Artificial UV Test Scenario

[Timber]

I was thinking if we could create a test scenario to use for UV testing. Like we take some materials that can be easily found in any household and which has different UV response, and build up a scenario with it, so if someone has no access to flowers due to weather/location could still test a lens, lightsource, filter, camera or whatever they want. Like cotton ear-buds seem to me to be brighter in UV compared to, let's say, plain paper. I also seen that orange is almost black in UV and if I am not mistaken lemon juice is dark in ultraviolet light (we used it for writing "invisible messages" as a kid) so we could also consider something like ear-buds tipped in different liquids... I will try a few liquids with various PH value to see if it's a viable way to test UV pattern rendering... :D

 

if you have a little time then could you shoot (or just examine) some household items with good UV lenses (like the UV-Nikkor)? So far my best lenses are the Meritar, EL-Nikkor 50 f2.8 and the Tokina RMC 28 (hopefully the Soligor 35 will arrive soon)... so I can do some test already :)

[Timber]

I quickly grabbed some liquids and run a test with artifical light source (Hanimex X140 flash). It's not a perfect test just a very first brief try, but already shows some good results (at least I am happy with it :D) The two lens I've used was a E.Ludwig Meritar 50mm f2.9 and a Sony SEL 18-55 f3.5-5.6... both at f8 and ISO 800 (to be fair I should have use ISO 200 for the Meritar and ISO 1600 for the Sony to have roughly the same exposure IMHO... next time)

 

The very limiting factors of the test are the following:

- the small flash can not be controlled from the camera (yet) so the lighting of the scenario was not similar, therefore you can not really compare the two results with each other, you can only see the "UV pattern" for different liquids.

- the Meritar has an awful close focus distance, so I will need some M42 macro tubes or I should consider to use the EL-Nikkor 50mm f2.8 for future tests (or wait until I lay my hands on a EL-Nikkor 80mm :))

 

http://clancode.hu/!uv/liquiduv.jpg

 

My observations:

- Milk is really bright in UV!

- Balsamic Vinegar is really dark and Lemon Juice (as expected) shows up dark as well

 

My plans:

- trying to find a visible dark liquid which could be transparent in UV, such as Coca Cola being dark in visible light but transparent in IR. My guess is that any liquid that looks dark but purple/violet color when a strong light is placed behind it could have such feature in UV as Coca Cola shows similar behaviour with a deep red color. If my memories are right some red wine had a purple characteristic against strong white lights...

- do a test with a clear, non UV glass/plastic container with an image under it to see how transmission of light is affected by these liquids, by filling the container at different levels.

- compare the same liquids in UV and IR

- trying to find a not exotic, common fruit that has very significant UV pattern... outside and inside as well (for example I already checked pear slice and you can really see the fibers in UV)

 

if anyone has some ideas please share :) I am focusing on liquids / objects that can be easily found in any households, regardless of location and season (for example winter time you can't really find flowers, but you can always find lemon juice (or even better: a lemon!)

[JCDowdy]

Sounds like you need to take your camera grocery shopping! :D

 

I took a photo of my son's art set last week. Colored pencils, crayons, watercolor paints - but no joy.

DMC-G3 ISO-160 1/5sec Baader-U 50mm Cassar S f/11 mid-afternoon sunlight

 

PS,

I recall someone started a thread on this a while back, I think perhaps before you joined us Timber. Photos of various items in UV for a reference other than flowers.

I cannot find it now, anyone remember where it was?

 

PPS,

Found it!

Useful Reference Objects for UV Test Photos

Started by Andrea B. Feb 25 2014

[enricosavazzi]

One of the difficulties in a "standardized" test of commonly available materials in UV is that we don't have a standard UV source. 365 nm UV LEDS can have quite different spectra. Electronic flash, fluorescent lamps too. Solar spectrum is no standard either, it depends on latitude, altitude, place, hour, season, weather etc. The only relatively constant standards I can think of are deuterium lamps and low-pressure mercury arc lamps (if one uses only one emission line and filters out all others).

