The Ideal Product Is Neither the Most Expensive Nor the Cheapest
Before we dive into this discussion, let’s clarify the following terms:
- Specification Sheet (Specs Sheet): The product testing document provided exclusively by the manufacturer.
- Photocathode Sensitivity: Refers to the photocathode’s ability to convert light (photons) into electrons; higher sensitivity indicates better efficiency in capturing and converting low light, which enhances the overall device performance.
- FOM (Figure of Merit): A performance index of the image intensifier tube, calculated by multiplying spatial resolution (lp/mm) by the signal-to-noise ratio (SNR). A higher FOM indicates superior tube performance.
- SNR (Signal to Noise Ratio): Indicates image clarity. A higher SNR helps you see more clearly in low-light conditions.
- Resolution: Refers to the tube’s ability to distinguish fine details, measured in lines per millimeter (lp/mm). Higher resolution means a clearer, more detailed image; however, beyond 64 lp/mm, the human eye cannot discern further improvement. Nevertheless, resolutions above 64 lp/mm can be beneficial in night photography or astronomy.
- Luminance Gain: Measures how much the tube amplifies the incoming light.
Depending on your budget, different options are available. The most critical factors influencing tube performance are photocathode sensitivity, luminance gain, and FOM, which is the product of SNR and resolution.
If these values are high, you can expect the price to be correspondingly higher.
Therefore, when choosing a product, carefully consider the context in which you will use it and your available budget.
A good tube will have all values balanced. For example, a tube with a very high SNR but low resolution and low gain will not perform as well as one with medium to high values across all parameters.
Classification of Term Values:
SNR:
- Below 20: Poor
- 25: Good
- 27: Very Good
- Above 30: Excellent
Resolution:
- Any value above 64 lp/mm is considered good, depending on usage context. For night photography or astronomy, a resolution of 74 lp/mm is recommended.
FOM:
- 1400: Acceptable
- 1600: Good
- Above 1800: Very Good
- Close to 2000: Excellent
Photocathode Sensitivity:
- 100–300 µA/lm: Poor
- 300–600 µA/lm: Medium
- 600–800 µA/lm: Good
- 800–1000 µA/lm: Very good
- Above 1000 µA/lm: Excellent
(Values may vary depending on tube generation.)
Luminance Gain:
- Below 6380 cd/m²/lx : Low
- 9500 cd/m²/lx: Medium
- Above 10 000 cd/m²/lx: High
- Above 15 000 cd/m²/lx: Very High
(Units may vary depending on tube origin. Each product will specify gain, and necessary conversions will be provided.)
One Last Aspect: Phosphor Color in Night Vision Devices
You can choose between white phosphor and green phosphor. The phosphor color does not affect device performance—it is purely a matter of personal preference. It is often said that white phosphor is more “modern” or “trendy.”