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<blockquote data-quote="Bob Blaylock" data-source="post: 500329" data-attributes="member: 16749">Re: converting camera lens MM to spotting scope power (X)I'm trying to think of the geometry involved, here.&nbsp; I would expect that the magnification factor should be relative to a “<a href="http://en.wikipedia.org/wiki/Normal_lens" target="_blank">normal lens</a>”, with the “normal lens” being 1×.&nbsp; Since the sensor in your D3200 is 23.2×15.4 millimeters, the purest “normal lens” to go with it would match the diagonal of that sensor, which would be √(23.2² + 15.4²) or 27.846mm—let's call it 28mm.&nbsp; From there, I think it's a simple linear relationship.&nbsp; Where…<ul style="margin-left: 20px">
<li data-xf-list-type="ul">N = the “normal lens” focal length for the sensor, or in other words, the diagonal measure of the sensor itself (28mm in the case of your D3200)…</li>
<li data-xf-list-type="ul">F = the focal length of the lens in question… 
…and…</li>
<li data-xf-list-type="ul">M = the magnification factor…</li>
</ul>&nbsp; The conversion would be…<ul style="margin-left: 20px">
<li data-xf-list-type="ul">M = F÷N 
…or…</li>
<li data-xf-list-type="ul">F = M×N</li>
</ul>&nbsp; So, on your D3200, a 200mm lens would be equivalent to a scope having a magnification factor of 200÷28 = 7.14×.</blockquote>

[QUOTE="Bob Blaylock, post: 500329, member: 16749"] [b]Re: converting camera lens MM to spotting scope power (X)[/b] I'm trying to think of the geometry involved, here. I would expect that the magnification factor should be relative to a “[url=http://en.wikipedia.org/wiki/Normal_lens]normal lens[/url]”, with the “normal lens” being 1×. Since the sensor in your D3200 is 23.2×15.4 millimeters, the purest “normal lens” to go with it would match the diagonal of that sensor, which would be √(23.2² + 15.4²) or 27.846mm—let's call it 28mm. From there, I think it's a simple linear relationship. Where…[indent][list][*]N = the “normal lens” focal length for the sensor, or in other words, the diagonal measure of the sensor itself (28mm in the case of your D3200)… [*]F = the focal length of the lens in question… …and… [*]M = the magnification factor…[/list][/indent] The conversion would be…[indent][list][*]M = F÷N …or… [*]F = M×N[/list][/indent] So, on your D3200, a 200mm lens would be equivalent to a scope having a magnification factor of 200÷28 = 7.14×. [/QUOTE]

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