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smaller refractor for planets, doubles, moon, etc?

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#1 ET_PhoneHome

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Posted 29 July 2020 - 12:35 PM

Hi all, I currently have a Celestron SE6, and a Meade 5" refractor (LXD55, I think, but I haven't used it for a long time).  Due to light pollution, I'm a bit limited, but I do enjoy planets, doubles, the moon and those sorts of things.  Would around a 4" refractor be good for this?  My issue with my 5-incher is it's huge, the mount is heavy and cumbersome, and it's just a paint to set up.  It's just not a very grab n' go scope.

 

It seems like a 4" refractor isn't going to be much better in that regard, but I see they also make short tube, fast refractors.  This sort of thing seems more to my liking, BUT I've also read these type of fast scopes aren't good for planetary viewing.

 

So in short, I'd like a lightweight, somewhat small scope with a GoTo mount.  Maybe I already have the answer, and it's my 6SE.  If not, any suggestions?  It would be a huge bonus if I could use the refractor with my 6SE mount, but I'm not sure that would work due to tube length (it might hit the mount when pointing towards zenith?).



#2 starryhtx

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Posted 29 July 2020 - 12:45 PM

Hi all, I currently have a Celestron SE6, and a Meade 5" refractor (LXD55, I think, but I haven't used it for a long time). Due to light pollution, I'm a bit limited, but I do enjoy planets, doubles, the moon and those sorts of things. Would around a 4" refractor be good for this? My issue with my 5-incher is it's huge, the mount is heavy and cumbersome, and it's just a paint to set up. It's just not a very grab n' go scope.

It seems like a 4" refractor isn't going to be much better in that regard, but I see they also make short tube, fast refractors. This sort of thing seems more to my liking, BUT I've also read these type of fast scopes aren't good for planetary viewing.

So in short, I'd like a lightweight, somewhat small scope with a GoTo mount. Maybe I already have the answer, and it's my 6SE. If not, any suggestions? It would be a huge bonus if I could use the refractor with my 6SE mount, but I'm not sure that would work due to tube length (it might hit the mount when pointing towards zenith?).


One of the shortest 4” refractors I’ve seen is the Explore Scientific 102 series. But those are triplets so they’re not very light. If you want a light 4” I’d say the Tak is one of the lightest.
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#3 dusty99

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Posted 29 July 2020 - 12:52 PM

Do you have the LXD55 mount, too?  Regardless, if I didn't want to go for more aperture (8-10" Dob; C8) I'd be happy with your 5" or C6.  If carrying the mounted 5" out is difficult just clear some space so you can carry out mount and scope separately.  I used the newer model of your scope (LX70 AR5) for a couple of years and kept it mounted in my garage and carried it out in one trip.  Your version is slightly longer and heavier than my old 1000mm but also likely a bit better optically.  Going down to a 4" will get you a little portability but it won't be a sea change.  A well-collimated C6 is about the most bang for weight and size out there, IMO.


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#4 ET_PhoneHome

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Posted 29 July 2020 - 12:57 PM

Do you have the LXD55 mount, too?  Regardless, if I didn't want to go for more aperture (8-10" Dob; C8) I'd be happy with your 5" or C6.  If carrying the mounted 5" out is difficult just clear some space so you can carry out mount and scope separately.  I used the newer model of your scope (LX70 AR5) for a couple of years and kept it mounted in my garage and carried it out in one trip.  Your version is slightly longer and heavier than my old 1000mm but also likely a bit better optically.  Going down to a 4" will get you a little portability but it won't be a sea change.  A well-collimated C6 is about the most bang for weight and size out there, IMO.

Yep, I do have the LXD55 mount.  It's a bit beat up, but still functional, AFAIK.  Ever since I got he C6, I really haven't played with the 55.  The other thing I was considering was maybe buying a 5" Mak.  Supposedly, those offer refractor like views.  I could just use it with my C6 mount.  From what I've heard though, the difference probably wouldn't be worth it.  Maybe the Mak, would be a hair sharper, but it'd also be an inch smaller.



