Scope like a Reflector or a Catadioptics has a central obstruction, when we want to calculate the effective aperture (that's the aperture size minus the central obstruction) as compared to a refractor, how should we go able doing it?
An example will be the Celestron Advanced Series C8-S Schmidt Cassegrain scope,
it has a central obstruction of 2.5", 10% by area and 31% by diameter. so how should be calculate the aperture? should it be :
a. 8" - 2.5" = 5.5" aperture as compared to a refractor or
b. 31400mm(sq) - 3066.4mm(sq) = 28333.6mm (sq) as compared to 31400mm (sq) in Area
c. 1256mm - 196.25mm = 1059.75mm as compared to 1256mm in perimeter?
Which should be the more accurate estimation?
calculate the effective aperture of a scope with central Obs
- weixing
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Hi,
This has been discuss before somewhere in the forum.... Anyway, I think the area will be a better estimation, since it determine the light gathering power of a telescope.
By the way, don't worry too much about the central obstruction, as long as you are not making your own telescope. Any decent brand telescope won't give a big central obstruction than necessary.
Anyway, the atmospheric condition will affect your ability to see more than any central obstruction...
Have a nice day.
This has been discuss before somewhere in the forum.... Anyway, I think the area will be a better estimation, since it determine the light gathering power of a telescope.
By the way, don't worry too much about the central obstruction, as long as you are not making your own telescope. Any decent brand telescope won't give a big central obstruction than necessary.
Anyway, the atmospheric condition will affect your ability to see more than any central obstruction...
Have a nice day.
Yang Weixing
"The universe is composed mainly of hydrogen and ignorance."
"The universe is composed mainly of hydrogen and ignorance."
Not Necassary, an 8" SCT with 2.5" has a surface area to capture light similar to a 7.6" Refractor, thus I am quite puzzled which one to use. Diameter values in this case MIGHT not be accurate.
7.6" Refractor will get a surface area of appromixately 28338mm(sq) pretty similar to a 8" with 2.5" Obstruction.
7.6" Refractor will get a surface area of appromixately 28338mm(sq) pretty similar to a 8" with 2.5" Obstruction.
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Hmm.. I dont remember seeing any mathematical/theoretical formula for calculating the effective aperture of an 8" SCT, but I have often read in reviews at cloudynights or astrogeek using the rule of thumb I mentioned.. I am quoting Markus from one of his replies in the Makscopes yahoogroups...
Quote ----
From: "APM_Telescopes" <apm_telescopes@w...>
Date: Sat Jan 17, 2004 5:14 pm
Subject: Re: [MakScopes] Re: TEC140 or MN86 or Nexstar11GPS
ADVERTISEMENT
we com pared last year in September in the Alps Starparty with excaptional seeing 1=/10 at Planets the 715 Standart, 703 Deluxe and TMB 130/6, we found the rules working, aperture minus secondary diamater is apo of same quality. The TMB have had very little edge over the Maks
best wishes
Markus
--- Unquote
cheers
Addy
Quote ----
From: "APM_Telescopes" <apm_telescopes@w...>
Date: Sat Jan 17, 2004 5:14 pm
Subject: Re: [MakScopes] Re: TEC140 or MN86 or Nexstar11GPS
ADVERTISEMENT
we com pared last year in September in the Alps Starparty with excaptional seeing 1=/10 at Planets the 715 Standart, 703 Deluxe and TMB 130/6, we found the rules working, aperture minus secondary diamater is apo of same quality. The TMB have had very little edge over the Maks
best wishes
Markus
--- Unquote
cheers
Addy
- weixing
- Super Moderator
- Posts: 4708
- Joined: Wed Oct 01, 2003 12:22 am
- Favourite scope: Vixen R200SS & Celestron 6" F5 Achro Refractor
- Location: (Tampines) Earth of Solar System in Orion Arm of Milky Way Galaxy in Local Group Galaxies Cluster
Hi,
Check out the below website for effects of the central obstruction. I found that what the website said is quite logical. Take a look if you are interested:
http://perso.club-internet.fr/legault/obstruction.html
Have a nice day and happy Chinese New Year!!
Check out the below website for effects of the central obstruction. I found that what the website said is quite logical. Take a look if you are interested:
http://perso.club-internet.fr/legault/obstruction.html
Have a nice day and happy Chinese New Year!!
Yang Weixing
"The universe is composed mainly of hydrogen and ignorance."
"The universe is composed mainly of hydrogen and ignorance."