Dilemma: Buy a 2" 32mm Konig mk80 (80deg afov, US$250 used) or 2" 32mm Konig (60deg afov, US$100 used).
Scope: 8" SCT @ f/6.3 (1280mm fl). No vignetting problem with either EPs, 5mm exit pupil. The MK80 will give me 2deg tfov while the other one 1.5deg.
Objective: See all Messier objects (most are much less than 1 deg in size, btw) in a single view.
Question: Since the two biggest M objects are about 1.8 deg and 1.3 deg in size only (see below picture), does it make any sense to buy the mk80? any other considerations?
Would appreciate any advices.
cheers,
Arief
Is 2deg tfov really necessary?
Is 2deg tfov really necessary?
Last edited by ariefm71 on Sun Oct 31, 2004 11:39 pm, edited 1 time in total.
Hi Arief:
You may find this website useful for your decision:
http://oldfield.uhome.net/star/sctfield.html
Oldfield@HK evaluates various ways to get the widest view. BTW, I personally doubt that you can go beyond about 1.5 deg without vignetting. For visual use, the better alternative to a F/6.3 reducer is Denkmeier StarSweeper because it is attached between a diagonal and an eyepiece. You don't need to take out the diagonal when you go from low power to high power.
BTW, what type of the WO diagonal are you using (SCT-type or refractor-type)? If you use the latter, what is the adapter you use to connect it to the SCT rear screw? Thank you.
Clear skies.
Anat
You may find this website useful for your decision:
http://oldfield.uhome.net/star/sctfield.html
Oldfield@HK evaluates various ways to get the widest view. BTW, I personally doubt that you can go beyond about 1.5 deg without vignetting. For visual use, the better alternative to a F/6.3 reducer is Denkmeier StarSweeper because it is attached between a diagonal and an eyepiece. You don't need to take out the diagonal when you go from low power to high power.
BTW, what type of the WO diagonal are you using (SCT-type or refractor-type)? If you use the latter, what is the adapter you use to connect it to the SCT rear screw? Thank you.
Clear skies.
Anat
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weixing
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Hi,
The apparent diameter of M31 is actually 178 arc minutes (~3 degree) and M45 is 110 arc minutes (~1.9 degree).
Anyway, if you are doing star hopping, a wide field is definitely going to help you finding those objects.
Have a nice day.
The apparent diameter of M31 is actually 178 arc minutes (~3 degree) and M45 is 110 arc minutes (~1.9 degree).
Anyway, if you are doing star hopping, a wide field is definitely going to help you finding those objects.
Have a nice day.
Yang Weixing
"The universe is composed mainly of hydrogen and ignorance."
"The universe is composed mainly of hydrogen and ignorance." Anat, thanks for the link! are there any reviews on starsweeper as a standalone FR? my WO diagonal is the refractor type (previously used with my MK67's crayford focuser), the sct adapter is from lumicon.
Weixing, I wrongly typed 1deg50' as 1.5deg (should be 1.8deg), it's been corrected. thanks!
Weixing, I wrongly typed 1deg50' as 1.5deg (should be 1.8deg), it's been corrected. thanks!
Last edited by ariefm71 on Sun Oct 31, 2004 11:50 pm, edited 1 time in total.
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acc
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I would say, definitely go for the 80deg FOV! After my very first experience looking through a 80deg FOV eyepiece, it became really painful looking through a standard plossol as its like peeping through a straw... IMHO, the 'being there' feeling you get with a large FOV can't be beaten. Only thing that gets beaten up is your wallet 8)
cheers
cc
cheers
cc
Arief:
Rod Mollise reviewed the starsweeper (F/5 reducer) with a binoviewer http://www.astromart.com/articles/artic ... icle_id=61. If you search Rod Mollise's SCT yahoo group or Talking Telescopes yahoo group, you will find some discussions for single-eyepiece viewing about half a year ago.
Anat
Rod Mollise reviewed the starsweeper (F/5 reducer) with a binoviewer http://www.astromart.com/articles/artic ... icle_id=61. If you search Rod Mollise's SCT yahoo group or Talking Telescopes yahoo group, you will find some discussions for single-eyepiece viewing about half a year ago.
Anat
Hi Mo, thanks for the comment.
Btw, I found this very useful site that shows how all m objects are shown on a typical low power plossl porthole (42 arcminutes) http://www.stargazing.net/Astroman/Scalemess.htm (as all of you know, full moon size is 30 arcmin)
Based on that website, i've extrapolated the view of M31 in a 1.5deg tfov ep (inner yellow ring) and 2deg tfov ep (outer yellow ring), see below pic.
Btw, I found this very useful site that shows how all m objects are shown on a typical low power plossl porthole (42 arcminutes) http://www.stargazing.net/Astroman/Scalemess.htm (as all of you know, full moon size is 30 arcmin)
Based on that website, i've extrapolated the view of M31 in a 1.5deg tfov ep (inner yellow ring) and 2deg tfov ep (outer yellow ring), see below pic.
hmm.. i checked with starry night. it seems that a c8/6.3 + 31 nagler, if it would work properly, would offer the same tfov as my 3" with just a 20mm plossl. m31 would fit nicely, m45 will fit nicely with space left.
but the main idea of having a large tfov, for me, isn't really for framing objects. i think only a dozen of objects would need such a large tfov to fit. the extra large tfov allows easy hunting of objects, since u will be sweeping a rather large area.
when hunting for object, i do not really feel the need for wide angle eyepieces, since the human eye can concentrate on maybe 30-40 degrees only.
gd luck on ur hunt for wider fields. do inform us of any progress.
~MooEy~
but the main idea of having a large tfov, for me, isn't really for framing objects. i think only a dozen of objects would need such a large tfov to fit. the extra large tfov allows easy hunting of objects, since u will be sweeping a rather large area.
when hunting for object, i do not really feel the need for wide angle eyepieces, since the human eye can concentrate on maybe 30-40 degrees only.
gd luck on ur hunt for wider fields. do inform us of any progress.
~MooEy~
Re: Is 2deg tfov really necessary?
Dude, why don't you just get a set of pentax XL? 70 degrees is a good compromise and save all these headaches.ariefm71 wrote:Dilemma: Buy a 2" 32mm Konig mk80 (80deg afov, US$250 used) or 2" 32mm Konig (60deg afov, US$100 used).
Scope: 8" SCT @ f/6.3 (1280mm fl). No vignetting problem with either EPs, 5mm exit pupil. The MK80 will give me 2deg tfov while the other one 1.5deg.
Objective: See all Messier objects (most are much less than 1 deg in size, btw) in a single view.
Question: Since the two biggest M objects are about 1.5 deg and 1.2 deg in size only (see below picture), does it make any sense to buy the mk80? any other considerations?
Would appreciate any advices.
cheers,
Arief