#5 dusty99

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Posted 29 July 2020 - 01:03 PM

The C6 on your goto mount would be a functional, relatively lightweight combination as well.



#6 sg6

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Posted 29 July 2020 - 01:10 PM

Will come down to "How good?"

I have a 90ED and that I suspect would do exactly what you want. The goto mount may be a problem.

According to the number the AZ GTi should handle the scope but with owning both I am hesitant.

 

I would avoid the ST refractors. They are F/5 and achro, even an f/5 triplet is pushing your luck. If you do go that way then expect CA and that wipes out a lot of the detail I suspect you would like.

 

Rather simply f/5 achros are poor scopes and poor scopes deliver poor views.

 

For planets you will need say 120x for Saturn, Jupiter is less. Moon is easy and doubles need clarity.

How about an 80ED of the Az GTi ?

Would work and do what you appear to want. The everyday problem is buying the rig.


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#7 gnowellsct

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Posted 29 July 2020 - 01:18 PM

Hi all, I currently have a Celestron SE6, and a Meade 5" refractor (LXD55, I think, but I haven't used it for a long time).  Due to light pollution, I'm a bit limited, but I do enjoy planets, doubles, the moon and those sorts of things.  Would around a 4" refractor be good for this?  My issue with my 5-incher is it's huge, the mount is heavy and cumbersome, and it's just a paint to set up.  It's just not a very grab n' go scope.

 

It seems like a 4" refractor isn't going to be much better in that regard, but I see they also make short tube, fast refractors.  This sort of thing seems more to my liking, BUT I've also read these type of fast scopes aren't good for planetary viewing.

 

So in short, I'd like a lightweight, somewhat small scope with a GoTo mount.  Maybe I already have the answer, and it's my 6SE.  If not, any suggestions?  It would be a huge bonus if I could use the refractor with my 6SE mount, but I'm not sure that would work due to tube length (it might hit the mount when pointing towards zenith?).

You want a fast refractor for planets....that is cold fire and hot ice.  Let us say you get the very short AT 92 (f/5.5).  You would need a 5 or 6 mm ocular just to get to 92x which is not a lot on planets....better than nothing, but not a lot.  But to get to 184x you're going to need a 3mm (or a little less) eyepiece and you're going to be observing at 0.5 mm exit pupil.  

 

Those oculars exist, you can do it.  But you're stretching the capacity of the scope and your eye if you want to do this for a long time.  You might also discover what is in the "attic of your eyeball" which is to say all the dust and grime in there that you didn't know about and don't want to know about.

 

I have had different experiences with small aperture viewing.  First of all I think if you're going to get a small refractor you might be better with a longer one like the Vixen ED81s which is now marketed as the SD81.  Because it's f/7.7.  Now you're looking at a 4 mm to get to 160x and that may not sound like much but at the high end these small increments matter.  This is a popular scope on CN, I bought it because of the rave reviews and because people were snarking that I shoudn't knock 80mm viewing till I tried it.  So I tried it, and they're right, you can see quite a bit in 80 mm.  And in fact you can see quite a bit if you use the dustcover (it has a hole with a removable cap) to make a 40 mm telescope.  Amazing what you can see in 40 mm.   And even though the SD81 is f/7.7 it *might* be short enough for your mount.  You would need to get the measurement.

 

Again, on behalf of small aperture viewing, I always have a refractor on top of my SCT and the other night was viewing Jupiter in the 92mm f/6.9 and the C14.  First point:  A friend and I agreed it was a terrific view.  I said I couldn't believe it was only 128x (my 5mm ocular).  And I realized reaching into the box that it WASN'T 128x, it was 180x, because I had grabbed the 3.5 instead of the 5 mm.  So I was at peak power and the view was razor sharp.  And at 0.5 mm exit pupil. And you could see things.  You couldn't see what you see in the C14, but there was enough there to view.

