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Dumb Question of the Day-FOV calculation |
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Nixterdemus
Optics GrassHopper Joined: October/05/2011 Status: Offline Points: 30 |
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Yes, rise Lazarus rise or was that Vlad the impaler? Perhaps the Mummy would be more PC as I risk peril in awaking the dead thread.
In a variable riflescope specs is ER 3.3-3 imply that at the lowest end of magnification the ER is 3.3mm whilst the highest end ER is 3mm? Thus in the case of a listed 3.3-3.6 ER the shorter ER would correspond w/the lowest power as the longer ER relates to the highest power?
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Online Points: 13182 |
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Not necessarily. Typically, eye relief of most scopes is shorter at high power, but there are a few out there with longer eye relief at high power. Scope manufacturers do not list it in any sort of a consistent manner, so by looking at the specsheet there is not easy way to tell. Typically, the smaller number is for the highest magnification, but not necessarily. ILya
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Nixterdemus
Optics GrassHopper Joined: October/05/2011 Status: Offline Points: 30 |
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Thanks for the reply. So, my point is moot eh? C'est la vie, mon frere.
Maybe I've distorted yet another personal conclusion as well in which your expertise could be of service. If nothing else freeing me from even more ignorance. No claims to whether or not it'll take. When looking at specs of variable power riflescopes I multiply each low/high power by its corresponding FOV. I determine bias betwixt the twain by which has the higher value. As a rule the higher power finds favour in a slightly better FOV percentage wise when compared to the lower power/FOV. Or so it seems to me. I always presumed that was due to the lower magnification having somewhat ample FOV, comparitively speaking, and especially in a SFP a bit extra FOV is handy at maximum power which usually subtends w/reticle at that power. Any nuggets to be gleaned here or is me wee formula total crappola? I take my results w/a grain of salt. Mainly use it for comparision amongst similar priced optics.
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Online Points: 13182 |
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With most scopes, FOV does not scale linearly at low magnifications. There are some where it does, not with most. If you start at maximum magnification and measure FOV at intermediary steps as you lower magnification, you will see it change linearly for a while until you get close to the minimum magnification where it starts to deviate from linearity.
That is a form of tunneling where internally, the limiting aperture transitions from one stop to another. For similar reasons, you will also notice that at low magnification, most scope do not use the entire objective lens. At high magnifications, the limiting aperture is the objective lens diameter, but at low magnifications, it is some internal aperture that acts as a stop. Also, many scopes do not have the actual claimed magnification range, so if it is marked 5x to 25x, it is not necessarily a 5x erector ration. They sometimes round up a little. ILya
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