Sean100uk Posted July 22, 2014 Report Share Posted July 22, 2014 Will a 5 to 125 mm cs mount manual zoom lens be good for. A spotter Quote Link to comment Share on other sites More sharing options...
FalconFN Posted July 22, 2014 Report Share Posted July 22, 2014 Yes. Assuming you are using a 1/3" sensor then 125 mm should give you somewhere in the order of 8 - 10 x mag. The lower the f number the better but yours will probably be f1.8 (?) which will be pretty good. Quote Link to comment Share on other sites More sharing options...
Sean100uk Posted July 22, 2014 Author Report Share Posted July 22, 2014 It's f 1.6 Quote Link to comment Share on other sites More sharing options...
FalconFN Posted July 22, 2014 Report Share Posted July 22, 2014 Even better. Quote Link to comment Share on other sites More sharing options...
Sean100uk Posted July 23, 2014 Author Report Share Posted July 23, 2014 Lol whys that then I don't know what it really means Quote Link to comment Share on other sites More sharing options...
FalconFN Posted July 23, 2014 Report Share Posted July 23, 2014 Basically the f number represents the relationship between the focal length (the 5-125 mm bit) and the diameter of the hole in the lens that allows light to get through. F1.0 is the maximum aperture size which lets the maximum amount of light in and then each successive number in the sequence will allow half the light of the previous number. The sequence goes: f1.0 - f1.4 - f2 - f2.8 - f4 - f5.6 - f8 - f11 - f16 - f22 so a f1.4 will allow 2 times as much light through the lens as f2, 4 times that of f2.8 and 8 times that of f4. Quote Link to comment Share on other sites More sharing options...
onatangent Posted July 23, 2014 Report Share Posted July 23, 2014 the f number is the size of the aperture which is measured back to front to common sense. Small number, ie f1.6 is a large opening and f22 is small. So for night work a large aperture is preferred to gather as much light as possible. Adjustable might be preferred depending on ambient light/moon light pollution. This reminds me.....I need a night rig for my pcp :-) I should've typed faster lol. as just noticed falcons reply after I posted. Quote Link to comment Share on other sites More sharing options...
Sean100uk Posted July 23, 2014 Author Report Share Posted July 23, 2014 Cheers guys Quote Link to comment Share on other sites More sharing options...
evo Posted July 23, 2014 Report Share Posted July 23, 2014 please also realise which everyone has failed to mention ,,, the lower the number of aperture the shorter the depth of field atb Evo Quote Link to comment Share on other sites More sharing options...
Dave-G Posted July 24, 2014 Report Share Posted July 24, 2014 (edited) please also realise which everyone has failed to mention ,,, the lower the number of aperture the shorter the depth of field atb Evo Very true - a clever man might exploit that aspect and make a slip on parallax ring with revised distances on it for very effective NV range finding if done with a fully open iris and maximum focus fussiness. Edited July 24, 2014 by Dave-G Quote Link to comment Share on other sites More sharing options...
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