It’s a 1902 B&L scope, and in the case was a set of crystal polarizer and analyzer parts for it.
![Image](https://s20.postimg.cc/dgoa3zdz1/BF259_C13-45_AD-4_D88-_B910-_CCC505_C4_AA17.jpg)
Imbedded in the parts are two crystals through which the light path passes length-wise.
![Image](https://s20.postimg.cc/zfuor6n3h/39_C1_D052-48_AF-4562-_A45_A-7_A7219_D516_EB.jpg)
![Image](https://s20.postimg.cc/judd778kd/B1535_B1_B-8921-49_CD-8_D38-7_E3519_B840_E8.jpg)
The polarizer fits into a swing-out condenser housing that has an iris just under the stage, and can be rotated to cross the polls.
![Image](https://s20.postimg.cc/is36onxgt/ECEAACE0-_F883-4701-_A4_F0-_BC7_A8389_C782.jpg)
The analyzer crystal screws in between the tube and the objective and is threaded to the Royal Society standard. I had to adjust the slide tube to get an image without spherical aberration.
Also, the added length at the objective turns the scope into a potential slide-crusher if the operator is careless.
![Image](https://s20.postimg.cc/vw8r1cx8d/59_DB0_C7_D-_E11_B-463_A-8_FB0-458_A2_B0_E9_BA0.jpg)
Time seems to have taken a toll on the crystals but turning the bottom crystal alternates between predominantly red/orange and predominantly green/blue. I had to capture these with my phone, the occuler diameter is ~ 27 mm so I couldn’t adapt the cc camera.
Tylenol 10x? Objective crystal polarizers AO 735 Illuminator
![Image](https://s20.postimg.cc/7shzd44hp/FBD6_C789-09_CA-42_D1-92_D1-5_F2_D616_E7288.jpg)
![Image](https://s20.postimg.cc/yqbweuhf1/D6_AA4605-_E7_C0-414_A-8_EBD-2838_E0_B4_DA79.jpg)
I recall seeing mention of this technique in one of the B&L or Spencer histories on line, but never thought I’d see one much less have one in my collection.
I wasn’t really sure whether to put this post here or in illumination techniques, but I think it fits better here.
Please enjoy,
Jim / Radazz