Entomology grad student eager to learn about flower UV!

[Ella J. Branham]

     Hello! My name is Ella J. Branham and I grew up in Utah. I absolutly love the desert and the mountains. My favorite passtimes there are to rock hound, look for insects, and just explore outdoors. I just recently moved to Mississippi and I am continuing exploring by looking for aligators, salamanders, insects, and snapping turtles. I have come to love Mississippi, but Utah will always be my favorite place!

 

     I am a new graduate student working on my masters degree at the University of Southern Mississippi. I am going to be traveling to Puerto Rico during the summer months to research mosquito nectar feeding on flowers. I am interested if mosquitoes prefer flowers with certain kinds of UV reflection patterns. I am new to UV photography and as such I am excited to participate and learn more. I am currently writting up my "game plan" for Puerto Rico and as such I am doing a lot of investigating and happened upon this awesome community. 

 

I definitly have lots of questions regarding UV and how to interpret photos taken with UV, i.e., how to determine if one flower is more or less UV reflective than another flower. I may reach out to some of you fine people and ask some questions! Thanks for having me! :D

[colinbm]

Lovely photo.
Welcome to UVP & your progress in UV photography.

[dabateman]

Reflectance is a good question.  One that might not be able to be solved with a camera.

You may want to see if you can borrow or if you have the budget for a JAZ portable usb type spectrometer.

https://www.oceaninsight.com/globalassets/catalog-blocks-and-images/manuals--instruction-ocean-optics/spectrometer/jazinstallationandoperation.pdf

 

I bought a used one years ago and it might solve that problem with the correct probe and light source. 

[ulf]

Hi Ella,

A warm welcome to UVP!

I really like your picture, even if I hate mosquitos. 

David's recommendation above about a JAZ-system might be difficult to follow as that system is very old and became obsolete many years ago.
I have never tried using it but from the manual it appear to have been a quit flexible system.

For research it might be good to measure the absolute reflectance, but such measurements can be tricky to do correctly.
As David saias it would not be possible to do such measurement with a mere FA-converted camera as the resulting images are affected of many different factors.
However what you said you wanted to do was to determine and possibly compare if flowers are more or less reflective to UV. That is quite possible to do.

With a broadband UV-lightsource like the sun and a camera equipped with an UV-capable lens add a suitable UV-Filter/Filter-stack you will be able to take pictures that can show false colours from the UV-A band.
Those colours will give an indication of the rough wavelengths reflected, even if there are no way of getting accurate detailed wavelength information.

If the reflected light is mainly from close to the upper UV-A band below 400 nm the false colour will be bluish or purple. Further down (below maybe 375-380 nm) that false colour will shift to yellow, (without passing green). 

There are alot of information about suitable lenses and filters to be found on the forum.
Depending on your budget, if you want to buy equipment for taking such pictures there are many alternatives and I am sure we can give you some advices for that.
 

 

[Andy Perrin]

Nice to meet you!

[Lou Jost]

Hi Emma, welcome! I'm a botanist. Unlike the more experienced members above, I think measuring the relative UV reflectance of flowers  could be easy and uncomplicated, if you just care about ranking from high to low and if you are interested only in the longer wavelengths of UV light reaching the earth's surface .

 

A good standard reference reflector would be several layers of white teflon tape. Just put an appropriate narrow-band UV filter on a UV-transmitting lens and take a picture (with a UV transmitting lens on a UV-sensitive camera) of the flower and tape with a full-spectrum camera. You can interpret the resulting grayscale photo by making a reference sequence of photos of the teflon tape at each successive f/stop. If the lens aperture is accurate (and you can test this in regular light by making sure the metered shutter speed changes by a factor of 2 for each stop change), then you can match the observed shade of the flower with the corresponding shade of the reference sequence. This will give you the approximate relative total amount of energy in the reflected light. The narrower the filter pass-band, the more accurate the results will be, since transmission and sensor sensitivity do vary with wavelength.

 

You do have to figure out what range of UV you are interested in, in order to choose the lens and camera and filter. For your research question you will only care about the part of the solar spectrum that reaches the ground. The air removes deep UV below about 320nm so you don't have to worry about that part. The amount of UV in sunlight drops rapidly with decreasing wavelength, so most of the biologically relevant light would probably be in the range of 330-400nm.

 

With narrow-band filters you could look at reflectance in different spectral bands; again no spectrometer needed for the degree of precision that would be relevant to this biological work. You do need to choose your lens and camera carefully if you want to measure wavelengths below about 350nm. But I bet you could do a useful study just with the light from 365nm-400nm. This can be easy and cheap.

