How Does Side Focus Work Exactly?

Discussion in 'Long Range Scopes and Other Optics' started by Sean K., Aug 23, 2008.

  1. Sean K.

    Sean K. Active Member

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    My apologies in advance for the stupid question but I'm new to variable power optics and just bought my first one.

    My experience with scopes is limited to cheap fixed 4X Bushnells on rifles out to 300 yards.

    I decided to spend a decent amount of money (for me), justifying it by saying this will be my only long range rifle for target shooting to 600 yards or so and for hunting up to 300, maybe 400 at most.

    I went with the IOR Sniper's Hide edition FFP 3-18x42mm.

    This scope has side focus but at the distances I've been able to check it (short b/c I'm in AZ and right now it's 110ยบ outside) I can't seem to make it focus clearly (at least at 3-4X). Since I'm in a metro area, I can't really point this thing out the window to get a longer distance look with higher power magnification without freaking people out I'm sure. ;)

    I found that there is a ring on the very back of the scope at the ocular (hope I'm using the right term)....rear most lense by your eye...that rotates and will focus the image very sharply.

    My question is: when do I use side focus and when do I use the ring at the back of the scope? Is one a fine adjustment versus a coarse one and if so, which is which? Is one for higher magnification at longer distance vs. the other and which do I use for in close vs. far away?

    Again, sorry for the dumb questions.....I just am completely new to this and don't know what I'm doing.

    Any help is appreciated.

    Sean
     
  2. Mikecr

    Mikecr Well-Known Member

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    The eypiece is for crosshair focus, and you should be set this immediately with quick glances of the sky. Tighten the ring and your done there.

    The side focus is for elimination of parallax at high power.
    You will adjust it with every change in range, especially at 18x.

    I'm not familiar with the detailed design of side focus, but I'm glad to have it over adjustable objective. This, because it's easy to use for each shot, -while in exact shooting position.
     

  3. Sean K.

    Sean K. Active Member

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    I'm following you now....the eyepiece is for focusing the crosshairs. I don't understand what you mean by "tighten the ring". Is there a set screw or something once I focus the cross hairs that needs to be tightened?

    Thanks,
    Sean
     
  4. boomtube

    boomtube Well-Known Member

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    Mike is correct and gives you some good advise.

    It is very important to do as he says when focusing the ocular lens. The objective (front) lens is adjusted by the factory to project an image on the cross wires at the factory by non-AO scopes, usually at 150 yards for hunting scopes.

    To make your eye also focus on the cross wire is best done by looking at a blank wall, or sky as he suggests. Since our eyes tend to "pull" into focus if we look at anything for long we must limit ourselves to brief looks at the cross wire while adjusting the objective. When it appears to be in immediate sharp focus when you look at it, you are done.

    The AO allows us to change the parallax at any distance by changing the focus for that specific range. Be aware than the calibration marks for any scope are only approximations, YOU will have to make it right for your situation. To do it, first pick a specific small target at your distance, then move your head from side to side, left and right. Staring is okay here! If the cross wires seem to move in relationship to the target adjust the scope until the appearent shift is corrected.

    Understand that parallax is of no consequence IF we hole our eye directly in the center line of the scope. Parallax ONLY comes into play when we are looking off-center at the target.

    "Tighten the ring" is refering to the narrow locking ring immediately in front of the objective housing. Snug it up so the objective can't be turned off focus too easily.
     
  5. MachV

    MachV Well-Known Member

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    Unfortunatly the IORs do not lock but a ring of black tape will work or just mark it with a scratch or white marker. A butler Creek cap works too as it kinda locks the eye ring in place.
     
  6. Sean K.

    Sean K. Active Member

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    Thanks very much for both responses! I understand what you are saying regarding focusing the cross wires and how to understand parallax, but....

    I don't seem to have a narrow locking ring or any set screws I could detect (unless they are underneath the rubber ring over the moving eyepiece).

    Here's a pic:

    [​IMG]

    I don't know if you can tell, but there's a 3/16-1/4" wide rubber ring on the back of the scope at the eyepiece. This is what I turned to focus the cross wires. I don't see any other lock down mechanism. I'm assuming it doesn't have (or may not need) one.

    Thanks for the help.

    Sean
     
  7. Sean K.

    Sean K. Active Member

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    Ah-ha.....you posted just as I was posting my last reply. Thanks. That is very useful info. I have the BC caps and it doesn't seem like it will rotate unless I actually turn it myself.

    Thanks for the help.

    Sean
     
  8. Jon A

    Jon A Well-Known Member

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    Yeah, no locking ring but I've never found the need for one. I like them without.

    Anyway, the quick setup I use--set the sidefocus to infinity, put it on 18X pointing at the sky (or white wall or something letting your eye focus like it's the sky) focus the crosshair with the ocular focus ring using quick glances trying to get it in the middle of the range where it's sharp.

    Then you're done with that unless your eyesight changes (happens more often than some think) or you want to do some fine tuning. Now the target at various ranges should come into focus the same time parallax is eliminated for that distance. Always check by wiggling your eye though, that scope as a very large depth of field so it's really easy to bring things into focus (not nearly as "touchy" as some other scopes).

    Also note it's not going to do much on the lower powers, so if you're turning it around on 3X and it's not doing anything...that's OK. ;)
     
  9. Sean K.

    Sean K. Active Member

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    Oh, okay....I understand now. I am running it down too low. I'll turn it up to 18X and adjust the ocular from there. I didn't realize that the side focus wouldn't do much at lower power.

    Thanks for the help Jon! :)

    Sean