Ask an old bird who has experience in observing or using various astronomical telescopes to ask a question?

Generally, the focal length difference of 80-90 caliber APO refractor is about 700-900, and the focal length of 5-inch Zeca is about 1200- 1500.

Visually, Zeca is better. After all, the aperture of 127 is much stronger than that of 8090, and the focal length above 1200 can also be enlarged with an eyepiece with a longer focal length. For example, a 15mm ultra-wide-angle eyepiece can reach 100 times, and it is very cool to look at the starry sky with a 15mm ultra-wide-angle eyepiece.

Compared with 900 focal length refractor, it needs 9mm eyepiece to reach 100 times, and the observation angle is much smaller, and the brightness will be reduced, not to mention adding 2X3X Barrow lens, which is far from the effect. Photography is another matter, you know, APO is completely refracted.

Besides, APO has no visual value. I have an APO with a caliber of 120, with a value of 15000+, which is specially used for photography. Visually, it is similar to the 90-caliber APO that I bought at a price of 1000 (in terms of color difference). Of course, the brightness and clarity are definitely not as good as the large-caliber APO)