I recently purchased an unusual accessory for my FLIR Exx series camera and thought others might be interested in it.
I often search for FLIR supplementary lenses but on this occasion I found a supplemental temperature range doubling "lens" for my FLIR Exx series camera. I had not seen one of these adapters before so it immediately caught my eye. It looks like a normal Exx series supplemental lens but it is a very different beast inside that barrel.
What I had found was the FLIR High Temperature Adapter for Exx and Txxx series cameras. It is available under two part numbers, T197993 and T199235 as is common with FLIR accessories that serve more than a single product line. Bothe part numbers use the same hardware and lens mount.
The adapters specifications are as follows:
Compatability: FLIR Exx and Txxx series cameras (Calibration required)
HFOV: 25 Degrees
Min Focus: 0.4m
Focal Length: 18mm
F Number: 1.3
Transmission: 50% (2um to 16um)
Temperature range : 200C to 1200C (2000C)
Now these specifications are a little misleading to those without the adapter in their hand. At first glance the sight of HFOV, Min Focus, Focal Length and F number might suggest that this is some form of lens. This is not the case. It is a flat piece of Germanium, like a window, but it is coated to form a reflective-absorptive Neutral Density FILTER that has a transmission characteristic from 2um to 16um of 50%. Only half the energy that enters the filter, passes out of it and into the cameras optics.
This ND Filter is rated for operation up to 2000C but, as a range doubler, it would require a camera with a 1000C Max Range to achieve this and thermal protection might be required for the camera and operator. On my E40(E60+) the adapter increases the maximum temperature measurement of the camera to 1200C.
OK so this is an ND filter with a 50% transmission figure..... you can slap it on any thermal camera and it will double the cameras temperature range right ? ...... ummm sadly no, life is never that simple
This adapter halves the energy that enters it in order to permit a thermal camera to view and measure temperatures twice that normally available with the standard built in ranges. but, and it is a big BUT, the Planck curve needs to be considered. Using the ND filter the Planck curve of higher temperatures is different to that in the cameras normal calibrated measurement range. See the attached Planck Curve for a number of temperatures. Just fitting the filter to a camera and doubling all measured readings would result in an error. This error could be calculated by the user familiar with Planck curve tables but that is a royal pain the in the derriere ! It is far better to have a camera compensate for the use of the ND filter and to be calibrated to provide accurate measurements. This is the path that FLIR have taken. The Exx and Txxx cameras for which this adapter was created contain support for it and the required compensation tables to provide accurate temperature measurements from +200C up to +1200C. FLIR state that the camera should be calibrated with the adapter and this is understandable. The filter option is not even visible on some cameras and it needs to be enabled before the filter is used. It may also be necessary to carry out a two point calibration on the camera whilst the filter is in the optical path as a reference against which to apply the corrections to measurements.
So it is not just a simple case of slapping one of these high temperature adapters onto your camera and getting accurate measurements up to 2000C
I am OK on this front as I have Exx cameras that support the ND filter adapter and contain the required Service Menu with full 'Lens' calibration routines
I also own the required accurate Blackbody calibration references to calibrate the camera with the ND filter attached
So how much does one of these high temperature adapters cost from a UK FLIR Agent ? Expect to pay around £2K plus the cost of calibration of the camera by FLIR
Not exactly cheap then
I looked at the cost of an equivalent 2um-16um 50% transmission ND filter from one of the specialist providers and this large diameter ND Filter would cost around $700 +TAX and is just a bare filter with no mount ! Eeek !
Those of you who take a close look at the pictures I provide will notice something strange about the FLIR High Temperature adapters appearance. Yes its casing looks normal enough, but look at the filters mounting....... it is angled ! This is not a fault due to transit damage, nope this is deliberate on the part of the designer. This angling of the filter makes for a complex filter holder design. So why is the filter angled ? In truth, I am not certain but I have met angled Germanium windows in thermal cameras before. I am thinking it may be to do with combating Narcissus effects or deflecting radiated energy away from the target rather than back at it "on-axis". remember, we are potentially dealing with high energy levels at close range when using this high temperature adapter. I am also aware that angling a filter can change its characteristics and presume this has been taken into account by the designer. I am nor expert on reflective-absorptive optics !
Well that is about it for this introduction to the FLIR High Temperature Adapter type T197993/T199235. I have never before seen such an adapter so they are likely not that common. I am pleased to have added it to my Exx camera kit though
A FLIR Exx 10mm wide angle lens will also be arriving soon to keep it company in the case
I have been very lucky finding the adapter and the wide angle lens in the last couple of weeks
Fraser