Have been doing a lot of reading between first and second focal plane scopes lately and I know that the advantage of the first focal plane is you are able to range at any power. You are not able to do this with second focal plane scopes because the reticle does not increase just the object. (Correct me if I'm wrong) my question is that if you have a second focal plane and you zero on 10 power then shoot on 20 or even 40 power does you zero still stay the same. Kinda new to this so easy on the ignorance lol. Thanks in advace for the help
Second focal plane scopes
- Thread starter cnorm129
- Start date
As long as your point of aim is the center of the cross hare, yes it will not change at any power. Any hash marks or mildots for holdoff will change though.
Yes, the reticle elements of first focal plane scopes get wider as power is increased. With some FFP scopes the crosshairs are so fine, to compensate for this, that they can be a real pain to see at low powers. I haven't had a problem being limited to one specific power to range with an SFP scope, but then I'm neither very good at ranging with a scope, nor am I presented with the need to do so very often (probably a main reason I'm not really good at it, lol).
What type of shooting do you want the scope for? FFP or SFP really depends on the application. I tried a few FFP scopes for target shooting, but the center dot gets huge at high power....its only passable, not optimal.
BoydAllen
Gold $$ Contributor
The only reason that I can think of for a variable power FFP scope is if you mean to use a mil dot reticle for ranging. and before you decide that that might be a neat thing to try, I suggest that you do a few simulations, using targets of unknown size, and distance, just to get a feel, before the light comes on, and you order a laser rangefinder, and a SFP scope.
cnorm129 said:
There is another big advantage at FFP scopes:
When you change the magnification (vor excample from 24x to 10x) on the SFP system the POI (point of impact) changes.
Good scopemaker have a difference between 0,5-3cm (0,2"-1,2") / 100 Meter / yards. But I have also seen cheaper scopes with much more.
On FFP scopes this mistake is not possible - there is no shift of POI when changing the magnification.
For Long Range scopes with high magnification FFP is the better solution and the thicker reticle can be compensated, when it has a fine center dot for aiming.
For scopes that are used up to 300 meters / yards and with a lower magnification (3-9x or 4-14x) there won`t be a problem with SFP because 99% the maximum magnification will be used and the lowest magnification only on short distances (hunting), where the small shift of the POI is not important.
Here is a nice test of 14 scopes.
Take a look to the area "Änderung der Visierlinie bei Vergrößerungswechsel/ 100 m" = "shift of POI when changing the magnification".
1 BE = FFP
1cm / 100 Meter = about 0,4" / 100 yards = 4" / 1000 yards
The mistake at SFP scopes happens, when the reticle is not 100% perfect centered mounted and it`s not dependent by the brand, it`s dependent how accurate the person who assemble the scope mount the reticle and also by the quality management of the company.
http://media.repro-mayr.de/41/235741.pdf
This is my prefered reticle for FFP scopes:
Ing. Michael W. Mayerl said:cnorm129 said:
There is another big advantage at FFP scopes:
When you change the magnification (vor excample from 24x to 10x) on the SFP system the POI (point of impact) changes.
Good scopemaker have a difference between 0,5-3cm (0,2"-1,2") / 100 Meter / yards. But I have also seen cheaper scopes with much more.
On FFP scopes this mistake is not possible - there is no shift of POI when changing the magnification.
For Long Range scopes with high magnification FFP is the better solution and the thicker reticle can be compensated, when it has a fine center dot for aiming.
For scopes that are used up to 300 meters / yards and with a lower magnification (3-9x or 4-14x) there won`t be a problem with SFP because 99% the maximum magnification will be used and the lowest magnification only on short distances (hunting), where the small shift of the POI is not important.
Here is a nice test of 14 scopes.
Take a look to the area "Änderung der Visierlinie bei Vergrößerungswechsel/ 100 m" = "shift of POI when changing the magnification".
