Print Page | Close Window

locking vs non locking focus?

Printed From: OpticsTalk by SWFA, Inc.
Category: Scopes
Forum Name: Rifle Scopes
Forum Description: Centerfire long gun scopes
URL: http://www.opticstalk.com/forum_posts.asp?TID=12506
Printed Date: November/13/2018 at 12:49


Topic: locking vs non locking focus?
Posted By: 30mikemike
Subject: locking vs non locking focus?
Date Posted: August/23/2008 at 00:11
Although they can be a pain, the ocular lens focus systems that have a locking ring (like Leupod) dont move once locked down. I have noticed on a scope with the quick focus, a schmidt & bender, that when the focus is away out (bad eyes with glasses) that the eyepice can be moved left to right, up to down a little bit and the crosshairs appear to move about 1" at 200 yards. Now it doesn't stay moved once you let it go but I wonder if that's normal or not and should I be concerned?



Replies:
Posted By: Jon A
Date Posted: August/23/2008 at 00:33
Originally posted by 30mikemike 30mikemike wrote:

should I be concerned?

No.  Look again really closely--the target is moving with the reticle so even if it did stay (which of course it won't) POI wouldn't change at all.

Also, the Leupold type certainly can come loose if you don't make them "pipe wrench tight," and that makes them a PITA anytime you want to move them in the future.


Posted By: 30mikemike
Date Posted: August/23/2008 at 20:11
Thanks for yout advice, The reticle moves on the target, it does not maintain the same point on the target. I had a Steiner a few years ago that did the same thing. One day it was a one hole scope, the next, groups like a coach gun with 00 buck. Never used a pipe wrench on a lock ring style, a dab of blue (low strength) locktite will keep them were you want them.


Posted By: Jon A
Date Posted: August/23/2008 at 21:38
First, if you know the answer why are you asking the question?

Second, how carefully are you making the observation that the reticle is moving on the target?  I ask because, unless you have a relatively rare SFP S&B, it's physically impossible to move the reticle relative to the image of the target by wiggling the focus ring unless you're shaking the entire scope.


Posted By: Kickboxer
Date Posted: August/23/2008 at 21:45
Originally posted by Jon A Jon A wrote:

First, if you know the answer why are you asking the question?Second, how carefully are you making the observation that the reticle is moving on the target?  I ask because, unless you have a relatively rare SFP S&B, it's physically impossible to move the reticle relative to the image of the target by wiggling the focus ring unless you're shaking the entire scope.

My NcStar does it...

-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: Jon A
Date Posted: August/23/2008 at 22:15
And your NcStar has what in common with a FFP S&B?  They're both black?


Posted By: Kickboxer
Date Posted: August/23/2008 at 22:20
Originally posted by Jon A Jon A wrote:

And your NcStar has what in common with a FFP S&B?  They're both black?

Well, it obviously escapes you that they have at least ONE thing in common, other than being black.

-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: helo18
Date Posted: August/24/2008 at 00:11
Originally posted by Kickboxer Kickboxer wrote:

Originally posted by Jon A Jon A wrote:

And your NcStar has what in common with a FFP S&B?  They're both black?

Well, it obviously escapes you that they have at least ONE thing in common, other than being black.


Laugh%20Above  I just think that response is great Kickboxer!  I wouldn't think that moving the focus piece should move the reticle.  I would say there is something wrong with it.  Never had that happen on a scope before.


-------------
To be prepared for War is one of the most effectual means of preserving peace.

GEORGE WASHINGTON


Posted By: Jon A
Date Posted: August/24/2008 at 00:19
Originally posted by Kickboxer Kickboxer wrote:

Well, it obviously escapes you that they have at least ONE thing in common, other than being black.

Could you give us a brief description of the procedure you use to display this phenomenon? 


Posted By: Kickboxer
Date Posted: August/24/2008 at 00:32
Move focus ring, RETICLE moves relative to target image... rather wildly at times. If care is exercised, the reticle can be, shall we say, "adjusted" so that accuracy and focus is maintained. However, if care is not exercised, POA and POI are not the same while the scope will be in focus. I do not know if this is common to NcStar scopes, I have never seen the effect before and it does not occur in any of the other scopes I have.

