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C6 vs 4" doublet for air travel (visual only)

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#1 Ihtegla Sar

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Posted 10 January 2020 - 05:08 PM

So, I am posting this in equipment because it compares an SCT with a refractor so it doesn't fit well in either the Cat/Cass or refractor forums.

 

Since the 92 Stowaway is not an option, I am wanting to get a good travel scope that will fit in a carry on bag (22" by 14" by 9").   The C6 is probably the largest aperture scope that will fit, but the AT102ED (and other similar small 4" f/7 doublet) should also fit in a carry on if you remove the focuser, and/or dew shield. 

 

Seems like advantages to the AT102ED are wider field, maybe more contrast due to lack of central obstruction and maybe quicker cool down. 

 

Advantages of the C6 would be significantly more aperture and half the price of an AT102ED.

 

Either should ride fine on a Twilight 1, which would easily fit in a checked bag.



#2 vtornado

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Posted 10 January 2020 - 05:32 PM

I don't do air travel, but a 100mm f/7 on a TW1 would be right at the limits of the mount if you are doing high power.

I have a 100 f/9 and it is not good on the TW1, high power focusing is difficult.

The C6 would be fine on the mount.

 

I don't know about contrast either.  I believe contrast is a function of aperture and central obstruction,

(other things such as fit/finish being the same).

Can  a 6 inch obstructed telescope pull ahead of a 100mm unobstructed refractor in contrast? don't know.

 

I do know that My 127mm MCT and 100mm ED are about equal in performance when comparing high power

planetary views.


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#3 Ihtegla Sar

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Posted 10 January 2020 - 05:40 PM

Topic for discussion is what's the best/largest travel scope that will fit in a 22" by 14" by 9" carry on bag?   I am posting this in equipment because it compares an SCT with a refractor so it doesn't fit too well in either the Cat/Cass or Refractor forums.

 

I have  narrowed it down to the C6 and a 4" f/7 doublet.  For discussion purposes,  am going with the AT102ED for the 4" doublet, although there are other brands that would be similar. Either the C6 or the AT102ED should ride fine on a Twilight 1 or similar small Alta-Azimuth mount, which would easily fit in a checked bag.

 

Here's what I have got for pros and cons for each scope:

 

C6

 

The C6 is the largest aperture scope that will legally fit in a carry on.  I have heard of people carrying a bigger scope like a C8 but they are taking a risk of not making it through since a C8 is slightly larger than what is legally allowed so it is somewhat risky trying to get on a plane with one -- you may end up having to check it or leave it behind.  Too much risk in that. 

 

So the biggest advantage of the C6 would be significantly more aperture and half the price of an AT102ED.  But the C6 would have slower cool down than an AT102ED but the C6 should still cool down in a reasonable amount of time.

 

 

AT102ED

 

The AT102ED (and other similar 4" refractors) should  fit in a carry on if you remove the focuser, which isn't too much trouble compared to the hassles of air travel.

 

Seems like the biggest advantage of the AT102ED would be the wider field, which would be helpful when navigating unfamiliar skies on a manual anti-azimuth mount.  The AT102ED should have better contrast due to lack of central obstruction and quicker cool down time.  But, at twice the cost of the C6.

 

 

What would your preference be?  Any other advantages/disadvantages between these two scopes? 

 

Any other recommendations for the largest/best visual telescope that will legitimately fit into a carry on bag?  Obviously, the  "Stowaway 92" springs to mind but those are not available and the wait list is closed and they are about ten times more expensive than a C6.  There might be other 4" triplets that would fit into a carry on bag, but I am not sure the increased cost of a triplet would be worth it for a visual only scope used for air travel where it might get damaged.  Plus, if you spent a bunch of money on a triplet for travel, you would always be wishing it were a Stowaway.

 

 

 

 



#4 junomike

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Posted 10 January 2020 - 06:07 PM

I think you've already sorted it out.

 

Wide Field DSO's = Refractor

     Planets/DSO's = C6


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#5 Ihtegla Sar

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Posted 10 January 2020 - 06:09 PM

I think you've already sorted it out.