1 BE = FFP
1cm / 100 Meter = about 0,4" / 100 yards = 4" / 1000 yards
The mistake at SFP scopes happens, when the reticle is not 100% perfect centered mounted and it`s not dependent by the brand, it`s dependent how accurate the person who assemble the scope mount the reticle and also by the quality management of the company.
http://media.repro-mayr.de/41/235741.pdf
This is my prefered reticle for FFP scopes:
Thank that was really my question was that if you zero on 10x on a SFP when you switch power with your zero come off. The only thing that with chnge will be the spacing between your mil dot ( if using a mil dot scope ) when you go to a higher magnification
I am a bit confused here. So if i zero,ed my rifle at 100 yards with a 5-25x50 scope sfp and i am hitting dead center starting out on 5 power ( lets say 1/4 inch 3 shot groups in the bullseye) and i bump my power by 5 until i am at 25 power my point of impact will no longer be where it was at when i started at 5 power?
cnorm129 said:
When the magnification is changed, the picture gets bigger or smaller but the reticle will not be increased or scaled down. So the mil lines or dots can only be used at one magnification. Most it is the maximum magnification or the correct magnification is marked.
BoydAllen
Gold $$ Contributor
As a practical matter, I rarely change magnifications while shooting a group, and in the field, working with a rifle that was sighted in at the scope's highest power, I have not experienced problems hitting small rodents at closer ranges, with the power dialed down. The one exception was an old steel tube Weaver that I owned probably 25 years or more back (and it was far from new when I got it). It showed a lot of movement from power change, and I got rid of it. Currently, I have a couple of variable scopes, that are not expensive, and they do their jobs quite well. Most scopes in this country are SFP, and their owners seen to get by pretty well. Like a lot of things, the equipment that you choose will depend on the use that you plan. I do think that it is a good idea to test scopes by shooting at various magnifications in the same group, and recently I spoke with a friend who has found that a couple of his side focus scopes shift as they are focused to different distances. One of these days, I am going to have to make up a test mount that can be secured to a concrete bench, or similarly sturdy object, so that I can do these sorts of tests, without depending on the accuracy of a rifle, or consistency of conditions. My target scopes are fixed power, so this is not an issue.
Some years back I tested a couple of Burris SFP variables that had mil dot reticles. In the instructions, the proper power setting for ranging was given. If I remember correctly, on the 4-16x it was the highest power, and on the 8-32x there were two setting that were supposed to be correct, 16x and 32X (if I remember correctly). As long as you were on the correct magnification, you could use the mil dot system. I went through the whole mil dot thing years back, and quickly determined that it would be of little use to me. (I also assisted a friend with a test of every laser rangefinder that was being sold for hunting use at the time, and so had a greater than usual familiarity with their characteristics.)
The reason that I mentioned targets of unknown size was because, as was pointed out, the estimate of distance, using mil dots, is only as good as your information about the target's size.
Some years back I tested a couple of Burris SFP variables that had mil dot reticles. In the instructions, the proper power setting for ranging was given. If I remember correctly, on the 4-16x it was the highest power, and on the 8-32x there were two setting that were supposed to be correct, 16x and 32X (if I remember correctly). As long as you were on the correct magnification, you could use the mil dot system. I went through the whole mil dot thing years back, and quickly determined that it would be of little use to me. (I also assisted a friend with a test of every laser rangefinder that was being sold for hunting use at the time, and so had a greater than usual familiarity with their characteristics.)
The reason that I mentioned targets of unknown size was because, as was pointed out, the estimate of distance, using mil dots, is only as good as your information about the target's size.
dtucker said:
Thats correct. When you zero the rifle with 5x magnification, every SFP scope will have an other POI with 25x. So it`s better to zero with 25x and test, how much it will shift with 15x and 10x. Most good scopes have a very small shift but for competition or long range it`s usefull to test it.
The biggest shift in my life was about 10cm / 100 meter. That are about 4".
In the test of the 14 scopes (see my post above) the biggest shift was 4,9cm (1,9") with a VIXEN scope, the NIKON has 2,5cm (1"), the MicroDot 2,9cm (1,1") and the Nightforce 1cm (0,4").
Scopes with FFP are marked with "1 BE = FFP" because FFP scopes have no shift.
BoydAllen
Gold $$ Contributor
To: Ing. Michael W. Mayerl
Rarely are we so lucky to have someone with your qualifications post on a thread. Thank you for doing so. I hope that you will continue to favor us by contributing.
