The Masch­er view­ing case is a fold­able view­er made of wood and cov­ered with leather. The device con­sists of a base plate on which the lens pan­el and the hold­er with the daguerreo­type are placed. Nei­ther com­po­nent can be locked in posi­tion, which makes view­ing some­what cum­ber­some. It is eas­i­er to place the daguerreo­type in the palm of the hand and hold the lens pan­el between the thumb and forefinger.
John Fred­er­ick Masch­er aimed his view­ing case at the mass mar­ket, and it was pro­duced in a vari­ety of sizes and styles. He held a near-monop­oly on the man­u­fac­ture of these cas­es and sold tens of thou­sands with­in a short peri­od. As daguerreo­types declined in the ear­ly 1860s, the cas­es were adapt­ed for ambrotypes and tintypes.
In addi­tion to the stan­dard mod­el, two alter­na­tive mod­els were pre­sent­ed lat­er. In the sec­ond mod­el, the lens pan­el was attached to the stere­oview hold­er by four struts, one at each cor­ner. The lens­es were remov­able. A third mod­el was designed as a fold­ing wood­en box.
(from: Com­pendi­um of Stereoscopes)