It can sometimes be useful to extend the focal length in astrophotography. If you want to do this then this Svbony set can be useful. There are 4 different lengths of extension tubes 5mm, 10mm, 15mm and 20mm and they have male and female threads so they are versatile and can be combined to give different spacing lengths. They are made of metal and are therefore durable and will last a long time. They are useful to allow the photographer to get the right image scale or to get the spacing needed for reducers or field flatters. They are very quick to use.
Svbony M42x0.75 Extension Tube Adapter
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