The test that you posted a link to is of great interest to me, having never seen a formal evaluation of shift caused by magnification change of SFP scopes, and your information as to the source of that shift was enlightening.
If you would be so kind, I have one question about scopes' eyepiece adjustments. I am under the impression that the only difference between eyepiece adjustments is the number of turns that encompass the full range of adjustment, and that all systems simply move the entire eyepiece to what ever point best matches a shooters vision. A friend is of the opinion that there is something that he refers to as a "true diopter eyepiece adjustment" that does more than that. I think that this is because he can see a more obvious change due to the more rapid movement of what we refer to as a European or fast focus eyepiece, and that that style allows for the use of diopter markings, because the entire range of adjustment is accomplished within one turn, rather than the multiple turns of a typical, fine threaded adjustment that is common on American scopes. Please, if you would, sort out this friendly disagreement.
Boyd Allen
Rarely are we so lucky to have someone with your qualifications post on a thread. Thank you for doing so. I hope that you will continue to favor us by contributing.
The test that you posted a link to is of great interest to me, having never seen a formal evaluation of shift caused by magnification change of SFP scopes, and your information as to the source of that shift was enlightening.
If you would be so kind, I have one question about scopes' eyepiece adjustments. I am under the impression that the only difference between eyepiece adjustments is the number of turns that encompass the full range of adjustment, and that all systems simply move the entire eyepiece to what ever point best matches a shooters vision. A friend is of the opinion that there is something that he refers to as a "true diopter eyepiece adjustment" that does more than that. I think that this is because he can see a more obvious change due to the more rapid movement of what we refer to as a European or fast focus eyepiece, and that that style allows for the use of diopter markings, because the entire range of adjustment is accomplished within one turn, rather than the multiple turns of a typical, fine threaded adjustment that is common on American scopes. Please, if you would, sort out this friendly disagreement.
Boyd Allen
BoydAllen said:
Hallo
First: I`m not an optics expert. I`m an engineer for firearms design. My knowledge about optics is only skin deep.
In my opinion the difference of the two system (US and european) is only the rise of the okular thread. European scopes have a bigger rise and a higher range to adjust the scope to the eye. But the result should be the same.
At Leupold scopes I have noticed, that the adjustment range is very small. For me no problem but many older customers from me with older eyes get trouble with this scopes and change to european type scopes with a higher adjustment range to solve the problem.
And I have also noticed, that it`s an advantage to check the eyes at the eye doctor. A wrong eye pressure can worsen the quality of the picture when sighting with the scope dramatically. Most people who notice that the diopter adjustment range of the scope gets too small, have problems with the eye pressure and this should be corrected by the doctor first. To buy another scope and eyeglasses is not the right way.
And sorry for my bad english.
Thank you for this thread! I have often wondered what the differences were between ffp and spf scopes. However, I'm left a little confused on the same token. I am a varmint hunter, that ranges targets with a range finder, and then acquires said target in the scope, adjust elevation/windage for the shot and dispatch. I don't use reticles that have mildots/bdc because I feel they "clutter" the view in the scope! A target dot doesn't bother me much but, I prefer a fine crosshair. Am I correct that a sfp scope is better for varminting because the reticle size doesn't change with magnification changes? Also, if a rifle's poi is centered on the crosshairs does the poi change with magnification changes? These two questions are what have me confused! Thanks in advance for the clarification!
Mike
Mike
BoydAllen
Gold $$ Contributor
Although it does not change size, the reticle in a FFP scope will appear much bigger (thicker) at high magnification than low, and given your preferences, I do not think that you would like that, because the cross hairs would cover up too much for someone shooting small targets a long ways away. I generally sight in at the highest magnification that I will use in the field, and only go to less magnification for closer shots. If you think about it, you are shooting a larger target on those shots, so you will not have a problem, because the change in point of impact will fall within the target. On the other hand, I think that it is always a good idea to test a new scope. To do this, I work up a good load, and then use at target that is designed to be able to be used with the lowest power, and shoot a couple of groups, one at the lowest and another at the highest, shooting carefully, using wind flags (on a good day).
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