 

Wide Field DSO's = Refractor

     Planets/DSO's = C6

Thanks.  I am thinking for things like Eta Carine and Omega Centauri the C6 would be better because of the greater aperture?

 

Also, somehow I have two threads going and I didn't mean for that to happen. I have asked the moderators to consolidate them.



#6 junomike

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Posted 10 January 2020 - 06:34 PM

Thanks.  I am thinking for things like Eta Carine and Omega Centauri the C6 would be better because of the greater aperture?

 

Also, somehow I have two threads going and I didn't mean for that to happen. I have asked the moderators to consolidate them.

As long as the objects fit you can't beat aperture!


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#7 Sam M

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Posted 10 January 2020 - 08:23 PM

I suppose it would depend partly on if you have another scope(s) that you are trying to complement.  

 

As Mike pointed out, the AT102 is better for wide field while the C6 is better for high magnification.  I have and love both scopes. If I could only have one with a special focus on air travel, I'd take the C6.  The 102 is sharper and more contrasty at low power, and gives better rich field views.  The C6 resolves globular clusters better, and is better with planets.  The C6 also gives very good wide views.  Mine is crisp at 250x under good seeing, and I can get about 1.75 degrees TFOV with a 24mm 68 degree eyepiece and a 6.3x focal reducer.  The cool down time isn't too bad with the C6.  I keep mine in a backpack, which I set outside a little while before I observe.

 

The mount is going to be the larger/heavier item to consider for air travel.  You might want something other than a Twilight 1.  It's the bulkiest/heaviest of it's class (I think).

 

I've done air travel with my C6, and Porta II with TL130 tripod.  It worked well.  See pics below.  The C6 is in a camera backpack, and the tripod and mount are in a full size checked bag.

 

IMG 2789
IMG 2790

Edited by Sam M, 10 January 2020 - 08:28 PM.

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#8 Jon Isaacs

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Posted 10 January 2020 - 08:46 PM

I'd find a 100 mm F/5 achromat and be done with it. An old Celestron C-102 F/5.  No need for ED..Rugged, relatively light, good for the low power stuff..

 

Traveling with an SCT seems like a recipe for heartbreak.  

 

I know Tony Flanders took an Orion 80 mm GoScope, it's F/4.5. I'd probably take an ST-80 with a 2 inch focuser. 

 

Jon



#9 Sam M

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Posted 10 January 2020 - 08:56 PM

Traveling with an SCT seems like a recipe for heartbreak.  

I've dragged that C6 backpack into a lot stranger places than an overhead compartment.  Like bouncing up the side of a mountain in a 4WD.  Should I be more worried than I am?



#10 Jon Isaacs

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Posted 10 January 2020 - 09:41 PM

I've dragged that C6 backpack into a lot stranger places than an overhead compartment.  Like bouncing up the side of a mountain in a 4WD.  Should I be more worried than I am?

 

In a vehicle you can adequately protect your scope. I never see stories about damaged objective lenses. Stories about broken corrector, want ads for replacement correctors are relatively common.

 

Jon



#11 Ihtegla Sar

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Posted 10 January 2020 - 09:46 PM

I suppose it would depend partly on if you have another scope(s) that you are trying to complement.

As Mike pointed out, the AT102 is better for wide field while the C6 is better for high magnification. I have and love both scopes. If I could only have one with a special focus on air travel, I'd take the C6. The 102 is sharper and more contrasty at low power, and gives better rich field views. The C6 resolves globular clusters better, and is better with planets. The C6 also gives very good wide views. Mine is crisp at 250x under good seeing, and I can get about 1.75 degrees TFOV with a 24mm 68 degree eyepiece and a 6.3x focal reducer. The cool down time isn't too bad with the C6. I keep mine in a backpack, which I set outside a little while before I observe.

The mount is going to be the larger/heavier item to consider for air travel. You might want something other than a Twilight 1. It's the bulkiest/heaviest of it's class (I think).

I've done air travel with my C6, and Porta II with TL130 tripod. It worked well. See pics below. The C6 is in a camera backpack, and the tripod and mount are in a full size checked bag.


