The ideal product is neither the most expensive nor the cheapest.
Before we delve into this discussion, we'll clarify the following terms:
- Spechshee" represents the product's testing sheet (by the manufacturer); this is only provided by the manufacturer. "Photocathode Sensitivity" refers to the photocathode's ability to convert photon light into electrons; higher sensitivity indicates better efficiency in capturing and converting low light, which enhances the overall performance of the device.
- FOM - Figure of Merit is an index of the performance of the image intensifier tube and is calculated by multiplying spatial resolution (lp/mm) by the signal-to-noise ratio (SNR). A higher FOM indicates better tube performance.
- SNR (Signal to Noise Ratio) - the signal-to-noise ratio indicates image clarity. A high SNR will help you see clearly in low light conditions;
- Resolution - resolution refers to the tube's ability to distinguish fine details and is expressed in lines per millimeter (lp/mm). Higher resolution means a more detailed and clearer image, but beyond 64 lp/mm the human eye can no longer distinguish the resolution difference. A resolution above 64 lp/mm can help you with night photography or astronomy;
- Luminance Gain - This term measures how much the tube amplifies the received light; Depending on your budget, there are different options. The most important things that matter for a tube's performance are photocathode sensitivity ("Photocathode Sensitivity"), gain ("Luminance Gain"), and FOM (Figure of Merit) which is the product of SNR (Signal to Noise Ratio) and resolution.
If the values of these terms are high, rest assured that their price is accordingly high. Also, if you want to sell the device at some point, on the second-hand market, consider that a "clean" tube will sell closer to its purchase price on the sh market than a blemished tube.
Thus, when you want to choose a product, think very carefully about the context in which you want to use it and what budget you have.
Consider that a good tube will have all balanced values. A good tube will have all high values, for example, a tube with a very high SNR and very low resolution and gain will not perform very well compared to a tube that has all balanced values.
We will now discuss how we categorize the values of the terms discussed above:
- SNR: under 20: weak, good: 25, very good: 27, excellent: over 30, extraordinary: over 35 (found on super-gain tubes);
- Resolution: Any resolution is good over 64 lp/mm, but it depends on the context in which you will use the device. For night photography, we recommend a resolution of 74 lp/mm, the same for astronomy;
- The FOM is influenced by SNR and Resolution. A decent FOM is 1400, a good one is 1600, a very good one is over 1800, a very good one is around 2000, and an extraordinary one will go over 2500.
- Photocathode Sensitivity: 100-300 µA/lm: Weak; 300-600 µA/lm: Medium; 600-800 µA/lm: Good; 800-1000 µA/lm: Excellent; Over 1000 µA/lm: Extraordinary; values vary between generations. Luminance Gain: Below 20,000x: low, 20,000x - 30,000x: medium, 30,000x - 50,000x: high, Over 50,000x: very high; this term has different units of measurement depending on the origin of the tube. The gain will be specified for each product and the necessary conversion will be made.
One last aspect to discuss is the color of the phosphor used in night vision devices. You can choose between white phosphor and green phosphor. The color of the phosphor does not affect the performance of the devices and is a matter of personal preference. We can say that white phosphor is "fashionable".