Preventing leaf curl for macro photography

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Sharnbrook
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Preventing leaf curl for macro photography

Post by Sharnbrook »

I am presently taking shots of leaves, mostly grasses, to illustrate various plant diseases. In many instances, the grass leaves 'roll up' either on the plant, or after they have been picked and taken to the studio for imaging.

My current method involves trying to flatten them, and press them, prior to photography. Ideally, I need shots of the whole leaf, say 150mm to 250mm long, (6 to 10 inches), and then comparative side-by-side shots of a short length of the grass, say 75mm (3 inches), and then in some cases, macro shots of certain lesions, fungi, colouration etc.

In each case though, It is important to have a relatively flat leaf to display the characteristics and appearance of the symptoms as they present in the field. My concern is that pressing the leaves, will change the appearance, either by changing the colour as it dries, or remove some of the symptoms, for example any fungi. (Maintaining the fungi spores will be a problem with pretty much whatever I do.)

My hope is that there is a Plant Pathologist out there who will give me a magic formula that will provide flat photogenic specimens.

I have asked Dr Google, but he is not being helpful, though I live in hope that someone here will be able to assist.
Regards,

Mike

ChrisR
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Post by ChrisR »

How about holding it under thin glass?
I admit I have an ulterior motive for the suggestion, so apologies if it looks tangential - but it might work anyway.

Thoughts are going like this:
Specialist picture glass is available at 2mm thickness.
I have it in my head that
  • an NA around 0.4 is the limit for using no coverslip with an objective where one 0.17mm is specified.
    Coverslip Spherical Aberration error is proportional to NA^4.
OK so 0.17 * (0.4^4) is a limit , 0.004352
you get the same number with about
2 * (0.216^4)
So with an NA 0.2 objective, you should be OK. All other things be equal, which they almost certainly aren't : :smt100

Blundering on - at 1:1 that's an f/2.5 lens (or smaller), so no problem.

You could use http://www.edmundoptics.com/optics/wind ... ows/45255/

Or they do 3mm coated at 75mm square/round.
which would be "OK" at NA 0.195, still no problem.

I'm expecting someone to tear this to shreds...
Image

Sharnbrook
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Post by Sharnbrook »

G'day Chris,

Thanks for your suggestions. In fact, it is something I have considered, especially as a friend who has a framing business was saying just the other day that she has a new 'wonder glass' that gives virtually no reflection, yet still allows pictures to have the vibrancy that the older non relective glass didn't. I shall try to get a small sample to see if it works, and if so, I'll experiment further. I shall give her a ring to find out the name of the glass.

However, I still have hopes that 10 parts of this, 7 parts of that, and 13 parts of something else, mixed with 70 parts of rain collected on a Friday evening will do the trick, if applied in a clockwise direction with an owl's feather. (Anti clockwise in the Antipodes or course).

Seriously though, thanks for the comments, I'll give it a go, and let you know.
Regards,

Mike

Lou Jost
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Post by Lou Jost »

Would the leaves still roll up if they were transported in a closed vertical tube with distilled water in the bottom, and if you kept their bases in water during the photography?

Pau
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Post by Pau »

Maintaining the fresh look when dried will be really difficult, of course no idea about the magic formula (maybe you could visit Lenin's mausoleum and ask to the conservators) :roll:

To preserve some features for further study making microscope slides after fixation should be adequate but BTW you'll lose the natural look

Just to hold the leaf flat for photography an useful trick in some cases could be to glue it with double sided tape to a microscope slide or other flat surface
Pau

ChrisR
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Post by ChrisR »

Someone must have tried freeze-drying leaves?

Chris S.
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Post by Chris S. »

Howdy Mike,

Like you, I have a strong interest in plants. And also like you, I've noted that without special care, many plant specimens, when transported to the macro studio, lose water in ways that interfere with accurate photographic documentation.

My personal approach to reducing this large source of error involves several steps. For the first step, I carry a plastic cup of water and a sharp pair of scissors out into the field when I collect plant specimens. I quickly snip and immerse in water the cut specimens. This often suffices, but in some cases, is insufficient because pockets of air may still develop within the plant's capillary tubes. In these cases, I bring the plant cuttings indoors and cut them again, under water, and transfer these cuttings--while remaining underwater--into photomacrography "vases"--really just water-containing sections of brass tube epoxied to magnetic bases and sealed at the bottom to prevent water from running out. (Though some of my "brass bases" are rigged to let me add additional water, for use with plant specimens that rapidly lose water.)

When I examine plant parts under magnification, I usually combine the above-described protocol with a mounting assembly that holds a stem in water, with the leaf above it taped fast to a microscope slide, with strong light shining on the leaf, causing it to photosynthesize. This approach, in many cases, encourages the plant part under consideration to continue normal function.

Apologies if this explanation is poor. It's a subject on which I've long meant to post on in depth.

--Chris

Sharnbrook
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Post by Sharnbrook »

Thank you Chris S, as well as Chris R., Pau, and Lou for your comments and suggestions.

