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smaller refractor for planets, doubles, moon, etc?

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#26 Jon Isaacs

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Posted 30 July 2020 - 07:41 AM

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.

 

 

With a steady mount with slow motion controls, it's not much of a problem.  I have found I prefer manual tracking.  But, like most things, it's not just any old piece of gear, it takes the right mount that's setup properly.

 

Jon



#27 Hesiod

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Posted 30 July 2020 - 10:52 AM

If found too large the 5" on its eq mount, do not think a 4" would be much lighter; and if are disappointed by the C6, guess what could be downsizing to 80mm...

I have a light-weighted 4", which use with a sort of mount especially designed for travels, but even so it is a 12-15kg (depending on the tripod I use) telescope:

gallery_215679_8115_79883.jpg

 

Your SE6 is already a nice compromise between performance and portability, that being its main virtue; on the other hand, refractors have the worst aperture/size ratio.

If are not pleased by the C6, IMHO your best course of action would be to get another "folded" telescope.

Intes Micro made excellent samples, with really good optics and decent mechanics, their biggest disadvantage being their "bulkiness" if compared to Celestron's SCTs: my M500 (5" f/10) has roughly the sizes of your C6, the 6" (of which two "visual" models were made, f/10 and f/15) runs in the same league as the C8.

Unless your C6 is a "lemon", IMHO however  would make not much sense to downsize to an M500, unless are interested in its greater flexibility as well (the telescope can properly handle 2" eyepieces and reach* a fov around 2°)

 

 

 

*the focal I have measured is around 1500mm with 2" diagonals



#28 gezak22

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Posted 30 July 2020 - 11:12 AM

Small refractors are popular with the double star folks!



#29 Sarkikos

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Posted 30 July 2020 - 12:36 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?).

A 4" ED/APO would be good - but not great - for planets, doubles and the Moon.  A 4" achro would not be so good unless the focal length is very long.

 

The 6" SCT will probably show you more as long as it's well collimated and acclimated.  Aperture does count for something.

 

Mike


Edited by Sarkikos, 30 July 2020 - 12:41 PM.


#30 mikeDnight

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Posted 30 July 2020 - 12:53 PM

I'm mainly a lunar and planetary observer and I'm more than happy with the high definition views provided by a 100mm refractor. I've used a Tak FC100DC for the last five years and have just recently replaced it with a FC100DZ. I've owned a Tak FS128 and FS152 and they were great, but I've never been happier than I've been with these 100mm FC refractors. Moon and planets can be mindbowingly detailed. The Tak takes some beating if you're looking for high definition views.

 

My FC100DC was so light and easy to use it wore me out.

2016-12-20 22.56.49.jpg

 

The DZ is a little heavier and longer at F8 but not by much. With a binoviewer these scopes are powerful lunar & planetary instruments.

IMG_7067.jpg


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#31 barbie

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Posted 30 July 2020 - 01:12 PM

Agreed Mike! Although 4 inches became a little too heavy due to my shoulder problems, I've found that a 3 inch in the hands of an experienced observer can reveal much detail on the planets, especially a Tak fluorite apo like we use!!  I simply don't buy the explanation of those that say a 3 inch won't show much!! I've seen the proof of the contrary!!  Sure, larger aperture is nice, but what good is it if you're unable to physically handle it or worse yet, have it but don't use it as often or at all!!  As Spock once said in Star Trek, "Having is not so great a thing as wanting"!!  I've had the large beasts, I know what they can and can't show. I would rather have a top notch small refractor that CONSISTENTLY shows razor sharp images and that gets used than a large refractor(or other type of scope) that may do the same but doesn't get used much because of its weight/ mounting requirements. Been there, done that!!


Edited by barbie, 30 July 2020 - 01:16 PM.

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#32 ET_PhoneHome

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Posted 30 July 2020 - 02:15 PM

Thanks for all the input!  I decided to go with an 8" SCT.  So much for going lighter and more portable, haha.  In reality, though, it's only 3 lbs heavier than my current 6" scope.  Maybe someday I will look into a nice Tak refractor.


