OpticsTalk by SWFA, Inc. Homepage SWFA     SampleList.com
Forum Home Forum Home > Scopes > Rifle Scopes
  New Posts New Posts RSS Feed - Scope on limit of adjustment
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Visit the SWFA.com site to check out our current specials.

Scope on limit of adjustment

 Post Reply Post Reply
Author
Message
Gerry Atric View Drop Down
Optics Journeyman
Optics Journeyman
Avatar

Joined: April/21/2011
Location: Sweden
Status: Offline
Points: 340
Post Options Post Options   Thanks (0) Thanks(0)   Quote Gerry Atric Quote  Post ReplyReply Direct Link To This Post Topic: Scope on limit of adjustment
    Posted: March/24/2019 at 06:27
Read about parallax and black ring, was taught that "trick" at young age, I was also taught that one should never use the last part of turret adjustment because the image get deteriorated at the scope edges. I have lived by that "rule" by using adjustable bases and Burris Signature Zee rings but what happens optically with a deviation from the optical axis and how bad is it?

The question is on my bucket list of knowing-before-dying, have not planned a hasty departure but.......


Gerry Atric 
Back to Top
Gerry Atric View Drop Down
Optics Journeyman
Optics Journeyman
Avatar

Joined: April/21/2011
Location: Sweden
Status: Offline
Points: 340
Post Options Post Options   Thanks (0) Thanks(0)   Quote Gerry Atric Quote  Post ReplyReply Direct Link To This Post Posted: April/06/2019 at 01:12
Should I leave this fantastic life without an answer to above mentioned question ?

Gerry Atric
Back to Top
bugsNbows View Drop Down
Optics God
Optics God
Avatar
bowsNbugs

Joined: March/10/2008
Location: North Georgia
Status: Online
Points: 11201
Post Options Post Options   Thanks (0) Thanks(0)   Quote bugsNbows Quote  Post ReplyReply Direct Link To This Post Posted: April/06/2019 at 07:11
PM Ilya. 
If we're not suppose to eat animals...how come they're made of meat?
               Anomymous
Back to Top
Kickboxer View Drop Down
MODERATOR
MODERATOR
Avatar
Moderator

Joined: February/13/2008
Status: Offline
Points: 23679
Post Options Post Options   Thanks (0) Thanks(0)   Quote Kickboxer Quote  Post ReplyReply Direct Link To This Post Posted: April/06/2019 at 08:41
Here are two references that should help you out:



ILya's article on this is an excellent treatise on how things really work.
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living
Back to Top
Gerry Atric View Drop Down
Optics Journeyman
Optics Journeyman
Avatar

Joined: April/21/2011
Location: Sweden
Status: Offline
Points: 340
Post Options Post Options   Thanks (0) Thanks(0)   Quote Gerry Atric Quote  Post ReplyReply Direct Link To This Post Posted: April/06/2019 at 13:40
Thank´s bugsNbows and Kickboxer I will PM my headaches to Ilya. Have read both references before, it could be that I´m struggling with a foreign language but I don´t see the answer to my question in any of those excellent references.

Gerry Atric
Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: April/06/2019 at 23:50
There is a mechanical limit to the adjustment range of a riflescope.  The erector tube assembly moves inside the maintube and there are stops that at some point arrest its movement in all four directions.

There is also an optical limit to how far you can move the erector tube and still get a good quality image.  Ideally the mechanical limit and the optical limit should match and in some scopes they do.  However, in a many scopes, at the end of adjustment the image gets vignetted or distorted.  However, many times it is still OK for aiming although edge performance suffers.  This is really specific to a particular design.

Optically, this is sorta what happens or at least I think this is a good way of explaining it.  Objective lens creates an image of a particular size in the front focal plane.  The erector system samples a small portion of that image.  Depending on where inside the larger image created by the objective that is, the erector is looking at a different segment of the FOV.  Essentially imagine a small circle (image sampled by the erector system) inside a large circle (image created by the objective).  

