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However, chlorophyll does emit IR as fluorescence in natural light. This would of course be much weaker than the reflected light though.

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 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. . .

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?

I'm familiar with the digital methods, I've been filter stacking and channel swapping for months at this point. I find it interesting the variety of methods people use to get to similar results. I imagine that the halations of HIE are not perfectly able to be replicated, but could closely emulated in Photoshop or another editor in a fairly non-trivial way. I did see someone take a very fine grit sandpaper to the back of a fungus-y lens to try to get the effect... You wouldn't catch me doing that, even if the lens did have fungal growth!

HIE lacked any antihalation dye in the plastic film base; coupled with the natural tendency of IR to find its way into tight spaces, this explained the strong halation observed with it. As it was originally sold for medical diagnostic use, the antihalation properties were not deemed necessary. One of the Efke IR films (Aura) also had no antihalation measures. The infrared Ektachromes did not have this property, nor do the few IR-sensitive emulsions still available. These last films were an implementation of IRG cross-sampling, wherein red represents infrared, green represents red, and blue represents green. The closest digital equivalents are those that also follow this recipe, but require more complex acquisition or post-processing strategies to achieve. A rival image type, IGB, looks somewhat similar but can be produced directly in-camera with the right filter (such as what Kolari is selling.) In this latter paradigm, the green and blue output channels are not cross-sampled and infrared is substituted for red.

Thank you for the welcome! It does seem like there are literally dozens of us trying to make a working solution for digital. Meanwhile kolari chrome sells "red tree filters" like hotcakes... I'm hoping to take my full spectrum to Corfu next month so maybe I can get some nice sun and palm trees like you have here! I think that something else may have happened with that very green shot by the way, apparently E4 films showed extreme reticulation if they were cross processed in C41 as the first stage of E4 processing was a hardening chemical to make the emulsion more resistant to heat. EDIT - Never mind I just saw you mentioned 1982 in the title, so this would be E6? It really is bizarre, parts of the film are positive and some are negative. I think you're right - this has been processed as a negative, and the thing that can happen with slide film on bright light points has happened on the balloon and people's backs. It's like the inverse of the effect you get when you catch a flash in a reflection on instant film.

All very interesting photographs and sicsussion.

Chromatic aberrations are the bane of my existence. Every thing I've posted here has been on the Nikon 28-80G which is an okay lens, but I do notice those fringes a lot, and getting them down takes a lot of work. Fortunately, as it's a full frame lens on an APS-C camera, the performance isn't as bad as it could be.

I have no personal experience with the triple bandpass filter, but have experimented with different configurations of filters, mostly just deep yellow and orange. I have also tried adding different IR-reducing filters like KG3 and GBR3 to several different filters. That indeed increase the attenuation of the colours. I think adding the IR-reducing filters have mainly been a way to emulate the response of the IR-films, but there is another advantage. As digital sensors have IR-sensitivity deeper into the NIR band all chromatic aberration in the lenses will also be more visible. That is especially true for the more complex optical designs of wide angle lenses. That can be quite annoying.

Yes, you're absolutely right I got it backwards - infrared light is reflecting off the internal structures of the leaves and not the chlorophyll. Would have thought I'd studied photosynthesis enough to remember that it's blue and red light that is absorbed. Oh well... Thank you for the correction.

The first part of the statement is mostly correct, but the proposed explanation is not. The Wood Effect (named for physicist Robert Wood, not because it’s seen in the woods…) is caused because chlorophyll is transparent in IR so the light passes through it and is scattered efficiently by the material behind it, very much like snow scatters white light. Re “every species reflects about the same amount of IR”: Evergreens seem to reflect less IR than deciduous trees. But I mostly agree with that comment.

I've been experimenting on aerochrome emulation for the last 8-9 months using a lot of information from all over the web (a lot of which I found on here). The main thing that I have found is that in order to get very distinct variations in foliage, the amount of incoming infrared light needs to be cut. It seems as though pretty much every species of tree and plant reflects the same amount of infrared (which makes sense as chlorophyll a is highly conserved between all land plant species). To this end, the triple bandpass 550/660/850 from MidOpt is attached to the rear of my lens and the HOYA X1 to the front. This leaves me with images that are extremely green, but have the correct amount of red and IR light for a successful conversion. My workflow then generally involves desaturating the greens in lightroom and then performing the standard channel swap in Photoshop. Even with somewhere between -60 and -80 saturation applied to the greens in lightroom there's is still plenty of colour left to give the deep blue sky with white fluffy clouds that I'm after so much, without having to worry about the magenta cast that I've seen mentioned before. I'll keep iterating through, and I have seen Fandy's post about using a linear colour space so I may try that out on some existing files. I also need to try out a circular polariser to see if I can get the sharp drop off in the skies that I've also seen from some film photos.

Thank you very much

Thank you! Yes, I have basically been attempting to get the look of the aerial photo that Birna very kindly posted some time ago. I've been reading the forum for a long time so I figured it was finally time to join! These photos are all converted tiffs from the original camera RAW files, so I have a lot of latitude for changing the colour balance after the fact as well as before.

Of course! I use the triple bandpass 550/660/850 from midopt on the back of the lens and a Hoya X1 on the front as a red and IR cut. I'm drafting a thread of my workflow, but I'm currently on mobile so I think I'll have to wait until this evening when I have access to my PC. I've been a lurker for some time and I've seen and actually tried out your filter stack, but I found that I would get blown out skies due to the foreground being so dark.

Great colors in the UVs !

Hi and Welcome ! You went for a cool white balance, that's nice !

Same for me ! May I ask what your filter setup is ?

Great Fandy ! I'll share some of my latest images later. I'm impressed by your linear rec709 hack. The separation beetween green light and infrared light is very articulated. It doesn't seem that infrared ligh is influencing the green and red channels, which is surprising without any Ir reducing filter.

I believe I have had success. Thanks to all. This is a horrid multispectral photograph of a part of my back yard that I took yesterday before it got dark. I took it then because I had just received my filters! It was a little windy so you can see the colors as a result of movements between filter changes. Filters are Midwest Optical BP735, BP810, & BP880. Camera is Nikon Z 7 converted by Kolari and lens was that little plastic 40mm f/2 Z job set to f/2.8. For all three source images, I only used the data output from the red filter of the CFA. After assigning the data to BGR color channels, I messed around with the sliders in Properties > Levels to improve the mid-tones. Tom

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: The reflectance is high reasonably constant over a wide wavelength range, including UV and NIR 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.

Thanks @Fandyus.

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.

Beautiful collection.