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#33 BillP

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Posted 30 July 2020 - 03:48 PM

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.

 

Find an old Celestron 102 ED Doublet f/9, same as the SW 100 f/9.  Very much full apochormats.  Celestron build is quite light and rides on a Porta-II mount just fine.  Got mine used for around $300!  A light, easy, and planetary capable rig.
 


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#34 Marcus Roman

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Posted 30 July 2020 - 05:15 PM

The most grab and go refractor with exquisite optics I ever looked through, great on planets and moon, is the fluorite doublet multi coated Mizar FA80, blue tube, first run 1983. As an owner of Vixen FL80 and Taka FC76, I don’t think I am biased by the fact I own it.

If you can, try on Jupiter or Saturn at 200x and in steady nights at 300x.

A mystery for a mere 7,5 focal length. Star test is great, better than my Pentax 105SD.

 

Attached Thumbnails

  • E81A0A65-2BE5-4A88-BB66-5EC39391DA78.jpeg

Edited by Marcus Roman, 30 July 2020 - 05:17 PM.

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#35 StarWager

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Posted 30 July 2020 - 05:30 PM

Thanks for all the input!  I decided to go with an 8" SCT.  So much for going lighter and more portable, haha.  In reality, though, it's only 3 lbs heavier than my current 6" scope.  Maybe someday I will look into a nice Tak refractor.

LOL!  So in the space of 24 hours, you did a 180!

I will save my comments then, on my 80mm triplet, for portability and viewing.  laugh.gif



#36 ET_PhoneHome

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Posted 30 July 2020 - 07:07 PM

LOL!  So in the space of 24 hours, you did a 180!

I will save my comments then, on my 80mm triplet, for portability and viewing.  laugh.gif

Haha, yeah.  Most of the godo refractors are a lot more than I want to spend at the moment.


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#37 bobhen

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Posted 31 July 2020 - 06:20 AM

Thanks for all the input!  I decided to go with an 8" SCT.  So much for going lighter and more portable, haha.  In reality, though, it's only 3 lbs heavier than my current 6" scope.  Maybe someday I will look into a nice Tak refractor.

A C8 is a very capable telescope and brings a lot of ergonomic advantages to the party. But to perform at their best Cassegrains need some more attention than  do refractors.

 

You will need to collimate the telescope, but that isn’t too hard. The most important thing you need to do for high power observing on the moon and planets “after collimation” is develop an “aggressive” acclimation strategy. Cooling/thermals can be detrimental to high power observing.

 

Some acclimation strategies to consider…

 

1. If you get a Celestron Edge, you can get the TEMPest cooling fans from Deep Space Products: they work. You can also use the fans while observing
2. Some have had success with wrapping the OTA in insolation: If you do, you need to wrap the complete tube including the back and dew shield
3. Setting the scope outside (in the shade) for a 2 – 5 hours depending on temperatures can also work: You need to plan ahead
4. Keeping the scope in an unheated garage will give you a jumpstart on cooling/acclimation

 

Have fun

 

Bob


Edited by bobhen, 31 July 2020 - 08:00 AM.

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#38 MalVeauX

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Posted 31 July 2020 - 07:53 AM

Thanks for all the input!  I decided to go with an 8" SCT.  So much for going lighter and more portable, haha.  In reality, though, it's only 3 lbs heavier than my current 6" scope.  Maybe someday I will look into a nice Tak refractor.

This is a good choice, C8's are very popular for lots of great reasons. Lots of aperture in a small package. Long focal length so easy on eyepieces and great for small subjects that you want to magnify rapidly without exotic eyepieces. Small and portable and easier to mount than some 4" and 5" refractors! The mirror is still not super big so it doesn't take hours to reach thermal equilibrium.