 

But on the other hand the C14 was rendering MUCH more at 224x or 1.6 mm exit pupil.  This is a much more comfortable viewing range and I was getting much more detail and color rendition--the blessings of aperture.  

 

But I was fascinated by the view in the smaller scope and kept going back to it until this long semi transparent filament placed itself between me and Jupiter.  I tried looking left and right, jumping up and down, but it insisted on staying right there covering jupiter from N to S.  

 

There was no filament at all when I looked in the C14.  When I went back to the refractor, there it was again.  (No it was not on the ocular)  

 

So the point about observing planets in a fast refractor is that you will want to push the magnification below 1 mm exit pupil and below 1 mm ex pupil all sorts of eyeball critters can make themselves known, at a time and place of their choosing.  They're called floaters.  

 

On an unrelated matter if you *do* get a fast refractor for high power viewing of planets make sure you get the best one you can afford.  Because fast optics tend to stretch the limits of design and execution.

 

Greg N


Edited by gnowellsct, 29 July 2020 - 01:20 PM.

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#8 gnowellsct

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Posted 29 July 2020 - 01:26 PM

Here's a pic of two 80mm, the Skywatcher Esprit f/5 and the Vixen ED81s f/7.7  I just measured the Vixen it is 23.25 inches end to end, not counting diagonal and the necessary extension to reach focus.  I would add maybe five inches for that.  It will give you an idea.  --GN

 

vixen and skywatcher- cn size.jpg

 

 


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#9 ET_PhoneHome

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Posted 29 July 2020 - 01:30 PM

Will come down to "How good?"

I have a 90ED and that I suspect would do exactly what you want. The goto mount may be a problem.

According to the number the AZ GTi should handle the scope but with owning both I am hesitant.

 

I would avoid the ST refractors. They are F/5 and achro, even an f/5 triplet is pushing your luck. If you do go that way then expect CA and that wipes out a lot of the detail I suspect you would like.

 

Rather simply f/5 achros are poor scopes and poor scopes deliver poor views.

 

For planets you will need say 120x for Saturn, Jupiter is less. Moon is easy and doubles need clarity.

How about an 80ED of the Az GTi ?

Would work and do what you appear to want. The everyday problem is buying the rig.

Thanks!  Those sound like good options.  I like the compactness.  Is this the 80mm you are talking about?

https://www.telescop...2160/p/9895.uts

 

I also found this one (at twice the price).  The one cool thing is the tube length is only 15.5 inches, and it's very light.  I bet this would work with my 6SE mount.

https://www.telescop...60/p/101422.uts

 

I could always go 90 or 100mm, but then I'm looking at getting a new mount, too.  And then the big question: will any of these options be as good as my 6SE?  Just wondering if I'm going to be happier looking at planets like Saturn and Jupiter through an 80mm refractor or my 6" SCT?  Or a 5" mak?  So many options smile.gif



#10 gnowellsct

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Posted 29 July 2020 - 01:35 PM

The C6 on your goto mount would be a functional, relatively lightweight combination as well.

For whatever reason the C6 as a planet observing tool has not made it into consideration.  

 

Based on what I have in inventory the c8 is something I could use: relatively quick set up, just slap it on the DM6 + telepod.  But the downfall would be the rapid speed with which dew forms on sct correctors.   Once I need to put on wires and lug a power supply out it is no longer a quick set up.

 

That would lead me to choose the 5" refractor instead.  No need to get into the eternal apo vs SCT wars.  The refractor is heavier than the c8 but the massive triplet lens is an asset when you want something above ambient to prevent dew.

 

The 3.6 inch refractor is, as I have said, very capable.   But you're working against a number of small aperture effects: not so much engrossing detail, and exit pupils below 1 mm.  Even if you have perfect color correction at high power, floaters can be real impediment to discerning and enjoying planetary details.

