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Lighting for macro photography of fern gametophytes
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jsp



Joined: 28 Mar 2015
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Location: United Kingdom

PostPosted: Sat Dec 05, 2015 3:00 am    Post subject: Reply with quote

I've got an idea. If I get two big pieces of worktop (which I already have) and sandwich between them a single layer of the yellow stretchy men (below), I think that would give enough of a vibration-absorbing layer, but still keep the whole system stable and flat. Does that seem good?

The stretchy men are only 7p each and are very very stretchy/rubbery, so should be just the thing.

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ChrisR
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PostPosted: Sat Dec 05, 2015 3:56 am    Post subject: Reply with quote

I haven't been introduced to the world of the stretchy guy, but I fear he may not be squishy enough.
By squishy, we mean for a wide range of frequencies of wobble, from low (snoring) upwards. Long, soft springs, if you like.
If the whole of your "stiff board" which is sitting on top, moves together, that's not a problem as long as the subject itself doesn't waggle about. For that, the board has to move slowly enough, which is helped by being heavy.
You may get away with a cushion off your sofa - if you look up Sorbothane you'll get the idea.
http://www.sorbothane.com/vibration-isolation-pad.aspx

For your subject I'd try a tube of plain white paper, lit by a single flash from one side. The inside of the paper acts as a fill reflector, so you can adjust it by altering distances. For a highlight, an extra sheet of paper with a hole in it, flash-side, produces a slightly brighter spot. More than that will probably cause you burn-out problems.


Last edited by ChrisR on Sat Dec 05, 2015 5:30 am; edited 1 time in total
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Lou Jost



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PostPosted: Sat Dec 05, 2015 5:26 am    Post subject: Reply with quote

It would be worth trying the stretchy men just for fun. I can imagine how your setup will look...a sandwich of granite slabs with heads and arms of stretchy men sticking out from the edges--it would be unique!
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jsp



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PostPosted: Sat Dec 05, 2015 7:05 am    Post subject: Reply with quote

Thanks :-) Good to have options.
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rjlittlefield
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PostPosted: Sat Dec 05, 2015 11:40 am    Post subject: Reply with quote

I love the stretchy men! The fact that they both stretch and stay where they're put strongly suggests to me that the material is a good energy absorber. And they're dirt cheap compared to the Sorbothane feet that I put under my optical breadboard. My biggest concern is that they may be too thin to be optimal. Rolling up the body, or folding the legs up over the body to make a two-layer sandwich, might help if that's an issue. You'll have to play with it. Since these things are toys they're probably very soft compared to Sorbothane.

I'm definitely looking forward to the report.

Do pay attention to ChrisR's description of "Long, soft springs". A fixed amount of absorber will generally do a better job when arranged as relatively tall columns with a small cross section, versus short columns with a large cross section. Those Sorbothane vibration pads are engineered for heavy loads -- the web page mentions "a 3800 pound load ... with a .25x4x4 pad". Scale that down to a 50 pound load, and you'd be looking at a pad that's still 0.25 inches thick, but in cross section less than 0.5x0.5 inches instead of 4x4. For light loads, Sorbothane makes softer material in shapes like hemispheres. The ones under my breadboard are cylinders that started off 1 inch tall and 1.5 inches diameter, according to the specs, but in use they're squished down to 0.8" high and 1.7" wide, with an obviously barrel shape.

--Rik
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Chris S.
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PostPosted: Sat Dec 05, 2015 11:02 pm    Post subject: Reply with quote

Sorbothane's products come in a vast array of shapes, sizes, and levels of squishiness, because these need to match the mass of the object you want to isolate and the vibration frequency you want to isolate from. A poor match can not only fail to help, but cause hurt.

If the goal is to be making good pictures soon, I'd suggest purchasing carefully-selected Sorbothane feet from a reliable source like Newport or Sorbothane itself (not eBay, as it would be easy to receive a counterfeit item with, say, a different durometer specification). For selecting your feet, the quick and dirty approach is to purchase feet specified so that each foot is bearing close to its recommended weight limit. Or for those inclined, a better job can be done by going to Sorbothane's Website, downloading the Sorbothane Design Application and Design Guide pdf, and determining what you need. Edit to add: The Sorbothane Standard Products Guide contains both useful general information and a long list of off-the-shelf isolators. Also, I have no personal experience with Sorbothane isolators, as I work in a very quiet basement.

