How to Select a Scope ~ Light Gathering and Adjustable Objective Issues

Published on October 8, 2022
Duration: 19:11

This video provides expert guidance on selecting rifle scopes, focusing on objective lens size and its relation to light gathering, and the necessity of adjustable objectives (AO) for higher magnifications. The instructor emphasizes that larger objective lenses don't inherently gather more light but facilitate entry, and that the 'light gathering' ratio (magnification x objective diameter) is a key metric. He advises against excessively large objective lenses (over 40mm) due to mounting height and weight issues, recommending that shooters can increase light gathering by simply reducing magnification. The video also details how AO is crucial for correcting parallax and focusing at higher powers (above 9x) for target shooting and varmint hunting, but is often unnecessary and adds weight for general hunting applications.

Quick Summary

For rifle scopes, the 'light gathering' ratio is often calculated by multiplying magnification by the objective lens diameter. A ratio of 5 (e.g., 7x35) is standard. Larger objective lenses facilitate more light entry but can cause mounting issues. Reducing magnification effectively increases light gathering, and Adjustable Objectives (AO) are crucial for scopes above 9x magnification to correct parallax.

Chapters

  1. 00:01Introduction to Objective Lens Size
  2. 00:15Light Gathering Explained
  3. 01:09Standard Light Gathering Ratio (5x)
  4. 02:09Bird Watchers & Light Gathering
  5. 02:25Rifle Scope Standard Ratio
  6. 02:55Adjusting Power for Light
  7. 04:00Navy Marine Binoculars (7x50)
  8. 05:33Objective Size vs. Hunting Scopes
  9. 05:49Impact of Large Objectives on Mounting
  10. 06:04Evolution of Rifle Stocks for Scopes
  11. 07:11Cheek Weld Issues with High Objectives
  12. 08:04Standard Ring Height
  13. 08:26High Rings & Cheek Weld
  14. 08:59Recommended Objective Size Limit (40mm)
  15. 09:32Adjusting Power for Standard Ratio
  16. 10:15Recommendation: Smaller Objective Lenses
  17. 10:56Gaining Light Gathering by Reducing Power
  18. 11:34Power Needed Per 100 Yards
  19. 12:02Debunking High Power Scope Necessity
  20. 12:25Adjustable Objective (AO) Explained
  21. 12:52Parallax Defined
  22. 13:32Fixed Power Scope Parallax Setting
  23. 13:50Parallax Setting at 100 Yards
  24. 14:17Eye Position and Parallax
  25. 14:29When AO is Necessary (Above 9x)
  26. 14:44AO for Target & Environment Shooting
  27. 15:12Adjusting AO for Range and Focus
  28. 16:11AO Not Needed for Hunting Scopes
  29. 16:45AO for 10x or Higher Power Scopes
  30. 17:16Eye Position for Parallax Avoidance
  31. 17:34Parallax Importance for Small Targets
  32. 17:45Summary: Objective Lens & AO
  33. 17:59Small Objective Tube Scopes (20mm)
  34. 18:34Concluding Remarks

Frequently Asked Questions

What is the standard 'light gathering' ratio for rifle scopes?

The standard light gathering ratio for rifle scopes is often considered to be a ratio of 5, calculated by multiplying the magnification by the objective lens diameter. For example, a 7x35 scope would have a ratio of 5. This ratio is considered adequate for most hunting scenarios, especially when the magnification can be adjusted.

Why is a large objective lens size (e.g., 50mm) not always ideal for hunting scopes?

Large objective lenses, typically over 40mm, can significantly increase the scope's height off the rifle, making it difficult to achieve a proper cheek weld without higher scope rings. This can compromise shooting stability and speed. While they facilitate light entry, the benefit is often outweighed by mounting challenges and added weight for typical hunting applications.

When is an Adjustable Objective (AO) necessary on a rifle scope?

An Adjustable Objective (AO) is generally considered necessary for rifle scopes with magnifications of 9x or higher. It allows the shooter to correct for parallax errors and fine-tune focus at specific distances, which is crucial for precision shooting in target or varmint hunting scenarios.

Can I improve light gathering on my scope without a larger objective lens?

Yes, you can effectively increase light gathering by simply reducing the magnification on your scope. Lowering the power increases the light-gathering ratio, making the image brighter and clearer, especially in dim conditions. This is a key advantage of variable power scopes.

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