A camera module sits in a metal tube with a silica window.
Place an inner tube inside the outer tube. The inner tube extends nearly to the window. Cool air will be blown in the inner tube, pass by the window and exit thru the outer tube. The space between the two tubes can be maintained with ceramic fiber spacers
Kiln peepholes are 1 1/4″, (31.75 mm).
1 1/4″ steel tubing available from McMaster w/ 0.035″ (0.889 mm) wall.
1 1/4″ aluminum tubing with 0.028″ (0.71 mm) ID is available.
Perhaps the outside could be ground down to be a hair smaller and fit in the peephole.
The steel tubing gives 29.5 mm ID. With 1mm clearance, inner tube would be 27.5 mm, with 2 mm clearance, inner tube would be 25.5 mm. So figure 1″ OD inner tube. Aluminum tubing with 1″ OD and 0.028″ (0.71 mm) ID is available. This gives an interior space of 24 mm.
Need to find a camera module that will fit in the space. Either have the cable extend (6″+) outside the kiln and have the microcontroller module there, or try to find/build a thin module that fits inside near the camera.
Spy Camera for Raspberry Pi, 5MP
Camera Module Dimensions: 8.5mm x 11.3mm / .34″ x .45″ (8.6 mm x 8.9 mm)
Cable Length: 289 mm / 11.4″
Angle of View: 54 x 41 degrees
Field of View: 2.0 x 1.33 m at 2 m
Full-frame SLR lens equivalent: 35 mm
Fixed Focus: 1 m to infinity
with a close-up 4x or 10x diopter lens
Or Raspberry Pi Camera V2 ($30) with a Arducam IMX219 Auto Focus Camera Module ($25).
Found a camera module that fits the Raspberry V2 board, but with a 6 cm cable. This will allow the V2 board to be placed on edge (23 mm). Details:
IMX219-77 Replacement Camera Module with 77° FOV for Raspberry Pi V2 Camera, Depth of Field (Focusing Range) 20cm – infinity
How to fix the window in the end of the tube, sealed to prevent high pressure air from pushing it out? Perhaps put a silicon o-ring in a groove, push the silica glass against it, then add a compression ring inside the tube against the silica glass.
Silicone o-rings that work up to 310C (Kalrez 9500) are available on ebay for $10. Kalrezx 1045 works up to 260C.
Add temperature sensors to monitor the unit.