens,

and also the Kuri shot was purposely not focused to make the light more 'scrambled' like the no lens shot.

These details probably don't matter too much, but to anyone wanting to duplicate this test, it makes it more clear and easier to do than using a pinhole, which is not needed for that test.

 

This could be tried with any lens capable of transmitting below and beyond 320nm, such as a UV-Nikkor, etc., in place of the 'no lens' shot.

 

One more thought I should bring up that I have had today, that the diffraction grating may have a limit, I am sure it does have some limit, and it may very well be limited to something above 300nm.

The grating is not usually used for UV, more used for visual, but I have seen good examples of it being used all the way up past 1000nm. It works very good for IR.

 

Here is the stuff I used:

312086925890

 

They make it in slide mounted versions, which have "300nm ... 700nm" on the slide frame,

312087807823

but I know for a fact that it works way above 700nm, but I don't know the actual limits.

[JCDowdy]

They make it in slide mounted versions, which have "300nm ... 700nm" on the slide frame,

312087807823

but I know for a fact that it works way above 700nm, but I don't know the actual limits.

 

We have discussed this limitation with the Star Analyser.

 

Send me a sample of your material and I will happily post the transmittance.

 

Also, I the setup really needs to image an isolated zero order point source, like a single star, and the diffraction spectrum in one frame.

 

This enables the software to be calibrated for wavelength. The higher lines per mm will be an advantage in imaging UV bandpass spectra but I expect a fused silica transmittance grating may be required.

[Cadmium]

I don't have the 'Star Analyzer'. I have a Cokin 040 Diffractor Cosmos filter.

So here is a quick hand held Sparticle transmission test stack comparison of the 040 filter and 1000 line diffraction grating used by Andrea above.

The 040 does have some strong attenuation of UV transmission, but the 1000 line grating transmits very well, I can even see the dim 325BP10, as with the top shot.

Below 325nm, I have no idea how well it works.

[JCDowdy]

Looks better than the 'Star Analyzer'.

 

I misunderstood you had the 5 ft. roll, and might spare a test sample.

 

No worry, I found a single slide for $0.99 (eBay item number:270818868831)

[Cadmium]

I have no experience with or knowledge of the 'Star Analyzer'.

This 1000 line grating transmits UV well, same as no grating for the lower BP filters. The slide is the same as the role. My role was originally 1 foot long x 6 inches wide,

sold by the same vendor (the item number I posted above is what they are selling at the moment).

They have different versions, 500 lines, 1000 lines, 13,500, and they have linear and double axis, and I think linear is the best to use for this (I think the 13,500 lines is only available in double axis version).

Mine is linear x 1000 lines, sheet and slide are the same material, from the same seller.

I don't see a 1 foot role in their listings right now.

I can send you one mounted in a filter ring of your choice, like Andrea has if you want.

[Andrea B.]

Gear: Panasonic Lumix GH1 + Novoflex m4/3-Nikon Adapter + UV-Nikkor 105/4.5 + LaLa Diff Grate @1000 lines/mm + BaaderU UV-Pass Filter

 

I made a right, middle and left view because the band seemed long, and I was afraid I would omit a color on the ends. However, the middle view doesn't cut off too much. Besides which, the colors aren't on the ends. They are on the top, middle and bottom.

 

Someone want to explain this color verticality to me?? :D

What did I do wrong?

^{As before, converted in Photo Ninja using a GH1 color & WB profile.}

 

 

 

[Cadmium]

Andrea, I don't know.

When I rotate my grating it rotates the line, I think... it has been a while, I will try it again.

[JCDowdy]

I can send you one mounted in a filter ring of your choice, like Andrea has if you want.

 

No worry, I have some on the way.

[JCDowdy]

Besides which, the colors aren't on the ends. They are on the top, middle and bottom.

Someone want to explain this color verticality to me?? :D

What did I do wrong?