 

Per your other comments, there's no magic in refractors, maks, newtonians relative to cassegrains when you're comparing aperture. There's minute differences, but a 150mm Mak does not compete with a 200mm SCT for example, Maks are not magical or special in some way, they're just another design. Aperture is aperture though. The only key minute difference is that an unobstructed optic will have the highest throughput of light and highest contrast (if well figured and corrected) for the aperture compared to a similar size aperture of a mirror design with folded light path and a second mirror (resulting in obstructed optics and the light throughput is reflected and it's not 99%, it's less, so you lose some light both to the obstruction and the mirrors themselves). A Mak is obstructed just like a SCT, the difference in obstruction size is small and not worth splitting hairs over. 150mm aperture for example will not "hold its own" against a 200mm aperture when comparing a Mak & Cassegrain. They're more similar than not. The only competition would be something like a 127mm refractor holding its own or besting a 150mm Mak or SCT, that is a more true comparison for the reasons mentioned above. But even refractor magic doesn't beat a much larger aperture (assuming well figured, well collimated, thermally acclimated). Lots of magic mystical things out there on tiny refractors and various designs people are just fond of. But at the end of the day, a larger aperture, well figured, collimated and thermally acclimated will simply do what those tiny instruments cannot do because of non-mystical physics and the instruments were built according to physics and not magic. You're set! waytogo.gif

 

Next step is to get binoviewers if you don't already have them. C8 + binos + planets is just an incredible, compact, portable package for this (and no corrector needed on a SCT to come to focus so you can use the eyepieces at native focal length).

 

Larger aperture will win the day (assuming collimation is good, thermal acclimation is good, figure of optics are good at least in the center area), take a look at this (assuming you want to keep around 1mm exit pupil for brightness after magnification):

 

102mm aperture (4") 714mm focal length will hit 1mm exit pupil with 102x magnification

127mm aperture (5") 1500mm focal length will hit 1mm exit pupil with 125x magnification

150mm aperture (6") 1500mm focal length will hit 1mm exit pupil with 150x magnification

200mm aperture (8") 2000mm focal length will hit 1mm exit pupil with 200x magnification

 

Notice the relationship between magnification, exit pupil and aperture? So if you want to view something at higher magnification and maintain enough light (exit pupil) to see it, you need aperture.

 

Very best,


Edited by MalVeauX, 31 July 2020 - 07:58 AM.

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#39 mikeDnight

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Posted 31 July 2020 - 08:02 AM

Haha, yeah.  Most of the godo refractors are a lot more than I want to spend at the moment.

Skywatcher ED's are seriously good refractors, so don't let their relatively low cost lead you into believing they are no good. A SW 100mm or 120mm will play very happily alongside a Takahashi. Try one visually alongside an SCT and see how they compare! Chalk and Cheese comes to mind!



#40 Chris Johnson

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Posted 31 July 2020 - 08:08 AM

If you are going to mount the 8” on the SE mount you will have to remove the bezel. The 6 & 8 SE mounts use different-lasting bezels. I have removed the bezel from mine to make mounting the scope easier and replaced the bezel with a flat plastic piece. You can check yours by removing the bezel and see if there is a 6 or 8 molded on the inside.


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#41 bobhen

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Posted 31 July 2020 - 08:20 AM

 

Notice the relationship between magnification, exit pupil and aperture? So if you want to view something at higher magnification and maintain enough light (exit pupil) to see it, you need aperture.

 

Very best,

You make some good points but living in Florida is one thing (Florida has pretty good seeing and more stable temperatures) whereas living in the northern parts of the country requires different and more aggressive seeing and acclimation strategies.

 

With regard to magnification, you can’t just assume that a larger telescope will take magnification and remain sharp just because it is larger.

 

If the SCT has optics that are not as well figured as say a high end mak or refractor or Newtonian (which they are not) then it will get softer sooner when magnification is pushed, even if it is larger.

 

The moon and planets are bright so light gathering is not as important as high quality optics.

 

Resolution is also limited by seeing and it is much more likely that an 8” telescope will be seeing limited than a 4-5” telescope.

