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Frac / dob / frac / dob / frac / dob.....


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Hi everyone

I've been without a scope for a few months now after selling a cumbersome 8" eq newt that had been neglected for some time. I've been enjoying the time rediscovering things with some 20x80 bins and have been genuinely impressed with what can be seen, especially the lovely wide-field views.

My original plan had been to buy a sizeable Dob - somewhere between 12 and 16". I'm staggered at what is available nowadays within a reasonable budget. I would be prepared to stretch to the £2k + range for the larger end of this size range.

But recently, having read some great observing reports from Nick (Cotterless45) and also some of the wonderful Stephen O'Meara books, I'm strangely tempted by a 4" to 6" frac. Something like a SW StarTravel. I can't really explain why but something's really grabbed me, particularly around portability and probably getting better use.

My main interest is deep sky, but I also enjoy some planetary and lunar and, more recently, a bit of solar through Baader film. I'm almost exclusively visual, but have toyed with the idea of limited AP. I'm by no means advanced, but have been on and off into astro for 20 years, although a recent tally betrayed the fact I've only tackled around a third of the Messier objects (oh, the shame!).

So I could do with some help identifying the relative pros and cons of the two sorts of scope. I've listed below what I've thought of, but would really welcome anyone else's input. I'm always blown away at how much wisdom there is on this forum!!

BIG DOB (say 12" for argument's sake)

Pros: aperture, value-per-inch, it's what I'm used to, wow factor on bright deep sky

Cons: Cumbersome, cool-down time, missing short windows of opportunity, collimation faff, less portable for family holidays (unless I went down the ultra-light route).

4 - 6" FRAC

Pros: Portability; no cool-down (= being opportunistic); contrast; no need to collimate; use for limited AP (not a high priority, but a nice to have); wider, rich fields to exploreCons: disappointing views compared to my old 8"?, might not quench the aperture fever, chromatic aberration (likely to be there in a fast frac I suppose)

Can anyone suggest what I might have missed? Budget can be up to around £2k; if it was a frac I'd probably want to spend less.

Thanks

Paul

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What are you going to mount the Frac on? A 6" Frac will need an HEQ5 (you might get away with an EQ5), you're then in similar territory to the Newt you just got rid of.

A 16" Dob is only £1700, well within your budget - http://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-400p-flextube-dobsonian.html. Cool down won't be an issue, Dobs are generally easier and quicker to set up than EQ setups. And another bonus is that collapsed they take up far less room, and they look a little like R2D2 :)

You could then have enough left to get a smaller sob (the 6" F8 Skywatcher dob is great) for family trips / holidays.

Cheers

Ant

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Hi Paul,

I agree with Moonshane - I did both though I went with the dob first. I just knew that buying one would encourage me to ponder the 'what if's ' so I went smaller on both to start with until I knew where I wanted to be ultimately.

I would go smaller and higher quality in both scopes from what you initially think you want - easier to use and convince yourself to get out in the freezing cold, easier to transport, and perhaps easier to sell on when you upgrade.

Regards

Dannae

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Hi Paul

Might be worth noting that, Mr O'Meara has done much of his observing under very dark skies.  Fast, wide field refractors are wonderful under those conditions.  Any contrast increase is minimal with LP.

Your 20x80s would give similar views to a small frac. when on a tripod?

I wouldn't go too big with a cheap dob.  They are usually very heavy (MDF) and bulky.  Keep it cool to avoid cool down issues?  Maybe a 10 - 12" collapsible SkyWatcher?

You may find that it is a compromise whichever route you take...  :)

Good luck

Paul

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Hi there I had a two grand triplet frac thinking that this would make me happy it did to a point but reflectors are king in my eyes ,fracs for me are for imaging ,the images of dso work visual do not do it for me

You could buy both as suggested but if it was me I would go for a big second hand dob there plenty of trustube ones out here as for holidays a pair of good binos will do why spoil a relaxing holiday with a scope,

Pat

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If you want a scope to run outside at an oppertune moment then a 6" refractor is not aplicable, a 4" might just be, however if you are looking at the Startravel you will get a lot of CA and that sounds as if it is something you are not overly used to.

A large dobsonian sounds as if that is what you want, my concern is that people go bigger and bigger then sell up. I would think they are bought for the wrong reason or they just become too big. If the reason for selling the 8" was losing interest then I doubt a 12" is going to do much. Bigger, heavier, more hassle I suspect they may show things better but not realistically more things.

There seems to be a lack of nice 80-90mm refractors in the UK, the Rother Valley 80/600 might be a good grab and go achro, but still need a reasonable mount for it. The Vixen Mini Porta might do a good job. However that eats up £400.