 

Greg N 


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#11 gnowellsct

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Posted 29 July 2020 - 01:43 PM

Thanks!  Those sound like good options.  I like the compactness.  Is this the 80mm you are talking about?

https://www.telescop...2160/p/9895.uts

 

I also found this one (at twice the price).  The one cool thing is the tube length is only 15.5 inches, and it's very light.  I bet this would work with my 6SE mount.

https://www.telescop...60/p/101422.uts

 

I could always go 90 or 100mm, but then I'm looking at getting a new mount, too.  And then the big question: will any of these options be as good as my 6SE?  Just wondering if I'm going to be happier looking at planets like Saturn and Jupiter through an 80mm refractor or my 6" SCT?  Or a 5" mak?  So many options smile.gif

The 5 inch Mak sounds like it most suits your needs but you haven't said why the 6" SCT is no good.  The C6 gets good reviews here (usually).  

 

Generally speaking I would not want to go out for a couple of hours of planet viewing with an aperture less than 5 inches.  

 

I don't really think the 5 inch Mak is good for much BESIDES planet viewing.  And it may not be optically better at that than your C6.    

 

My personal view is that I like my telescopes to be good on a wide variety of objects.  I have scopes that perform well on planets but I don't call them "planetary scopes."   This is a term I find irksome because what it means is that the user wants to employ said telescope on planets; and also, it implies that other scopes are NOT planetary scopes.  Well,  all scopes can do *something* with the planets.  But an f/5 80mm telescope is not the first pick for that function.   Planets like magnification and viewing planets is more relaxing at 1mm and larger exit pupils.  So slow refractors are a good pick in small apertures.  

 

Greg N


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#12 bobhen

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Posted 29 July 2020 - 02:17 PM

Hi all, I currently have a Celestron SE6, and a Meade 5" refractor (LXD55, I think, but I haven't used it for a long time).  Due to light pollution, I'm a bit limited, but I do enjoy planets, doubles, the moon and those sorts of things.  Would around a 4" refractor be good for this?  My issue with my 5-incher is it's huge, the mount is heavy and cumbersome, and it's just a paint to set up.  It's just not a very grab n' go scope.

 

It seems like a 4" refractor isn't going to be much better in that regard, but I see they also make short tube, fast refractors.  This sort of thing seems more to my liking, BUT I've also read these type of fast scopes aren't good for planetary viewing.

 

So in short, I'd like a lightweight, somewhat small scope with a GoTo mount.  Maybe I already have the answer, and it's my 6SE.  If not, any suggestions?  It would be a huge bonus if I could use the refractor with my 6SE mount, but I'm not sure that would work due to tube length (it might hit the mount when pointing towards zenith?).

Short, fast 4” refactors can be fine planetary telescopes IF they have high quality triplet objectives.

 

But for your observing targets/needs, there is no need to go fast, as fast triplets can be expensive.

 

I think some of your issues are: portability, quick setup and ease of use – so...

 

A 4” Takahashi apo doublet like the FC 100DC (only 6.2 pounds OTA) or the new 100DZ will deliver sharper images than the C6. For your targets: Moon, Planets Double stars the brighter, and some not so bright, deep sky targets, a high quality refractor like a 4” Takahashi will deliver the goods. The Tak doublets also acclimate quickly.

 

You don’t really need GOTO for those targets and you could get a nice alt/az mount that would make things portable and easy to setup. Some alt/az mounts do have tracking and GOTO and will accommodate a refractor, if you feel the need. 

 

If you want a 4” apo that meets your needs and the targets you want to observe, I wouldn’t skimp on performance to save a few dollars. A 4” telescope is a small telescope so you want really superb optics – and Takahashi optics are superb.

 

If one of the scopes you own is too big and you are not using it, sell it to help fund the 4” refractor. If the other scope is now too close in size to the refractor, sell that to help fund the refractor as well.

 

With a 4” Takahashi on an alt/az mount you get…

1. Quick setup
2. Quick acclimation
3. Superb optics
4. Low power to high power capability
5. An excellent platform for white light or hydrogen-alpha solar observing, with the appropriate filters of course.

 

Bob


Edited by bobhen, 29 July 2020 - 02:20 PM.