 

So its not just “get the larger scope because it WILL be better”. On the moon and planets – other things must be considered like: location (with regard to seeing) quality of the optic (the higher the quality the better) and acclimation (some telescope designs are better than others)

 

Bob


Edited by bobhen, 31 July 2020 - 08:24 AM.

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#42 Jon Isaacs

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Posted 01 August 2020 - 08:08 AM

Per your other comments, there's no magic in refractors, maks, newtonians relative to cassegrains when you're comparing aperture. There's minute differences, but a 150mm Mak does not compete with a 200mm SCT for example, Maks are not magical or special in some way, they're just another design. Aperture is aperture though.

 

 

Aperture is aperture.. 

 

And optical quality is optical quality.  

 

That's where there's magic.  

 

Jon



#43 ET_PhoneHome

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Posted 01 August 2020 - 11:58 AM

Hopefully, the 8" I ordered (Meade LX65 ACF) will be a noticeable upgrade for visual observing.  I am also interested in trying my hand at some photography, and it sounds like a lot can be done with a small refractor.  I'm getting a iOptron StarGuider Pro, and since I already have a good DSLR with a lot of lenses, I'm going to try shooting with that for a while.  If that works well, I may look into a refractor like the Orion 80mm ED.  Although, I'm not sure how much of a difference that would be compared to my 200-500 lens, which is f/5.6 and has a 95mm front element?



#44 ET_PhoneHome

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Posted 03 August 2020 - 11:36 PM

So I think a refractor may be back on the table smile.gif  I tried the 8" SCT on my 6SE mount, and IMO, it's not stable enough.  Also, even though it's just a bit heavier, the 8" scope is pushing the limits of a quick and easy setup.  My 6SE is great, but I'm basically just looking to add something new to the stable.

 

It seems a 4" refractor would be a good size.  At the moment, I have a Meade 5", but it's an achro.  Also the mount/tripod is almost 20 years old, and it's acting up.  At this point I'm thinking I keep the 6SE, and maybe just add a refractor.  I'm also thinking that I'd just get a new mount, too, since even if the refractor is light enough, it's going to be awckwardly long on the 6SE mount which was meant for an SCT.

 

Those 100mm Taks looks nice, but I think that's beyond what I want to spend right now.  Is there something similar in quality, but a little less? And then there's the mount.  At the very least, I'd want a tracking mount, but would really prefer a goto.  I'm guessing most refractors in this size range are around 10 lbs or so.  What would be a good goto mount that would pair up nicely with a scope like that?  The ideal thing would be a package deal with the mount and scope, but it seems a lot of packages come with mounts that are too weak for the scope. confused1.gif



#45 Hesiod

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Posted 04 August 2020 - 12:34 AM

Usually "APOs" are sold as OTA.
If want a goto mount may look for the az/eq5, or light eq mounts in the class of your Meade.
iOptron minitower is, beside the az/eq5, your only option for an alt/az at such price range.
As for the refractor itself, Skywatcher 100ed and 120ed (size-wise are very close) are good options, but by now there is a large selection of models rebranded under several labels at similar prices.
Mind however that the full telescope will be more or less as large and as cumbersome as your current 5" Meade
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#46 213Cobra

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Posted 04 August 2020 - 02:36 AM

So I think a refractor may be back on the table smile.gif  I tried the 8" SCT on my 6SE mount, and IMO, it's not stable enough.  Also, even though it's just a bit heavier, the 8" scope is pushing the limits of a quick and easy setup.  My 6SE is great, but I'm basically just looking to add something new to the stable.

 

It seems a 4" refractor would be a good size.  At the moment, I have a Meade 5", but it's an achro.  Also the mount/tripod is almost 20 years old, and it's acting up.  At this point I'm thinking I keep the 6SE, and maybe just add a refractor.  I'm also thinking that I'd just get a new mount, too, since even if the refractor is light enough, it's going to be awckwardly long on the 6SE mount which was meant for an SCT.