But if the goal is to have fun along the way, by all means experiment with those squishy men. (And make sure to report your findings! Very Happy) The word "experiment" is key here, as you will probably need to spend a few hours or days figuring out what works best, if at all.

I tried plugging the little fellows into Sorbothane's calculator to see what could be seen. This is very unscientific, as I had to make a bunch of assumptions, such as the big one that the material the squishy men are made from behaves like Sorbothane elastomer. I also assumed a length of 2 inches, a width of 0.75 inches, thickness of 0.25 inches, and a durometer (measure of squishiness) of 30 (similar to gel shoe insoles). While Sorbothane's calculator allows for a number of shapes, "humanoid" is a oddly omitted. So I went with "rectangle." If this is at all predictive, Rik is quite right that a single layer of squishy men is unlikely to benefit you. In fact, it may to amplify vibration and make things worse.

Here's a case with four squishy men supporting a 14 lb rig (yellow highlights mine):



As you can see, that system rings at 100 hz (which, I suspect, is a pretty common region for problems, and can be heard here. Interestingly, it helps quite a bit at 200 hz or above.

But simply doubling the thickness to 0.5 inches begins to produce useful results. Notably, to get good results, you need to put a fair amount of weight on the elastomer, so spreading the squishy men widely under the bottom of your platform is probably the opposite of what you want to do. Not only is it better to have a taller elastomer column, also a more heavily loaded column.

I'd be tempted to get a bicycle inner tube of the smallest possible diameter, cut short sections out of it, stuff them cut-up bits of squishy men, and tie off the ends. I'll bet a local bike shop would happily give you a cast-off inner tube. In the calculator, a 1-inch tall, 1-inch thick cylinder works well down to about 30 hz. (To hear any frequency, plug it into an online tone generator.)


JSP wrote:
There are a few things that I'd like to achieve with lighting. I want to have my specimen lit beautifully, as if it was a professional model on vogue, to really bring out the best in it. I was taught that I should have a fill light in front, one a little to the side to bring out the depth and a light at the back "like they do to highlight the hair of a model". I've looked at photos and fiddled with lighting and I think it's absolutely true that this is what is needed, and I'd like to really try to do it well.

JSP, I photograph tiny bits of plant quite often, have similar lighting goals, and agree with you about providing in the macro studio the same degree of lighting control used in other studio photography. The lighting stage I use for this is shown here. Like Charlie, I no longer use flash for this sort of things, as I greatly prefer being able to see how the lights play while adjusting them. Now, the articulating arms hold fiber optic light guides for a halogen illuminator. This approach is very adaptable, and keeps the heat of the lamps is far from the photographic subjects. (LEDs have improved a lot since I bought my illuminators, and the case is now pretty strong for LED lighting.)

To get the sort of images you describe, you will indeed want a combination of front light and backlight, and the ability to adjust each independently. Partial backlight is especially nice with things like fern gametes, which are thin enough to be translucent. My general workflow is to set up key lights and modifiers, then the back lights and modifiers. Then add fill light to adjust the density of the shadows. (The easier and vastly more common approach has already been described—put a light tent around your subject and flood it with broad, diffuse light.)

Pau’s advice to use cross polarization, and his examples of it early in this thread, are well worth noting. For things like fern gametes, I'd call this advice "crucial." I do not think you’ll get the sort of images you describe without using cross pol.

As has been discussed, it’s not easy to keep cut plant bits from drying out, or from moving. An approach I find helpful is to supply water to the piece of plant during the shoot, with a tiny, home-made vase of water that sits on my subject stage. Here, continuous light helps, as a plant part that is actively photosynthesizing will often take up the water nicely. And to reduce movement, one can clamp or tape down any portion of the plant that is not in the picture.