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#13 dusty99

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Posted 29 July 2020 - 02:26 PM

Greg, you bring up a good point that I often forget: I live in a dry climate and almost never need a dew shield, and on the dampest nights the factory plastic dew shield has been all I've ever needed.  The OP didn't say where he lives but I should remember that for many folks, SCT's do come with an extra issue that mine don't have.

 

Also, I'd generally pick my C8 over the C6 for planets (or most else), too.  It just so happens that I bought a Porta II on a Berlebach report during Vixen USA's recent sale a couple of months ago and have been having a lot of fun with it, the C6 and my new f/7 AT80ED.  I'm a dyed-in-the-wool GEM guy, but it's been a blast to pick up that small, light rig and move it around my yard without a thought of messing up my north alignment, even if it takes (at the most) two minutes to realign my GEMs.  That's the reason I've been getting reacquainted with frequent use of my C6 for the first time since I bought my SW120ED.

 

BTW, for the OP and posterity, the C6 on the Porta/Berlebach is even lighter and easier to handle than the 80mm and reveals more, although both are well within grab and go limits.  The little 80 is sharp and wide, though, so it may edge out the C6 for travel.  At some point it gets hard to argue with 2+ more degrees FOV.

 

 

For whatever reason the C6 as a planet observing tool has not made it into consideration.  

 

Based on what I have in inventory the c8 is something I could use: relatively quick set up, just slap it on the DM6 + telepod.  But the downfall would be the rapid speed with which dew forms on sct correctors.   Once I need to put on wires and lug a power supply out it is no longer a quick set up.

 

 

Greg N 


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#14 ET_PhoneHome

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Posted 29 July 2020 - 02:40 PM

You want a fast refractor for planets....that is cold fire and hot ice.  Let us say you get the very short AT 92 (f/5.5).  You would need a 5 or 6 mm ocular just to get to 92x which is not a lot on planets....better than nothing, but not a lot.  But to get to 184x you're going to need a 3mm (or a little less) eyepiece and you're going to be observing at 0.5 mm exit pupil.  

 

Those oculars exist, you can do it.  But you're stretching the capacity of the scope and your eye if you want to do this for a long time.  You might also discover what is in the "attic of your eyeball" which is to say all the dust and grime in there that you didn't know about and don't want to know about.

 

I have had different experiences with small aperture viewing.  First of all I think if you're going to get a small refractor you might be better with a longer one like the Vixen ED81s which is now marketed as the SD81.  Because it's f/7.7.  Now you're looking at a 4 mm to get to 160x and that may not sound like much but at the high end these small increments matter.  This is a popular scope on CN, I bought it because of the rave reviews and because people were snarking that I shoudn't knock 80mm viewing till I tried it.  So I tried it, and they're right, you can see quite a bit in 80 mm.  And in fact you can see quite a bit if you use the dustcover (it has a hole with a removable cap) to make a 40 mm telescope.  Amazing what you can see in 40 mm.   And even though the SD81 is f/7.7 it *might* be short enough for your mount.  You would need to get the measurement.

 

Again, on behalf of small aperture viewing, I always have a refractor on top of my SCT and the other night was viewing Jupiter in the 92mm f/6.9 and the C14.  First point:  A friend and I agreed it was a terrific view.  I said I couldn't believe it was only 128x (my 5mm ocular).  And I realized reaching into the box that it WASN'T 128x, it was 180x, because I had grabbed the 3.5 instead of the 5 mm.  So I was at peak power and the view was razor sharp.  And at 0.5 mm exit pupil. And you could see things.  You couldn't see what you see in the C14, but there was enough there to view.

 

But on the other hand the C14 was rendering MUCH more at 224x or 1.6 mm exit pupil.  This is a much more comfortable viewing range and I was getting much more detail and color rendition--the blessings of aperture.  

 

But I was fascinated by the view in the smaller scope and kept going back to it until this long semi transparent filament placed itself between me and Jupiter.  I tried looking left and right, jumping up and down, but it insisted on staying right there covering jupiter from N to S.  

