Sizing & Fit Guide – How to Measure for a Slip-On Solar Filter

To choose the correct slip-on solar filter, you must measure the outer diameter (OD) of the front of your optic – not just the clear glass size and not the filter thread size marked on camera lenses. The solar filter slips over the sky end of your optical tube for a depth of about 1" (25 mm), so you need to make sure your measurement covers anything that flares or gets larger within that first inch.

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1. How to Measure Your Optic (Any Device)

If you prefer, you can still use your existing measurement diagram image above or below these instructions.

Step-by-step:

1. Identify the front (sky) end of your optic:
   • Telescope or spotting scope: objective end / dew shield
   • Camera: front of the lens barrel
   • Binoculars: front objective housings
2. Remove any lens hood, cap, or cover. Slip-on filters must attach directly to the rigid barrel or objective housing, not to a hood.
3. Check the first 1" (25 mm) of the tube. The filter cell typically slips over about 1" of depth, so look for:
   • Any flare, ridge, or decorative ring that sticks out
   • Rubber armor or trim that is thicker than the very front edge
   • Any place within that first inch that is wider than the front lip
   Your measurement must cover the widest point that the filter will need to slide over in that first inch.
4. Measure the outer diameter (OD) across that widest point using:
   • Calipers (best), or
   • A ruler or tape measure (if used carefully).
5. Measure in millimeters if possible. If you measure in inches, multiply by 25.4 to convert to mm (for example, 4" ≈ 102 mm).
6. Write down your OD measurement. You will choose a slip-on solar filter size whose inside diameter (ID) range is just larger than your OD.

Important: Do not use the filter thread size (the Ø symbol on camera lenses) as your only reference. The slip-on filter grips the outer barrel, which is usually larger than the thread size.

Example: If your optical tube measures 4" (102 mm) across the outer casing at the front, and the size chart shows a filter with an inside diameter range starting at about 4.25" (114 mm), you would choose the 4.25" (114 mm) filter because it is the size just larger than your measurement.

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2. Device-Specific Sizing Help

For more detailed sizing examples and recommendations by device, see:

• Camera Solar Filters – measuring camera lenses and choosing between Helios glass and Hyperion film.
• Telescope Solar Filters – measuring tubes/dew shields and selecting the right slip-on size.
• Spotting Scope Solar Filters – using sunshades and objective housings for measurements.
• Binocular Solar Filters – measuring objective housings and choosing binocular kits (pairs).

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3. Single Filters vs Binocular Kits

• Single slip-on filters are for:
  • Telescopes
  • Spotting scopes
  • Cameras (single lens)
• Binocular filter kits include a pair of filters sized for both objectives:
  • Use only matched pairs on binoculars.
  • Never filter just one side of the binoculars.

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4. Film vs Glass – What to Expect Visually

Our slip-on solar filters are white-light ND5 filters designed for safe solar viewing and imaging when installed correctly. The visual appearance differs by material and coating:

• Helios glass (titanium-coated) – produces a yellow/orange solar image with stable, high contrast.
• Helios glass (chromium-coated) – produces a slightly different yellow/orange tone with similar contrast and sharpness.
• Hyperion thin-film – produces a darker, rich orange solar image, with lightweight construction ideal for travel and handheld use.

Glass generally provides the most stable, repeatable contrast and sharpness over time, while film offers a lighter-weight, economical option. Both must be used only on the front of the optic, securely installed, and inspected before use.

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5. Next Steps – Choose Your Filter

Once you have your OD measurement:

1. Decide whether you prefer glass (stability, durability, yellow/orange view) or film (lighter, darker orange view, budget-friendly).
2. Choose the correct product type:
   • Single slip-on filter for cameras, telescopes, and spotting scopes.
   • Binocular filter kit (pair) for binoculars.
3. Match your OD measurement to the size range listed on the product page. Select the size whose OD/ID range is just larger than your measurement.

If you are between sizes or unsure, contact us with your OD measurement and device details, and we can recommend a size before you order.