This is probably the question we get asked the most: If Echos are run-offs of the Photonis INTENS 4G line due to blemishes, how many blemishes should I expect and how bad are they?
Let's call a spade a spade right off the bat and be honest - Echos are higher-performing and more affordable than any other comparable image intensifier tube available, but yes, they have blemishes in the form of small dots in the image. Rather than try to describe the blemishes, we thought we would show you via the standard NSN 5855-01-548-9489 spot chart.
This chart conveniently divides the viewable area of any tube into three zones: 1, 2, and 3. Zone 1 is probably your most critical zone and likely where your eyes will naturally focus. You will likely find yourself centring your head to whatever you're aiming so that your target falls within this zone. Notice however that Zone 1 is actually quite small in comparison to Zone 2. Zone 2 will be where you'll likely pick up surrounding information to form "the bigger picture". Lastly, Zone 3 is a very narrow band on the outer edges. Typically this zone, while somewhat useful, suffers from slight edge distortion and light fall-off (vignetting) from optics. This is what we would consider the periphery and the limits of detectable information, and probably the least critical of the three zones.
Next, moving onto the spot sizes, the chart conveniently provides reference blemishes located above the Zone 1 ring, starting with 0.003" and going up by 0.003" increments up to 0.015".
Using a representative sample size of 50 Echo tubes, we're including a through-tube photo of what we would call the "worst" out of the batch. You can click on the image for a full-resolution version (opens a new window).
Working our way through the zones, there is one Zone 1 blem that's roughly 0.003" and two smaller ones that - because they are smaller than 0.003" are not considered blemishes; two Zone 2 blem, one at 0.003" and another at 0.006" in size; and finally three 0.003" blemishes in Zone 3.
On the opposite end of the spectrum, within that same batch, here is a tube photo of the "best" tube.
There is a single Zone 3 blemish that is 0.003" or less in size.
Bear in mind that the above represents a random sample of 50 tubes. Formally, Echo tubes have the following blemish tolerances. Any tube with more blemishes than these specs are automatically rejected and destroyed by Photonis. Note that the existence of any blemishes above 0.012" in size are automatically rejected also.
|Blemish Size||Zone 1||Zone 2||Zone 3|
|0.009" - 0.012"||0||1||2|
|0.006" - 0.009"||1||2||4|
|0.003" - 0.006"||2||4||6|
There may be instances where there are more blemishes of smaller size than is allowable per zone. For example: three 0.003" blemishes in Zone 1 are allowable.
Finally, fixed-pattern noise such as honeycombs (typically most obvious during high light situations) and slight shading are not considered blemishes.
All of our systems are built with these tubes described above and will be drawn at random for builds. We will work with you to determine eye dominance and place the tube with the cleanest image over your dominant eye.
We capture each and every tube image at the time of build completion and store it in our database with its respective serial number and spec sheet.