UV imaging of a stuffed toy (UVA and B in daylight)

[JMC]

A little bit of fun today. For a talk I'm writing I needed some photos of a subject in UVA and B captured in daylight, to be able to compare those with a different light source - mercury xenon lamp. My usual model (my wife) is currently away, so I called upon the services of one of her little stuffed toys to fill that role. Here's the toy in daylight, sat next to a Labsphere 20% diffuse reflectance standard. Taken just using the camera phone.

 

UV imaging was done with a monochrome converted Nikon d850 and Rayfact 105mm UV lens (f8 and ISO800). Filter for UVA was 365nm Edmund Optics 10nm bandpass filter combined with a Hoya U-340 4mm. Filter for UVB was a 313nm Edmund Optics 10nm bandpass filter, again combined with the Hoya U-340 4mm.

 

UVA image (365nm, 1/4s exposure, f8 ISO800)

 

UVB image (313nm, 4s exposure, f8 ISO800)

 

I checked for leaks in UVB image by using a Hoya R72 in combination with the filters and got a completely black image.

 

I was actually really surprised by how different the UVA and B images looked - must be the dyes in the wool. Looking at the RAW files the UVB image is about a third of a stop darker than the UVA one, but it was close enough for what I need it for.

 

UVB imaging in daylight is a huge challenge, even with a monochrome converted camera and 'non-glass' UV lens. The Edmund Optics filter alone, despite being OD4, was not up to the job of filtering unwanted wavelengths. Using it in combination with a Hoya U-340 4mm did the trick though.

[colinbm]

Huge differences Jonathan, yes surprising, including the white going darker then some of the dark colours...!

[Stefano]

Very interesting. UVB imaging with a standard camera with Bayer filter, coverglass and a glass lens is more than challenging. I got basically more noise than images.

[dabateman]

Next you need to test with your CFA cameras to see if there is an interesting color shift.

Going from visible brown hair, the UVA blonde, to darker UVB hair is really surprising.

Now you have a great control model.

 

Would your wife be upset if you smeared sunscreen on its hair?

Can you easily wash her to test out other formulas?

 

You may need one made for you for more testing.

[colinbm]

Oh, my, boys playing with dolls.....

[diant]

I was actually really surprised by how different the UVA and B images looked - must be the dyes in the wool.

Really impressive, and our usual visual skill get a shake. Jonathan, how long were both your expositions - 365 and 313?

[JMC]

Yeah, I don't think I'll be playing with the doll again anytime soon guys. This was a one off for the talk.

 

Anton, yes I should have mentioned the exposures. I'll add them to the original post.

[Andrea B.]

Jonathan, that is a great find!! It isn't easy to find subjects which vary so much between UVA and UVB. Thanks so much for this topic documenting your find.

 

It makes a certain amount of sense that such a subject would be found amongst the various dyes. And that made me remember that I have a box of embroidery threads of all different colors. I'm going to dig those out and see what I can discover.

[diant]

The difference in exposures is only 16x. Hm... I thought that it should be some more. So it means that there is no an acute shortage of UBV in London.

[JMC]

Andrea, yes, a bit of a surprise, but in hindsight it makes sense with the dyes. After all, it's dyes that give us the difference between UVA and B in the Bayer sensor.

 

Anton, 16x is roughly what I'd expect. My monochrome converted Nikon d850 has about a 2-3 stop difference in sensitivity between 313nm and 365nm, and the sunlight irradiance spectrum I took on the day showed about 4x the value at 365nm compared to 313nm. The transmission through the 313nm plus Hoya U-340 is a bit more than the 365nm bandpass filter plus the Hoya U-340. Put them all together and I'd expect roughly 4 stop difference.

[diant]

Jonathan, Nikon UV 105 is great lens, as I see, and you have an excellent experience with it and with imaging in UVA/UVB on the whole.

 

I have not such lens but of course I am dreaming to have something like it, but for me it would be desirable a some of its equivalent in 16-38mm range (that is dictated by my interests). All my lens are from "common brothers" cohort, and I select them by their UVA capability with a simple hand-made spectrograph with a quartz collimator, plastic grates and UVA/B-sensible astronomical cameras (with sony imx178 mono sensor more frequently).

 

Of course such test is limited by grates' transmissions (UVB is excluded), but it the same time it allows to compare different lens with each other not only by their UVA transparency but also by their focal shift vs wavelenght. And for UVA such test is very useful and simple. As I have time to learn here, many of members UVP use similar tests with grates.

 

Here is what I see usual with such test (this is of course simple lenses with 3-4-5 elements, no more).

 

The incoming light I use is Exoterra UVB lamp. Its main working hill in spectrum starts somewhere around 350-360 and rises in short direction, reaching a plate around 310-320, but lens and grate transmission (its absence more correct) cut off this "working hill" earlier it reach its heights... as it may be seen in first spectrum of 3-elements small triplet lens.

 

(Excuse me for my English, please. Seldom, very seldom I use to write in it.)

[JMC]

Anton, Your English is fine, no problem there.