 

 

[Andy Perrin]

I think everyone has been pretty consistent about what the options are. To summarize:

 

1) Absolute reflectance requires a spectrometer (expensive, and hard to use accurately without training/experience). But this may not be necessary. 
 

2) ranking relative reflectance in UV-A (320-400nm) can be done with a converted camera and filters and is easy. 

[Lou Jost]

I suspect that relative measures are the only ones that matter for this application, since the absolute amount of incident daylight varies tremendously with atmospheric conditions, solar elevation in the sky, etc.

[Andy Perrin]

13 minutes ago, Lou Jost said:

I suspect that relative measures are the only ones that matter for this application, since the absolute amount of incident daylight varies tremendously with atmospheric conditions, solar elevation in the sky, etc.

Reflectance is the percentage of light reflected (either overall, or as a function of wavelength), and it doesn't depend on the incident light. Absolute reflectance would be a percentage, like "60% of UV-A is reflected by the flower." That would still be a true fact at night, even with no actual light being reflected, since it's a fact about the surface of the flower.

 

But I do agree that a ranking like "flower A reflects more than flower B" is probably all that matters for insects, who don't sit around calculating things! Or checking things like whether the flowers that show bullseye patterns get more insect-love.

[Lou Jost]

I had thought that absolute reflectance referred to an absolute energy measurement of the reflected light, not a relative percent. I stand corrected.

 

From the relative reflectance (as I described above) and knowledge of the absolute reflectance of thick teflon, the absolute reflectance of the flower could be calculated.

[Andy Perrin]

Unfortunately optical terminology is far from standardized between fields, so it's not out of the question that you could have seen reflectance used in a different sense somewhere. I think MOST fields use it to mean the fraction that is reflected rather than the intensity or radiance reflected. Radiance itself is power per unit solid angle. (Intensity and radiance mean the same thing usually, but those are another pair of words that can vary by field!) The INCOMING light power per solid angle is the "irradiance." 

 

For a head-spinning good time, check out these pages:

https://en.wikipedia.org/wiki/Radiance

https://en.wikipedia.org/wiki/Reflectance

 

[dabateman]

Best practice would be to have a standard light, with known amount of emitting photons in the wavelength of interest and then a standard object to compare with like a 50x50mm x15mm block of PTFE. 

Then you could get an exposure value with your light from your reference (block of PTFE)  and exposure value from your flower.  That wouldn't be too hard.

Problems without a standard light and standard reflectance target, would include many.

But flower age, health and hydration could change your reflectance value or rate. 

Also if just using the sun, when? What time of year, time of day will affect the light amount. As would location, with closer to the equator being different than up North. 

 

I now read Lou's first reply above. I missed it earlier.  This is good advice.  But I would add that using a standardized UV light would help you. I just think there is too much variation in solar UV amounts. Thus why we have a UV index and its not constant day to day. 

You could even calibrate a 365nm led light to use and calibrate between measurements, to be consistent. 

[lonesome_dave]

20 hours ago, dabateman said:

Best practice would be to have a standard light, with known amount of emitting photons in the wavelength of interest and then a standard object to compare with like a 50x50mm x15mm block of PTFE. 

When I hear folks talking about 'thick' PTFE I thought any solid piece was thick enough compared to several wraps of teflon tape.
I've been using 100 x 100 x 3mm PTFE slabs as reflectance targets for basic spectroscopy (comparative, not quantitative) when bright sources such as lasers or direct sunlight are being measured.
Should I be using something closer to 15mm?

[dabateman]

I can pass uv light through 3mm thickness.  I have actually used that as a diffuser with UVC light.

So I would go for thicker, if you want more reflectance.

[ulf]

2 hours ago, dabateman said:

I can pass uv light through 3mm thickness.  I have actually used that as a diffuser with UVC light.

So I would go for thicker, if you want more reflectance.

Here I disagree as the gain with thicker material would be miniscule.

 

Even if PTFE is a tiny bit diffusely transparent and can be used as a diffusor the amount passing 3mm is very small. 
The light scattered back will be very dominant.

 

There are a few reasons for using pure PTFE as a calibration target:

1. The reflectance is high reasonably constant over a wide wavelength range, including UV and NIR
2. It is a bit diffusely transparent and if the surface is given a rough suitable structure, or ideally a grainy sintered structure, the reflected directional pattern can approach a Lambertian form that is essential to blend out incoming light without specular reflections.

The high end material for such targets Spectralon is made of such sintered superpure PTFE powder.

The cleaning instructions for Spectralon targets is to sand them under flowing water with water sandpaper. https://labsphere.com/wp-content/uploads/2021/09/Spectralon-Standards-Care-and-Handling-Guidelines.pdf

 

I have made well functioning DIY PTFE targets of 2mm thick PTFE sheets that was placed against nature or black anodised aluminium surfaces.

