Vevor SC240M "reverse vignetting" / halo

[federigo]

   Hi everyone,

longish (1 yr) time lurker, first time poster here. I bought my first thermal camera based on what I read on this board, and I went for a Vevor SC240M.

I also succesfully used joe-c's software to import and analyse the irg data. I'm very happy with my choice.

I have a question thou: I know some kind of vignetting is considered normal, but it was my impression that the vignette is "colder". What I noticed during use is that I have some kind of "warm halo" on left/bottom side of the image. This is less noticable depending on NUC/range of what I have in view (though it is still noticeable by rotating the camera), but when pointing to a uniform surface is quite evident (picture attached of the camera pointed at a paper sheet).

The hottest point is always in the bottom-left side corner and the temperature difference between that spot and the coldest spot is always in the range of 1.8-2.2 °C



Can this considered "normal" or do I have a defective unit?

Also, the unit didn't come with any emissivity table in any form, it's set at 0.95 / 25 °C ambient temp / 0.5 m distance, how important is it to set these parameters if I don't care (too much) about absolute temperature measurements? I'm more interested in temperature differences and a rough indication of the actual temperature (if it's 30 °C instead of 35 °C is not important).

Thanks. 

[Bill W]

I have a question thou: I know some kind of vignetting is considered normal, but it was my impression that the vignette is "colder". What I noticed during use is that I have some kind of "warm halo" on left/bottom side of the image.

Two possibilities.
Most likely a reflection of a hot component inside back off the lens mount.

Or, when the flag is closed to do a NUC calibration, that corner looks a bit colder to the sensor, or the rest of the area is warmer.  That error then gets stored in the one-time shutter flag calibration, or maybe the flag is hot / not covering correctly.

Also, the unit didn't come with any emissivity table in any form, it's set at 0.95 / 25 °C ambient temp / 0.5 m distance, how important is it to set these parameters if I don't care (too much) about absolute temperature measurements? I'm more interested in temperature differences and a rough indication of the actual temperature (if it's 30 °C instead of 35 °C is not important).

If trying to adjust for emissivity, the first question to ask is 'what is the temperature of the reflected energy ?'.  It is impossible to answer that, so in many ways emissivity cannot be adjusted at all.  Most cameras will just guess at 'ambient' measured somewhere if you are lucky, then scale back the apparent scene temperature accordingly.

[federigo]

I have a question thou: I know some kind of vignetting is considered normal, but it was my impression that the vignette is "colder". What I noticed during use is that I have some kind of "warm halo" on left/bottom side of the image.

Two possibilities.
Most likely a reflection of a hot component inside back off the lens mount.

Or, when the flag is closed to do a NUC calibration, that corner looks a bit colder to the sensor, or the rest of the area is warmer.  That error then gets stored in the one-time shutter flag calibration, or maybe the flag is hot / not covering correctly.

Thanks for the possibile explanations. That makes a lot of sense. I do understand the physics of it all, but this is precious information for me as I'm entering this world as hobbyist and I do really appreciate it.

In your opinion, given the construction of this kind of devices, would you consired it a defect of some sort that hinders the proper use of the instrument (i.e. should I return it?) or is something I could live with? I'm asking for advice here because at the moment I don't see it being a problem, but since the camera is brand new if it's to be considered a defect I prefer to have it fixed.

Also, the unit didn't come with any emissivity table in any form, it's set at 0.95 / 25 °C ambient temp / 0.5 m distance, how important is it to set these parameters if I don't care (too much) about absolute temperature measurements? I'm more interested in temperature differences and a rough indication of the actual temperature (if it's 30 °C instead of 35 °C is not important).

If trying to adjust for emissivity, the first question to ask is 'what is the temperature of the reflected energy ?'.  It is impossible to answer that, so in many ways emissivity cannot be adjusted at all.  Most cameras will just guess at 'ambient' measured somewhere if you are lucky, then scale back the apparent scene temperature accordingly.

Thanks. I'm going to experiment a bit with some thermocouples and compare the results, but I feel that I can probabily leave it as it is for my usage.

Would also love to hear from someone with the same Vevor/Infiray/Topdon device.

[Bill W]

Thanks for the possibile explanations. That makes a lot of sense. I do understand the physics of it all, but this is precious information for me as I'm entering this world as hobbyist and I do really appreciate it.

In your opinion, given the construction of this kind of devices, would you consired it a defect of some sort that hinders the proper use of the instrument (i.e. should I return it?) or is something I could live with? I'm asking for advice here because at the moment I don't see it being a problem, but since the camera is brand new if it's to be considered a defect I prefer to have it fixed.

If I had designed/built a camera doing that, it would get fixed.  2°C across the scene is not OK if they quote an accuracy of 2°C
Hopefully someone with the same camera can add a comment, otherwise send them the image and ask if it is OK or not.

There is a risk they would say 'not problem' and charge you for returning it.

[federigo]

Thanks for the possibile explanations. That makes a lot of sense. I do understand the physics of it all, but this is precious information for me as I'm entering this world as hobbyist and I do really appreciate it.

In your opinion, given the construction of this kind of devices, would you consired it a defect of some sort that hinders the proper use of the instrument (i.e. should I return it?) or is something I could live with? I'm asking for advice here because at the moment I don't see it being a problem, but since the camera is brand new if it's to be considered a defect I prefer to have it fixed.

If I had designed/built a camera doing that, it would get fixed.  2°C across the scene is not OK if they quote an accuracy of 2°C
Hopefully someone with the same camera can add a comment, otherwise send them the image and ask if it is OK or not.

There is a risk they would say 'not problem' and charge you for returning it.

Thanks again. I bought it on Amazon (ship and sold) for this exact reason, and have a replacement coming. I'll see if it has the same issue.

Hopefully it doesn't as I read good things about this entry level device.

[Harrow]

I get similar but it does not bother me because I am using the camera to see if electronic components are overheating and a 1 or 2 degree variation does not matter. I don't expect a budget product to work as well as one that costs 2 or 3 times the price, I just want it to do the job that I bought it for.