A 4″ f/15 refractor telescope, while offering high-quality views, may have several drawbacks that make it unsuitable for many users. First, its long focal length makes the telescope physically long and cumbersome, potentially difficult to transport and set up. This can be a significant consideration for those who prefer portability or for observers with limited space.
Second, the narrow field of view, inherent in a telescope with such a high focal ratio, makes it less ideal for observing large celestial objects or wide star fields. This limits its versatility, particularly for those interested in rich field or deep sky observing.
Third, the high focal ratio results in longer exposure times for astrophotography, making it less suitable for casual astrophotographers who may prefer faster setups with more forgiving exposure requirements.
Additionally, high-quality lenses for long refractors can be expensive, and as the aperture size increases, so does the cost, potentially making it less budget-friendly compared to other types of telescopes with similar aperture sizes.
Finally, the narrow field of view and long tube design can make it less adaptable to certain types of mounts, and it may require a sturdier, more expensive mount to ensure stability. These factors combined may lead many to opt for more compact and versatile options that suit a wider range of astronomical tasks.