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Adjustable Objective, How improtant?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/29/2007 at 01:37
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Optics GrassHopper
Optics GrassHopper


Joined: November/27/2007
Location: Somerset, Kalif
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I'm still looking for a scope for my 1895 Guide Gun. But I probabley will not be able to see through it after all the internet research I've been doing!

I'm looking at a Sightron II Big Sky 3-9 X 36 with an Adjustable Objective. Is this useful for ranges 25 to 150 yards or is the parallax for hunting porposes insignificant? Or would you prefer a 42mm Objective lens over the 36 with AO? At what power would that extra 6mm of objective lens come into play? And finally, can all this be answered in one post?

http://www.swfa.com/pc-10617-1511-sightron-3-9x36-sii-big-sky-riflescope.aspx
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/29/2007 at 05:15
8shots View Drop Down
Optics Jedi Knight
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Lord Of The Flies

Joined: March/14/2007
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An AO is more usefull for target shooting and precision shooting at short distances such as the 25-150yds you mention. So if you are hunting ladybugs and small critters, the an AO would be beneficial for hunting. If you are hunting bigger game the AO can be a hinderance as it is an additional item to adjust etc. The 3-9 is such a low power that I think the AO is of little benefit. Rather put the money to better use. AO would be more helpful on a 14x or bigger
The size of the objective lens has little to do with the power or magnification of the scope, but more with light gathering.
Therefore on a bright sunny day a 36mm, 42 mm or 50mm Objective would all have the same viewing ability. However, as the light fades, or it becomes overcast, the 50mm would be clearer than the 42 and the 42 clearer then the 36. So if you hunt in low light or in dark gloomy forests, go for the 42mm.
Off course there is the exit pupil to consider, which is 7mm on a healthy eye.
So 36 divided by 7 = 5x magnification.
42 divided by 7= 6x magnification.
So at 5x and lower the 36mm objective will have an exit pupil of 7 and higher, thus giving max light gathering to your eye. A 42mm  lens will be up 6x.


Edited by 8shots - November/29/2007 at 05:27
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/29/2007 at 06:01
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Optics Master
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Conquistador!!

Joined: June/05/2007
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8Shot has given you a pretty complete answer to your questions. I would add AO becomes very important at long range on smaller targets but in a big game rifle its importance is rather limited and it can become a distraction if you allow it. I will say however I hate the term "light gathering" as it implies a scopes objective is pulling in extra light somehow. The objective size passes a given amount of light according to its size.........the lens quality, lens coatings, internal stray light dampening, and number of lenses play a large role in determining how much and what spectrum actually reaches your eye. Get the 3x9x42 for your purpose.......

    Focus


Edited by Focus - November/29/2007 at 06:02
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/29/2007 at 10:03
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Optics GrassHopper
Optics GrassHopper


Joined: November/27/2007
Location: Somerset, Kalif
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Hey, Thank you guys very much. You pretty much answered my question. No AO for me.
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