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General optics (physics?) question.

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/26/2009 at 11:10
wolfee View Drop Down
Optics Apprentice
Optics Apprentice


Joined: October/21/2004
Status: Offline
Points: 76
All other things being equal, what difference does the TUBE LENGTH make?  My Weaver 4X rimfire is very long (over 10 inches) and has a fairly narrow FOV at 100yds--about 22 feet.  My Leupold 4X rimfire is a lot shorter but has a 28 feet FOV at 100yds.   However, the Weaver clearly has a greater depth of field.  Without touching any adjustments I can see things clearly a lot closer AND farther than the Leupold.  Same with parrallex.  It seems the Leupold reticle starts to move more than the Weaver when you get too far in front or behind the preset distance (about 60 yds).  Is this a function of tube length?  What other optical advantages/disadvantages are there to shorter/longer tubes?  This isn't terribly important, but I notice such a difference in these two 4X scopes, I am curious.  Maybe one of our SWFA moderators is an optical genius and can tell me.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/26/2009 at 11:33
Dale Clifford View Drop Down
Optics Jedi Knight
Optics Jedi Knight


Joined: July/04/2004
Location: United States
Status: Offline
Points: 5087
all things being equal a longer tube doesn't need to bend the light rays as much to as the radius on the glass will be less. thus a better picture is projected on each lens surface. this probably reduces the cost of manufacture.  of course its hard to draw comparisions accross product lines, especially in hobby optics. usually leos are shorter in comparison to others in the same class, and perhaps one reason for the perception of higher cost.
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