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Pinned specimen orientation
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elf



Joined: 18 Nov 2007
Posts: 1384

PostPosted: Thu Sep 24, 2009 9:15 am    Post subject: Reply with quote

Only one surface needs to be spherical. The base can just be a cylinder. The big problem with this approach is getting to 90 degrees. You may need several units stacked together to do this.
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Charles Krebs



Joined: 01 Aug 2006
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PostPosted: Thu Sep 24, 2009 9:46 am    Post subject: Reply with quote

Barry,

I'm a big fan of the "compact, spherical" approach. In looking at your latest diagram, it think one thing needs to kept in mind. If the subject is something like a small fruit fly, then this approach would work OK. But if you have a subject like a fairly large, pinned grasshopper specimen, and you are interested in photographing just the "face", your subject areas will be considerably de-centered.

While I was being casual with my reply to Chris (I'd hate to see him get in an accident after prying off one of his cars blind-spot mirrors Wink) , this is why I think a simple device needs to utilize some "preparer's input". A simple removable "jig" of some type can be placed on the platform that would indicate the center point. As the mounted subject is positioned in the putty or cork, the photographer can place the area of interest (and orient the desired "plane") at the center of movement. This would greatly diminish the need for greater range of movement of the device (as Elf has pointed out) since the photographer has "roughed in" his desired composition and should be able to fine-tune it within the degree of movement provided. This could all be accomplished more "elegantly" with a much more complex mechanism, but for most purposes I don't think it would be necessary.
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Barry



Joined: 18 Jan 2009
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Location: Netherlands

PostPosted: Fri Sep 25, 2009 6:38 am    Post subject: Reply with quote

A grasshopper....I see the problem.
In such case, the mounting surface of the positioner could be flat, rather than concave. Now you can position the pin/base such that the grasshoppers' face is in the centre. But as you say, Charles: what is the centre?

One could find out when looking perpendicular to the flat surface, and the centre is indicated (through a little hole, see image). The other option is to have a separate indicator (see other image, the white part), which indicates the centre. But ofcourse, there will always be subjects where the indicator could be in the way (a butterfly with open wings).

(the transparent ball is to show where the actual centre is)

Cheers,
Barry


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Charles Krebs



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PostPosted: Fri Sep 25, 2009 8:57 am    Post subject: Reply with quote

Barry,

Your third image is exactly what I meant when a mentioned a removable "jig". The "eye" is remarkably good at centering something when it has clear guides. Certainly one or two such "jigs" and a center mark the platform could work well for the vast majority of uses.

(hmmmm.... intrersecting laser beams.... Think ... just kidding!)
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ChrisR
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PostPosted: Fri Sep 25, 2009 12:55 pm    Post subject: Reply with quote

Add a clip - ... grasshopper face...
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elf



Joined: 18 Nov 2007
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PostPosted: Fri Sep 25, 2009 6:48 pm    Post subject: Reply with quote

Here's one based on the magnetic toy and a ring from a rather large thrust bearing:


Just need to add the pin and insect:)

If a gimbal mount were added we could call it a semi-universal stage...

p.s. The thrust bearings came from Boeing Surplus quite a few years ago for just a couple of dollars. Unfortunately they stopped selling to the general public a couple of years ago. Any large metal (ferrous) ring could be substituted.
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ChrisR
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PostPosted: Sat Sep 26, 2009 10:12 am    Post subject: Reply with quote

Clever! In a gimbal mount the horizontal ring would have to be a magnet, I think, to stop the vertical one falling over. I haven't seen "super-magnets" with the right sort of dimensions, but loudspeaker magnets are very much in the right range.
The specimen would certainly go round nicely in the ball race!
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Barry



Joined: 18 Jan 2009
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PostPosted: Sun Sep 27, 2009 9:26 am    Post subject: Reply with quote

So, in the toolkit, there should be a variety of specimen holders: magnet with fixed pin, magnet with clamp, magnet with chop of clay...

How large (diameter) would the platform have to be? And what angle of adjustment?
If interested, I could make some.

Cheers,
Barry
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lauriek
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PostPosted: Sun Sep 27, 2009 9:35 am    Post subject: Reply with quote

I haven't chipped into this thread so far, too many good ideas already! However I just wanted to mention, Barry if you can make a few of one of these ideas then I'm definitely interested in one! Smile Those goniometers are a bit pricey for me at the moment!

Are all of these insect pins made of steel? I'm wondering if this holder ends up with a big pin stuck in it (to place the bug at the center of rotation), could one of those tiny pins be stuck to the big pin with a couple of tiny but strong Neodymium magnets? something like these?
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elf



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PostPosted: Sun Sep 27, 2009 6:37 pm    Post subject: Reply with quote

Here's what the gimballed version could look like. It could easily be scaled up or down.

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Barry



Joined: 18 Jan 2009
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PostPosted: Tue Sep 29, 2009 5:28 am    Post subject: Reply with quote

OK, will make some. (including that "jig").

How would 2" / 50mm be as diameter of the disc? Or smaller?

Cheers,
Barry
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Graham Stabler



Joined: 20 Dec 2007
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PostPosted: Tue Sep 29, 2009 6:47 am    Post subject: Reply with quote

I have made a few jigs using ball bearings and car body filler such as "Bondo" you grind a flat for your sample attachment, wax the ball and set in a lump of filler. You can cut the filler neatly with a rasor blade if you catch it just before it goes really hard, also a good time to loosen the ball a little. You can do the same with any ball, could be plastic or whatever.

Graham
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ChrisR
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PostPosted: Tue Sep 29, 2009 11:22 am    Post subject: Reply with quote

Barry - small disc for some folk probably. But then it would be jerky to move, so a handle like a frying pan's, perhaps 50 - 150mm long, would make small movements easier.
Or even two, or three...!

Code:

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ChrisR
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PostPosted: Sat Oct 03, 2009 12:28 pm    Post subject: Reply with quote

Another thought. With a horizontal setup the most difficult direction to adjust seems to be the Z, vertical. If the support tube in the above suggestions were two pieces with a screw thread between, I think it might be useful.

The world of plumbing just happens to have a wide range of sizes, in plastic and brass!
Brass as far as I can remember goes 4mm pipe to 159mm
and plastic commonly 22, 32, 40, 50, 110 and some other sizes.
There's iron as well, but probably less suitable.
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ChrisR
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PostPosted: Thu Oct 08, 2009 9:26 pm    Post subject: Reply with quote

Rotating & X-Y base from a site survey theodilite (weighs 10lb/3kg) £20
Gimbals from a boat £4
Mini stage $25. For the other axis squeeze the Blu-Tack



Is there a Tongue-in-cheek emoticon?
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