Thanks! It's good to hear from someone who owns both. I have several telescopes including an old C-8 from the 1990s, so I already have the 6.3 reducer. I've also got two 4" refractors (an f9 apo and an f5 achro). The f9 apo is too long for carry on and the f5 achro is not great for anything but low power.

Sounds like the C6 might be the best choice. Thanks for the pics of it in the backpack. Looks like it packs well.

#12 Sam M

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Posted 10 January 2020 - 10:13 PM

This is the backpack...

https://www.amazon.c...577281486&psc=1

 

It fits the C6, grab handle, three eyepieces, barlow, focal reducer, diagonal, red dot finder, star charts and a couple filters.

 

If you want something more secure, I've seen a pretty nice setup with a C6 in an inexpensive Pelican style road case with pluck foam.

https://www.cloudyni...-6-grab-and-go/


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#13 Ihtegla Sar

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Posted 10 January 2020 - 10:24 PM

I'd find a 100 mm F/5 achromat and be done with it. An old Celestron C-102 F/5. No need for ED..Rugged, relatively light, good for the low power stuff..

Traveling with an SCT seems like a recipe for heartbreak.

I know Tony Flanders took an Orion 80 mm GoScope, it's F/4.5. I'd probably take an ST-80 with a 2 inch focuser.

Jon

I just happen to own a Celestron 102 wide field f5 that I bought for birdwatching ten years ago. It would be a decent travel scope but it doesn't handle high power very well. Great for wide field low power though.

I just got back from a trip to Vietnam where I took an 80mm Meade Infinity (ST80 clone). That is certainly an easy scope to travel with, but the purpose of the Vietnam trip wasn't so much astronomy as it was visiting my wife's family so I wanted something really easy to travel with since I wasn't going to get much opportunity for astronomy on the trip. The focus of our next trip will be more on astronomy, so I may want more aperture and higher power capabilities.

At $400 for a C6 OTA, I wouldn't be too heartbroken if something happened to it, as long as it happened on the way home instead of the way there. :)

Edited by Ihtegla Sar, 11 January 2020 - 12:49 PM.


#14 bobhen

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Posted 11 January 2020 - 08:12 AM

Under the stars the aperture difference between these 2 scopes is not that significant. The CO and light scatter in the SCT compromises its performance somewhat compared to the refractor. 

 

But it really depends on what you want to do.

 

If you are taking a scope to dark skies to observe deep sky objects “only” then a 4” F5 achromatic refractor will do the job really well.

 

If you want to do “both” planetary and deep sky observing, I would choose the AT102 ED refactor for all of the attributes that have been mentioned. Don’t underestimate ease of use, especially in unfamiliar surroundings.

 

The refractor will also be a better daytime spotter and birding scope if that is important.

 

I’ve been using a 102mm F5 achromatic refractor as my air travel scope for 15-years (works out great) but I only fly to dark skies to observe deep sky objects.

 

Bob


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#15 Ihtegla Sar

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Posted 12 January 2020 - 02:12 PM

Under the stars the aperture difference between these 2 scopes is not that significant. The CO and light scatter in the SCT compromises its performance somewhat compared to the refractor.

But it really depends on what you want to do.

If you are taking a scope to dark skies to observe deep sky objects “only” then a 4” F5 achromatic refractor will do the job really well.

If you want to do “both” planetary and deep sky observing, I would choose the AT102 ED refactor for all of the attributes that have been mentioned. Don’t underestimate ease of use, especially in unfamiliar surroundings.

The refractor will also be a better daytime spotter and birding scope if that is important.

I’ve been using a 102mm F5 achromatic refractor as my air travel scope for 15-years (works out great) but I only fly to dark skies to observe deep sky objects.

Bob


Why wouldn't the difference in aperture between 4" and 6" be significant under the stars? Even with the central obstruction taken into account the C6 would still gather about 90% more light than a 4" refractor. I'm not sure I understand why that wouldn't be significant when looking at deep sky objects under the stars.