You seem to be in the Fens so it should be dark whereever you are, if not your garden then a short trip outside.

I suspect the answer is based on why did the 8" go.

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If you want to run outside quickly with a lot of aperture, a 6" frac is indeed rather a lot. A 4" frac is definitely better. My choice would be the C8: same weight but more compact than the 4" frac of a colleague, and about 4x more light. I also use a frac: 80mm F/6, which is nice and portable, but strangely does not set up much quicker than the C8. Cool-down time can be an issue, but I simply store the OTA in a garage which is close to ambient temperature.

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I think the answer depends a lot on your circumstances. Do you live somewhere dark, where you can observe in your garden? Do you like to take a scope away on holiday with you? How big is your car? Etc etc

Whilst I'm known for a minor, but untreatable obsession with Apo refractors, I do know that one day I would love an 18" truss dob to take to dark sites. I also know that at the moment I wouldn't use it because family circumstances would not allow it and I live near Heathrow so light pollution is bad.

My most used scopes are my small refactors which I can put out for quick half hour sessions when I get the chance, or can take away to dark sites when I go on holiday. They are also great for solar with a herschel wedge.

I think I concur with other comments that you could easily get both types within your budget. I would probably go for something like a 250px Dob as that will give you fabulous views whilst still being fairly easy to handle.

You could perhaps consider a used 120ED refractor which would give lovely planetary, lunar and brighter DSO images particularly from a dark site, plus would not have the mounting requirements of an f8 6" achro, a decent alt Az giro style mount would do.

You could always also get an ST80 for cheap, portable widefield views wherever you go. Obviously similar to the binos but with more magnification potential. Could go on a photo tripod.

Just a few thoughts from a different angle.

It's strange actually, my 12" dob in many ways is much quicker to setup than my fracs. It is one trip down the garden with it on the sack truck, whereas the fracs are generally 3 or 4 with more assembly involved. Despite this there is some psychological block in my mind which means I more often use the fracs, and under my skies actually the difference is not as big as you might expect.

Anyway, good luck with your choice.

Stu

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From the edge of town , I have found very little difference in views between a 10" Dob and a 6" achro. I think your choice of weapon depends on what you 'd like to observe and your light pollution.

I prefer 1200mm ota's and a top end magnification of x200, stretching to a bit more under good seeing. I had the 8" OO f6 on an SP mount out this morning and the Jupiter views were just stunning , before cloud came in. It's a very handy size for general observing and in either eq or Dob form is easy to grab and go or transport.

I really think you've got to see scopes in use. What appears on websites can give you little idea of the weight and size or how fast scopes don't enjoy reasonably priced eyepieces.

I started off with a simple 8" Dob. With a Telrad and a handy seat , I thoroughly enjoyed learning the skies and star hopping. As your interest grows, you might decide that a more specific scope suits you. I find faint fuzzies increasingly difficult from home, but in any aperture they are easier from dark sites. I like bright planetaries , planets and stars now.

A 6" achro is a light gulper, it'll show the faint stuff , pick up M1 , M82 and NGC 7331 for example. It'll show you the brightest nicest planetary nebulae. It'll get you sub 1" splits on double stars.

It'll also stun with star clusters, the stars being clean and pin sharp . It will however need at least a 16" extension pillar on an Heq5 mount minimum.

F8 may bother you with a bit of ca, which a Baader semi apo filter will control. You may need to figure in a decent focuser, rotatable will make life easier.

My objective cell is collimatable, not really an issue, but I like to check it now and again. You're also going to figure in a dew heater and a leisure battery power source for tracking , if need be.

It's quite a handful putting this up on the mount.

I can only give you my experience with a 10" Lightbridge. It's heavy, I move the ota out, then the base. It is a truss and you're wise to figure in a shroud and a dew shield. A comfortable table bench , 18" high will make viewing delightful. The whole lot will collapse down to the base, the top section and the poles. Very handy when filling up the car. Close down the aperture and you'll be fine with planets and double stars.

I've looked through big Dobs at dark sites. It's easy to get blown away with the views. These don't really translate to going home to light pollution.

I'd like a crack at a 5" achro with a 1200mm focal length. I wouldn't go longer, you need to have no wind, pretty good mount and a comfortable seating position for a long beastie.

I think that whatever you decide on, you'll be affected mostly by your sky conditions. In that respect , a refractor will blast through haze and with a 2" focuser give you enough to bring a smile . A 4" will provide you with greater contrast , but you'll be missing some fine deep sky objects.

