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Arthur Strange's Variable Amplitude Contrast Method - VAC 2
October 17, 2013
18:51
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Well,here it is – VAC 2Surprised

The  stops are made like this :-

1/ Cut a disc of polarising material to fit your filter holder

2/ Cut another disc of polarising material the size you would use for a D/F stop

3/ A full quadrant should be cut out of the large disc.

4/ Center the small disc on the larger disc and rotate the small disc to the point of full extinction and fix in position – it must be precise!

You now have the stop made  (you will need to make the central disc to the size of stop you would use for D/F,which means you will need different sizes for each objective)    I've attached an image of how the discs should lookSmileI think !!

This works well on it's own ,but for full "variable"effect you will need to have another polariser on your light source.You will need to rotate one of polarisers,whichever is easier

I hope I've made the method of construction clear,but if you have questions please ask.

As some of you know I'm having a bit of difficulty with my photographic skills so I would refer you The Postal Microscopical Society website.Click on "colour supplement" and scroll down to"VAC Contrast" by Brian Singleton to view the possible results

October 17, 2013
19:45
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July 31, 2013
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Hi Microgreen,

Thank you very much for generously sharing this information.

I cannot find  the attachment with the image of the discs' arrangement ?

Could you be kind enough to attach the picture or drawing of the discs again (a picture is worth a thousand wordsWink)

 

It would also be nice if you could provide a link to the website with the photographs using VAC 2

 

Thank you and best regards.Laugh

Let there be (oblique) light.
October 18, 2013
02:14
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January 16, 2012
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Tony, I would like to echo LKOLTON's appreciation for your providing the details of the VAC-2.  I'll try to implement it and try it on my Olympus CHA microscope because I can get close to the condenser iris.  I've tried to make a drawing based on your instructions, and I'm taking the liberty of posting it here (I know it is not very clear how to upload images directly to the forum– I host my images on an external image hosting website, so it is easy to provide a link here).  Please let me know if, despite your very clear instructions, I managed to misunderstand them:

http://i1070.photobucket.com/albums/u494/micritter/VAC_2.jpg~original

 

LKOLTON, this is a link to the VAC-2 images of Brian Wilkinson (I'm not sure if this was what Tony meant):

http://myweb.tiscali.co.uk/pos…..trast.html

October 18, 2013
11:29
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Gekko

Thank you for your excellent drawing of the filter – it is "spot on" if you will forgive the slight punWink

I have just logged on to provide the link and found that you have got there first and you're correct it is Brian WILKINSON.( I must have had a bad dayConfused)

Tony

East Riding of Yorkshire(UK)

October 18, 2013
13:35
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microgreen said:
Thank you for your excellent drawing of the filter – it is "spot on" if you will forgive the slight punWink

Thank you, Tony.  And a spot-on pun!

October 21, 2013
17:02
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IMG_8135.jpg

Attachments
October 21, 2013
17:14
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Above is how the filters look – these are a little crude Embarassed,but with more care taken in the constuction they give much better results.

I'm a little short of polarising material so these will have to do for nowCry

 

If anyone in the UK knows of an inexpensive source of polarisers I would like to know please

 

Tony

East Riding of Yorkshire(UK)

October 21, 2013
22:05
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