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# 35 mm tube IOR's

#43
11-23-2003, 07:02 PM
 Silver Member Join Date: Oct 2003 Location: Washington State Posts: 120
Re: 35 mm tube IOR\'s

If you aren't confused by this discussion, you should be, so lets interrupt the thing for a few facts.

1. All my variable scopes are made by USO and all are first focal plane reticle design. All of those have the parallax adjustment in the objective housing and diopter adjustment in the eyepiece.

2. The diopter adjustment in the eyepiece will adjust to your eyesight to make the reticle appear clean and sharp.

3. The function of the parallax adjustment is in effect to focus the target and to assure the alignment of the target with the focal plane of the reticle for varying distances.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> Parallax can be defined appropriately to riflescopes as: The
apparent movement of objects within the field of view in relation to the reticle.

This adjustment of the objective part of the optical system would ensure that the target can be brought in the exact focal plane of the reticle at any distance.<HR></BLOCKQUOTE>

Now as to the reticle:

First focal plane scope reticles grow in proportion to the magnification. This means that the reticle will subtend the same amount on the target regardless of power. A very useful feature on a ranging reticle scope.

Second focal plane reticles appear the same size regardless of power. They change the amount of subtension as the power is changed. This means that they often must be calibrated to subtend a certain amount at a specified power. Often 10x or some other value.

Like my old math teacher used to say, I can't help it, thats the way it is!

D. [img]images/icons/smile.gif[/img]

[ 11-23-2003: Message edited by: DMCI ]
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#44
11-23-2003, 09:27 PM
 Junior Member Join Date: Sep 2003 Posts: 14
Re: 35 mm tube IOR\'s

Guns and Glass you said this earlier. "First focal plane reticules GROW as the power is increased."
Now I know Springfield Armory Scopes aren't that popular but they make them with first focal plane reticules that Grows as the power is increased. I used to have them and thats one of their big advertisements.
So whey later did you say that they are a second focal plane scope. Also IOR makes their scopes in either the first or second focal plane system.
#45
11-24-2003, 03:27 AM
 Platinum Member Join Date: Jun 2001 Location: Palmer, Alaska Posts: 2,539
Re: 35 mm tube IOR\'s

G&G, you posted:
The growing/shrinking of BOTH the target AND reticle only occurs in the 1st focal plane.

In the second reticle always stays the same, but the target can grow or shrink.
Ie, when the power is increased the reticle gets smaller.

NOW, you've really got me guessing what you mean... Are you saying the NF is in the 2nd plane now???

When you say smaller, bigger, grow, same, or what ever, please indicate weather it's relative to the target, or what.

.....

1) yes, if I understood the question right?
2) yes, if it's adjusted properly.
3) When I adjust the eyepiece, I do it at 200 or 300 yards after I eliminate the parallax, then I focus the reticle.

The ocular is adjusted after the target is parallax free and focused.

BTW, Schmidt \$ Bender doesn't specify 1st or 2nd, just ocular or objective. Any other referance?

I beleive the FIRST, as in first focal plane, is referancing the first plane the light image passes through, which is the objective plane, the ocular would be the SECOND plane it passes through.
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Brent Moffitt
#46
11-24-2003, 03:45 PM
 Bronze Member Join Date: Dec 2002 Location: FL Posts: 45
Re: 35 mm tube IOR\'s

#47
11-24-2003, 07:28 PM
 Bronze Member Join Date: Oct 2003 Location: Princeton, Ks. Posts: 62
Re: 35 mm tube IOR\'s

Ok, I've got a question. I understand the theory behind the first focal plan scope being more accurate. But what is the margin of error between the two when applied to pactical shooting. For instance. I have 2 2.5-10x42 tactials, one is first forcal plane and the other is second focal plane. I can shoot better groups with the second focal plane scope. I have attributed that to the fact that I can have a more presise point of aim. Another words the crosshairs are thiner and I can see the target better.
I would think that this effect would be magnified with the use of higher power scopes.

So my question is, what is the margin of error between the first focal plane scopes coverage area (by the crosshairs) compared to the second focal plane scopes coverage area? Where would that put the advantage. First or second focal plane?

I talked to Val at IOR today. He thinks were all crazy. He said " it doesn't matter, the second focal plane scopes are just as accurate as the first focal plane scopes. If you have to have a first focal plane scope we'll custom order one." It'll cost just as much as a Nightforce but at least you'll be able to see the target through it! [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img]

Boy it's going to get fun now!

Jim
#48
11-24-2003, 08:45 PM
 Platinum Member Join Date: Jun 2001 Location: Palmer, Alaska Posts: 2,539
Re: 35 mm tube IOR\'s

It'll cost just as much as a Nightforce but at least you'll be able to see the target through it! [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img]

Ouch!! [img]images/icons/shocked.gif[/img] [img]images/icons/grin.gif[/img]

I'm still not sure I understand why they clain the 2nd plane scopes are potentially less accurate or repeatable. I've certainly found no problem with mine, but most of my shooting has been on 22x mainly?

.....

As an add on, I did shoot a group with my brothers 338/378 WBY that was about 1 MOA while testing once, it was at 100 yards. I scratched my head a bit as I wondered why so big??? [img]images/icons/confused.gif[/img] Well, I noticed it was on 10x not 22, so I turned it up to 22x and fired some more groups... they all came near .5 MOA after the switch. I attributed it to a more consistant POA, kind of like you stated, Jim, same basic issue. I've never seen it shoot a group near that large, or I'd of questioned something else. When it grouped as usual after switching to 22x, It definitely made me wonder if I'd do "even" better at longer range with a 32x. POI did not shift, group size was all that changed.??

[ 11-24-2003: Message edited by: Brent ]
__________________
Brent Moffitt
#49
11-24-2003, 10:59 PM
 Bronze Member Join Date: Dec 2002 Location: FL Posts: 45
Re: 35 mm tube IOR\'s

there is no problem with accuracy with either one...the advantage of the first focal is when trying to range targets and adjust poi to poa without having to have your scope set at one power setting only.
for example the other day i was shouting with my 4.5-14x leupold with gen2 reticle and i had forgot that i had it set at 9x, i was shouting half a mill low i measured it and i adjusted it poi to poa..if i had done this with a second focal scope i would have been all over the place before i remember i had to set it back at 14x to measure the poi to poa..

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