-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: Kickboxer
Date Posted: August/24/2008 at 00:35
Originally posted by helo18 helo18 wrote:



Originally posted by Kickboxer Kickboxer wrote:

Originally posted by Jon A Jon A wrote:

And your NcStar has what in common with a FFP S&B?  They're both black?

Well, it obviously escapes you that they have at least ONE thing in common, other than being black.
Laugh%20Above  I just think that response is great Kickboxer!  I wouldn't think that moving the focus piece should move the reticle.  I would say there is something wrong with it.  Never had that happen on a scope before.

I agree Helo, must be a scope problem.

-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: Jon A
Date Posted: August/24/2008 at 02:59
I agree.


Posted By: Dale Clifford
Date Posted: August/24/2008 at 10:35
put this question up on SH-- 61 hits and not one explanation-- it would seem that theory and experience are colliding.


Posted By: 30mikemike
Date Posted: August/24/2008 at 10:38
Update: called S&B and they said rare but possible. Send it back and they will analyze and fix for free if necessary. To put an NC in the same room with an S&B is like saying a Pinto and GT40 are both cars!


Posted By: tahqua
Date Posted: August/24/2008 at 10:53
Originally posted by 30mikemike 30mikemike wrote:

Update: called S&B and they said rare but possible. Send it back and they will analyze and fix for free if necessary. To put an NC in the same room with an S&B is like saying a Pinto and GT40 are both cars!


Aren't they?
I don't think KB was putting his NC "in the same room" as S&B. He was just stating that he has seen this issue with his scope. Everyone here knows the Schmidt & Bender is an outstanding scope. Most also know what an NC is.

Doug


Posted By: Dale Clifford
Date Posted: August/24/2008 at 11:24
Probably impossible to make the statement that wobble was the only problem in either case also.


Posted By: tahqua
Date Posted: August/24/2008 at 11:38
Originally posted by Dale Clifford Dale Clifford wrote:

Probably impossible to make the statement that wobble was the only problem in either case also.


For sure and I think 30mm is on the right track. It should be sent back for inspection.
Adjusting focus has never changed POI for me, either.


Posted By: Gunshow75
Date Posted: August/24/2008 at 14:05
Originally posted by Dale Clifford Dale Clifford wrote:

put this question up on SH-- 61 hits and not one explanation-- it would seem that theory and experience are colliding.

Scopes have an optical axis. Lets assume that both the center of the image formed by the objective and the center of the reticle are perfectly aligned on the optical axis. Focusing the scope by adjusting the objective lens is intended to move the image along the optical axis such that image and the reticle lie in the same plane.

Imagine what would happen if the mechanical motion of the lens was such that moving the lens caused the image to move away from the optical axis. It might move left, right, up, down, or whatever, but away from instead of along the optical axis. In that event, even though the image and the reticle were in the same plane, the center of the image will not remain aligned with the center of the reticle.


-------------


Tom





Posted By: Jon A
Date Posted: August/24/2008 at 14:26
Originally posted by Gunshow75 Gunshow75 wrote:

Focusing the scope by adjusting the objective lens is intended to move the image along the optical axis such that image and the reticle lie in the same plane.

OK, now you're talking about an adjustable objective to eliminate parallax?  I agree this certainly could change POI if there's slop. 

But that's not what we're talking about here.


Posted By: tahqua
Date Posted: August/24/2008 at 14:46
Originally posted by Jon A Jon A wrote:

Originally posted by Gunshow75 Gunshow75 wrote:

Focusing the scope by adjusting the objective lens is intended to move the image along the optical axis such that image and the reticle lie in the same plane.

OK, now you're talking about an adjustable objective to eliminate parallax?  I agree this certainly could change POI if there's slop. 

But that's not what we're talking about here.


