RX Action Cam Mask sizing guideline chart

Q: What is the difference between nearsighted and farsighted lenses?

Nearsighted (myopia) lenses use negative SPH values to correct distance vision. Farsighted (hyperopia) lenses use positive SPH values to help with close-up vision.

Q: How do I find the sphere (SPH) value on my prescription?

Look for SPH or Sphere. It can also be labelled Power or PWR. A minus sign (-) is nearsighted and a plus sign (+) is farsighted.

Q: How should I adjust my prescription for clear vision underwater?

For most people, choose 0.50 diopters weaker (towards zero) than your normal SPH, then select the closest available 0.50 step. This helps because water creates natural magnification and mask lenses sit further from your eyes than glasses.

Q: I have astigmatism (CYL). What should I choose?

Use your SPH (sphere) for each eye. For CYL (astigmatism), the sign does not matter, use the CYL magnitude. Nearsighted (minus): CYL 0.00 to 0.75 start 0.25 to 0.50 weaker than SPH; CYL 1.00 to 1.75 start at SPH or 0.25 weaker max; CYL 2.00+ start at SPH for comfort. Farsighted (plus) lenses come in whole steps only (+1 to +5). CYL 0.00 to 1.75 round down to the nearest whole number for comfort. CYL 2.00+ round to the nearest whole with a comfort tie break: if SPH ends in .25 or .50 round down, if SPH ends in .75 round up. Special case: if SPH is +0.50 or +0.75 start at +1.00. More help: https://oceansoptics.com/pages/choosing-prescription-snorkel-mask-lenses-with-astigmatism

Q: I can’t find my lens strength in the dropdown. What should I do?

The dropdown shows all available strengths for that mask. If your exact number is not listed, choose the closest available option using the guidance above. Upload your prescription or email info@oceansoptics.com if you want us to confirm the best match.

Q: How do I stop my mask from fogging?

Try the toothpaste trick: rub a small amount of toothpaste on the inside of each lens in circular motions for a few minutes, then rinse thoroughly. Repeat if needed. Before each session, you can also use a tiny amount of baby shampoo or dish soap mixed with water, rub a thin film on the lens, then lightly rinse.

Q: Do you have a guide to help me use my mask properly?

Yes. Mask 101 guide: https://cdn.shopify.com/s/files/1/0798/8055/2781/files/Mask_101.pdf?v=1728895468

How to measure your face for a prescription mask (width & height)

Rx Action (Large)

Size Category: Large — roomy fit for broader/longer faces.

How to measure

1Width: straight line from outer eye corner to outer eye corner (don’t wrap).
2Height: from just under your nose to just above your eyebrow line.

Mask Size Ranges

	Min (in)	Max (in)
Width	4⅛ ″	5¼ ″
Height	3¼ ″	4½ ″

Options: Nearsighted (−1.00 to −9.00) · Farsighted (+1.00 to +5.00) · Skirt: Black · Frame: Black · Integrated action-camera mount.

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Frequently Asked Questions

What is the difference between nearsighted and farsighted lenses?

Nearsighted (Myopia) lenses: Negative SPH values (example: -2.50) to help you see clearly at distance.

Farsighted (Hyperopia) lenses: Positive SPH values (example: +2.50) to help with close-up vision.

How do I find the sphere (SPH) value on my prescription?

Look for the column labelled SPH or Sphere. It can also be labelled Power or PWR. A minus sign (-) is nearsighted. A plus sign (+) is farsighted.

How should I adjust my prescription for clear vision underwater?

Underwater adjustment: For most people, choosing a lens that is 0.50 diopters weaker (towards zero) than your normal SPH gives the best comfort and clarity underwater.

Why: Water creates natural magnification, and mask lenses sit further from your eyes than glasses. Reducing by 0.50 helps keep vision feeling natural and comfortable underwater.

Examples: If your SPH is -2.25, choose -2.00. If your SPH is -2.75, choose -2.50.

Our lenses are available in 0.50 increments, so choose the closest available option.

I have astigmatism (CYL). What should I choose?

Our standard prescription options are based on SPH (sphere). If you have astigmatism (CYL), the sign does not matter. Use the CYL number (for example, treat -2.00 and +2.00 the same).

Nearsighted (Minus -) lenses

CYL 0.00 to 0.75: Start 0.25 to 0.50 weaker than SPH (towards zero), then select the closest available option.
CYL 1.00 to 1.75: Start at SPH or 0.25 weaker max.
CYL 2.00 to 3.00: Start at SPH. (Some people choose slightly stronger for sharpness, but comfort-first starts at SPH.)
CYL 3.25+: Start at SPH. (Comfort-first starts at SPH.)

Farsighted (Plus +) lenses

Our farsighted lenses are available in whole steps only: +1.00, +2.00, +3.00, +4.00, +5.00.

CYL 0.00 to 1.75: Round down to the nearest whole number for comfort (towards zero).
CYL 2.00+: Round to the nearest whole number with a comfort tie break:
- If SPH ends in .25 or .50, round down
- If SPH ends in .75, round up

Special cases (Plus +): If your SPH is +0.50 or +0.75, we recommend starting with +1.00.

If you want the full explanation and examples, see our guide: Choosing prescription snorkel mask lenses with astigmatism .

If you are unsure, upload your prescription and we will quickly check your selection for you.

I can’t find my lens strength in the dropdown. What should I do?

The dropdown shows all strengths available for that specific mask. If your exact number is not listed, choose the closest available option using the guidance above.

If you want us to confirm the best match, upload your prescription on the product page or email us at info@oceansoptics.com.

Can I choose different lens strengths for each eye?

Yes. You can select different strengths for left and right eye. You can mix and match any combination available in the dropdown menu.

How do I upload my prescription during checkout?

On the product page you can optionally upload your prescription so we can check your selection before we build it. You can also leave a note in the cart, or email us at info@oceansoptics.com.

How do I stop my mask from fogging?

A simple method is the toothpaste trick. Rub a small amount of toothpaste on the inside of each lens using circular motions for a few minutes, then rinse thoroughly. Do this before your first use (and repeat if needed).

Before each session, you can also use a tiny amount of baby shampoo or dish soap mixed with water. Rub a thin film on the inside of the lens, then lightly rinse so a fine layer remains.

Do you have a guide to help me use my mask properly?

Yes. Here is our Mask 101 guide: Open Mask 101 (PDF).

What happens if I accidentally choose the wrong lens strength?

Message us as soon as possible. If the order has not entered the build or shipping stage yet, we can usually update the lens selection.

Are your lenses safe for both snorkeling and scuba diving?

Yes. Our lenses are HD tempered glass and are suitable for snorkeling and scuba diving up to 100 ft (30 m).

How long does delivery take, and can I track my order?

Most orders arrive in 5 to 10 days, but we recommend allowing up to 14 days to be safe. You will receive a tracking number by email once your order ships.

What is your return or exchange policy for prescription masks?

Your satisfaction, guaranteed.
You have 30 days from delivery to request a return, as long as the item is unworn, unused, with tags, and in original packaging. For full details, visit our Return Policy.

Country/region

RX Action Cam Mask sizing guideline chart

How to measure

All our masks

Frequently Asked Questions