Reducers/Flatteners

Improve your astrophotos with Reducers & Flatteners

Whether you are beginning night photography or already working on serious deep-sky projects, a reducer and a field flattener are among your most important tools. These lenses correct the focal length and curvature of your field of view, keeping stars pointed all the way to the edge of your image and shortening your exposure times.

• Reducers: reduce the focal length by factors of, say, 0.8× or 0.5×. This means a wider image and shorter exposure times - ideal for capturing faint nebulae faster.

• Field Flatteners: remove the bulge that distorts stars toward the edges. This gives you a consistently sharp image across your entire sensor, without having to crop or apply software corrections later.

Our reducers & flatteners are compatible with most common refractors and astro cameras. Each model is precisely aligned and tested to minimize star distortion and vignetting.

20 Frequently Asked Questions about Reducers & Flatteners

1. What is the difference between a reducer and a flattener?
   A reducer shortens your focal length and enlarges the field of view; a flattener only corrects the curvature of that field.

2. How do I choose the right factor (0.8×, 0.6×)?
   Apply a 0.8× for slightly shortened focal lengths, 0.5× for maximum image field extension.

3. Does a reducer add additional aberrations?
   Well-designed reducers reduce aberrations; however, cheap models may introduce more coma or chromatic lines.

4. How much backfocus do I need?
   Consult manufacturer: usually between 55 and 85 mm for optimal image performance.

5. Can I use a reducer and a flattener at the same time?
   Some combo models combine both functions; otherwise, you follow the reducer first, then the flattener, with the appropriate intermediate rings.

6. Does a flattener cause light loss?
   It barely dampens; the coatings provide >98% transmission per surface area.

7. How does a reducer affect my exposure time?
   A 0.8× reducer increases speed by about 1 stop; a 0.5× by more than 2 stops.

8. Do I need to re-collimate the optical axis after mounting?
   Yes, always check collimation and focus after installing a reducer or flattener.

9. What order of accessories is ideal?
   OTA → reducer → flattener → filter wheel → camera.

10. Is every flattener suitable for all refractors?
    No, design is brand specific; pay attention to focal length and sensor size.

11. How do I test vignetting after installation?
    Make flat-frames: an evenly lit surface; dark corners indicate vignetting.

12. Does the field not seem quite level yet?
    Check the backfocus and whether you are using exact model-sensor combination.

13. Can I combine intermediate rings with reducers?
    Yes, if you need extra backfocus, use high-quality aluminum or T-2 rings.

14. Are IP-coated lenses necessary?
    Multi-coatings (FMC) usually suffice; IP coatings add additional scratch protection.

15. How do I avoid reflections between reducer and flattener?
    Use angled joints and matte black interior walls or stockings against internal reflections.

16. What is the effect of focal length reduction on magnification?
    Your magnification decreases proportionally with the factor (0.8× reducer gives 20% less magnification).

17. How much does a typical reducer/flattener weigh?
    Ranging between 200-450 g, depending on diameter (1.25″ or 2″ version).

18. How do I clean a flattener?
    Start with blower, work on stains with a lint-free cloth and mild optical cleaner.

19. Can I use a reducer for visual observation?
    Yes, you will get a wider image with slightly less magnification.

20. What is a “coma corrector” versus a flattener?
    A coma corrector limits coma formation, a flattener limits field curvature; some models combine both.