Exactly, we are talking about focusing the ocular lens for a clearer reticle.
I certainly have seen changes, not in POI, but in my groups. Being able to put a clean, crisp reticle on the target is necessary for me.
Also, getting back to the locking ring. I never had problems with my Leupold, Burris and other locking rings in the past. Now that I wear progressive lenses I find myself adjusting the focus more often. I haven't had problems with the fast focus on Monarch, 4200 and Kahles so far. I was worried about it moving, too. A little nail polish on the ring lets me know where my sweet spot for focus is, should it move.
Once set I shouldn't have to move it but I'm still getting used to the sweet spot on these glasses. Shooting from the bench, offhand and prone changes my eye/scope relationship and is probably the problem.

Doug


Posted By: Gunshow75
Date Posted: August/24/2008 at 15:26
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.

-------------


Tom





Posted By: tahqua
Date Posted: August/24/2008 at 15:51
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.


Posted By: Gunshow75
Date Posted: August/24/2008 at 15:54
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.

-------------


Tom





Posted By: Gunshow75
Date Posted: August/24/2008 at 15:56
My second mistake today. I meant to say that I always think of OBJECTIVE lens when I see the word Focus.

-------------


Tom





Posted By: Kickboxer
Date Posted: August/24/2008 at 20:27
Originally posted by 30mikemike 30mikemike wrote:

Update: called S&B and they said rare but possible. Send it back and they will analyze and fix for free if necessary. To put an NC in the same room with an S&B is like saying a Pinto and GT40 are both cars!

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.

-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: Kickboxer
Date Posted: August/24/2008 at 20:29
Originally posted by tahqua tahqua wrote:


Originally posted by 30mikemike 30mikemike wrote:

Update: called S&B and they said rare but possible. Send it back and they will analyze and fix for free if necessary. To put an NC in the same room with an S&B is like saying a Pinto and GT40 are both cars!
Aren't they?I don't think KB was putting his NC "in the same room" as S&B. He was just stating that he has seen this issue with his scope. Everyone here knows the Schmidt & Bender is an outstanding scope. Most also know what an NC is. Doug

Doug, quite true. I have found nothing to recommend an NcStar to anyone, while I have found nothing which would not recommend S&B.

-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: 30mikemike
Date Posted: August/24/2008 at 20:36
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!)


Posted By: Kickboxer
Date Posted: August/24/2008 at 22:09
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.



-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: crispycritter
Date Posted: August/24/2008 at 23:59
Originally posted by Kickboxer Kickboxer wrote:

Well, this is a battle you can't win because I have HAD the playmate of the month in my hottub... on MANY occasions.

 
 
 
 
Do tell, how did you keep the magazine from falling apart?Big%20Grin


Posted By: Kickboxer
Date Posted: August/25/2008 at 06:40
Originally posted by crispycritter crispycritter wrote:

Originally posted by Kickboxer Kickboxer wrote:

Well, this is a battle you can't win because I have HAD the playmate of the month in my hottub... on MANY occasions.

 
 
 
 
Do tell, how did you keep the magazine from falling apart?Big%20Grin
 
Endeavor to persevere...


-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: Gunshow75
Date Posted: August/25/2008 at 07:23
Originally posted by Kickboxer Kickboxer wrote:

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.

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.

-------------


Tom





Posted By: Jon A
Date Posted: August/25/2008 at 13:24
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. 


Posted By: Gunshow75
Date Posted: August/25/2008 at 14:32
Originally posted by Jon A Jon A wrote:

... I don't think it should happen on any decent SFP .. 

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.

-------------


Tom





Posted By: Jon A
Date Posted: August/25/2008 at 17:05

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.



Posted By: Kickboxer
Date Posted: August/26/2008 at 18:11
Originally posted by Gunshow75 Gunshow75 wrote:

Originally posted by Kickboxer Kickboxer wrote:

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.

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.

You got it, Gunshow. You read me well.



-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: brodeur272
Date Posted: August/27/2008 at 11:00
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.


Posted By: Ed Connelly
Date Posted: August/27/2008 at 21:30

                                    

 
                                                                                  Bandito



Print Page | Close Window