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Flash advice for macroscopy

 
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NickM



Joined: 19 Mar 2006
Posts: 8

PostPosted: Tue Mar 21, 2006 9:41 pm    Post subject: Flash advice for macroscopy Reply with quote

Well it has become glaringly obvious that photographing fast moving aquatic critters at 10 - 30x (copepods and all) isn't going to happen without flash. Having spent a few hours looking into it, I'm hopelessly unsure.

My rig includes a Coolpix 5000 sitting atop a leica c-mount, above 3 leica fixed focal length plan/acro objectives. There's a mechanical stage without a base light or mirror. Water in the dish is 1/8 - 3/16" deep with plant material protruding slightly.

Here are my false assumptions. Feedback, comments and castigations would really be appreciated.


    A light dome of some sort will need to sit above the dish in order to minimize glare on the water surface?

    Flash will hang down from the camera by off shoe adapter (stuck to what?).

    Something like a Nikon SB600 flash is suitable.

I was looking on a Jetson's trivia website to see if the town had a name. Looking at animals buzzing in and out of aquatic moss reminded me of the traffic outside SpacePad Apartments. Anyway, there was no town name but I found this:

"The Jetsons live above a psychiatrist with a safety net outside his window"
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Wed Mar 22, 2006 3:42 pm    Post subject: Reply with quote

Nick,

Your stuation should be pretty easy to accommodate since the Coolpix 5000 actually has a flash shoe. Just about any of the Nikon flashes on a remote cord would do the trick. (You could probably even "slave" a flash if you did not want to have a cord).

If you angled the flash properly, reflection from the water surface should not be a problem. (Although if the built in flash still "fires" as well, you may need to block it from hitting the water surface).
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NickM



Joined: 19 Mar 2006
Posts: 8

PostPosted: Wed Mar 22, 2006 8:18 pm    Post subject: Reply with quote

Do you think some sort of diffuser (maybe a dome) is necessary or useful?

Just got the Coolpix but I heard about the double flash problem. Was this ever corrected in a firmware upgrade.

Thanks for your input. Smile
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Wed Mar 22, 2006 11:17 pm    Post subject: Reply with quote

Nick... a diffuser could be useful with some subjects, but with subjects in water you would have to pay closer attention to reflections off the surface.

A quick check showed that firmware 1.7 allowed using an external flash without the camera flash firing during exposure.
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NickM



Joined: 19 Mar 2006
Posts: 8

PostPosted: Fri Mar 24, 2006 8:50 pm    Post subject: Reply with quote

Thanks for the input. This is helpful. Checked the firmware and it is 1.8 Very Happy

I am under the mistaken impression that the diffuser would help stop the reflections. That was my intention. What's the deal? The water is quite shallow, and with moss shoots protruding out - and all the surface tension - the surface is more wavy than flat.
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Wed Mar 29, 2006 1:33 pm    Post subject: Reply with quote

Nick... diffusers and reflectors are great for eliminating hard specular highlights, such as you might encounter on a shiney beetle, or a glossy black insect. But it does this by "expanding" the light source, so that more care is needed when looking down through a water surface, where you need to be careful of glare on the water surface
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rjlittlefield



Joined: 06 May 2005
Posts: 727
Location: Richland, WA, USA

PostPosted: Wed Mar 29, 2006 8:43 pm    Post subject: Reply with quote

NickM, another way to kill reflections off the water surface is to use crossed polarizers. You put polarizing film in front of your flash, a polarizing filter on the camera, and adjust the filter rotation until the reflections disappear. See this posting and this article for details.

But if the water surface is not flat, your image may be blurred because the water acts like a lens with aberrations.

You might be better off to add enough water to make the surface flat, then position the flash so that it does not reflect into the lens.

Or perhaps position a piece of glass at the water surface so that it's wet on the bottom and you are looking as if through the side of an aquarium.

You could probably simplify this task by cutting a small piece of glass and running a bead of aquarium caulk around the outside to make sort of a "glass-bottomed boat" that will just float.

--Rik
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NickM



Joined: 19 Mar 2006
Posts: 8

PostPosted: Thu Mar 30, 2006 10:17 pm    Post subject: Reply with quote

Thanks. Polarizers sound great. I'm used to using Canon polarizers for EF lenses. For this setup, I have a Nikon Coolpix 5000. This will require looking into. Not sure if anything'll fit between the UR-E6 and MDC.

I like the glass surface idea since the water surface is currently shaped like sand dunes. Can't go any deeper or currents become a problem. As it is, the surface tension seems to hold everything really still. A lid would also help in other ways. Since the water is only a few mm deep, it would take longer to dry out. Also, the floating debris would be gone.

On the other hand, there are bubbles. Blast! Well I'll just have to try it out. Thanks again.

Nick
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