--Chris
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jsp



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PostPosted: Sun Dec 06, 2015 12:23 am    Post subject: Reply with quote

Thanks for all this. This is great. I didn't know about sorbothane at all before.

I've made a start by taking apart my newer scanner and it is now all stripped down with the four wires ready to be attached to my raspberry pi. It's trickier to do as the four were combined in ribbon wire. I'm going to need to solder the ribbon wires into jumper wires for the next stage. I'm hoping to have a go at that today. Then I'll need to figure out which wire is which and sort out my python programme to make it all work. It might take a wee while, but I'll report back as soon as I have something to report. Very Happy
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Charles Krebs



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PostPosted: Sun Dec 06, 2015 12:50 am    Post subject: Reply with quote

One thought...

I don't know where your set-up is located or what the environmental vibration issues might be. All the advice presented here is good. But a great many people do not really need to go to extra lengths to diminish environmental (external) vibration issues.

With a subject in focus that has bright point highlights, and your Canon set to live-view at the 10X magnification you should be able to see clearly if there is any "jiggling" of the image relative to the sensor caused by an external source.

Nothing wrong at all with setting up the most vibration resistant base you can, but if it is not an issue, your efforts and attention might be better spent with other concerns.
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rjlittlefield
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PostPosted: Sun Dec 06, 2015 1:22 am    Post subject: Reply with quote

To record some musings...

Many thanks to Chris S. for raising the point about resonances and noting that there's a handy calculator for Sorbothane.

For reference, the calculator can be downloaded as a Windows application from http://www.sorbothane.com/Data/Sites/31/media/SorbothaneDesignGuide.exe, linked from http://www.sorbothane.com/engineering-design-guide.aspx.

In the example shown above, the basic problem is that the material is not compressed enough. That's why the nasty red "Warning!" indicator. When you're running the calculator, if you hover over the "Assumed Percent Deflection" label, it turns into a link, which when clicked produces a popup that says "Assumed displacement of the given thickness. Iterate until with 3% of the calculated Percent Deflection." (I assume that's intended to be "until within 3%", based on the program's behavior.)

Increasing the thickness to 0.5" does help, but it doesn't get rid of the red warning with still only 6.22% deflection.

According to the calculator, an alternate and pretty effective solution would be to simply make the pad smaller. Keeping the thickness at 0.25 in but shrinking it laterally to be 0.8 x 0.5 in produces this improved situation:



The key thing to recognize is that the absorbers have to get squashed. If they don't get squashed, then they're acting like stiff springs, and those won't provide isolation.

Switching subjects, and since I see that I'm posting after Charlie, I'd like to second his concern about making sure that you really do have a problem with environmental vibrations.

Reviewing this whole thread, I see several comments about EFSC and silent mode, but I don't see a statement by jsp that his sample images were shot that way. So while the images of coin versus plants still suggests vibration, I can't tell whether that was picked up from the environment or induced by the camera mirror or shutter actions. Any word on that?

--Rik
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ChrisR
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PostPosted: Sun Dec 06, 2015 3:38 am    Post subject: Reply with quote

We've spent a few hours on researching this.

Modelling a suitably massive substrate and optimal suspension, the dynamic absorption characteristics through a range of environmental frequency spectra were established.

The team was obliged to employ estimation for the parameters of the time-variable elastomeric properties of the materials concerned.

Further evaluation of the schema would be required to correlate empirical data with computed analysis.

A working prototype is suggested, (do not scale drawing).
The basal frame proposed is an inverted, nonspecific, quadropedal, horizontal domestic support facility.
Technical Drawings
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Chris S.
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PostPosted: Sun Dec 06, 2015 4:28 am    Post subject: Reply with quote

Hah, Chris! Very Happy

While agreeing with Charlie and Rik that lots of people don't need vibration isolation, and not using using it myself for high-mag continuous light. I still think that many people do stand to benefit from it. Charlie's proposed test can help determine which folks are which.

