Flash setup for photomicrography

[ddy5]

Some folks asked about the flash setup I used for the photos in the ‘Slender ciliates’ post over in Pictures and Videos.

The core of the system is a Profoto D2 studio flash. It’s almost seven pounds and awkwardly big. However, the high light output, short flash durations, and several other features make it a good choice for the job.

The attached photos will give you an idea of the setup.

Beyond the flash unit and the heavy-duty supports necessary for it (last photo), there are two major components:

1. The beam-splitter assembly utilizes Thorlabs 60mm cage components. The stock lamp has a condenser lens, and there is a second lens plus diffuser in the base of the microscope. I played with lenses in the flash's light path and ended up using a single plano-convex condenser lens.

2. The D2 is coupled to the beam-splitter assembly with a metal cone that was part of a Nikon photomicrography setup from many, many years ago. I tried various snoots, but this worked best. The cone is lined with reflective foil. The flash tube of the D2 is circular, so the direct+reflected light at the bottom of the cone is reasonably uniform.

I worried that the greater distances from the light sources to the microscope compared to the normal, stock arrangement could cause problems setting up Köhler illumination or have other bad optical consequences. That was not the case - everything works fine.

Other than color temperature, I can’t see any difference illumination-wise between photos taken with the two light sources.

Cheers, David

Note: I have more recently replaced the stock halogen light with a COB LED light (Wescott L60-B).

D2 set-up A copy.jpg (148.84 KiB) Viewed 1054 times

D2 set-up B copy.jpg (187.9 KiB) Viewed 1054 times

D2 setup C copy.jpg (246.81 KiB) Viewed 1054 times

[macnmotion]

Thanks for this post. I'm still trying to understand it all. I have a studio flash with hot shoe trigger. When you use the beam splitter, are the two light sources being added together or are you using one or the other at a time? Adding the light source in essentially the same pathway as the light box, what makes your lighting different other than it just being a much stronger light source?

[ddy5]

Yes, both sources provide light at the same time. I normally reduce the constant source to a low level when taking the flash shot. The flash is very much brighter than the halogen source, so the halogen has no detectable effect on the images.

The goal was to make the optics of the flash pathway as similar as possible to the halogen pathway. The difference is simply that the flash produces a very short burst of light. For the D2, I measured the durations at my most used intensity settings: 1/10,000 - 1/20,000 sec. (t0.5). That's fast enough to freeze any motion I've so far encountered with protozoa, including cilia motion.

Although not really important for the photos themselves, it was not great to have such different color temperatures (the halogen at low intensities is very orange compared to the flash). The new COB LED source I mentioned solved that and provides more light as well.

Cheers, David