microscope depth of field

nhcowboy1961

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Thread starter #1
Hi all, just a basic theory question. To increase the depth of field on a binocular microscope (the distance between the lenses and the work in my case to be greater to get my hand underneath better), is that accomplished by getting different lenses in a great magnification or of lesser magnification? Mine are currently a wide field 10X-20X on an Amscope microscope.

Essentially I wish I had more working distance, as my hand cannot fit completely under the scope as I'd wish with a graver at a high angle and have the work be in focus. I can raise the scope just fine to get my big paws under but I've lost my focus at that point. I have about 4" of working space at furthest in focus zoom. I hope I'm making sense, I just wondered if a different lens would give me a greater length or if it's the design of the scope and its limiting factors. Thanks a bunch!
Paul
 

diandwill

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#2
A 7 with a 1/2 barlow lens gives a 3.5X mag with about 6-7" of working distance. You may be able to get a 1/2 lens for your scope that would increase the focal distance some.

Will (enjoyed that class with Diane!!)
 

nhcowboy1961

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Thread starter #3
A 7 with a 1/2 barlow lens gives a 3.5X mag with about 6-7" of working distance. You may be able to get a 1/2 lens for your scope that would increase the focal distance some.

Will (enjoyed that class with Diane!!)
Howdy Will, nice to hear from you again! Thank you SOOOOOOO much for your advice, it opened up a whole new world for me this morning and I'm happier than a kid at his best Christmas ever! With my Amscope came two lenses for "CCTV/VIDEO", one a .5X and the other a 2X. I never attached them since I have no need for a camera but it was what I needed (the .5X one) to dramatically increase my focal length and I still have more than ample magnification. Now I have at least 6" of work space, can fit my entire upright fist under the scope with several inches to spare-it's exactly what I had wished for all along.

You've helped me to increase my abilities and ease of engraving dramatically and I'll bless you each time I engrave with a huge smile, laughing inside at myself for having the answer in front of me all along :)
God bless,
Paul
 

mitch

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#4
Ok, Cowboy, first of all you're confusing "depth of field" with "working distance". Depth of field is the distance within a given lens system that is reasonably, usefully, in focus. For example, at a very low magnification you might find you can easily work on something that has high & low areas varying by as much as an inch without refocusing, whereas on a high magnification hardly any variation at all in the surface height/depth requires refocusing.

What you need is more working distance, and the only way to get it with a modern stereomicroscope is by using a reducer, or "Barlow", lens on the objective end of the scope (as opposed to the 'ocular' ends, which are the eyepieces you look thru). A 0.5X reducer will double your working distance (from, say, 4" to 8"), a 0.32X will roughly triple it (from 4" to 12"). The trade-off is the reduction in the overall zoom range of the scope. If it was 6x-40x, it will be 3x-20x, or 2x-13.3x (assuming 10x eyepieces).

If you need a really big working distance and ALSO high magnification, most systems have higher magnification eyepieces. It starts to run into some significant $$$, but if you need 12" underneath and a full zoom range of 6x-40x, it can be done with the right optional lens.
 

jerrywh

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#5
What you need is a .5 barlow lens on the bottom . Another name for a barlow lens is objective lens. Put your .5 lens on the bottom and you will be fine.
 

nhcowboy1961

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Feb 27, 2008
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Thread starter #6
Thanks guys, for the advice and the explanation, this forum always comes through and the help is greatly appreciated. I did put a .5X lens on my scope and now it is better than ever and the zoom is plenty fine too- the best of both worlds.
Thanks again, my engraving life just got not only a lot easier but a lot better too.
Paul
 

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