 

Those 100mm Taks looks nice, but I think that's beyond what I want to spend right now.  Is there something similar in quality, but a little less? And then there's the mount.  At the very least, I'd want a tracking mount, but would really prefer a goto.  I'm guessing most refractors in this size range are around 10 lbs or so.  What would be a good goto mount that would pair up nicely with a scope like that?  The ideal thing would be a package deal with the mount and scope, but it seems a lot of packages come with mounts that are too weak for the scope. confused1.gif

Have you considered going slightly sub-4" in the form of the Astro-Tech AT92 triplet. It's f/5.5 and has incisive, high resolution and contrast optics. It's short, so the moment arm won't be challenging to your chosen mount, and because of the very high optical quality, you can get to longer effective focal lengths via Barlow or Powermate if you don't want the expense of a bunch of short FL eyepieces for higher magnifications. Good focuser and build quality. Easy for when you're in a fiscal situation arguing against a 100mm Takahashi and a yard cannon mount.

 

Phil


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#47 Simon B

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Posted 04 August 2020 - 02:40 AM

The most grab and go refractor with exquisite optics I ever looked through, great on planets and moon, is the fluorite doublet multi coated Mizar FA80, blue tube, first run 1983. As an owner of Vixen FL80 and Taka FC76, I don’t think I am biased by the fact I own it.

If you can, try on Jupiter or Saturn at 200x and in steady nights at 300x.

A mystery for a mere 7,5 focal length. Star test is great, better than my Pentax 105SD.

 

Underrated comment right here  -  the Mizar FA80 is a rare, almost mystical scope in Japanese circles. The only scope to dethrone the already impossibly sharp Vixen FL80S....

 

And you have a Pentax 105SD as well.....  bow.gif

 

 

 

What was the thread about again? Oh yeah, right. -  if the Tak 102 is too expensive (can't blame ya), then maybe an AT102ED would suit your needs, or an Explore Scientific 102 Triplet, for something a bit fancier with better colour correction  (*Haven't actually used these, but I would strongly assume the ES triplet would have better correction than the AT doublet)

 

Skywatcher 100ED F9 is a popular one, but you said you value portability, so...


Edited by Simon B, 04 August 2020 - 02:40 AM.


#48 dweller25

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Posted 04 August 2020 - 03:12 AM

I have a bad back and have been experimenting with a C6 on the planets and Moon.

it’s rather good - very light and short but it needs managing thermally.

I wrapped mine with two layers of refectix and it improved its usability dramatically - no more long waits for it to cool down and dewing of the corrector takes significantly longer.

I think you may already have the scope you want waytogo.gif


Edited by dweller25, 04 August 2020 - 09:37 AM.

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#49 ET_PhoneHome

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Posted 04 August 2020 - 07:05 AM

Have you considered going slightly sub-4" in the form of the Astro-Tech AT92 triplet. It's f/5.5 and has incisive, high resolution and contrast optics. It's short, so the moment arm won't be challenging to your chosen mount, and because of the very high optical quality, you can get to longer effective focal lengths via Barlow or Powermate if you don't want the expense of a bunch of short FL eyepieces for higher magnifications. Good focuser and build quality. Easy for when you're in a fiscal situation arguing against a 100mm Takahashi and a yard cannon mount.

 

Phil

Yeah, that might be a good option.  I'm not dead set on 4".  I basically just want something that's more manageable than my 5" Meade, that's not an achro (like the Meade) and has better optics.  I keep reading that the AT scopes are very good.  Sounds like the AT is something I could also use for imaging, so that's another plus.



#50 ET_PhoneHome

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Posted 04 August 2020 - 07:06 AM

I have a bad back and have been experimenting with a C6 on the planets and Moon.

it’s rather good - very light and short but it needs managing thermally.

I wrapped mine with two layers of refectix and it improved its usability dramatically - no more long waits for it to cool down and dewing of the corrector takes significantly longer.

I think you already have the scope you want waytogo.gif

Could be smile.gif  I do like the C6 a lot, but was considering a refractor to add some variety to the mix.




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