Point of Aim vs Level of Magnification

Desette

Desette

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Hey,

I tired to search for this because when I was talking to a few people they said it was obvious but it still doesn't make sense so I think this needs to be addressed by our top Marksman's :)

So I was looking up Sightmark scopes (http://www.sightmark.com/) and I couldnt find if they were good or a POS. (still wondering if you have 1st hand experience)

So somewhere in the abyss of the web I found someone who talked to their staff and asked a few questions and one was about Point of aim while changing magnificaitons.

They explained if you set your zero at for example 5x and zoom in or out it will change the point of aim and that most lower end scopes do this.

This confused me a lot since it didn't make logical sense at all.

So my questions:

Is this true?

What scopes generally do this?

What scopes generally don't do this?

If it's true how can you adjust for it easily?



If I didn't make sense I appolgize and let me know so I can try to explain further. This was a confusing issue and now I am worry about my groups changing if I go to a multi-power scope.
 
This should be in the Optics forum.

Anyways, if your POI changes with magnification take your scope back, it is broken. period.

A good, working scope will not do this. I had a scope do it to me and I sent it back for warranty repair and they sent me a new scope.

I can't say anything about sightmark, but they look like Chinese knock off scopes. If you want a cheap scope with target turrets you can usually find a Bushnell Elite 3200 10x on the EE from time to time in the 200-250 range. Most inexpensive target scope that I can think of that is reliable and has good glass.
 
One thing when dealing with Mil-Dot scopes changing the magnification will effect the measurements between mils most mill-dot scopes will have one setting where the mil-dots are supposed to be used 10x is the norm.
 
What scopes generally do this?
Click to expand...
Cheap ones.
What scopes generally don't do this?
Click to expand...
Expensive ones.
If it's true how can you adjust for it easily?
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Don't use variable power. Sight it in at the magnification you intend to shoot with. Alternatively save your money and buy a good fixed power scope or get a quality variable magnification scope like a Leupold, Zeiss, Swarovski etc..


There is hardly anything in the world that some man cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey.... John Ruskin
 
Buying quality optics always pays off. It's like buying oats: If you want top quality oats, you can expect to pay a premium price. If you don't mind oats that have already been through the horse, you can buy 'em for cheap!! Eagleye.
 
Likely to be less of a problem with shifting POI with zooms unless they are really crappy. The elements responsible for the "variable" power in a scope are at the rear of the scope, with the reticle and front objective assemblies towards the middle and front. The whole rear element group sits on a helicoid, which moves these elements front or back as it is rotated. This creates the magnification.

The answer is simple: If the scope will shift POI, you will see it. Because the reticle and front elements remain stationary relative to the rear elements. If you could mount the scope in something rock solid, try adjusting the magnification. If the picture moves, the POA(aim) will move.

FYI... The same principles apply to parallax adjustment (which is not just "focus"). This elements in the front of the reticules responsible for bringing the sharpest image in the same plane as the reticule can affect POI. It is important to ensure you set and forget the parallax for your given distance.

Here is a pretty decent article on scopes with links to other really good articles

As to the quality of the scope you mentioned... never heard of it.

http://www.6mmbr.com/optics.html
 
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When I was a kid I had a scope that had that feature (broken), it was an old redfield and it saved the lives of many a squirrel when I changed the magnification and forgot to adjust my point of aim :)
 
Eagleye said:
Buying quality optics always pays off. It's like buying oats: If you want top quality oats, you can expect to pay a premium price. If you don't mind oats that have already been through the horse, you can buy 'em for cheap!! Eagleye.
Click to expand...


Moral of the story - Stay away from those pre-enjoyed scopes... err oats !!
 
well I know Nightforce sometimes comes with this extra feature, or at least so it appeared last weekend......
 
Doesn't this have more to do with First Focal Plane scopes compared to Second Focal Planes? With the FFP scope the point of aim won't move because the reticle doesn't move but with the SFP scope the reticle does move.
 
Slavex said:
well I know Nightforce sometimes comes with this extra feature, or at least so it appeared last weekend......
Click to expand...

With which feature?

@EVERYONE: Thanks for that I figured it was stupid that it would shift POA and if I ever find the time to grab a sight-mark I will let people know how they preform and if they do this :)

I am currently going to be using a Bushnell Elite 3200 10x40 Tactical with Mil Dot reticle and quick adjustment knobs on my 6.5x55 :D
 
Sako223 said:
Don't use variable power. Sight it in at the magnification you intend to shoot with. Alternatively save your money and buy a good fixed power scope or get a quality variable magnification scope like a Leupold, Zeiss, Swarovski etc..


There is hardly anything in the world that some man cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey.... John Ruskin
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True, if you want nonchanging POI buy quality fixed power scope. All variables change POI, cheap ones change it a lot, expensive ones change it a lot less. Variables would never change POI only if there were no manufacturing gaps between mooving parts but in this instance the power turning ring would be permanently frozen.
 
the extra super duper feature of POI shift of course, lets say around 35-40ft at 940yds. when going from 5-22 power. also not just up and down either, but 10-15ft sideways too. It's awesome!
 
meh, it's a fluke to see this with the Nightforce I'm sure. I went through 3 S&B's due to paint on the inside of the glass, #### happens. What counts is the company doing right by the customer, and I am sure Nightforce will, just as S&B did for me. I get zero drift with my 5-25, although I shoot most of the time at around 16x, as it's more comfortable for me for some reason.
 
FIxed power scopes are hot good for long distance shooting in sunlight or in high mirage.
I have a fixed 36 I took to 600 in Chillwack and will never repeat that experiment. In the BC Provincials, I - and most of the other F-Class guys - were dialed back to 20X
 
and it appears it's not the scope but the shooter. we'll get the gun and shooter out this week and see if we can figure this out.
 
Desette said:
With which feature?

@EVERYONE: Thanks for that I figured it was stupid that it would shift POA and if I ever find the time to grab a sight-mark I will let people know how they preform and if they do this :)

I am currently going to be using a Bushnell Elite 3200 10x40 Tactical with Mil Dot reticle and quick adjustment knobs on my 6.5x55 :D
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Been using this scope on my .270 for about 5 yrs happy with it for the price.
 
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