A pair of metal filter caps is ideal for that, as then the carefully sanded front surface can be protected by the second half when not in use.

Such caps can be bought for different filter sizes. I chose the same size as the filters I normally use for UV-photography, 52mm to make it fit into my filter storage. 

Some kind of aluminum foil against the rear side will work well too.

When sanding the surface it is important to do that in random directions.

[Ming]

Can a thin PTFE sheet (0.1mm thickness) like this https://www.amazon.com/Teflon-Thickness-Temperature-Resistant-Coated/dp/B07K8P6GC5/ be used as a diffuser?

 

[photoni]

@Ella J. Branham  you made me curious, we know a lot about exchanging channels to emulate bee vision,

I wonder what criterion can be used for mosquitoes or other insects.
I made a composition of possible variations with 6 filter combinations that I have, using different color channels.
It all seems very questionable to me, considering that we use a full spectrum camera with the usual standard RGB colors on the sensor.

.

.

 

[lonesome_dave]

16 hours ago, ulf said:

There are a few reasons for using pure PTFE as a calibration target:

1. The reflectance is high reasonably constant over a wide wavelength range, including UV and NIR
2. It is a bit diffusely transparent and if the surface is given a rough suitable structure, or ideally a grainy sintered structure, the reflected directional pattern can approach a Lambertian form that is essential to blend out incoming light without specular reflections.

Yes, this is why I am using sanded PTFE for basic spectroscopy.

A third item is that it doesn't fluoresce under UV illumination. You'd be surprised how many folks use white paper as a reflectance target. As most members here know almost all white paper fluoresces blue under UV (including sunlight) and the resultant emission will pollute the spectrum.

[Ella J. Branham]

On 4/24/2024 at 4:22 PM, Lou Jost said:

Hi Emma, welcome! I'm a botanist. Unlike the more experienced members above, I think measuring the relative UV reflectance of flowers  could be easy and uncomplicated, if you just care about ranking from high to low and if you are interested only in the longer wavelengths of UV light reaching the earth's surface .

 

A good standard reference reflector would be several layers of white teflon tape. Just put an appropriate narrow-band UV filter on a UV-transmitting lens and take a picture (with a UV transmitting lens on a UV-sensitive camera) of the flower and tape with a full-spectrum camera. You can interpret the resulting grayscale photo by making a reference sequence of photos of the teflon tape at each successive f/stop. If the lens aperture is accurate (and you can test this in regular light by making sure the metered shutter speed changes by a factor of 2 for each stop change), then you can match the observed shade of the flower with the corresponding shade of the reference sequence. This will give you the approximate relative total amount of energy in the reflected light. The narrower the filter pass-band, the more accurate the results will be, since transmission and sensor sensitivity do vary with wavelength.

 

You do have to figure out what range of UV you are interested in, in order to choose the lens and camera and filter. For your research question you will only care about the part of the solar spectrum that reaches the ground. The air removes deep UV below about 320nm so you don't have to worry about that part. The amount of UV in sunlight drops rapidly with decreasing wavelength, so most of the biologically relevant light would probably be in the range of 330-400nm.

 

With narrow-band filters you could look at reflectance in different spectral bands; again no spectrometer needed for the degree of precision that would be relevant to this biological work. You do need to choose your lens and camera carefully if you want to measure wavelengths below about 350nm. But I bet you could do a useful study just with the light from 365nm-400nm. This can be easy and cheap.

 

 

Wow this is really helpful! Like you were saying I don't need to get super specific I just need a general range/ranking system. I am going to talk to my advisor and show him this post as well as others. I am really excited to get to work on this!

[Ella J. Branham]

     Sorry for the late reply, grad school keeps me busy! I am amazed at all the thoughtful responses I have recieved! I want to reply to each of you individually, but that might make this a bit thread a bit messy so I will just respond here. Thanks for all your advice, I am definitly going to show my advisor this. We were just about to purchase some super expensive standards, so if we can get this to work, it would be awesome. I'm very glad I found this community! :D

 

     Also thanks for the nice compliments about my mosquito photo! Fun fact, the flower that the mosquito (Culiseta inornata) is on is a showy milkweed (Asclepias speciosa). Asclepias spread their pollen in the form of pollina. Insects will accidentally slip their tarsi into the slit where the pollina are and pull free with the pollina stuck to their legs. Mosquitoes are not strong enough to pull away so they actually get stuck and die! I have many photos of dead mosquitoes and other dead insects who have gotten trapped by the milkweed. Mosquitoes love milkweed a lot and survived bet on it in my experiment I did. So I guess it is worth the risk! The mosquito in the photo is actually stuck, but hadn't died at that point, hence why she posed so nicely for me lol.