 

There was no filament at all when I looked in the C14.  When I went back to the refractor, there it was again.  (No it was not on the ocular)  

 

So the point about observing planets in a fast refractor is that you will want to push the magnification below 1 mm exit pupil and below 1 mm ex pupil all sorts of eyeball critters can make themselves known, at a time and place of their choosing.  They're called floaters.  

 

On an unrelated matter if you *do* get a fast refractor for high power viewing of planets make sure you get the best one you can afford.  Because fast optics tend to stretch the limits of design and execution.

 

Greg N

Very good points, thank you.  The floaters thing is something to think about as well.  I noticed when looking at the sky or a bright white wall, I do have some floaters.  I had an eye exam a year or two ago, and they said it was normal, just a small annoyance.



#15 dusty99

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Posted 29 July 2020 - 02:43 PM

You may gain a bit of perceived sharpness over a well-collimated C6 but will there be more information?  

 

 

A 4” Takahashi apo doublet like the FC 100DC (only 6.2 pounds OTA) or the new 100DZ will deliver sharper images than the C6. 


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#16 ET_PhoneHome

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Posted 29 July 2020 - 02:48 PM

The 5 inch Mak sounds like it most suits your needs but you haven't said why the 6" SCT is no good.  The C6 gets good reviews here (usually).  

 

Generally speaking I would not want to go out for a couple of hours of planet viewing with an aperture less than 5 inches.  

 

I don't really think the 5 inch Mak is good for much BESIDES planet viewing.  And it may not be optically better at that than your C6.    

 

My personal view is that I like my telescopes to be good on a wide variety of objects.  I have scopes that perform well on planets but I don't call them "planetary scopes."   This is a term I find irksome because what it means is that the user wants to employ said telescope on planets; and also, it implies that other scopes are NOT planetary scopes.  Well,  all scopes can do *something* with the planets.  But an f/5 80mm telescope is not the first pick for that function.   Planets like magnification and viewing planets is more relaxing at 1mm and larger exit pupils.  So slow refractors are a good pick in small apertures.  

 

Greg N

The C6 that I already own seems very good based on my medium-level of experience.  My main questions are: is there something as good, or better, for planets, that is even easier to set up (lighter, smaller).  It sounds like I'm probably best off just sticking with the C6 since it pretty much meets all my needs.  However, if there was a scope that'd be better suited for brighter objects, I'd be open to getting it.  I was thinking maybe a different design like a Mak or refractor might be better for heavy light pollution.  Also, I think I'm just a little obsessed with Maks because they look cool.  For around $400, I thought maybe it wouldn't hurt to try one out and just put it on my C6 mount.  On one hand, two scopes are better than one =)  On the other, I'm a little worried it'd perform so similarly to my C6 that it wouldn't be worth it.



#17 ET_PhoneHome

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Posted 29 July 2020 - 03:10 PM

Greg, you bring up a good point that I often forget: I live in a dry climate and almost never need a dew shield, and on the dampest nights the factory plastic dew shield has been all I've ever needed.  The OP didn't say where he lives but I should remember that for many folks, SCT's do come with an extra issue that mine don't have.

 

Also, I'd generally pick my C8 over the C6 for planets (or most else), too.  It just so happens that I bought a Porta II on a Berlebach report during Vixen USA's recent sale a couple of months ago and have been having a lot of fun with it, the C6 and my new f/7 AT80ED.  I'm a dyed-in-the-wool GEM guy, but it's been a blast to pick up that small, light rig and move it around my yard without a thought of messing up my north alignment, even if it takes (at the most) two minutes to realign my GEMs.  That's the reason I've been getting reacquainted with frequent use of my C6 for the first time since I bought my SW120ED.

 

BTW, for the OP and posterity, the C6 on the Porta/Berlebach is even lighter and easier to handle than the 80mm and reveals more, although both are well within grab and go limits.  The little 80 is sharp and wide, though, so it may edge out the C6 for travel.  At some point it gets hard to argue with 2+ more degrees FOV.

