Does Differant Mag Settings = Differant P O Impact (Newbie)

[sparkycrew 22]

Ok newbie help please,if i zero my scope at 25 metres 6x mag and change nothing but mag to 9x and adjust AO to compansate paralax/focus,does my point of impact change if the same point of target is used,i must stress nothing else will change between each shots eg pellet,shooting position rifle ,time etc

thanks nick

[De_Tomaso 0]

This happens on all SFP (second focal plane scopes). POI changes with magnification change. However with the best SFP scopes (Zeiss Victory HT, Swarovski Z6, Kahles Helia 5, Leica Magnus...) this shift is normally less than 1cm/100m.

 

On cheaper scopes however this shift is much bigger.

[Deker 3,478]

This happens on all SFP (second focal plane scopes). POI changes with magnification change. However with the best SFP scopes (Zeiss Victory HT, Swarovski Z6, Kahles Helia 5, Leica Magnus...) this shift is normally less than 1cm/100m.

 

On cheaper scopes however this shift is much bigger.

 

 

 

Over what magnification range change?

Edited April 22, 2013 by Deker

[De_Tomaso 0]

Zeiss is stating that on their Victory HT this shift is so small over entire magnification range (1.5-6x, 2.5-10x, 3-12x). Others do not state this info but just say that this shift of POI is small.

[Kent_keith 46]

Or you can get FFP, (first focal plane) like the falcon menace, the POI does not change regardless of mag changes.

[paulus 26]

i have to say ive never noticed any change, it must be that small it only could make a difference when paper punching or extreme long range shooting

[Deker 3,478]

i have to say ive never noticed any change, it must be that small it only could make a difference when paper punching or extreme long range shooting

 

 

This may be a factor in some cheaper scopes, but if the engineering is right and optics properly ground it simply shouldn't happen!

[De_Tomaso 0]

In SFP scopes it happens always!!!

 

Build quality and good engineering however are the key factors that this sift is small.

[Deker 3,478]

In SFP scopes it happens always!!!

 

Build quality and good engineering however are the key factors that this sift is small.

 

Can you reference this please, perhaps I missed it but I see no mention of this on the Zeiss website for the Victory!

 

Zeiss is stating that on their Victory HT this shift is so small over entire magnification range (1.5-6x, 2.5-10x, 3-12x).

[dadioles 68]

In my experience, although when next out I shall test it thoroughly, the point of impact does not change with magnification.

It may be that I generally shoot on full magnification and also zero at full magnification. I will sometimes reduce the magnification for quarry that is nearer but that means my target is bigger and therefore I probably would not notice.

To clarify...

Rifle zeroed at 100 yards using 16x magnification.

Shoot a rabbit in the head at 16x mag at 100 yards bullet hits within an area the size of a pound coin.

Next rabbit is at 30 yards, I may reduce the magnification to 8x. Because the rabbit is so much nearer, it looks bigger. Any discrepancy in point of impact will be taken out by the fact that the target is closer and therefore appears larger.

 

If the optics, or perhaps more importantly the mechanics, of a scope are true, then winding the magnification up and down should not, in my view, alter the point of impact. It will just make the target look bigger or smaller. The other effect of course, as you increase the magnification and "zoom in" is that you become more aware of your pulse and other tiny movements of the rifle.

It is the photographic equivalent of "camera shake". Holding a wide angle lens steady is easy. Use a telephoto lens and you need a steady hand.

 

Another effect of "zooming in" and using high magnification is that the "depth of focus" is reduced. At lower magnifications everything seems to be in focus. At higher magnifications the focus becomes more critical.

That has implications for using the scope as a rangefinder. You must use it at maximum magnification to finely set the focus and can then read the distance off the scale. That is why I prefer side focus or side parallax rather than a lens where you have to rotate the lens at the far end.

 

That brings us, finally, to where I think people get confused and throw in terms like "first focal plane" and "second focal plane" (google it if you are interested).

What is happening here is not the point of impact changing with varying zoom but the scale or size of the mildots or whatever reticule you have compared to the target may be altering.

 

Most scopes are "second focal plane" and that means that as you zoom in and out the target gets bigger and smaller but the reticule looks the same size.

The cross hairs will stay centred in the same place on the target but the mildot spacing will alter relative to the target as the target shrinks and grows. So if you want to use mildots you must always use the same magnification

 

As you zoom a scope with "first focal plane" the reticule gets bigger and smaller in proportion to the target. These scopes are not so common but perhaps becoming more popular. One down side is that if you have a thick cross hair, the cross hair will appear to get thicker as you zoom in and in the case of a small distant target it may actually hide the target.

 

If the center of the cross hairs is on target at 16x, the centre of the cross hairs will still be on target at 4x. Not a problem if you judge holdover and holdunder based on "half an inch above the base of the rabbits eye" rather than "2 mil dots".

 

There is a lot of information about this whole subject on the internet including some clear and instructive videos on youtube. Go and do some homework.

[De_Tomaso 0]

 

In SFP scopes it happens always!!!

 

Build quality and good engineering however are the key factors that this sift is small.

 

Can you reference this please, perhaps I missed it but I see no mention of this on the Zeiss website for the Victory!

 

Zeiss is stating that on their Victory HT this shift is so small over entire magnification range (1.5-6x, 2.5-10x, 3-12x).

 

 

 

I got this information when I was on educational course at Zeiss and they are very proud on this, since only a few other manufacturers are achieving similarly small shift in their scopes. Swarovski on their course for partners doesn't even mention this matter.

 

Regarding the web-pages I haven't seen this information anywhere either.

Edited April 30, 2013 by De_Tomaso

[rimmer 33]

IMO thats a load of codswalup!!!!! in 25 years i have never noticed a change in POI due to change of mag. I always zero on about 5x mag but shoot upto to 10/14x mag, I have used scopes ranging from £30.00 to £1500.00, i have even had training shooting at long distances and have never heard it mentioned.

Aiming becomes a more technical thing at higher mag but thats about it as far as i am aware.