 

White paper is a very variable material, because it contains wildly different amounts of UV fluorescent chemicals. This is why it literally looks whiter than white (at some wavelengths it emits more VIS than it receives from incident light, because some of the emitted VIS is fluorescence generated by incident UV). I don't know whether the cotton in cotton buds is also treated to look whiter (i.e. to absorb UV and fluoresce in VIS). Even Spectralon targets can vary, because contamination by hydrocarbons in atmospheric pollution reduces their UV reflectivity over time. It would be great to find some relatively constant standard materials among household items for diffuse UV reflectivity, but it is not going to be easy. We do have aluminium mirrors that reflect over 95% of incident UV, but this is not very useful.

[Timber]

Enrico: The purpose of that test is to see different liquids reflectance in UV light and compare them with each other. If we apply them on the same material then it should not affect too much the results as the material is the same, the light is the same and the receiver is the same, so the only difference is the liquid itself. But to see this I've made a test on different type of papers. The result was on pair with the cotton buds, except for cardboard, which turns dark in UV no matter what liquid I've used. But plain photocopier paper, papertowel and toilet rolls resulted almost the same as the cotton buds, except some got a little darker when wet (but not as much as the cardboard).

 

Another test subject is from this morning's breakfast: a pear (again :D)

Sony NEX 6, Meritar, Hoya U360 + Schott BG40, "Sunlight*"

--- VIS ---- UV ----- VIS + UV as Luminosity ---

http://clancode.hu/!uv/pearuv.jpg

 

* - I mean the thing they call sunlight in UK... :)

[Andrea B.]

These are all fascinating tests, Timber. Good for you to try them as a curious and creative UV photographer!!

 

I've wanted to do the same for quite some time, but am constantly "too busy" with so many tasks and chores that I never seem to get around to it. Most recently the local RB Chamber Music Society board meeting was at my house which entailed a housewife's frenzy of cleaning and preparation. I wear many hats besides my UV hat. :D

 

As Enrico has pointed out, our primary technical "failure", so to speak, as UV photographers is not having a uniform, calibrated (measured) source of UV illumination. However, we should not let that stop us from performing these kind of tests!! What we must do is always to be very clear about the equipment used and the source of UV illumination, such as it is. That way anyone viewing the tests will immediately understand the parameters of the presented material, yes??

 

So, to that end, I propose we standardize the way we present the photo data. Call it a kind of forensic labeling, perhaps? Everyone can help me with this and make suggestions. Then I will incorporate it into our Guidelines where it can be lifted as an easily filled out template for the photographs.

 

Subject:

Equipment: Camera + Lens

Filter:

Light Source:

Exposure: f/xx for yy" at ISO zzz

Converter:

 

The subject should be briefly described. For example, the pear above - what kind of pear is that? For the balsamic vinegar, what is the brand and what is the strength of the vinegar?

If sunlight is the UV source, then give time of day, the approximate altitude/latitude and whether indoors/outdoors.

 

ADDED:

 

Example from JD's post above: the string DMC-G3 ISO-160 1/5sec Baader-U 50mm Cassar S f/11 mid-afternoon sunlight becomes the following. (I'm guessing at a couple of things, of course.)

 

Subject: School art supplies, Color Checker Passport, Spectralon Standard

Equipment: Panasonic Lumix G3 + Steinheil 50/2.8 Cassar-S

Filter: Baader-U 2" UV-Pass

Light Source: Sunlight, indoors at 3PM, 1200'/35°N.

Exposure: f/11 for 1/5" @ ISO-160

Converter: XYZ

 

Forensic tests must be repeatable insofar as it is possible given the problem of our UV illumination. If we present the relevant data in a consise & uniform manner, then someone else can try the test to confirm the results.

 

If you are not using a standard filter like the Baader-U, then describe your filter stack.

For example

Filter: Schott UG11 2mm UV-Pass + Schott S8612 1.75mm IR-Block

 

You can also save your template data for either botanical, forensic or other photo labeling in your My UV Kit post in our Lists, Lists and More Lists board. You may also create a My Label post there. Then you can copy/paste templates easily.