I am a lab technician working in a microbiology lab where we would like to photograph the colonies on petri dishes. We have a camera (microscope camera with a macro lens attached) and light setup, but I would like some help modifying the lighting.
We currently have two fluorescent flood lamps (like the worklights you can buy from Home Depot), but I am looking for a way to minimize the reflections/light-glare that show up on the bacterial colonies. What could I use as a diffuser?
Alternatively, if some reasonably inexpensive lights are available that could be placed on a bench-top, we can replace out current lights with something that will work better.
The best way to eliminate the reflections completely is the cross-polarization method. This means, polarization foil in front of the light sources (in common orientation) and a polarising filter in front of the lens. Of course, this takes some light power but I assume that you can make do with it.
Have you considered using less light and a longer exposure? Are these things moving such that you would experience motion blur during a couple of seconds exposure?
As long as I can shoot from the top, then I could do something like that for the macro shots. I just can't move the microscope-based camera from looking down.
We do have a second microscope (dissecting scope) where a light tent wouldn't work. So while it may work for the macro shots, I would still need something for the main lights.
digadv wrote:
Have you considered using less light and a longer exposure? Are these things moving such that you would experience motion blur during a couple of seconds exposure?
The colonies are unmoving. At the moment our light sources are constant (I am not exactly sure what wattage). If I could put something in front of the lights to "dim" or diffuse them, then perhaps playing around with the settings would work.
PeterBerressem wrote:
The best way to eliminate the reflections completely is the cross-polarization method. This means, polarization foil in front of the light sources (in common orientation) and a polarising filter in front of the lens. Of course, this takes some light power but I assume that you can make do with it.
I'll have to look into cross-polarization. I suppose a lens polarizing filter alone might also help reduce glare. It hadn't occurred to me to try something like that in this situation.
phluxos wrote:
...I am looking for a way to minimize the reflections/light-glare that show up on the bacterial colonies. What could I use as a diffuser?
The most important factor in creating a diffuse light is the size of the light relative to the subject.
Simply placing diffusing material directly in front of a bulb, for example, won't make it more diffuse, but moving the lamp further away and shining it through a large diffuser that's close to the subject will. That's the principle behind light tents.
The question in your case is the type of lights used with your microscopes. Are they seperate or attached? If they're seperate, then pull them back and set up some sheets of tracing paper or similar hung next to the 'scope. The paper will then become the light source.
Since you're using constant lights, you can move the sheet(s) around to find the position that best reduces specular reflections yet still gives some shading to show texture and dimensionality.
BTW, not related to diffusion, but while we're talking shop:
I don't know if you need color-accurate images or not (since color is part of the morphology, you probably do), but if you do, don't forget to make a custom white balance after your lights are set up. The best way would probably be to put a small WhiBal card on the platform and take a shot of it.
If you're not using a digital camera with custom WB capability, you can still use the shot of the WhiBal card as a color reference in post processing.
What about lighting to illuminate the bottom of the petri dishes with a light source like a light-table and shoot through the petri dishes as I recall most bacteria are transparent or semi-transparent
I work in hospital laboratory too. HEre's what you do:
Get a big old box from supply/receiving. Similar to the light-tent deal, you're going to cut the sides out of the box, creating a window, and then replace that with several sheets of printer paper taped together. Aim the lights at the paper, it should create a nice diffuse light source at little to no cost.
