Guide to Scopes By Tom Eby March 22, 2004 This guide was originally an interactive presentation given at the January 22, 2004 meeting of the Twin City Rod & Gun Club. The author claims no special expertise and the opinions expressed are based on his own research and experience. The Intent of the presentation was to provide an aid to the selection and use of telescopic sights. “Ha! Another great shot Magoo! Wall-hanger for sure! No need for a fancy scope on this old smokepole!” Or for many of us older-type Sharpshooters… THEN And……… …..NOW! Basic Parts of The Rifle Scope (American Style) Forms Image Windage Inverts Image, X-Hair Elevation Magnifies Magnifies Knobs • W & E knobs move Image up/down, left/right on X-hair • Reticle is in 2nd Image Plane, Reticle does NOT move • Image only is Inverted & Magnified Basic Parts of the Rifle Scope (European Style) • Reticle is in 1st Image Plane, W & E knobs move the Reticle. • Image AND Reticle are Inverted & Magnified Simultaneously by Lenses Magnifying the X-Hair? – American vs. European Optics American European Reticle in: 2nd Image Plane 1st Image Plane Mag. Setting Optics - European “EXIT PUPIL” What is It? Diameter of the Light Shaft Exiting the Eye Lens (Ocular) How to Calculate? Objective Diameter / Magnification Example: for 3x9 40mm Scope: At 3x : 40/3 = 13.3mm exit pupil At 9x: 40/9 = 4.4mm exit pupil Hold scope at arm’s length, point to light, image you see is the Exit Pupil SIZE OF MAX. IRIS OPENING vs. AGE AGE MAXIMUM IRIS OPENING <25 7.0 mm 30 6.5 35 6.0 45 5.5 60 5.0 80 4.5 Bottom Line: Gets harder to see in twilight as you get old. EXIT PUPIL vs. IRIS OPENING Variable Scope with 50mm Objective 7mm exit pupil Matches 7mm Iris of 25 year old eye -- 7x setting 7mm exit pupil Larger than 5mm Iris of 60 year old eye at 7x setting - Wasted Light! --Set scope to 10x, image is as bright as at 7x. “PARALLAX” What Is It? Target Image Plane Is Not Coincident With Crosshair Plane Most Rifle scopes set for Zero Parallax at ~100 or 150 yards. Corrected by Adjustable Objective (AO) PARALLAX • Important Over 10-12x Magnification • Causes Error in Bullet Point-Of-Impact, Up to ½” at 100 Yards • Check for Parallax by Moving Your Head around while Looking thru the Scope aimed at a Target – But Focus Reticle First! • If the Crosshair Appears to Move in Relation to the Target, Parallax Exists Basic Parts of A Telescopic Rifle Sight PARALLAX How To Correct ?? Sighting – In 25 yards 100 yards Scope Actually Points Down! Minute of Angle 1” at 100 yards Rifle Scope Optic Reticle Adjustment (1st Image Plane) FEATURES TO LOOK FOR: Most American Scopes: 3.0 – 4.0 inches European Scopes: 2.5 – 3.5 inches ……………Rubber Eyepiece Rims Help Prevent Scope Cuts! Optical Coatings On The Lenses Coatings on Scope Lenses BEST: FULLY MULTI-COATED GOOD: MULTI-COATED OK: FULLY COATED Ugh… COATED As a Rule….More Coatings, The Better! Loss of Light is Due to REFRACTION Formula: ((1-ρ)/(1+ρ))2 = Reflection Loss ρ = index of glass (1.5) /index of air (1.0) Wow! Coatings Reduce Loss of Light Much Better! Reticle Types Leupold alone offers 17 Styles! Take ur pick Illuminated Mil-Dot Reticle Not “Military Dot”! Mil = Milliradians = 3.6” at 100 yards = 1 yard at 1000 yards, etc. Range Estimation with Mil-Dot Reticle Formula: (Height of Target in Yards) x 1000 ------------------------------------- = RANGE # of Mils Subtended Example: Deer = 1.25 yards high (45”), 3 Mils 1.25 x 1000 ------------- = 415 yards 3 mils So: 1 yard x 1000 ---------------- = 500 yards 2 mils Bambi is 36” Tall at Back - Subtends 2 Mils - Range = 500 yards Use Mil-Dot Master to Calculate the Range & Holdover for your Rifle & Load Or…. 18 Inches -- Set Magnification to Bracket Deer & Read the Range off the Scope (Or… just cheat and use a Laser Rangefinder) Posi-Lock Springs 1 Spring Ring Inserts 2 Springs Posi-Lock • Nitrogen Purged - Prevent Fogging • Good Eye Relief • Adjustable Objective for Parallax if > 10-12x • Fully Multi-Coated Lenses • Strong Mechanical Construction - Costs $$$ • Reproducible Reticle Settings - ¼ or ½ MOA • Adjustable Focus Eyepiece • Optics sharp to edge of Field Temperature Compensated Basic Setup and Mounting • Clean Rings, Bases of any oils • Square up Rings to be Parallel - Avoid Stress on Tube - Use Dowel or Leupold wrench • Loosely Mount Scope in Rings • Adjust for Eye Relief • Keep X-Hairs Orthogonal • Snug up Rings - alternate tightening • Check scope alignment as you tighten • Mechanically Center Up the X-Hairs • Adjust Eyepiece focus for your Eye - Reticle Must be Sharp! • Bore-sight (Fred will Help) or…. Target at 100 Yards Bolt-Action Rifle Flip-Up Caps Anti-Reflection Caps Adjustable Objective …..RESULTS Namibia, Africa 550 meters 7mm/08 Mil-Dot Master ↑ Bullet ↑ Drop ↑ Read off Mils Why a Scope? • Magnify Small Targets • Take Advantage of Rifles Accuracy • Extend Low Light Visibility • Range Finding w/appropriate Reticle • Ready Spotting Scope • Convenient Carrying Handle COST COMPARE Schmidt&Bender Zeiss (German) Kahles Swarovski $900 - $1800 Leupold Nikon Burris Weaver Zeiss (Conquest USA) $350 - $1000 Simmons Bushnell, Bausch & Lomb, Bushnell etc. $150 - $300 COST is PROPORTIONAL to QUALITY U.S. OPTICS $3000 + .