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10-07-2016, 03:01 AM   #1
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Highly reflective surface products (Petri plates) photography for science.

Dear forum members.
I am looking for advice. At work we often deal with taking pictures of Petri plates with bacteria on them. Plates are 9 cm diameter.
Plates are plastic and highly reflective. Thus I always can find phone or camera reflections on the plate surface. Sometimes even self-portraits.
If I understood correctly, I need either light tent or copy stand with the appropriate lights set placed under 45 degree angle to avoid reflections. Pictures should be taken mostly strictly from the top.
I am leaning toward buying this copy stand set:
Kaiser R2N CP Image Capturing Set 205304 B&H Photo Video

But would like to hear other opinions.
Thank you in advance for your help.
Best regards,
Yuriy

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10-07-2016, 03:37 AM   #2
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That light stand looks pretty convenient. Should work if you angle the lights appropriately. If there are sill reflections try using a polariser.
10-07-2016, 04:11 AM   #3
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Thank you Nass.
I actually found that they have diffusers and polarisers for the lights.
Yuriy
10-07-2016, 04:42 AM   #4
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Well what you want is a polariser over your lens, not for the lights.

Sure, you can also add polarisers over the light sources as well but doing so probably complicates matters (it is called cross polarisation, aka xpol). Typically you buy polarising sheets that you put over your light sources for x pol, I use flash and the heat from that breaks the sheets. So I wouldn't bother with xpol yet, just try ordinary polarisation first (ie add a polariser over the lens when you're shooting this, and rotate the polariser so it cust out most reflections). I'm also not sure if xpol is really what you want, as it'll show the stress patterns in your petri dish. google cross polarisation and you'll see what I mean. I used xpol on very different subject, it did cut out all reflections but I didn't have a petri dish surrounding the subject


Last edited by Nass; 10-07-2016 at 04:50 AM.
10-07-2016, 06:43 AM - 1 Like   #5
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With petri dishes, you can also try to put them on a white transilluminator, which you may already have in the lab, and take the picture by transparency directly from the top. Usually, this works very well.
10-07-2016, 08:01 AM   #6
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If you need to shoot the subject directly from above without distortion of perspective and scale you need to use a shift lens. This removes the camera from the reflected field of view so it won't appear in the image. The next best thing is using a good polarizing filter. You will often find that the effectiveness of a polarizer is reduced as the plane of the filter moves parallel to the reflective surface (i.e. shooting head on). Polarizers work better at more acute angles of reflection.
10-07-2016, 08:48 AM - 1 Like   #7
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QuoteOriginally posted by JeffB Quote
If you need to shoot the subject directly from above without distortion of perspective and scale you need to use a shift lens. This removes the camera from the reflected field of view so it won't appear in the image. The next best thing is using a good polarizing filter. You will often find that the effectiveness of a polarizer is reduced as the plane of the filter moves parallel to the reflective surface (i.e. shooting head on). Polarizers work better at more acute angles of reflection.
But if the subject is lit from underneath and translucent the ambient lighting can be much lower and reflections can be nearly non-existent. I've done this with bifringence shots.

10-07-2016, 09:24 AM   #8
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QuoteOriginally posted by UncleVanya Quote
But if the subject is lit from underneath and translucent the ambient lighting can be much lower and reflections can be nearly non-existent. I've done this with bifringence shots.
Good call, might well work for the OP
10-07-2016, 09:26 AM   #9
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QuoteOriginally posted by CarlJF Quote
With petri dishes, you can also try to put them on a white transilluminator, which you may already have in the lab, and take the picture by transparency directly from the top. Usually, this works very well.
Had to google transilluminator and yeah, good call too. fyi a transilluminator is a lighting platform from underneath that you sit your thing on
10-07-2016, 10:19 AM - 1 Like   #10
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QuoteOriginally posted by Nass Quote
Had to google transilluminator and yeah, good call too. fyi a transilluminator is a lighting platform from underneath that you sit your thing on
Yes, it's similar to the white table we, old guys, were using to look at negative sheets. It's been many years since I had to document petri dishes but it's the standard way it's done. Not only for petri dishes, but for anything on/in a transparent/semi-transparent media or matrix.

For petri dishes, the additional advantage is that colonies (the things growing on the media) usually are more or less opaque relative to the media and back lighting thus greatly increase the constrast. They really stands out against the background, similar to a high key background. Obviouly, we're not talking here of doing an artitstic picture. But for documenting, it's fine and very reproducible. You can even find commercial scientific imagery system based on this...

The other "classical way" is to put the dishes on a black background and illuminate them with two light sources positioned each side on the lens, picture taken from the top. It's about the same idea as doing a macro with two flashes, but not macro... This also works well but one usually need to use a dedicated system for this kind of picture.

Last edited by CarlJF; 10-07-2016 at 10:37 AM.
10-07-2016, 11:34 AM - 1 Like   #11
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QuoteOriginally posted by Nass Quote
a transilluminator is a lighting platform from underneath that you sit your thing on
That doesn't sound too comfortable!
10-07-2016, 12:09 PM - 2 Likes   #12
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Being able to bark "Transilluminator to maximum power!" to a lab assistant makes all other methods inferior.
10-07-2016, 12:16 PM   #13
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Thanks a lot to everyone.
So, we do have transilluminator, but it is a part of DNA gel documenting system and only has UV lamps. Plus, only black-white camera system.
In addition bacteria that we are working with like to eat a good food - so all media are not transparent - we are using oat, soy powder to grow them. I am not sure if this will work.
I think we will just buy the copy stand with two lights and diffuser for them, plus polarizing filter for the camera. Will see how it will work. We got a good offer directly from Kaiser Fototechnik.
Thank you one more time. You are great community.
Yuriy
10-07-2016, 12:33 PM   #14
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QuoteOriginally posted by yurko_yr Quote
Thanks a lot to everyone.
So, we do have transilluminator, but it is a part of DNA gel documenting system and only has UV lamps. Plus, only black-white camera system.
In addition bacteria that we are working with like to eat a good food - so all media are not transparent - we are using oat, soy powder to grow them. I am not sure if this will work.
I think we will just buy the copy stand with two lights and diffuser for them, plus polarizing filter for the camera. Will see how it will work. We got a good offer directly from Kaiser Fototechnik.
Thank you one more time. You are great community.
Yuriy
Hi Yuriy,

This is a previously-solved problem. There are colony picking robots that rely on cameras to visualize colonies with high accuracy. This means that all companies building such robots have worked out this problem. You can take a look at various devices and see how it is done - usually by utilizing scattering of the media or transillumination.

colony picking robot\ - Google Search


By the looks of it,transillumination should work. The media seems only partially transparent, and more scattering if anything. If not, it is a cheap mistake ($32). I would buy a video LED lamp, for example this one:
https://www.amazon.com/NEEWER%C2%AE-Dimmable-Digital-Camcorder-Panasonic/dp/...led+lamp+video

If you put a diffuser on it (included) and then the plate on top this should give good pictures. It's 140x150 mm, so probably enough for a petri dish. We use a transilluminator for our petri dish photos.

And for the camera, I would invest in a tripod and a used olympus E-PM2 with a kit lens. Decent cameras are useful around the lab.
10-07-2016, 12:42 PM   #15
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Thank you Rrstuff.
We actually have such robot. But nobody is using it. People are still prefer to go with toothpicks.
I just found old white table in the storage room. Will try tomorrow.
Yuriy
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