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 +