A visit to a star party or the IAS is great. If you try before you buy and speak to users, you will get better opinions. Personally, if I had a bit of spare, I'd be tempted by Istar Uk 150 f8 on an Heq5 pro mount ( used).

Don't be swayed by the Jedi of the Big Dob Mob, they're all weight lifters !

Nick.

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I think the answer depends a lot on your circumstances. Do you live somewhere dark, where you can observe in your garden? Do you like to take a scope away on holiday with you? How big is your car? Etc etc

Whilst I'm known for a minor, but untreatable obsession with Apo refractors, I do know that one day I would love an 18" truss doc to take to dark sites. I also know that at the moment I wouldn't use it because family circumstances would not allow it and I live near Heathrow so light pollution is bad.

My most used scopes are my small refactors which I can put out for quick half hour sessions when I get the chance, or can take away to dark sites when I go on holiday. They are also great for solar with a herschel wedge.

I think I concur with other comments that you could easily get both types within your budget. I would probably go for something like a 250px Dob as that will give you fabulous views whilst still being fairly easy to handle.

You could perhaps consider a used 120ED refractor which would give lovely planetary, lunar and brighter DSO images particularly from a dark site, plus would not have the mounting requirements of an f8 6" achro, a decent alt Az giro style mount would do.

You could always also get an ST80 for cheap, portable widefield views wherever you go. Obviously similar to the binos but with more magnification potential. Could go on a photo tripod.

Just a few thoughts from a different angle.

It's strange actually, my 12" dob in many ways is much quicker to setup than my fracs. It is one trip down the garden with it on the sack truck, whereas the fracs are generally 3 or 4 with more assembly involved. Despite this there is some psychological block in my mind which means I more often use the fracs, and under my skies actually the difference is not as big as you might expect.

Anyway, good luck with your choice.

Stu

Sent from my iPhone using Tapatalk

My preferences are very similar to Stu's including that my 12" dob is the quickest of my scopes to set up and get using despite the others all being alt-azimuth mounted refractors !

For low to medium magnification viewing I can be using my 12" dob almost straight from the house. For high powers my refractors need some cool down time as well so it's "swings and roundabouts" as they say  :smiley: 

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You've got yourself into quite a quandary there Paul :)

I'd agree with moonshane. Funny that eh us both having similar taste in scopes...... :)

I like big dobs I also like fracs the reason I've not got a frac is twofold. First. I do nearly all my observing from dark sky sites and id be kinda loathe to drive for an hour or more to a dark sky site and only have brought a small aperture scope with me. Secondly I simply don't have the money for a frac and even if I did I'd spend it on eyepieces or something else for the dobs.

I should add that two observing buddies have lovely 5" and 6" Apo's so I get my frac fix from looking through theirs ;)

I guess thats the best advice I can give; observe with a few buddies with different scopes and get what ever compliments theirs.......Happy days.

Share your views with as many others as you can its great fun.

Good luck with your decision 

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I am in the one of each camp. My grab & go is an st120, I also have a 152mm Petzval Meade / Bresser. now only 32mm of apperture difference but miles away in terms of mounting.

Big dob, st120 and a few good ep's. May even have change for a Xmas drink :smiley:

Good luck with your choice.

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I'd definitely urge at least two options. I have the following scopes and just about feel it covers all eventualities.

  • 80mm f11 achromat - grab and go scope - almost instant cooling - sharp optics - great for lunar and double stars which are good targets between the clouds. occasionally used for white light solar with Lunt wedge.
  • 100mm f10 PST mod - HA specific
  • 120mm f5 Skywatcher achromat - used mainly as white light solar with Lunt Wedge. Occasionally, for wide field lower power views at night. Not bad on doubles and moon but 80mm f11 is better and dobs much better. All fracs mounted (max two) on Giro 3.
  • 150mm f11 dobsonian used on home made equatorial platform. Superb on doubles and solar system. Used often when the transparency is poor.
  • 300mm f4 dobsonian. My main scope of preference at night. Cools quickly and is pretty much my grab and go dob.
  • 400mm f4 dobsonian. Reserved now almost for two annual star parties or those autumn / spring nights when it looks like it will be clear from the afternoon. 

OK I have gone slightly over the top but it's great to have options.

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If you ponder the choice of Dob/Frac you often get the advice: get both (for good reason. If you want to go down that (ruinous ;)) path, in your case, I would get a dob first. The big advantage of my 80mm frac is not so much its compact size (the C8 is little longer and a bit heavier, and sits on the same mounts) but the wide FOV. This is where cheap fast fracs like the ST series shine. For high magnification they are not nearly as good as the much more expensive apochromats (or catadioptric scopes for that matter). As you already have 20x80 bins, they fill the wide field gap neatly (I use my 15x70 bins far more often than the little 80mm apo, even though the latter gives better quality and wider views). A set consisting of a dob with big bins covers more bases than a small frac with bins.

