Post subject: Re: proportion scope - which one and where to buy?
Posted: Mon Dec 09, 2013 12:57 pm
Platinum Member
Joined: Tue Jan 02, 2007 8:20 pm Posts: 2659
It is probably very similar to the old Diamond Proportion reticle and will work in almost any microscope. You might want to pick up a stage micrometer to go with it to calibrate the magnification. (the GIA unit comes with one I think) You just have to make sure the ocular they sell it with is a 30 mm or 23.2 mm . It used to be 23.2 in the days of AO and B&L Gemolites and now is probably 30mm. Helps also to have an exactly matching , mating ocular so you can use it with both eyes open. But you could use it with one eye if you didn't want to buy the second ocular.
Of course the measurements would be more accurate if done on a Wild M400 or M series with the "S type" carrier since the convergence angle would be eliminated. This convergence angle also does not exist in the separate free standing Diamond Proportion Analyzers which like the aforementioned two scopes are square and plumb over the object of view. Hopefully somebody at GIA did an error calculation of the error and determined that it is not significant. The measurement could also be expected to be more accurate with a Common Main Objective type stereo versus a Greenough type for the same reasons.
Post subject: Re: proportion scope - which one and where to buy?
Posted: Tue Dec 10, 2013 1:27 am
Established Member
Joined: Sat Dec 07, 2013 2:40 am Posts: 16
Thank you all for your input. I am keep using visual estimates for table width and pavilion depth as well as crown angle. From there I use the math for other details.
I will keep working on getting info from Chinese proportion scope. I will post whatever I find out.
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