I love portability, but how can you guys stand to observe without a motorized mount?  I can live without GoTo, but manual tracking non stop is not for me.



#18 dusty99

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Posted 29 July 2020 - 03:27 PM

I just give the little knob an occasional turn... lol.gif

 

 

I love portability, but how can you guys stand to observe without a motorized mount?  I can live without GoTo, but manual tracking non stop is not for me.


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#19 ET_PhoneHome

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Posted 29 July 2020 - 03:28 PM

I just give the little knob an occasional turn... lol.gif

That's what she said wink.gif


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#20 barbie

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Posted 29 July 2020 - 04:25 PM

For lunar, planets and double stars, I use a Takahashi FC76 DCU and extender CQ and I get excellent views!! Sure, the image won't be as big and bright as in a C6, C8, or C14 but it will be tack sharp. When I can push the magnification, 240X is no problem but your skies have to be able to support high magnification in the first place so for me and my sky, a 3 or 4 inch is the largest aperture I can practically use. A large SCT or reflector didn't help in the planetary detail deptartment when I had them.  If your situation is different, then a larger refractor, SCT, or Newtonian would be better if you can handle the weight or permanently mount one.


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#21 Jon Isaacs

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Posted 29 July 2020 - 04:38 PM

You want a fast refractor for planets....that is cold fire and hot ice.  Let us say you get the very short AT 92 (f/5.5).  You would need a 5 or 6 mm ocular just to get to 92x which is not a lot on planets....better than nothing, but not a lot.  But to get to 184x you're going to need a 3mm (or a little less) eyepiece and you're going to be observing at 0.5 mm exit pupil. 

 

Those oculars exist, you can do it.  But you're stretching the capacity of the scope and your eye if you want to do this for a long time.  You might also discover what is in the "attic of your eyeball" which is to say all the dust and grime in there that you didn't know about and don't want to know about.

 

I have had different experiences with small aperture viewing.  First of all I think if you're going to get a small refractor you might be better with a longer one like the Vixen ED81s which is now marketed as the SD81.  Because it's f/7.7.  Now you're looking at a 4 mm to get to 160x and that may not sound like much but at the high end these small increments matter.

 

 

In my mind, this is really a non-issue.  Any 4mm eyepiece with enough eye relief to be usable will be identical in design to a shorter focal length eyepiece.  To achieve 160X, the 81mm will require a 3.9mm eyepiece, the 92mm will require a 3.1mm eyepiece.   The 92mm has the aperture advantage so if it is of decent optical quality, it will provide better views. And of course, one can always use a Barlow.

 

But it all depends on ET's budget.  I see people suggesting scopes costing thousands of dollars to replace a C-6 and/or a 5 inch longer focal length achromat.  

 

The C-6 will give the 4 inch a good run for it's money and ET already has it.

 

Jon


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#22 ET_PhoneHome

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Posted 29 July 2020 - 05:10 PM

Thinking about the magnification issue, it seems sticking with a longer FL scope would be best.  I have a Baader 8-24 zoom eyepiece, a Meade 5.5 UWA and a few others.  On a 600mm FL scope, and 8mm EP is only going to give me 75x.  Seems like the zoom EP would be a more versatile on a scope similar to the C6 (1500mm FL).

 

I know they're not really lighter, but they're not much heavier, either, so I was thinking maybe an 8SE or a 150mm Mak would be a good upgrade from the 6SE.  It's a tough call because light pollution really ruins dark skies around here, so I'm not sure the extra aperture of the 8 would be worth it.  Supposedly, smaller Maks can hold their own against larger SCTs.  Then again, going to an 8" SCT is going to be a nice boost in light gathering compared to my 6, and it should fit on the mount I already own.  It's a tough call.


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#23 Mike W

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Posted 29 July 2020 - 05:40 PM

A TV102 f8.6 I use mostly for doubles and clusters but it does well on the planets for it's size.

 

5.jpg


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#24 gnowellsct

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Posted 29 July 2020 - 06:13 PM

I love portability, but how can you guys stand to observe without a motorized mount? I can live without GoTo, but manual tracking non stop is not for me.

