Barlow & reversing lenses

Barlow & Inverted Lens

Barlow and reversing lenses are indispensable tools for any serious observer. A Barlow lens increases the magnification of all your eyepieces without purchasing an additional lens, while a reversal lens (erector) offers refractor users a comfortable, upright view for terrestrial and astronomical applications. These lenses take both your visual and photographic performance to the next level.

1. What does a Barlow lens do?

• Doubling (2×) and tripling (3×): each eyepiece automatically gains two or three times its original focal length, ideal for planetary detail.

• Image quality: high-quality achromats with additional glass layers minimize color and coma aberrations.

• Ease of use: easily slide in or out of focuser, fits directly between eyepiece and diagonal.

2. When do you choose 2× or 3× Barlow?

• 2× Barlow: the most versatile choice; combines image sharpness while maintaining clarity.

• 3× Barlow: for really high magnifications on stable nights; suitable for lunar and planetary observations, seeing permitting.

• Compatibility: Check that your focuser has enough backfocus to accommodate the extra length.

3. The reversal lens (erector) explained

• Upright image: essential for terrestrial use, photography of bird and landscape observations.

• Mechanism: A compact lens system that corrects the image, often integrated into refractor accessories.

• Advantage in EAA: Combine with a camera for live images captured upright, without reverse orientation.

4. Build quality and coatings

• Glass: Choose ED or FPL glass in your Barlow for minimal chromaticity and depth of field.

• Coatings: multi-coatings >98% transmission, protective fluoride coatings for scratch resistance.

• Mechanics: CNC-machined aluminum housing with Delrin collar for smooth and secure mounting.

5. Backfocus & installation

1. Backfocus check: Beforehand, measure your total chain length (including Barlow + eyepiece + diagonal) on a flat surface.

2. Focuser Adjustment: adjust tension or clamps to compensate for extra weight.

3. Photography: Test your frames for sharpness and stellar detail; small adjustments in the clamp mount can make a world of difference.

6. Use tips for optimal results

• Start with standard eyepiece + 2× Barlow: learn about typical magnifications.

• Pair with a star diagonal: Maintain a straight line of light and avoid reflection.

• Avoid stacking multiple Barlows: leads to more aberrations and light loss.

• Use a fine fokuser or motor focuser at high magnifications to avoid backlash.

20 Frequently Asked Questions about Barlow & Inverted Lens

1. What is the difference between a 2× and a 3× Barlow lens?
   A 2× Barlow doubles the magnification, a 3× triples it; choice depends on desired magnification and seeing conditions.

2. Can I combine a Barlow lens with a zoom eyepiece?
   Yes, mount the Barlow before the zoom; test if you can still control the full focal length.

3. Does a Barlow always lead to more chromatic aberration?
   In inexpensive models yes; high-quality ED-Barlows have extra layers of glass to minimize that.

4. How much backfocus do I need for a 2× Barlow?
   Count on at least the length of the Barlow itself (30-50 mm) plus your eyepiece and diagonal distance.

5. What exactly is a reversing lens?
   An Erector lens module that corrects an inverted image to upright, often used in terrestrial refractors.

6. Are universal Barlow lenses available?
   Yes, most fit in 1¼″ and 2″ focusers with supplied reduction rings.

7. Can I use a Barlow in astrophotography?
   Absolutely, but expect a light loss of 0.5-1 stop; compensate with longer exposure times.

8. How does a Delrin collar prevent scratching?
   The soft plastic inner rim protects the anodization of your focuser and lens housing.

9. Can I stack two Barlows for higher magnification?
   It can be done, but leads to greatly increased aberrations and light loss; better is one 3× Barlow.

10. How do I clean my Barlow lens?
    Start with blower, then use microfiber cloth and optical cleaner; avoid spraying directly on the glass.

11. Is a 3× Barlow suitable for planetary?
    Only in stable seeing; in poor seeing, your image will become unsettled and out of focus.

12. How do I mount an inverted lens in my refractor?
    Replace or slide out the diagonal and insert the reversing lens into the focuser; lock gently.

13. Does a Barlow increase field curvature?
    A good Barlow adds minimal curvature; combine with a field flattener for photography.

14. How do I know if my focuser can handle the extra load?
    Test with your heaviest eyepiece + Barlow in vertical position; no noticeable deflection means enough bearing capacity.

15. Do I use Barlow before or after filters?
    Mount the Barlow in front of the filter wheel so that the filters always see the same field of view.

16. Can I use my smartphone on a Barlow?
    With smartphone adapter and short intermediate rings, it can be done for simple digiscoping.

17. Does an inverted lens reduce sharpness?
    A quality rector retains sharpness; cheap prismatic inverters may give some loss of detail.

18. How do I choose between 1¼″ and 2″ Barlow?
    For widescreen and photography, 2″ is preferred; 1¼″ is sufficient for purely visual use.

19. How do I avoid backlash at high magnification?
    Use a dual-speed focuser, clamp your Barlow firmly and avoid rail clearance.

20. Why do I sometimes see vignetting with a Barlow?
    The extra lens extends the light path; make sure you have enough opening in your focuser or use a lower magnification range.