Tube length is the physical measurement of a refractor telescope’s main barrel, expressed in mm. The correct length depends on your specific storage space, transportation needs, and the level of optical complexity you require for viewing.
Which Tube Length Suits Your Situation?
| If this is you | The Tube Length that suits you | Why |
|---|---|---|
| You need to transport your equipment frequently in a standard vehicle or carry it to a public park. | 300mm to 500mm | Shorter tubes are easier to manage in small trunks and reduce the risk of the telescope becoming unwieldy during transit. |
| You have limited indoor storage space and need to keep the telescope inside your home. | 400mm to 600mm | Mid-sized lengths provide a balance between optical performance and a footprint that fits on a standard shelf or in a closet. |
| You primarily observe from a fixed backyard and have a dedicated shed or garage for storage. | 700mm to 1000mm | Longer tubes allow for larger apertures and more complex optical designs that are difficult to package into compact frames. |
| You are an advanced user seeking high-contrast planetary imaging and have significant storage space. | 1000mm and above | Extreme lengths are often necessary to house large-aperture lenses or complex apochromatic systems that require significant physical space. |
Where these choices show up in our reviews
3 reviewed options, $109.99 to $179.99, with the full write-up behind each name.
70mm Aperture 700mm Focal Length Refractor Telescope
$179.99 price checked August 2026
Read our full 70mm Refractor Telescope review
If you are looking for a compact option, see our comparison of the best 70mm refractor telescope.
ESSLNB Telescope 700X70mm with K4/10/20 Eyepieces
$129.99 price checked August 2026
Read our full ESSLNB Telescope review
For those who need to travel light, view the best portable refractor telescope options.
80mm Aperture 600mm Refractor Telescope
$109.99 price checked August 2026
Read our full 80mm Refractor Telescope review
Understanding the distance light travels is vital, so learn how to select your refractor focal length.
How Do I Measure and Verify My Required Tube Length?
To establish your required tube length, you must measure your available clearance and identify the specific dimensions of the telescope’s barrel.
Where the number is located
Manufacturers usually list the tube length in the technical specifications as “Tube Length” or “Optical Tube Length” (OTL) in mm. This number refers only to the barrel itself, not the length of the tripod or the accessories attached to the front or back.
How to check your storage space
Measure the height of your storage area or the depth of your transport vehicle’s cargo space. Subtract at least 100mm from your total available space to account for the focuser, the eyepiece holder, and the fact that the telescope might need to sit at a slight angle rather than perfectly flat.
What Happens if the Tube Length is Too Short or Too Long?
Choosing a tube length that is too short or too long creates specific physical and optical limitations that affect the user experience.
The limitations of a short tube length
A tube length that is too short for your goals often limits the aperture size you can realistically use. Because larger lenses require more physical space to house the glass and the support structures, a very short tube often restricts you to smaller, lower-magnification optics.
Portability depends on mass, so explore how to choose the right refractor telescope weight.
The practical issues of a long tube length
A tube length that is too long creates logistical difficulties during transport and storage. Longer telescopes are more prone to “mount flexure” if the tripod is not perfectly balanced, and they can be difficult to maneuver through doorways or into smaller vehicles without hitting the sides.
What Do I Do If I Fall Between Two Tube Lengths?
If your requirements fall between two standard tube lengths, you should choose the shorter length unless you specifically require a larger aperture.
Why the shorter length is usually the safer choice
In most cases, a shorter tube length is easier to manage in daily life. If you do not strictly need the extra aperture provided by a longer tube, the shorter option provides a more portable and versatile experience without sacrificing the primary quality of the glass.
Checking for size-related returns
Because tube length is a physical dimension, it is important to check the return policy of the seller before ordering. Some retailers may charge significant shipping fees to return large, heavy items, so ensuring the mm measurement fits your space is a critical final step before purchase.