Longpass focus shift, lesson learned

[Guest]

Arriving home from work the other day I found this [insert species here] trying to grow up and over the stairs at my front door. Of course, I couldn't just cut it back without also taking the opportunity to have a look at it - in VIS, UV, and IR. This also served as another mini learning experience for working with the longpass filter I've chosen to use for UVIVF imaging.

 

Unfortunately, while I should have known better, I did not anticipate the slight focus shift generated by the longpass filter (I didn't notice until post-process because it looked fine on the camera's little viewfinder at the time of the shot). Notice how the focal plane shifted back slightly. This shouldn't be an issue moving forward, as I intend to shoot from the start with the LP filter in place. I'll chalk this one up to a 'learning experience'.

 

One thing I may try next is to repeat this kind of UVIVF, but extend it to nIR by using a broadband camera instead. This would help to show even more of the induced fluorescence (notice in the longpass filtered image above how some of the red cholorphyll fluorescence is just barely showing up in the leaves...). I'll have to work out some way of generating a comparable UV source free from IR. I'll also need to think of what to call it... UVIVandIRF?, UVIVIRF?, ?.

[Andrea B.]

That would be good old Pokeweed, Phylotacca americana. It is a very photographable plant. The young leaves are edible, but the berries are poisonous.

 

Very nice photography and nice explanation of your methods.

 

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One minor point: The term UV-signature refers to how a flower (or plant or whatever) appears in UV regardless of whether it has any particular "patterns". Similarly, for IR-signature.

 

The pokeweed flower's UV-signature would be described something like this: UV-absorbing with some evidence of specular UV reflections possibly due to structural iridescence.

 

The flower's IR-signature would be: uniformly IR-reflecting above 850 nm.

 

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That flower is so cool looking in the fluor photos!

I've never dug out anything about the advantages to the flower of this kind of biological fluorescence. But you sure have to think that it must mean something, eh??