And if I ever take the Bratcam on the road, I'd like to have some vibration isolators with me just in case. In a bit of checking tonight, I see a set of four hemispheres spec'ed and calculated to get my rig out of almost any vibration problem, for the whopping price to $20 total for a set of four (Sorbothane part number from self-adhesive hemispheres of 2" diameter, 1" height, durometer 30, from www.isolateit.com.) For me, that's worth ordering as shop's supplies.

And since it's such a useful idea to tie camera and subject together on a board/piece of steel or aluminum, granite, etc. anyway, adding $20 worth of Sorbothane isolators under the rig isn't a big deal.

Very clever of Rik to notice that cutting the little men to a smaller size improves calculated results. I've done such calculations for off-the-shelf products, but didn't think to do it to the little men.

Vibration is fascinating stuff.

--Chris
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jsp



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PostPosted: Sun Dec 06, 2015 4:52 am    Post subject: Reply with quote

Hi,

In my mind it's pretty clear that the vibration is caused by the fern rocking on the little bit of blue tack that it's mounted on. Ferns are very delicate and it's not possible to fix the fern down, so if there is any tiny vibration from the camera then the fern wobbles. In that respect it might almost make more sense to isolate the fern from the camera physically.

The camera was not on live view and I just triggered it with an infra red control. I think it had silent shutter enabled, but I'm not sure.

btw, I should introduce myself really, since you're all being so extremely kind in thinking about this. My name is Jennifer Deegan and I'm a stay-at-home Mum, but before my son was born I was an academic plant scientist as the Universities of Glasgow and Cambridge, and at the John Innes Centre and the EMBL-European Bioinformatics institute, all in the UK.

This is me: https://www.linkedin.com/in/chlorophyllosophy
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PostPosted: Sun Dec 06, 2015 5:24 am    Post subject: Reply with quote

I've done a bit more to my scanner. The wires are all soldered now and the connections are made from the Raspberry pi to the scanner. There's a small delay now though, while I paint about 40 metres of architrave to be fitted in my hallway tomorrow, and make everybody's lunch. :-)

I'm still reading though. There just will be a bit of a delay before I can report more progress. Very Happy Very Happy Very Happy
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ChrisR
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PostPosted: Sun Dec 06, 2015 5:24 am    Post subject: Reply with quote

HI Jennifer Very Happy
Mirror-slap would be disastrous, shutter-click would be significant.

Dealing with them is simple with the 5D/II, fortunately.

Separating the subject from the scene of the accident can help, eg if you're using a microscope, but not a good idea when you can simply remove the trauma. It becomes better to lock camera and subject together, to remove differential movements.

Many find that low-grade precautions are adequate at say up to 5x, to remove all environmental vibrations. But I have London at the end of my street. A laser pointer bounced off a saucer of water onto the ceiling, shows permament movement. 5x I can do ok without flash, certainly for web appllications, but I tend not to.

(Reading you Linked-In info, I wonder if you ever pinned Heather Angel down for her view of being a pro plant photgrapher. Friendly and inspirational.)
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PostPosted: Sun Dec 06, 2015 5:44 am    Post subject: Reply with quote

Hi Chris, Very Happy

I never did come across Heather Angel. Although I was in the PGPA for a year, I couldn't make it to any events because of baby-care responsibilities, so I didn't really meet that many people unfortunately. It was exciting to see names that I recognised on the mailing list though.

I'll put mirror-lock on my list (I'm making a list in my lab book from this thread so I don't forget any of these mighty helpful tips when the moment to take a photo actually comes.) I definitely did enable it at one point and I never did turn it off, but I think it would be good to go back and check.

tbh I get in so much of a flap dealing with the scanner and the raspberry pi that the shutter side of things gets a bit overlooked. One of the photos that I took was from 800 slices, taken every three seconds with me firing the shutter manually by remote control. It leaves very little energy for thinking about what else I should be doing. I'm hoping that my tiny ferns will not need so many, and that I'll have more energy left for remembering all the other factors.

What do you all do for your focus stacking? I'm not seeing dismembered flat bed scanners in the other setups that you've pointed out. Do you have something less frazzling?

Thanks!
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