Quote:
Originally Posted by Brian W
Hi Trevor, you summed up my dilemma quite nicely. Unless I go the replica route it is not going to be right in whichever way I choose to ignore. I can get the reflectivity close by downsizing the mirror but the fast versus slow is a serious problem. It has been suggested that if I went with an ep with a very narrow fov it would bring the balance in a bit.
Perhaps if I tried this from a different direction? J.H. describes the Triffid Nebula as having a line of 3 faint stars in its core. Stellarium software does show the 3 stars but my 8" reflector doesn't. (on a good night it does show 6 in the trapezium)
In your opinion what would be the minimum size reflector that would allow me to see the 3 
Brian |
Brian, not sure that this problem can be approached from this sort of comparison with a smaller faster mirror.
Just ran the spec's of Hershel's scope through a scope performance spreadsheet that I put together a long time ago.
His 18" would have had a limiting mag of about 15.8 with a theoretical resolution of 0.3 arc sec's. Now, I am very confident that from Slough in England this theoretical limit of resolution would never have been achieved.
I think that your best bet maybe to look for a scope with similar limiting mag. 14" aperture will give a theoretical limiting mag of 15.3 while 16" will be 15.5
Next problem is that, due to his long FL and his skill at making eyepieces he was able to use his scope at very high magnification and according to his observing notes, recorded by Williams sister Caroline, was able to use magnifications of over 1000 x.
Your problem is therefore coming up with a scope of similar limiting magnitude and capable of very high magnification. Obviously fast focal ratio and high magnification are not commodities that go together.
Sorry about this, I feel like I haven't helped one bit.
Regards
Trevor