Re: How do Adjustable Objectives work?
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but aside from allowing more light in,
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AOs dont let more or less light in. This is purely a function of Objective lens size (which is always fixed ie: 25mm 42mm 50mm) and the quality of the coatings on the lenses and the quality of the glass its self.
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could someone explain the technical end of it, and what is better,
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There is a great post at the top of this Long Range Optics section covering this exact thing. It is a good read. The answers above are good so I'll just add more in my own words. An adjustable objective is a way of placing the image coming through the scope (the deer you see) on the same focal plane as the cross hairs. Example: extend your hand and put your index finger pointing up. Now look past it at an object on the wall. Now move your head while leaving your finger still. Your finger will sppear to line up with another point on the object moving around relative to where your head is. Now the example of putting them on the same focal plane (or adjusting your objective). Go put your finger on the object on the wall. Move your head all you want and the finger is still lined up on the object. There is no movement of the image relative to your head.
Back to scopes. If you have a 4x scope that is adjusted for parallax (what I described above) at 150 yards and your target is at 100 yards the relative movement is going to be fairly insignificant. If you are shooting a deer at 650 yards the parallax will be more pronounced. Your head MUST be exactly in the correct place for every thing to be PRECISELY in line. But if you adjust the objective lens for 650 yards the effect is reduced to nearly zero and this error in sight allignment is again insignificant.
Which is better? It is dependant on your use of the scope is.
Lastly and quite simply the adjustment may be on the objective bell or on the port side of the scope with the other turrets. It will be called a side focus but it is not a focus. It is a focal plane adjustment. Your focus is on the Occular lens bell at the rear of the scope.
Now go read the long version written by smarter folks than me. I hope this helped.
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