You’re asking about stacking focal reducers, not Barlow lenses. In principle, adding reducers can further shorten the effective focal length, but in practice it usually causes problems.

A focal reducer shifts the focus point inward. Adding a second reducer moves it even farther, so you may not be able to reach focus with your camera at all unless the telescope is modified.

Also, every telescope has a maximum usable field of view. Past a certain point, extra reduction won’t reveal more sky — it may just make the image circle smaller, causing strong vignetting or black borders rather than a genuinely wider useful image.

So while the reduction factors may seem multiplicative on paper, stacking two 0.63× reducers is generally not a practical way to capture much larger targets on this setup. For very large objects like Andromeda, a shorter focal length telescope or a camera lens is usually the more effective solution.