 

You had me scratching my head before your last post. I am confused by seeing tree branches and grass in the background. This is not how I thought these transmission gratings were supposed to be used. Like I commented before, you need a small point of light, like a star would look through a telescope. I have seen projects online where people use a small hole or slit cut into a cardboard box or something. I saw one online made out of a cereal box. I am thinking the point source needs to be at a distance that the lens can focus on it, so your may need a larger light tight box depending on how close you can focus. Check out PublicLab.org DIY spectrometer for some ideas.

[Cadmium]

John, Here is a more advanced way of doing it:

https://publiclab.or...2-19-2013/ebert

 

This is just a low tech version, by stacking the grating in front of the lens + Baader U (or other range filter).

It has been a while since I tried this, I explained to Andrea that I put the grating on the front of the Baader U, shot a pic of the sky at about a 45 degree angle to the sun, rotating the grating so the 'rainbow' line is horizontal,

on a tripod, and changed lenses to compare lenses.

Andrea should probably explain to you how she actually got it to work for her, not me.

 

Like you say, slits are often used. But I like using the Sparticle so much more that I have not put too much time into the grating method.

I know someone who has used this idea a lot, and with IR filters also, with quite interesting and informative results. It is defiantly less expensive than multiple narrow bandpass filters.

[ulf]

Last spring I played a bit with linear grating films I bought on eBay:

 

The transmission for these films:

 

 

 

The lower wavelength range seam to cover most non-specialist UV-lenses.

[JCDowdy]

Ulf,

Those look exactly like what I ordered. Shame we cant find some in a nice UV grade PMMA, the fused Si are rather costly.

[JCDowdy]

Cadmium,

 

I saw one of DIY setups that used a black plastic plumbing pipe very similar to that vacuum cleaner pipe. I noticed most of the PublicLab designs use smartphone cameras. Is the rather wide angle perhaps why they are viewing off axis?

 

Here is a design that appears to be perpendicular to the grating. Such normal orientation is hoe these gratings are used in telescopes so that is what I will be trying when my gratings arrive.

 

I also agree that a Sparticle filter array is a superior approach. I seem to recall a older ISO standard that described a filter array for use in lens transmittance testing. I just think the transmittance grating looks like a fun project.

[Cadmium]

Ulf, Thanks, that pretty much shows me that even with a UV-Nikkor, or the like, I should not anticipate seeing any 'turquoise/green/blue' in the grating spectrum as I was previously hunting for in Anrea's test.

Just not enough reach with that grating.

However, they do make lower BP10 filters...

Three eBay sellers that sell 12.5mm BP10 filters. The first two sellers are both Omega, they make those filters, the third seller I don't know.

 

https://www.ebay.com/usr/omegabob2

https://www.ebay.com/sch/m.html?_odkw=BP&_ssn=omegabob2&hash=item2568649e56%3Ag%3ACHkAAOSwGIRXbEO2&item=160665214550&_osacat=0&_from=R40&_trksid=p2046732.m570.l1313.TR0.TRC0.H0.XBP+12.5.TRS0&_nkw=BP+12.5&_sacat=0

 

https://www.ebay.com/usr/bjomejag

https://www.ebay.com/sch/m.html?_odkw=&_ssn=bjomejag&hash=item488ff8cb93%3Ag%3A%7EvgAAMXQL99Salyk&item=311653092243&_osacat=0&_from=R40&_trksid=p2046732.m570.l1313.TR0.TRC0.H0.XBP+12.5.TRS0&_nkw=BP+12.5&_sacat=0

 

https://www.ebay.com/usr/electronicxeon

https://www.ebay.com/sch/m.html?_odkw=&_ssn=electronicxeon&hash=item3d54e99e8c%3Ag%3AlhUAAOSwl9RaTSBt&item=263417601676&_osacat=0&_from=R40&_trksid=p2046732.m570.l1313.TR11.TRC1.A0.H0.XBP.TRS0&_nkw=BP&_sacat=0