#16 junomike

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Posted 12 January 2020 - 05:12 PM

Why wouldn't the difference in aperture between 4" and 6" be significant under the stars? Even with the central obstruction taken into account the C6 would still gather about 90% more light than a 4" refractor. I'm not sure I understand why that wouldn't be significant when looking at deep sky objects under the stars.

Some people feel that the CO combined with "SCT Performance" negates the huge increase in light gathering advantage.

IME this is not the case the the SCT would easily show more stars and detail, but as always.....YMMV


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#17 mclewis1

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Posted 12 January 2020 - 05:41 PM

Steve, If you have a good example optically of a C6 and know how to perform a good accurate collimation (at high magnifications) then I'd definitely go with that over a 100mm ED. If you are still planning on buying either scope and you don't have any experience collimating an SCT then go refractor.

 

There is virtually no real issue of damaging a C6 travelling with it in carry on ... all those stories of broken correctors are due to issues from shipping. It's not like you are going to be storing it without the cap on the corrector end.


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#18 Ihtegla Sar

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Posted 13 January 2020 - 06:45 PM

Some people feel that the CO combined with "SCT Performance" negates the huge increase in light gathering advantage.

IME this is not the case the the SCT would easily show more stars and detail, but as always.....YMMV

Thanks.  That's what I thought he meant but I am not so sure the "SCT Performance" is going to be so bad that it would be beat by an achromat that has half the light gathering capability.

 

I have an old C8 that I haven't used in a long while so I may set it up next to my 4" refractors and do a side by side by side.  I have a Celestron 102 f/5 achromat and a Takahashi FC100DL.  I seriously doubt the 4" achromat can keep up with a much larger SCT, but  since I already have the C8 there's no harm in dusting it off for a side by side before getting a C6.

 

I do believe a premium refractor like my FC100DL could perform better than a C6 or even a C8 on planets.  My views of Saturn and Jupiter and the Moon in the DL do seem to be better than what I remember from the C8, but I have a hard time believing the the DL would outperform larger aperture on a faint fuzzy.  Guess there is no harm in doing a side by side with the C8 to find out what the differences are before getting a C6.  But even if the Tak were to outperform the C6 or the C8, the DL is too big to travel with, and although an FC100DC would fit in a carry on with focuser removed, that's more than I want so spend just for air travel.  And I doubt a more economical AT100ED would have the same performance as an FC100D series Tak.

 

Steve, If you have a good example optically of a C6 and know how to perform a good accurate collimation (at high magnifications) then I'd definitely go with that over a 100mm ED. If you are still planning on buying either scope and you don't have any experience collimating an SCT then go refractor.

 

There is virtually no real issue of damaging a C6 travelling with it in carry on ... all those stories of broken correctors are due to issues from shipping. It's not like you are going to be storing it without the cap on the corrector end.

 

Thanks!  That's what I am thinking.  I know how to star collimate a Newtonian primary and from what I have read, collimating an SCT is basically the same (but easier since you don't have to worry about the secondary, which is the part of collimating a Newtonian that gives me fits).  Back in the day I never had to collimate my C8 since it always seemed to be in good collimation but I will have to test it out if I dust it off.  Haven't really used the C8 since the late 1990s.  Think I will wait for some better weather to get a C6 so I can do a star test and then send it back if it is an optical dud.  It's been nothing but cloudy nights here in the pacific northwest for weeks.  



#19 Don W

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Posted 13 January 2020 - 11:23 PM

In 2005 I took a Televue 102i and Gibraltar mount to Australia. The scope was in one checked bag wrapped in bubble wrap and the mount in another. My eyepieces were with me as carry on.

 

Although we had a number of dobs available I spent some time just using the 4" refractor. I set the Argo Navis to show me globular clusters brighter than 9th magnitude. I could not believe how many there were. I spent several hours doing just that. I also turned it on the Tarantula Nebula and a number of other brighter objects. I was not disappointed.

 

For my next trip, I'm looking to put together a setup using a C6 and a Skywatcher AZ GTi and possibly doing some light imaging with an Astro-Tech 72ED.