I have today procured a small sample of etched glass, which is used for non reflective picture framing and have taken some shots of 'bush samples' of grass, ie growing wild, with a similar blade length to my real samples. I started by taping one end to a piece of melamine board, and I then slid the glass over the blades, ensuring that the grass was as near to flat as I could manage.

Within a few minutes of collecting the samples, (15 mins max), I took shots of the grass under the glass, illuminating the specimens with photo flood lights, with the light directed longitudinally with the blades, to prevent any shadows from the edges.

As a first trial, it worked quite well, but of course, the image is slightly soft because of the etched glass. I understand that the Museum Quality glass is 'optically good' (whatever that may mean), but to prevent the reflections, it is coated the same as spectacles, or a camera lens or filter. The drawback is the cost. A piece 600 x 500mm (24 x 20 inches) is A$280.

However, I have just spoken with another framer, who tells me that there is another manufacturer, and their price is very much more reasonable. A small sample will be on its way to me tomorrow, so I can conduct a trial.

Whilst image quality is important, it is only for printed reproduction in a handbook, at a maximum scale of 2:1, and I think if this metheod gives a true representation for determining diseases in the field, it will be quite adequate.

As an indication of the problems that I have had in the past couple of days, our temperature today has been 35 deg C, (95 deg F) with a RH of 21%, and a brisk wind blowing, which does tend to dry samples quite quickly. Tomorrow's forecast is higher still.

I shall keep you all informed of my progress, and much appreciate your interest and assistance to date
Regards,

Mike

rjlittlefield
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Post by rjlittlefield »

Sharnbrook wrote:I understand that the Museum Quality glass is 'optically good' (whatever that may mean), but to prevent the reflections, it is coated the same as spectacles, or a camera lens or filter. The drawback is the cost. A piece 600 x 500mm (24 x 20 inches) is A$280.
I recently purchased a 5 x 7 inch piece of "Tru Vue Museum Glass" from eBay for $16. I think that scales to about the same price you give, taking into account the size.

As you say, the material is coated, not etched, so it looks like a large rectangular UV filter. The thickness of my sample is 2.2 mm, which is thin enough to photograph through at low magnification but would start becoming troublesome around 10X (NA 0.25).

--Rik

Charles Krebs
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Post by Charles Krebs »

Glass can work great but...
depending on the moisture content of your subject, and the "atmospherics" of your workspace I think you will find that condensation onto the surface of the glass (in contact with the plant material) will often be a frustrating problem.

Chris S.
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Post by Chris S. »

A few thoughts:

For plants, while I often tape a specimen to a glass slide to hold it steady, I usually keep this slide out of the image path--above it on a horizontal rig. As Charlie says, such glass will often and quickly be deposited with condensed water droplets. (My sense is that these are mostly the result of photosynthesis from my continuous illumination, which I actively seek to maintain turgidity.)

Also, if I needed to image grass specimens of several inches length, I'd strongly consider using a common flatbed scanner. These can work remarkably well for certain forms of photomacrography. And if using a flatbed scanner for imaging grasses, I'd be tempted to lightly moisten the glass scanner surface before placing the plant specimen; there might well exist a level of moistening that would help the grass adhere, but not cause deformation in the shape of the grasses, nor deleterious visual effects.

--Chris

Sharnbrook
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Post by Sharnbrook »

Hi Rik, Charles and Chris S, thank you for your thoughts and suggestions. Apologies for the tardy reply, but we have had guests, and twice spent the day away from home.
One of the trips was to collect a sample of the Tru Vue - UltraVue Glass, which I understand is more reasonably priced than the Museum Glass.
http://www.tru-vue.com/products/ultravue

I have yet to try a comparison, or even try to take photos under it, but I shall do some trials in the next day or so, and submit my findings.
Regards,

Mike

ChrisR
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Post by ChrisR »

Scanners are interesting. I'd forgotten that I'd tried my printer/scanner with some sedges (with edges..) and found it less than ideal.
They vary, in their apparent depth of field. (With some you can change the focus height, but not with the general purpose machines.)
I think it's analogous to using a different-sized sensor on a camera, where your in-focus depth might be the same, but a slightly oof background is more objectionable with a bigger sensor.
The very excellent book "Mosses and other bryophytes - an illustrated glossary" 0-958224-7-9, uses techniques from DIC microscopy to a flatbed scanner, with great effect.
A page from the book:
Image
Last edited by ChrisR on Thu Nov 26, 2015 9:47 am, edited 1 time in total.

Pau
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Post by Pau »

I have had mixed experiences with flatbed scanners for this purpose:
My old Acer (SCSI driven) worked very well but my modern Canon (with much higher resolution) only works well if the subjet is completely in contact with the glass, with a more 3D subjet it produces nasty artifacts and not a smooth gradation on OOF parts like the old Acer. They use for sure different technologies but I'm not aware of their names
Pau

ChrisR
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Post by ChrisR »

That ties up with my experience. A big office machine might be better than a tiddler.

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