Therm-App threaded lens mount/extension for experimentation - useful item :)

[Fraser]

In case it is of interest or use to others, I am detailing a lens mount thread adapter that matches the Therm-App lenses.

The Therm-App uses an unusual thread for its lens mount. It is almost a standard C mount but sadly, not close enough ! The Thermal Expert uses a 25mm diameter threaded mount with a thread pitch of 0.5mm. The standard C mount uses a thread pitch of 32 TPI (~0.80mm pitch) and is slightly larger diameter, being a 1" mount (25.4mm).

I purchased a Therm-App 19mm lens for a reasonable price and wanted to create a lens mount for it to screw into. I could make one on a lathe but I prefer to buy well made commercial items where able. The finish is often better and the thread is likely better than what I can produce !

The 25mm diameter x 0.5mm pitch mount is better known as a "Schneider 00" mount and it is not that common when compared to other threaded mounts. I found a neat little adapter that converts a Schneider 00 lens for use on a Pentax M42 screw mount. At a cost of less than $10 delivered it made sense to order one. The adapter is perfect as a lens mount for the 19mm lens as there is a nice wide flat ring of metal around the M25 thread, plus, of course, the M42 x 1mm Pentax mount male thread. This facilitates all manner of mounting methods and adaptions to suit the project.

As stated, I wanted a nice M25 x 0.5mm threaded mount in order to make use of the Thermal Expert lens. The adapter is perfect for that application but it may also offer something to Therm-App camera owners ?

It has been known for some time that the Therm-App can provide excellent close focus, but the lens is at the end of its threads and almost coming out of the threaded mount in very close focus situations. The temporary addition of the M25 x 0.5mm adapter to the front of the cameras mount would provide a further 5mm of thread to support the lens barrel. In thermal imaging, 5mm of lens travel can be an awful lot when it comes to focus distance ! I see little reason why more than one M25 adapter could not be stacked to create a 10mm or longer extension for the lens. Not bad value at $10 each I think.

The adapters dimensions are as follows:

Female thread : M25 x 0.5mm pitch (Schneider 00 mount)
Male thread : M42 x 1.0mm pitch (Pentax M42 mount)
Outer flange diameter : 44.9mm
Outer flange thickness : 1.46mm
Adapter total thickness : 4.96mm
Female thread penetration into adapter : full thickness
Width of adapter ring face female thread ID to male thread OD : 8.63mm
Width of adapter ring face female thread ID to outer flange OD : 10.14mm
Adapter Material : Black anodised Aluminium

I hope this information is of interest and help to others. These M25 x 0.5mm adapters are not common so I am providing the sellers details here:

https://www.ebay.co.uk/itm/M25x0-5-to-M42x1-Screw-Thread-Lens-Mount-Adapter-Inner-M25-x0-5mm-Outer-M42-x1mm/372162509612?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Fraser