If you want flat images, you need a focal reducer/field flattener.
SVBONY 0.8x Focal Reducer
Time machines are not perfect. They are often trying to put a curved field of view onto a flat camera sensor, which means that things at the edges are often distorted. A Field Flattener/Focal Reducer (often just called an FF/FR) will help with that. It works by changing the time machine so that it sees a larger field of view, which means it gathers more light as well. Mine is the SVBONY SV193 0.8x FF/FR (also available at Amazon). It does two things:
- You can take faster pictures (which is always a plus!)
- The stuff at the edges is flatter and less distorted (which is also a plus!)
Since adding and removing the FF/FR means changing the entire imaging train for my imaging telescope, it usually just stays on all the time. Yes, it means my 714mm focal length is effectively reduced to 572, but it also means my f/7 aperture is effectively reduced to f/5.6. So despite not having the same field of view (and hence, the same magnification), it works "faster," which means I can take faster images and lose less detail from wobbles in the mount or fuzzy stars that move slightly when the tracking isn't quite right.
