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Message: <blockquote data-quote="Surveyor" data-source="post: 3147235" data-attributes="member: 50720">Kimmo, David, Binoastro;A little information about ISO light levels for resolution testing.“The resolution test target shall be illuminated uniformly (± 5 %) by means f a light source with a correlated colour temperature of 5 000 K to 6 000 K, condenser and diffuser for non-dazzling observation conditions. The illuminance of the resolution test target shall be optimum for observation of its image.”I use a standard light source that can be brought to the 5000 K point by increasing the voltage and setting the output illuminance by means of controllers. The specs for the bulb are shown below. This bulb puts out about 75,300 lux (close to EV=15 or noontime sunlight) at 25 mm, which is fed to a diffuser, the output of which is determined by the port selected, I get a very repeatable lux of 13,500 @ the 50mm aperture and 17,300 lux @ the 36mm port. Neither of these are enough to cause dazzling of the target in my collimator even with the naked eye. I can only see about group 2, 1 or 2, my VA averages about 100”, 90 on a good day. Note this light level is very close to what I see if I put the collimator on a tripod and point it at the north sky on a clear cold day around noon.I will have to leave the conversion of lux to cd/m^2 to David since I am not familiar with the conversion of different photometric (luminance and illuminance) units. I think that 1 lx = 1 lm/m2 = 1 cd•sr/m2   and a typical f:3 optic is .088 SR and a target at target at 10-20 meters would be considerably smaller than the FOV, I do not know what the cd/m^2 would be but assume about 1500 using Davids ratio of 3-4000 lux=300 cd/m^2 or 17,300 lux times the f:3 SR of 0.088. This level is not enough to cause dazzling of the target though I think it is close enough and repeatable for bino comparisons. I can get dazzling effects with 100 watt bulbs but cannot get the right color temp.David, let me know what the value of the conversion would be for 75,300 and 17,300 lux, I may not even be close.About the ISO method and a paper target. The ISO method uses a closed collimator with a diffuse light at the back of the target and direct collimated rays from target to observer. A paper target has a loss due to reflectance and some diffusion of the rays towards the observer.</blockquote>

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