Pinned specimen orientation

Charles Krebs · Post by **Charles Krebs** » Tue Sep 22, 2009 11:18 pm

Elf,

Nice diagram! (I was going to try something like that but it would have looked like...

)

I would probably have the platform no larger than 1" and keep the pedestal shorter. Naturally you could have a variety of platform sizes and configurations to meet different needs.

That's one thing I like about it. Pull the platform off and drop on another. You can have more than one specimen prepared for the photo "session", and you would not need to remove a subject from the platform in order to work with another right away. Nice if you need to re-shoot.

g4lab · Post by **g4lab** » Tue Sep 22, 2009 11:31 pm

Here is Zeiss' $567 answer to this problem. The photo does not show the ball very well but it is large. They used to have circular adhesive strips to hold the ball in one position if you wanted. I don't see those in the katalog anymore.

AndrewC · Post by **AndrewC** » Wed Sep 23, 2009 12:21 am

All those options surely suffer from the same problem - they are highly adjustable but you need a linear correction in xyz as you rotate your ball / platform. Perhaps not as a big a deal as global warming if you live in the Maldives, but ....

If you use goniometers on a rotation base, and position your subject at the intersection of all three axis of rotation, it doesn't move and there is no fov obstruction. Anyone who has done X-ray diffraction work or used a SEM will tell you this.

Google "2 axis goniometer melles griot" if you aren't sure what they look like.

rgds,

Andrew

augusthouse · Post by **augusthouse** » Wed Sep 23, 2009 12:26 am

Here are a couple of units that might be somewhat relevant to this discussion.

eBay item #: 230354774154
eBay item #: 230354772179

Craig

AndrewC · Post by **AndrewC** » Wed Sep 23, 2009 1:14 am

... also your disk on a sphere is being a bit over complicated IMO. What I do is use a large steel washer resting on the surface of the sphere magnet. I use 10mm washers on a 1/2" diameter spheres. The sphere magnet is epoxied onto a lump of plastic to raise it just a little to give a bit more freedom of movement as you guys have shown. The whole thing sits on an xyz linear stage.

Very little machining is needed - at most a countersink to form recess in the pedestal to help hold the sphere, and another recess in the plastic block I have on top of the washer. The washers I found at my local hardware store have a nicely rounded edge on one side (presumably they are stamped out of sheet with a not very sharp die) and have a smooth movement on the sphere.

The opposite technique is to use a ring magnet on a metal sphere, but I got busted by my son when I tried to borrow his big steel ball bearing

I'll post a picture of it this weekend if you want to see.

My biggest problem, to be honest, is securing my mountingpins to their mount. What I do is poke them through my background and then wedge them in a small slit cut in a plastic block.

Andrew

edit: actually, thinking about it, you don't even need the countersink - just stack washers together !

Barry · Post by **Barry** » Wed Sep 23, 2009 2:45 am

Some thoughts. Guess there is always a drawback...

The linear correction in xyz: I think this is a problem of all solutions.
I guess the Z is in the axis of the optics, in a vertical setup, and think this should always be corrected when manipulating the object.
For the remainder axis, it depends on where you mount the specimen. In a goniometer setup, if your specimen is not in the center axis of the guiding of that particular (topmost) part, the XY will shift as well. In the ball&socket positioners, if you are not using a small standard ballhead but half a ball in a socket, then the centre point of the ball will not suffer from any swift.
So as soon as you mount a pin with your specimen on the ball (or goniometer), it will not be in the centre again, and swift when manipulating.

In the first image of this thread, by NikonUser, you can see the specimen on the pin is not in the axis of the wooden handle. Any adjustment in angle will cause shift in at least 1 direction. Personally I would favour mounting the specimen somewhat lower so that rotation would not cause lateral shift.

The universal stages of Nikon (see Fluor Doublet's flickr page) or Leitz (see post Charles Krebs) are wonderful. Centre point is absolutely still, but pin mounting is a problem I guess.

So, probably:
- Ball&socket for easy manipulating,
- goniometers or spherical stages for precision manipulating in separate axis (stereo, 3D).

Simple, interchangeable platforms is a good idea, I think...

Cheers,
Barry

ChrisR · Post by **ChrisR** » Wed Sep 23, 2009 3:06 am

While you're all thinking outside the box, don't forget you can crawl inside:

Ping pong ball, hole about 20mm cut with circle cutter
Annular magnet
pin stuck inside, ok, it's fiddly, but blu-tack works.
light from outside through the ball
small ball bearings hold it down.