 

@lonesome_dave

@photoni

@Ming

@ulf

@dabateman

@Andy Perrin

@Lou Jost

@colinbm

[Lou Jost]

1 hour ago, Ella J. Branham said:

Wow this is really helpful! Like you were saying I don't need to get super specific I just need a general range/ranking system. I am going to talk to my advisor and show him this post as well as others. I am really excited to get to work on this!

We are all really glad to help. Let us know how this progresses!

[Aaron E.]

Hi Ella, 

 

Good to have you on the list. And your photo is great. Always nice to have something else hold the critter for you.

 

Like Lou, I have a background in ecology, botany, and entomology &c. Sparked by your observation that some mosquitoes are trapped by the pollinia, I'm sure someone somewhere has hypothesized that this could be botanical "protocarnivory" in action. But I would strongly doubt it!

 

I would note that all of the suggestions about relative reflectance presuppose at the minimum a camera whose sensor array has been modified to be able to detect the UV (i.e., a "converted" camera), a lens that will allow for sufficient UV transmission, and a high-quality UV bandpass filter. The possibilities are seemingly endless and can quickly stress your bank account. So another good question for yourself and your advisor is what equipment is already available and what is your budget?

 

Have fun!

 

 

[Ella J. Branham]

On 5/1/2024 at 5:55 AM, Aaron E. said:

Hi Ella, 

 

Good to have you on the list. And your photo is great. Always nice to have something else hold the critter for you.

 

Like Lou, I have a background in ecology, botany, and entomology &c. Sparked by your observation that some mosquitoes are trapped by the pollinia, I'm sure someone somewhere has hypothesized that this could be botanical "protocarnivory" in action. But I would strongly doubt it!

 

I would note that all of the suggestions about relative reflectance presuppose at the minimum a camera whose sensor array has been modified to be able to detect the UV (i.e., a "converted" camera), a lens that will allow for sufficient UV transmission, and a high-quality UV bandpass filter. The possibilities are seemingly endless and can quickly stress your bank account. So another good question for yourself and your advisor is what equipment is already available and what is your budget?

 

Have fun!

 

 

Yes, this stuff can definitly get expensive! Definitly interested in finding cheaper ways to do this that are still scientific and quantifiable to some degree, I don't need exact amounts of reflectance just a general idea if one flower is more or less UV dark than another. 

 

I have definitly heard the protocarnivory hypothesis, and while it is very interesting and fun to think about, I doubt it too hahaha. :)

[Andy Perrin]

1 hour ago, Ella J. Branham said:

Yes, this stuff can definitly get expensive! Definitly interested in finding cheaper ways to do this that are still scientific and quantifiable to some degree, I don't need exact amounts of reflectance just a general idea if one flower is more or less UV dark than another. 

 

I have definitly heard the protocarnivory hypothesis, and while it is very interesting and fun to think about, I doubt it too hahaha. :)

In our technical section, Ulf has done spectrometry on many lenses that can be found on eBay for (sometimes) affordable amounts. That is a good starting point. While it might be wise to repeat his spectrometry on your own specific equipment once you buy it, it at least gives a good basis for designing a setup. In particular, the EL-Nikkor 80mm/5.6 enlarger lens with the old-style metal rings is practically a must-have for every member on this board, as it's a wicked sharp lens that is corrected down to 380nm and still widely available on ebay at affordable prices. 

[dabateman]

A used Olympus Em1mk1 leaks enough UV that you don't even need to convert it. Then you could pair it with a bunch of different lenses.

But are you restricted to purchase orders? 

Does it have to come from a company and you used a purchase number to ensure its all legitimate sale?

That will restricted your options.  Unless its your own money and your own equipment.  Then you can do anything.  

The purchase order route you can buy a full spectrum converted camera directly from Kolari Vision with a lens. That might be cheaper than buying directly from MaxMax (LDP).

If you are owning and buying than let us know what you already have or like to photograph with. I like the Olympus cameras,  but many prefer Nikon. Fujifilm is starting to pop up more and I do like the Gfx system,  but quite expensive,  even used.

Nearly cheapest might be to build your own camera, using a Raspberry pi board and a HQ camera.  The stock HQ has CM500 filter and doesn't block UV to 350nm ish so can also be used. All software is free. You just need to assemble it. But you can make an extremely good camera for under $200. The C-mount lenses are also cheap. Than if you want to do crazy deep UV you can buy a MaxMax monochrome HQ camera.