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There is something that makes me think practicality.
We can all agree that a long focal length scope is better suited for planetary use than its short length brother which would be best suited for dso viewing or guiding/photo.
We can take those two (refractors) as an example: 90/900 and his brother, a 90/500 (and we will be using Plossl EPs)
Exit pupil is an important factor in viewing comfort.
Exit pupils are dependent on the scope's focal length, the EP's fl and the main lens diameter.
For example, to acheive 100x in the 90/500 we will need a 5mm eyepiece and to acheive the same mag in the 90/900 we will need a 9mm eyepiece.
The exit pupils of both scopes in those configurations will be 90/100=0.9mm
The theoretical magnification limit for both scopes lies at about 180x.
It is true that to reach this 180x you will need a 5mm EP in the 90/900 and a "2.8"mm EP in the 90/500 and those will probably make for an eyelash brushing eye relief... But looking at exit pupils up to 100x, those scopes do not seem to complement one another, but rather replace each other.
So, ignoring abberations, and not taking into account eye relief so much, wouldn't the faster scope be almost as practical and easy on the eyes for high-ish magnifications as the slower, heavier, harder to mount in the wind scope?
just my evening neurons buzzing...
lets imagine I wasn't to see a nice DSO about 15' size and I think it should look good nicely framed with a 1 deg field of view in the EP..
Which would give the better (or higher probability of seeing anything at all ) view from a semi urban light polluted home site (e.g Bortle 6)?
a) an 100mm f/6 refractor (fl 600mm) and a 10mm EP (60 deg afov, gain 60x = fov pf 1 deg)
(and exit pupil of 100mm / 60 = 1.6mm)
b) a 200mm SCT with focal reducer to give f/6 (fl 1200mm) and a 20mm EP (60 deg afov, gain 60x = fov of 1 deg)
(and exit pupil of 200 / 60 = 3.3mm)
My gut feeling is that the SCT should give a better view just based upon its 2xaperture - but Im not sure I understand fully the maths why.
Is the larger exit pupil going to result in a better / brighter / more successful view?
Or will the view be 'roughly' the same ?
Or have I got it all wrong.....
By Shooting star
Hello. True beginner given an Orion Skyquest XT8 (1200mm focal length; f5.9). I have had to collimate (all sorts of fun that was) as the scope had been moved quite a bit over time. Believe I have it very near perfect but will star test.
Scope came with an Orion 25mm Plossl eyepiece so I am exploring what range of additional eyepieces I would like. From what I’ve read this scope is capable of a theoretical 400x magnification. Again in theory that would take me to 3mm as limit of eyepiece.
But then I read about exit pupil limitations and scratching my newbie head. The majority of what I see suggests .7mm exit pupil minimum...? But it appears I would need to buy a much larger eyepiece focal length to avoid too small exit pupil.
I wear eye glasses so would be buying longer eye relief pieces in case that is relevant.
Advice truly welcome.
Had alot of fun observing galaxies last night, despite poor transparency.
Picking up dozens of galaxies in Virgo, Leo triplets, and M51, M63, M94.
I did however fail to detect the Galaxy cluster in Leos mane. (ngc 3185, 3189, 3193 etc)
I`ve observed them before (3 of them), but I cant remember the eyepiece focal length used.
Can you recommend the best optimal Power / exit pupil for these faint Objects?
I use 8"dob F6.
I am thinking about getting a panoptic 41mm for my VX 16 F4 dob (which has an FL of 1600/1840 with paracorr). I worked out though, that the Exit Pupil would be 10.25mm, or 9mm with the paracorr. That's pretty huge, and definitely bigger than anyone's maximum pupil dilation. It would give me the widest true field possible in my scope though (AFAIK). Are there any diasdvantages to having an Exit Pupil this big? Does it rob the view in any way?
If anyone has experience of using a similar combo, that would be great info. Cheers!