Tube Length for Reflector Telescopes: How to Choose Yours

How Do You Measure or Establish Your Required Tube Length?

To establish your required tube length, you must measure the physical clearance of your intended storage and transport area. You should measure the length of the telescope tube from the front of the primary mirror housing to the rear of the focuser or finderscope mount.

Measuring Storage Space

Measure the longest straight line available in your storage area, such as a shed, garage, or closet. Ensure you account for the extra space needed to maneuver the telescope into position, as a tube that fits perfectly into a corner might be impossible to rotate or move out of that corner.

Measuring Vehicle Space

If you plan to transport the reflector telescope, measure the interior length of your vehicle’s trunk or cargo area. A reflector telescope is a rigid structure; it cannot be folded. You must ensure the tube length, plus the length of the tripod legs when extended, fits within your vehicle’s dimensions.

Finding the Length on a Specification Sheet

The tube length is usually listed in the technical specifications as “Tube Length” or “Optical Tube Length” (OTL) in mm. Check the manufacturer’s data for the specific number to ensure it matches your measured clearances before ordering.

What Happens if the Tube Length is Too Long or Too Short?

Choosing a tube length that is too long or too short results in practical difficulties rather than a loss of image quality. The length of the tube is a physical constraint, not a performance metric.

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Risks of a Tube Length That Is Too Long

If the tube length exceeds your storage or transport capacity, the telescope becomes difficult to use. You may find that the telescope cannot fit into your car, preventing you from taking it to viewing sites. In a storage environment, a tube that is too long may prevent you from opening doors or accessing other items in your shed.

Risks of a Tube Length That Is Too Short

While a shorter tube is easier to handle, it is often a result of a design meant for portability. If you choose a very short tube to save space, you may find that the telescope is designed for lower-magnification use. A very short tube often indicates a wide-field design, which is excellent for large nebulae but may lack the focal length needed for high-detail planetary views.

What Should You Do if You Fall Between Two Tube Lengths?

If your measurements show that you are on the borderline between two different tube lengths, you should prioritize your most frequent use case. If you plan to move the telescope 90% of the time, choose the shorter length. If the telescope will stay in one place most of the time, choose the longer length.

Prioritising Portability

When caught between two sizes, selecting the shorter tube length is the safer choice for a beginner. It is easier to manage a smaller telescope and move it into position than it is to struggle with a larger, heavier tube that barely fits into your vehicle or storage area.

Prioritising Performance

If the telescope will be stationary, choose the longer tube length. A longer tube often accommodates larger primary mirrors or longer focal lengths, providing more versatility for different types of astronomical targets over the long term.

Checking Return Policies

Because tube length is a physical dimension, ensure you check the return policy of the seller before ordering. If a telescope arrives and is physically too long to fit into your vehicle or storage space, you need to know if the seller accepts returns for sizing issues.

Reviewed by the RecommendedOptics editorial team. RecommendedOptics writes these guides from the 68 most-reviewed reflector telescope listings in our retail dataset, not from manufacturer copy.