When you spin the turrets, a small circle moves inside the large circle.  If it never gets close to the edge of the large circle, image quality does not suffer (much), but as it gets close to the edge it starts picking up aberrations.

ILya
Back to Top
Gerry Atric View Drop Down
Optics Journeyman
Optics Journeyman
Avatar

Joined: April/21/2011
Location: Sweden
Status: Offline
Points: 340
Post Options Post Options   Thanks (0) Thanks(0)   Quote Gerry Atric Quote  Post ReplyReply Direct Link To This Post Posted: April/09/2019 at 13:23
Thank´s Ilya
Now I can hunt in peace in heaven (or hell) Slow Poke

Gerry Atric
Back to Top
tpcollins View Drop Down
Optics Journeyman
Optics Journeyman


Joined: January/12/2009
Status: Offline
Points: 428
Post Options Post Options   Thanks (0) Thanks(0)   Quote tpcollins Quote  Post ReplyReply Direct Link To This Post Posted: April/10/2019 at 10:14
I had a conversation with Vortex once when I was maxing out the elevation turret on my crossbow’s XBR scope, and the poi moved to the right.

He said if the scope rail isn’t perfectly centered with the centerline of the shooting rail, then the windage turret would need to adjusted to correct this - as is normal with most weapons. 

 If the erector tube is set to the left of center, and as the turret starts to max out on the up elevation, the left front edge of the erector tube hits the inside of the scope tube and pushes it over to the right.

This moves the reticle at the back of the erector tube to the left, and to bring it to the target you have to move the crossbow’s line of sight to the right which cause the poi to be further right than it was with less elevation.  


Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: April/10/2019 at 11:45
Originally posted by tpcollins tpcollins wrote:

I had a conversation with Vortex once when I was maxing out the elevation turret on my crossbow’s XBR scope, and the poi moved to the right.

He said if the scope rail isn’t perfectly centered with the centerline of the shooting rail, then the windage turret would need to adjusted to correct this - as is normal with most weapons. 

 If the erector tube is set to the left of center, and as the turret starts to max out on the up elevation, the left front edge of the erector tube hits the inside of the scope tube and pushes it over to the right.

This moves the reticle at the back of the erector tube to the left, and to bring it to the target you have to move the crossbow’s line of sight to the right which cause the poi to be further right than it was with less elevation.  



That is correct for cheap scopes.  Better scopes usually have internal adjustment limiters, so that the adjustment range is rectangular.

ILya
Back to Top
tpcollins View Drop Down
Optics Journeyman
Optics Journeyman


Joined: January/12/2009
Status: Offline
Points: 428
Post Options Post Options   Thanks (0) Thanks(0)   Quote tpcollins Quote  Post ReplyReply Direct Link To This Post Posted: April/11/2019 at 10:28
The Vortex PST XBR 2.5-10x44mm with illumination originally retailed for about $800 and sold for $600 before they were discontinued. Not sure if that’s considered a cheap scope or note.

Here a link - same exact scope, just different reticles, but with 1 MOA per click, I still own two.

Competitor link removed.


Edited by koshkin - April/11/2019 at 10:41
Back to Top
koshkin View Drop Down
MODERATOR
MODERATOR
Avatar
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 13182
Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: April/11/2019 at 10:40
Originally posted by tpcollins tpcollins wrote:

The Vortex PST XBR 2.5-10x44mm with illumination originally retailed for about $800 and sold for $600 before they were discontinued. Not sure if that’s considered a cheap scope or note.

Here a link - same exact scope, just different reticles, but with 1 MOA per click, I still own two.



I am familiar with that scope.  When Vortex first released, it had some unforeseen issues, so I ripped it to shreds.  They ended up being forced to re-design the eyepiece entirely.  It was still a bit of a failure with centerfires, but it found some success in the  crossbow world.

Generally, in that price range there should already be adjustment limiters.

ILya
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 0.711 seconds.