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#20 bobhen

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Posted 14 January 2020 - 09:01 AM

Why wouldn't the difference in aperture between 4" and 6" be significant under the stars? Even with the central obstruction taken into account the C6 would still gather about 90% more light than a 4" refractor. I'm not sure I understand why that wouldn't be significant when looking at deep sky objects under the stars.

Deep sky observing isn’t all about aperture (light gathering) it is also about contrast. That’s why you go to a dark site, because many deep sky objects need contrast.

 

SCTs have central obstructions; correctors and mirrors that all scatter or deflect light reducing contrast. A refractor, by the nature of its design, delivers high contrast views.

 

Of course, if the aperture difference were larger, than the contrast loss would not matter as much, but these 2 scopes are pretty close in size.

 

For example: On M13, I would suspect that the SCT would deliver slightly brighter stars than the 4” because M13 is an object that does not need contrast. Bright stars on a dark sky do not need contrast help. However, take the nebula M1 and you might get a better view in the refractor than the SCT because M1 is an object that requires contrast for the best view.

 

Dark nebula and a lot of nebula in general require contrast for the best view.

 

There is no perfect scope but for travel the refractor also has other attributes that are attractive as well.

 

Bob


Edited by bobhen, 14 January 2020 - 10:57 AM.

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#21 Jon Isaacs

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Posted 14 January 2020 - 09:37 AM

Steve, If you have a good example optically of a C6 and know how to perform a good accurate collimation (at high magnifications) then I'd definitely go with that over a 100mm ED. If you are still planning on buying either scope and you don't have any experience collimating an SCT then go refractor.

 

There is virtually no real issue of damaging a C6 travelling with it in carry on ... all those stories of broken correctors are due to issues from shipping. It's not like you are going to be storing it without the cap on the corrector end.

 

Not really.. correctors get broken a variety of ways.  

 

It's  a thin piece of glass. 

 

Jon



#22 Jon Isaacs

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Posted 14 January 2020 - 09:52 AM

Why wouldn't the difference in aperture between 4" and 6" be significant under the stars? Even with the central obstruction taken into account the C6 would still gather about 90% more light than a 4" refractor. I'm not sure I understand why that wouldn't be significant when looking at deep sky objects under the stars.

 

On paper, a 6 inch SCT has the through-put of a 5 inch refractor. The refractor has a few things going for it, thermal stability, better baffling. 

 

So there's a some advantage to the SCT at equal magnifications.

 

But the SCT lacks that whole low power, the scope is the finder, I just want to roam the skies and look aspect.. that's why I'd take a 4 inch F/5. Just pop in a 2 inch Wide Field an I'd be happy.

 

Jon


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#23 Ihtegla Sar

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Posted 14 January 2020 - 11:09 AM

On paper, a 6 inch SCT has the through-put of a 5 inch refractor. The refractor has a few things going for it, thermal stability, better baffling.

So there's a some advantage to the SCT at equal magnifications.

But the SCT lacks that whole low power, the scope is the finder, I just want to roam the skies and look aspect.. that's why I'd take a 4 inch F/5. Just pop in a 2 inch Wide Field an I'd be happy.

Jon

Jon, I thought you were a strict "aperture rules!" guy? 😊

By my math the C6 has 19.7474% more than a 5" refractor on paper and 87.10375% more than a 4" refractor. Celestron reports aperture is 5.9" and light loss from the central obstruction is 14%. So light gathering power of the C6 is 2.95*2.95*0.86=7.48415 (we can ignore pi for the comparison since it is a constant). The 5" would be 2.5*2.5=6.25. The 4" would be 2*2=4. Am I calculating all of this correctly?

Is the main reason you would prefer the 4" f/5 because of thermal issues and for wide field views at low power with a big 2" wide field eyepiece? Or do you believe that 87% more light isn't enough for the SCT design (with it's central obstruction) to overcome the high contrast views of an achro refractor on deep sky objects?

Edited by Ihtegla Sar, 14 January 2020 - 11:11 AM.