It works ok without the magnet and balls, if you don't mind it bouncing on the floor now and again. A ppb sits well in a brass 28mm compression plumbing cap.
Helps to have eg a 10x slwd objective, WD just longer at 20.4mm than a ppb radius.

There are lots of ways to alter the design
As a wrinkle to sometimes overcome the pin getting in the way, bend it near the subject, and push it through the ball, so you can twist it from the outside.

AndrewC · Post by **AndrewC** » Wed Sep 23, 2009 3:34 am

ChrisR wrote:While you're all thinking outside the box, don't forget you can crawl inside:

Now that is a neat idea

But how do you get the bug on the pin in the ball ?

Andrew

ChrisR · Post by **ChrisR** » Wed Sep 23, 2009 3:42 am

Bait.

AndrewC · Post by **AndrewC** » Wed Sep 23, 2009 4:05 am

Barry wrote: The linear correction in xyz: I think this is a problem of all solutions.
I guess the Z is in the axis of the optics, in a vertical setup, and think this should always be corrected when manipulating the object.
For the remainder axis, it depends on where you mount the specimen. In a goniometer setup, if your specimen is not in the center axis of the guiding of that particular (topmost) part, the XY will shift as well.

Linear correction is not needed for all solutions !

Yes, Z could be your vertical axis.
Subject is positioned at the rotation centre of all three axis.
The whole point of 2-axis goniometers is that the top (X) goniometer radius is shorter than the bottom (Y) goniometer radius. Exactly sized so that your XY rotation axes intersect at a common point above the unit. You position that intersection point along the Z rotation axis. Now you place your subject at that point and it doesn't move linearly in xyz as you rotate it. To shoot the stack you just index linearly along an axis aligned to your optics.

Interchangeable mounts are great - my first version simply used a mount held by Neodymium disk magnets onto my stepping stage. Makes it very easy to mount, inspect and clean and then transfer to the stepping stage.

Andrew

ChrisR · Post by **ChrisR** » Wed Sep 23, 2009 4:19 am

Sorry, couldn't resist and had to find the pic...

Ok, I put the pin up the bug's bottom - (I'm only using what you'd call window-sill flies and moths, nothing exotic, as I'm proving to be very bad at it) then get the pin in the ball. I've tried pinning into super-glued bits of rubber (ex tap washer) etc. Most results are more or less messy...

These forceps are very good, and I have some mini pliers from electronics days.

http://www.watdon.co.uk/the-naturalists ... g/D411.jpg

I drew the above from the side because I thought it easier. I've tried it more from above, as on a scope stage, where the hole and the ring start off parallel. The balls are in the background then of course, not ideal.

AndrewC · Post by **AndrewC** » Wed Sep 23, 2009 4:33 am

ChrisR wrote: Sorry, couldn't resist and had to find the pic...

Ok, I put the pin up the bug's bottom - (I'm only using what you'd call window-sill flies and moths, nothing exotic, as I'm proving to be very bad at it) then get the pin in the ball. I've tried pinning into super-glued bits of rubber (ex tap washer) etc. Most results are more or less messy...

These forceps are very good, and I have some mini pliers from electronics days.

http://www.watdon.co.uk/the-naturalists ... g/D411.jpg

I drew the above from the side because I thought it easier. I've tried it more from above, as on a scope stage, where the hole and the ring start off parallel. The balls are in the background then of course, not ideal.

For bending pins, look on eBay for dental wire bending pliers. Makes life a bit easier and more precise than ordinary pliers.

Barry · Post by **Barry** » Wed Sep 23, 2009 5:52 am

So (when bait is not available) a "divisible ping-pong ball", rotating in a cavity for positioning, with at the inside the possibility to mount pins on which specimens are prepared, would be good?

Would a magnet be absolutely a must, or would you thrust gravity in a vertical setup?

Cheers,
Barry

AndrewC · Post by **AndrewC** » Wed Sep 23, 2009 5:54 am

Barry wrote:....
Would a magnet be absolutely a must, or would you thrust gravity in a vertical setup?

Cheers,
Barry

Just don't sneeze next to it .....

NikonUser · Post by **NikonUser** » Wed Sep 23, 2009 6:50 am

Wow, some great ideas.
I believe that an absolute essential requirement is to be able to orientate the subject (insect) without having to touch the pin. Eric's ball and cylinder holder is OK for the standard pinned insect where the pin goes through the thorax and the pin has a head for easy handling.
However, current practice here seems to be to use the "stick method", a headless pin that penetrates only half way into the body (see the 1st post). For this setup one has to be able to orientate the insect remotely, i.e., without touching the pin. It is difficlt to accurately move the insect when the only contact you have is a pin shaft that is below the bug.

Pinned specimen orientation

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