 

I've been fortunate to be able to do some research on UV photography as part of my work, which has given me access to some equipment I wouldn't have been able to get otherwise. I've only been working with UV for about 3 and a half years now, and there are a lot of people on here with way more experience than me.

 

There aren't many options for 16-38mm lenses for UVB, especially if you need to be able to cover a full size SLR sensor. In fact I'm not sure I know of any lenses that can do that. Perhaps a single quartz lens would be an option, but obviously there is a softness that will come along with that. I have a 79mm fused silica aspheric lens from Thorlabs, which is a lot cheaper than a UV Nikkor but is too telephoto for your needs - https://www.ultravioletphotography.com/content/index.php/topic/4594-thorlabs-79mm-uv-aspheric-lens-for-imaging/page__view__findpost__p__45528 It is however is a good lens to use by itself.

 

There are a number of 35mm f3.5 lenses which will give some UVB transmission, and a quick search on here will bring those up.

[diant]

Jonathan, I'm guilty a little - I've not specified that UVB is not my a goal. Rather I want to have a good UVA lens which cover 320/330 to near IR. Here I meant not only transmission but as well focus stability. But transmission of course in the first place, as often I work in limited regions separately. And no, no - I need not full size SLR coverage at all. I work mainly on small (<1") special CMOS cooled sensors which allow me to have 1, 3, 5, 10, 30-min exposures with the same noise level as 1/8000 sec. Besides, with such cameras I have more convenient PC-contrlol with ability to calibrate images on the fly and have a LiveStack (stack images in real time with visual control of noise level). This last feature enables me to have noise-free images in most unthinkable conditions, were you have a possibility time-unlimited imaging.

 

Yours work is a good chance, yea :) I have not any such work and never hadn't . I'm a teacher of astronomy for a little children, no more.

 

There are a number of 35mm f3.5 lenses which will give some UVB transmission, and a quick search on here will bring those up.

So they should have even more UVA transmission!

What lens you speak about? Where I can see its spectral charts?

Now I have Industar 2,8/28mm (second spectrum above) which have cut off somewhere around 350-360, and triplet T-43 with little better UVA window, but with great focus shift.

[JMC]

Anton, there's a list here - https://www.ultravioletphotography.com/content/index.php/topic/1654-sticky-uv-capable-lenses/page__view__findpost__p__44612

 

That'll give you some ideas.

 

The Kuribayashi 35mm f3.5 is often quoted as a good one, as are some of the Prinz Galaxy ones. I've done some tests on transmission here - https://www.ultravioletphotography.com/content/index.php/topic/3406-lens-transmission-in-the-uv-latest-update/page__view__findpost__p__29227

 

Ulf has tested a lot of lenses, and they are in the Uv Lens Technical data section - https://www.ultravioletphotography.com/content/index.php/forum/643-uv-lenses-normal/

[Stefano]

These are some lenses with good transmission at 320 nm:

 

Soligor 35 mm f/3.5

 

Prinz Galaxy 35 mm f/3.5

 

Steinheil München 50 mm f/2.8 Cassar S

 

Leitz 50 mm f/4.5 Focotar-2

 

The Focotar-2 has an awesome transmission, the best reach among the lenses Ulf tested.

[diant]

Stefano, thank you! I'll learn they. 50mm is a bit large for me, but 35mm is ok.

O, Jonathan, I missed your post. Thank you too) Sinking in studying...

 

PS. I've totally plunged... My head is a kind of Earth-like ball, but I'm not ruined yet under that total volume of information on lenses I'm finding on UVP...

And first of all - my kind regards to Ulf: I've find his section "UV lens: normal", it is a great work really. I fear to ask Ulf - do you sleep at nights?

[dabateman]

There are these as options:

https://www.universeoptics.com/uvlens_assemblies/

 

But the focus isn't stable across the wavelengths and there is breathing as well.

But they will cover your sensor and give you UVB.

 

The UV2528B will actually cover the m43rds sensors. Its been used here by a bunch of users. The 12mm might cover your 1 inch sensor, even though its only rated for 2/3rd.

[Andrea B.]

Excuse me for my English, please. Seldom, very seldom I use to write in it.

 

Anton, we are an international forum with members from many different countries, so we all do understand that English is a 2nd (or 3rd or 4th) language for many members. Please do not worry at all about your English. We will ask for clarification from you if we need to better understand something you write.

 

We are happy to have you here on UVP and hope you enjoy this little corner of the world!

Cheers - Andrea B. :bee:

[diant]

We are happy to have you here on UVP and hope you enjoy this little corner of the world!

Speaking truly, I've sunk deeply in fathomless mare of technical information on UVP.

From one side this is what I sought.

From other I can't make a breath of fresh air a second day in a row... a lot of pages, a lot of information... I'm trying to cook it in my head...

But I'm not despairing. I came out from a deeper mares :)

[Fandyus]

I stacked the two images to illustrate the differences.

[Andy Perrin]

Well that is definitely ready for a horror movie.

[JMC]

I stacked the two images to illustrate the differences.

 

Interesting, thanks.