The saga continues...
Long-time readers will remember that I
acquired a large reflector lens some time ago. All I had to go on was the lens mount and the tantalising markings "LW" and "2.5°" - it sounds like a superb long-range LWIR lens.
Fast forward a year or so. With a lot of help from Fraser (
disassembling my Thermovision 900 and returning to me the mount and lens, not to mention a great deal of off-list advice) I managed to get some reasonably clear and well focused images from it using a Therm-App Pro as the imaging device.
![Second light on 'dustbin' lens 926630-0](https://www.eevblog.com/forum/index.php?action=dlattach;topic=229668.0;attach=926632;image)
Here's the whole caboodle - the big, wastepaper basket size lens is the big thing on the right; mounted on it (with Blu-Tack and hope) is the lens 'won' from the Thermovision 900 an on the left is a Therm-App Pro and a phone. Here's a closer view:
![Second light on 'dustbin' lens 926626-1](https://www.eevblog.com/forum/index.php?action=dlattach;topic=229668.0;attach=926628;image)
So what did I see? Well, first of all, let's look at a quickly snatched view using the ThermApp Pro alone with its 35mm focal length lens:
![Second light on 'dustbin' lens 926634-2](https://www.eevblog.com/forum/index.php?action=dlattach;topic=229668.0;attach=926636;image)
My first view through the lens was the roofline opposite (marked A in the previous image):
![Second light on 'dustbin' lens 926642-3](https://www.eevblog.com/forum/index.php?action=dlattach;topic=229668.0;attach=926644;image)
So far so good - this was using the 35mm ThermApp lens, held some way behind the big lens and focused at near-infinity. You can see a screw head, indicating that the image from the big lens is in the same plane as the mount.
After some more fiddling, I settled on using the 13mm ThermApp lens (which is not optimal for the sensor),
focused at well beyond infinity, mounted as seen in the second photo. This produced a much-enlarged image compared to earlier:
![Second light on 'dustbin' lens 926646-4](https://www.eevblog.com/forum/index.php?action=dlattach;topic=229668.0;attach=926648;image)
(By the way, the images through the lens are inverted - for ease of viewing I have rotated them here).
In summary, at the moment I'm getting a low contrast image with a central hotspot and some noticeable geometric distortion - but it IS an image and the magnification is significant. Work will continue, and I am optimistic that I'll get really good pictures in due course.
A quick bit of manipulation on images from a pan gives a panorama that, when I compare it to the image from the 35mm lens alone, indicates a focal length in the region of 150mm. I think the FL is probably significantly more than that, in fact, but that's approximately what I'm seeing at the moment.