Home Forums Hunting & Shooting Ask The Gunwriters Second Focal Plane - POI shift

I just read an article in the August-September issue of Eastman�s which is titled �Optics 101�. Under the sub-title �Riflescope Focal Planes� the author states, in part �whereas second image plane reticles shift their point of impact when you change the magnification�

My question is has any of you experienced this shift in impact and if so, how much of a shift are we talking about?

GK

I have with some low end Tasco's and it amounted to about a 4 inch elevation and 1 inch left shift at 50 yds going from 10 x to 24 x on a 22 LR. Not an issue as I simply leave it at 10 X for our ground squirrel shooting outings. It would be an issue if one was unaware.

I would have written "second image plane reticles CAN shift their point of impact."

I test 20-30 scopes a year and encounter very few with any noticeable shift, and by "noticeable" I mean ANY shift.

The only scopes I've seen any shift in cost under $300, and even then it's been rare.

All variable power scopes with reticle in 2nd. focal plane have an optimum power where scope is at it most accurate. Zeiss ballistic reticles address this for each cal. As does Leu. in their varmint scopes and others. Zeiss has info. on line as well as user manual. Leu . in manual also. The POI is negligible for most shooters. I prefer variable power scopes in 1st focal plane for this reason. Not too many out there. Been using Pride Fowler rapid reticle.
I feel most scope manufacturers are lacking in reticle development. Leu. has been playing catchup for years. They have become mass merchandisers and I don't care who thinks otherwise. Zeiss is slow to come to the new reticle game,they licensed their rapid Z stuff with P.F. Don't care for Swar, overrated. Schmidt and Bender excellent.
Cisco

It may be that the different posters on this thread are talking about different things.

POI shift with a ballistic reticle is basic optics with a 2nd-plane reticle. POI shift due to the internal workings of a 2nd-plane scope is something else again. It's hard to tell exactly what was meant by the short quote from the OP.

A scope with accurate, repeatable adjustments beats the hell out of any ballistic reticle at any range past 500 yards, regardless of 1st or 2ns plane.

Mule Deer,
Repeatable adjustments are fine for targets that aren't able to run off. To take your finger off the trigger and fiddle with the turrets when hunting big game is laughable.
Cisco

Yes I have had it happen but it has been awhile.....back in the 80's I had a Zeiss Diavari 3-9 that would shift up and right about 2" between 4X and 9X. It was returned to Germany and confirmed defective. I was given a new scope.

Second time was a Swaro AV a few years back that did pretty much the same thing; it had other issues as well.And once a Leupold 2.5-8 that was really just broken.....

Lately things have been swell and no issues with any variables I can recall.....I guess this sort of thing is not as common today.

if you are shooting much past PBR and have time to ping with LRF, you probably have time to dial elevation. if you don't have time to ping, let it walk, as you are just hoping for a hail mary shot.

Reading your prose is difficult for an old guy like me so that's why it took me so long to respond.

Your first statement is misleading at best. If you are using your scope and reticle to do ranging, a variable scope with an SFP reticle will only range precisely at one magnification. The same scope will be very precise at all magnification, provided it is of decent quality and is not broken.

In the early days of variable scopes, they were known to have shifting POA/POI issues, but that is the exception rather than the norm for the last few decades, again providing it's decent quality and is not broken.

My big issue with FFP is the way the reticle changes size as one increases or decreases magnification. For very precise shooting, the reticle may very well get in the way at higher magnifications. I do agree that it is faster to range with an FFP scope at various magnifications, but for long range shots, I would rather dial than guess, but that's just me.

In answer to the original question; it was true in the past (decades ago,) but not any more.

[/quote]

My big issue with FFP is the way the reticle changes size as one increases or decreases magnification. For very precise shooting, the reticle may very well get in the way at higher magnifications. I do agree that it is faster to range with an FFP scope at various magnifications, but for long range shots, I would rather dial than guess, but that's just me. [/quote]

True, the reticle does change size as you change magnification, but also does the target. The reticle covers the same amount of the target on min. magnification as it does on max magnification. For big game, I'd rather have a FFP with ranging reticle (works at any magnification). If I were shooting praire dogs or other small game where a precise aiming point is needed, I can see where a SFP with turrents would be beneficial.

Right you are, Creditman. It will certainly depend on your application. I do precision shooting and I find that FFP reticle are too coarse as the magnification increases for the type of shooting I do.

FTR,
You should have read my prose carefully.
My first statement is NOT misleading. I do NOT range with my scopes. Very difficult to range a mt. sheep, especially if he is laying down in the shade of a big rock, at over150-200 yds.At that distance you better not need to range. Now, one probably would have time to fiddle with the turrets while you are studying curl for legality.I don't fiddle with the turrets once I am sighted in.


