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locking vs non locking focus? |
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Gunshow75
Optics Apprentice Joined: December/23/2004 Location: Kentucky, USA Status: Offline Points: 209 |
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You are correct and I apologize; I looked at the first sentence of the original post and read it as adjusting the objective instead of the ocular.
If a reticle is not in the same plane as the image, moving the ocular could produce the same effect. |
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Tom |
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tahqua
MODERATOR Have You Driven A Ford Lately? Joined: March/27/2006 Location: Michigan, USA Status: Offline Points: 9044 |
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That's easy enough to make mistakes on. We have AO's, fast focus and various side focus scopes out there. It has sent me down the wrong path before, too.
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Gunshow75
Optics Apprentice Joined: December/23/2004 Location: Kentucky, USA Status: Offline Points: 209 |
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I suspect the reason I read it as an objective lens issue is because I always think of the ocular lens when I see the word focus.
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Tom |
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Gunshow75
Optics Apprentice Joined: December/23/2004 Location: Kentucky, USA Status: Offline Points: 209 |
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My second mistake today. I meant to say that I always think of OBJECTIVE lens when I see the word Focus.
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Tom |
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Kickboxer
MODERATOR Moderator Joined: February/13/2008 Status: Offline Points: 23679 |
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30MM, there is no comparison in almost any aspect between S&B and NcStar. NcStar is a toy, S&B is a tool. However, there are many toys and tools that have similar functions and perform in similar manners and therefore have a basis for comparison. Just because one scope is much cheaper than another does not mean that it cannot compare in MANY respects to another, more expensive, more capable piece of equipment. This carries true in all aspects of the Test and Evaluation world. |
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Opinion,untempered by fact,is ignorance.
There are some who do not fear death... for they are more afraid of not really living |
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Kickboxer
MODERATOR Moderator Joined: February/13/2008 Status: Offline Points: 23679 |
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Doug, quite true. I have found nothing to recommend an NcStar to anyone, while I have found nothing which would not recommend S&B. |
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Opinion,untempered by fact,is ignorance.
There are some who do not fear death... for they are more afraid of not really living |
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30mikemike
Optics GrassHopper Larry Root Joined: August/19/2008 Status: Offline Points: 10 |
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Yup and Rosie and the playmate of the month are both women too. I know who I would in my hot tub (hint there would still be water in it and it would not smell like a dead carp!)
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Kickboxer
MODERATOR Moderator Joined: February/13/2008 Status: Offline Points: 23679 |
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Well, this is a battle you can't win because I have HAD the playmate of the month in my hottub... on MANY occasions. Use an analogy that makes some sense.
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Opinion,untempered by fact,is ignorance.
There are some who do not fear death... for they are more afraid of not really living |
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crispycritter
Optics Apprentice Joined: July/30/2004 Status: Offline Points: 115 |
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Do tell, how did you keep the magazine from falling apart?
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Kickboxer
MODERATOR Moderator Joined: February/13/2008 Status: Offline Points: 23679 |
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Endeavor to persevere...
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Opinion,untempered by fact,is ignorance.
There are some who do not fear death... for they are more afraid of not really living |
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Gunshow75
Optics Apprentice Joined: December/23/2004 Location: Kentucky, USA Status: Offline Points: 209 |
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KB, your point is well taken. By definition, compare means to examine to find similarities and differences. Light will obey the laws of optics, whether in a toy or a tool, which is your point as I see it. |
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Tom |
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Jon A
Optics Journeyman Joined: March/14/2008 Location: Everett, WA Status: Offline Points: 670 |
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If the toy is SFP and the tool is FFP, comparisons on reticle movement might not be valid. While I don't think it should happen on any decent SFP, I can see it as "being more possible" than a FFP. That was the point.
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Gunshow75
Optics Apprentice Joined: December/23/2004 Location: Kentucky, USA Status: Offline Points: 209 |
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I am only trying to find an explanation for what is happening; nothing more. There are several members on the forum who dislike equations, but I am going to use one to share my thoughts. The Thin Lens equation relates the focal length of a lens to the distance an object is away from the lens and the distance the image of that object will occur from the lens. I will provide numbers so you can check the math. The Thin Lens equation is: 1/f = 1/O + 1/I, where f is the focal length of the lens, O is the distance of the object from the lens, and I is the distance from the lens that the image of the object is formed. Assume that our imaginary objective lens is a simple thin lens that has a focal lenght of 100 mm. An object that is 1000 yards away will have it's image formed at 100.011 mm behind the lens. An object 500 yards away will have it's image formed 100.022 mm behind the lens. At 200 yards, the image forms at 100.055 mm, and at 100 yards, the image forms at 100.109 mm. An object 50 yards away forms an image at 100.219 mm behind the lens. These displacements are propogated through the scope, and if the scope is a variable power having 3X gain, the displacements will become 3 times larger at the highest power. When the scope is set at the factory to be parallax free at 100 yards, the reticle is positioned to be coincident with the virtual image of the object that was 100 yards from the scope. We use the ocular lens to focus on the virtual image. For objects at any other distance, the virtual image of the object will be in focus at it's displaced distance in front of or behind the reticle. Toy or tool, the process is the same. I think that "jiggling the eyepiece" and holding one's eye stationary is the same as holding the eyepiece stationary and moving your eye. Both cause the same effect. |
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Tom |
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Jon A
Optics Journeyman Joined: March/14/2008 Location: Everett, WA Status: Offline Points: 670 |
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Oh, now I see what you’re getting at. Introducing parallax error when the parallax is not adjusted correctly. That could be, I never checked that. |
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Kickboxer
MODERATOR Moderator Joined: February/13/2008 Status: Offline Points: 23679 |
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You got it, Gunshow. You read me well. |
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Opinion,untempered by fact,is ignorance.
There are some who do not fear death... for they are more afraid of not really living |
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brodeur272
Optics Journeyman Joined: September/23/2007 Location: United States Status: Offline Points: 609 |
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Hhaven't had that type of problem that I can see. But after having the eyepiece adjustable focus rings, I haven't gone back to the Leupold/older Nikon style.
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Ed Connelly
Optics Retard God of no Chihuahua Joined: December/16/2007 Location: USA Status: Offline Points: 24225 |
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Edited by Ed Connelly - August/30/2008 at 12:35 |
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