Telescope Magnification Calculator
Magnification is simply the telescope’s focal length divided by the eyepiece focal length. Enter both — and a Barlow if you use one — to see the power any eyepiece gives you.
Telescope Magnification Calculator
Why use the Telescope Magnification Calculator
Buying random eyepieces without knowing the power they give wastes money. This shows the magnification for any pairing instantly.
How to get your numbers
- Telescope focal length (on the tube or in the manual).
- Eyepiece focal length, printed on it in mm.
- Barlow multiplier, if you use one.
Recommended for this job
How to use it
- Enter the telescope’s focal length (on the tube or in the manual).
- Enter the eyepiece focal length, printed on the eyepiece in mm.
- Add a Barlow if you use one — it multiplies magnification.
Frequently asked questions
How do I calculate telescope magnification?
Divide the telescope’s focal length by the eyepiece focal length. A 1,200 mm scope with a 25 mm eyepiece gives 48×.
What does a Barlow lens do?
A Barlow multiplies magnification — a 2× Barlow doubles the power of any eyepiece, effectively giving you a second set of eyepieces.
Is more magnification always better?
No. Beyond what your telescope and the night’s conditions allow, the image just gets dim and blurry. Low power gives brighter, sharper views.
What magnification is best for viewing planets?
Moderate-to-high power (often 100–250×) shows the most planetary detail — but only when the atmosphere is steady enough to support it.
Why is my telescope image blurry at high power?
You have likely exceeded the useful magnification for your aperture or the atmospheric “seeing.” Drop to a longer eyepiece for a crisper view.
What eyepiece gives what magnification?
Shorter eyepieces give higher magnification. Divide your telescope’s focal length by the eyepiece’s mm to see the power each one delivers.
Where do I find my telescope’s focal length?
It is printed on the tube or listed in the manual, usually in millimeters (e.g., 1,200 mm), sometimes shown as a focal ratio with the aperture.