#24 Jon Isaacs

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Posted 14 January 2020 - 12:02 PM

Steve:

 

The light loss from the CO is about 14%, the light loss from the mirrors and coatings is 16%.

 

That turns out right about 127 mm = 5 inches.

 

I would take the 4 inch F/5 because of its wide field capabilities.  But I dont where you're going.. I assume dark skies.  

 

I actually take my 80 mm F/7 apo. It's enough aperture and it's an excellent birding scope.

 

I do have large scopes but I also have small scopes. I'm a right tool for the job guy..  

 

Jon


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#25 Ihtegla Sar

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Posted 14 January 2020 - 12:37 PM

Steve:

 

The light loss from the CO is about 14%, the light loss from the mirrors and coatings is 16%.

 

That turns out right about 127 mm = 5 inches.

 

I would take the 4 inch F/5 because of its wide field capabilities.  But I dont where you're going.. I assume dark skies.  

 

I actually take my 80 mm F/7 apo. It's enough aperture and it's an excellent birding scope.

 

I do have large scopes but I also have small scopes. I'm a right tool for the job guy..  

 

Jon

Ahh, mirrors and coatings  . . . so the C6's light gathering power gets reduced to 56% more than a 4 inch refractor.  Makes sense.  I hadn't considered loss from mirrors and coatings.

 

Not sure where exactly we are going but somewhere in Hawaii.  We just got back from Vietnam where we went to visit her family, not for astronomy, but its 37 degrees further south of where we live so I packed my 80mm adventure scope and some cheap lightweight eyepieces and a ball head photo tripod.  I didn't time it well for astronomy because it was a family trip, so it turned out to be cloudy, smaugy  and mostly Bortle 8-9 skies where we were most of the time, and a full moon the only night we went to anything resembling dark skies.  But I was still able to see a few nice open clusters, including the Jewel Box and the Gem Cluster (I thought the Gem Cluster was more impressive than the Jewel Box)  and glimpse Omega Centauri.  I couldn't make out anything other than stars in Eta Carine.  I saw Ruby Crucis but only with averted vision and I couldn't see any color in it, although I saw lots of color in the Gem Cluster and some in the Jewel Box. 

 

The experience left me wanting a little more aperture and also wanting a scope that can take higher magnification better than a small f/5 achro.  Granted there were a few open clusters like the Southern Pleiades and the Wishing Well that were framed nicely in the wide field of an 80mm refractor that would not be much to look at in a C6. But most of what I looked at could have used more magnification than what an 80mm f/5 achro can comfortably manage.  

 

So we get back from the trip and my wife is wanting to swim in the warm ocean since it was too stormy for much swimming on our Vietnam trip and she is suggesting that our next trip should be Hawaii, so she can swim and I can do some astronomy.  She wants a beach she can swim in that has as few tourists as possible.

 

So, somewhere in Hawaii with less touristy beaches (so probably Bortle 2/3 skies?) and eventually back to Vietnam, where the skies will be Bortle 8/9 (Saigon area) for most of the trip but with a few days spent in darker (Bortle 3ish), less smaugy skies, with better timing this time so no full moon.  We stayed two nights at a nice beach side resort two hours south of Saigon with two story units that had rooftop decks that offered an unobstructed 360 view of the sky and not much in terms of local lighting.  Would have been perfect but for the full moon that night.

 

If I can ever swing an epic dedicated astronomy trip to a Bortle 1 area of  Australia or South America then I will probably take a 4" refractor in carry on and also pack a large dob in checked luggage and hope it survives.  Either that or rent a scope.  My wife is not really into astronomy so our trips are likely to be multi purpose and hence not Bortle 1 skies.  Light pollution has gotten so bad everywhere, you have to be really dedicated to astronomy to get to a Bortle 1 sky.  The only way I could swing that with my wife is if there were also a warm secluded beach nearby so she could swim in the Ocean while I slept in the hotel room waiting for sunset.  But if there is a hotel nearby its not going to be Bortle 1 . . .


Edited by Ihtegla Sar, 14 January 2020 - 12:45 PM.

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