I have two refractors that are airline portable. I have given a lot of thought over the years as to how one might travel with an SCT and a gemand once I even corresponded with Damian peach about it since he flies his c14 all the way down to the Canary islands. Or anyhow some island.

The thing can be done but it is expensive and cumbersome and then you have to rent a car and fit it all in.

And then there's the question of the battery.

So I thought well okay I could get a small battery and just take a refractor which has less need of dew control but still from the point of view of airline travel and packing this is something of a challenge.

And there are counterweights. They only function of a counterweight is to exist and manifest weight.

I do have a lightweight vixen mount but I really don't like using it that much because it uses a clutch lever system which I find inconvenient in annoying. It's a good little mount. But its other defective is that I'm spoiled rotten with regard to mount stability and traveling with a light duty mount would diminish the reason to travel which is to go somewhere else and enjoy a better sky.

After looking into the matter and getting a number of suggestions here it seemed to me that the best solution to airline travel is alt az with no battery power supply. And that I could get the stability I wanted with a DM6 and a tpod which I think could, if one were clever about it, fit into a hard and adequately protective suitcase. The setup time is lightning quick and I have encoders so I can find stuff with a computer if I want to. The last few times I've been out though I just star hopped around.

The investment has been successful there have been a number of situations where I didn't want to do the full 45 minute to 1 hour setup for say a 2 or 3 hour viewing window under conditions of dubious skies or a rising moon. I can drive somewhere and set up and be observing in 10 minutes and I believe I could carry this gear on an airplane and then carry it in a rental car.

The only catch to this plan is that the plague is upon us and now I'm not going to fly anywhere. But I think I am more confident now about how I could go somewhere with a good telescope on a good mount. The price is giving up tracking.

Edited by gnowellsct, 29 July 2020 - 06:16 PM.

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#25 MisterDan

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Posted 29 July 2020 - 06:29 PM

Preface:  I'm a mak fan and a planet junkie.  Not an astro imager.  Not a Schmidt-Cassegrain owner.  Got my MK67 almost 20 years ago.  My "biggest" refractors are 75mm and 80mm.wink.gif

 

I think you already have PLENTY in the 6SE, unless its optic is "wanting" or "blah."  Make sure it's collimated -- not merely "close enough," but as well as you can get it.  Also, make (and USE) a light/dew shield.  A 1/4-inch-thick closed-cell foam pad (exercise/yoga mat or kids camping pad), sharp scissors, duct tape, and about 5 minutes of your time is all you need).  If I had a quality 6SE optic, I would not replace it with a 5-inch Mak.  I'd consider any "gain" in portability to be minimal (practically negligible).  If I were to consider a 4-to-5-inch refractor, I'd target a wider field scope (i.e. f/6-7ish) so as to avoid "overlap" with the MK67.  Then I'd realize that my ~3-inch refractors already fill that "gap," and I'd forget about a 4-to-5er (be it maksutov or refractor).

 

If your target is a significantly more-portable scope package than the 6SE, then, no - I don't think there's a "better" option (my opinion, of course).  Again, if you're after big, wide fields, or if the 6SE's optic is less-than-good, then things might be different... but even then -- if it were me -- I'd target another 6-incher, rather than a smaller scope.

 

With regards to an UPgrade in aperture, light pollution is not a major impactor in planet observations.  Do what you can with unwanted/stray light (i.e. light shield, maybe even an observing hood) and try not to "overthink" things.  If you can manage an 8-inch SCT (i.e. still "portable enough"), then maybe give it a shot.  Perhaps you can borrow or test-drive a nearby astronomer's.

 

Your sky's "seeing," on the other hand, *can* be a significant factor in deciding whether or not to go bigger.  If your typical skies are turbulent and "swimmy," and they rarely allow for pushing your 6SE's limits, then an 8-incher likely won't help...with the planets, anyhoo.

 

Best wishes and clear skies. 


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