Coronado PST Field of View Very Small

[bendiddley]

I have a PST which has a very small field of view. When I look through a 25mm EP there is little space around the sun and very difficult to centre as a result, is this normal? I've measured the hole at the bottom of the eyepiece holder and it measures 5mm. I've just read somewhere that you can get a 10mm version, so I am assuming the 5mm is the issue? If this is normal, what are the advantages of the 5mm over the 10mm? Is there a benefit to a smaller field of view? Not sure I can see any advantages at the moment as it seems to make it harder to view the sun.

[vlaiv]

Point of solar scope is to observe the sun, and not much else can be seen around it. For this reason, and the fact that blocking filters are expensive to make - they are made in the least needed size, which depends on focal length of optics.

Larger the focal length - you need larger blocking filter (above imaged hole - or rather "colorful" glass inside hole) to fit the whole Sun disc onto it.

PST is 400mm focal length scope, and with such focal length half a degree (Sun's angular size is about 30', or half a degree - same as the Moon) gives projected image of about 3.5mm. This means that 5mm is quite large enough to fit the whole sun disc into view and have some room to spare for proms and for manual tracking.

Getting 10mm blocking filter for PST is simply waste of money. People do get 10mm blocking filter when they do for example thing called PST Mod, which includes disassembly of PST scope and use of some of its parts on scope with larger aperture and focal length. In that case, 5mm blocking filter is probably not going to be big enough to provide full solar disk viewing and getting diagonal with 10mm blocking filter is justified.

[bendiddley]

Ok many thanks, that's good to know!