Now, try to follow.
1] The difference is negligible between 1st and 2nd focal image scopes.Very hard, for the average shooter to discern the difference.Probably doesn't make much difference in normal hunting situations.
2]However, all that being said 2nd. focal plane scopes, will be most accurate at a designated[by manufacturer] power for your particular cartridge and load. Go to Leu.or Zeiss and check out their varmint scopes. Zeiss rapid Z in Conquest line. Check it out for yourself.I shoot several of each, .223 WSSM,Leu. 4x14x40x 30mm LR. .25 WSSM Conquest Rapid Z, .22 Hornet Leu. varmint, .280 Zeiss Conquest rapid Z, .260 Pride /Fowler rapid reticle, and many more, just a few examples of scopes and cals. I shoot.


3] The European post and crosshair reticles and other styles increased dramatically with 1st focal plane reticles. These scopes were not really long...long range scopes.They were more for conditions were it was hard to see the reticles. However, some manufacturers[Pride/ Fowler is one, with 1st focal plane reticles DO NOT increase in size enough to be a problem or to "block out " the animal. I would like the reticle to get even bigger for my old eyes.


All I can speak from is my experience with good quality and expensive scopes. My best shots were made with a Balvar 2.5X 8 B&L mounted on various rifles with Kuharsky bases. 1 scope many rifles..22-250, 7mag, .264 mag[a real killer],.300 H&H, and others.


I have lost whitetails in the woods, but never lost a long shot animal.Hell, the last 3 times I hunted in Alaska I never fired a shot. Most recent was last Sept. on a jet boat hunt on Chensana river.I am at that stage where I take much satisfaction with my pards doing the shooting.


I don't punch much paper except to sight in or work out a load, and who needs to reload with all the good factory ammo available now any way. Go look at some of these scopes and reticles and catch up. Hell, its 2010.


I shoot .22 LR at 200 yes 200 yds. with a Pride/Fowler 1st focal plane ballistic reticle.


Shot my 1st. sheep in the Yukon in 1970 with a .264 [140 gr. Nosler partition]Sako ..2.5 x8 Balvar at about 170 yds. , cream puff shot. Wish they still made scopes like that today.
Cisco,
You are right! much better shootist. Thanks

If you double spaced your paragraph breaks, I might even try to read your posts. Man is that difficult to read.

Thansk guys, looks like I shouldn't be too concerned about it. I will just check for poi shift when I'm testing at the range.

John, I noticed that you mentioned POI shift in your recent article in Guns Magazine, great article. Also enjoyed the one entitled "The Truth About Short Magnums".

GK

Shortmag, you are correct, it is not a concern unless the scope is defective.

Cisco, when you say "2nd. focal plane scopes, will be most accurate at a designated[by manufacturer] power for your particular cartridge and load" you are saying the exact same thing that I pointed was misleading in your first post.

Shortmag was talking about a possible issue with the POI shifting due to magnification change. If he did not mean, "using the same cartridge and load and at the same distance," then we have an issue because I took it to mean that he was saying something like this:

"I load my rifle with 5 rounds, all the same from the same box. I set my scope at the lowest magnification and I take 3 shots, with the crosshairs exactly on the target at 100 yards. Then I twist the magnification ring to maximum and I place the reticle on the target still at 100 yards, at the same spot as before and take 2 more shots. These two shots will not group with the first three shots." This is due to a defective scope that is not keeping the reticle in the same axis of the lenses as the magnification changes.

What you are talking about is the fact a BDC or mildots or whatever form of holdover you are using will only be reliable at a specific magnification setting. That is usually (but certainly not always) the highest magnification for the scope. This is because the apparent relationship of the reticle to the image is not constant as the magnification changes.

We are talking about two different things here.

FTR,

Thanks, this is exactly what my post was concerning.

GK

FTR SHORTMAG.
On quality scopes the POI at different power ranges on a 2nd.focal plane scope will be negligible. When the POI changes dramatically you have 2 factors, either it is a poor qualty scope and/ or defective, and cheap scopes often are both . I am lucky to not have cheap scopes.The other factor is poor shooting.Who can learn to shoot with a improper scope?

I would refer to Schmidt and Bender , arguably an extreme high quality scope. Most of their reticles are in the 1st focal plane because it is accurate at all powers. Even though generally the shooter cannot tell much difference in POI with a quality scope in 2nd focal plane , which unfortunatly most scopes are.

I have never noticed a significat POI change with my 2nd focal plane scopes. You are right if you are experiencing significant POI change something is wrong.

Cisco