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My first thought would be ask yourself the questions -  Why did I not use the Newtonian?  What was it about it that made me stop using it?

Whatever the answer is, make sure you don't make the same mistake again!

You say that you stopped using it because it was too cumbersome.  Will a large Dob or large refractor going to be signifcantly less cumbersome?

I'm a great believer on the old adage "the best telescope is the one that gets used"

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You've mentioned that you've not used your 8" Newtonian because it was too cumbersome - it makes me wonder about the logic of the purchase of a 12" - 16" Dob?   This certainly isn't going to be any less cumbersome unless you mean it was just the use of the GEM you found hard work?

I'd take your budget at split it in to 3 equal amounts:

1. If you are visual only at the moment look the mount first at what you prefer to use:  EQ or Alt/az.   This may end up costing quite a bit more than you first expected but a good choice here will save you money in the future if you choose to buy a 2nd scope so it would be worthwhile to get something fit to take a much larger scope.  For instance the Berlenbach tripod with an Alt/Az head like the Giro.

2. If you are looking for more portability or something that can be set up quickly for an hour's observing without having to wait for the scope to cool down then i'd recommend the refractor as your 1st purchase but step up from the SW Startavel series to the ED Pro series.  These are remarkably good value for money and the 4" OTA package is only £625 ish  with a reducer included.  As it's f9 this will be excellent for the moon and planets as well as some DSOs using the reducer to get the focal ratio down to f7.65.  Of course there are other options but definitely consider the ED lens.

3.  Leave the other amount to the side for the time being to make a decision on a larger aperture scope later on.   Instead of a Dob (cumbersome) you could probably afford to go for an SCT 8" or save a bit more for even more aperture up to 11" if you've chosen well the mount.   of course you could still go for the Dob...

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You've mentioned that you've not used your 8" Newtonian because it was too cumbersome - it makes me wonder about the logic of the purchase of a 12" - 16" Dob?   This certainly isn't going to be any less cumbersome unless you mean it was just the use of the GEM you found hard work?

I'd take your budget at split it in to 3 equal amounts:

1. If you are visual only at the moment look the mount first at what you prefer to use:  EQ or Alt/az.   This may end up costing quite a bit more than you first expected but a good choice here will save you money in the future if you choose to buy a 2nd scope so it would be worthwhile to get something fit to take a much larger scope.  For instance the Berlenbach tripod with an Alt/Az head like the Giro.

2. If you are looking for more portability or something that can be set up quickly for an hour's observing without having to wait for the scope to cool down then i'd recommend the refractor as your 1st purchase but step up from the SW Startavel series to the ED Pro series.  These are remarkably good value for money and the 4" OTA package is only £625 ish  with a reducer included.  As it's f9 this will be excellent for the moon and planets as well as some DSOs using the reducer to get the focal ratio down to f7.65.  Of course there are other options but definitely consider the ED lens.

3.  Leave the other amount to the side for the time being to make a decision on a larger aperture scope later on.   Instead of a Dob (cumbersome) you could probably afford to go for an SCT 8" or save a bit more for even more aperture up to 11" if you've chosen well the mount.   of course you could still go for the Dob...

I take it the Newtonian was on an EQ mount. That can require some gymnastics to get your eye to the EP, and can be a bit of a pain to set up. A dob tends to be easier in both respects.

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My vote-  OOUK VX12L dob + used SW120ED. Their aluminum dob bases are very compact and easy to carry, ditto the tube, carry by the ring(s).

My first proper set up was very similar to this but I had the Equinox 120 and the Flextube 300p. Needless to say between them they virtually covered all bases ( kicking myself for getting rid of both of them ). Something similar  eg 300p Flextube and 120ED frac still comes in at about 2 grand plus some decent eyepieces and you are good to go .

You can also go down the route of a Celestron C9.25 on a Alt Az mount  ( like the Altair Astro sabre mount ) . Also a good all rounder and much loved by the astro community.

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I suspect the answer is based on why did the 8" go.

Thanks for all of your helpful replies. The 8" went because it was a very heavy cumbersome equatorial (should have been permanently mounted) and the optics were past their best. I wanted a clean start - it had served me well since 1995 but had too many shortcomings optically and mechanically and convenience-wise to allow me to enjoy it under our rather fickle skies.

P

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I take it the Newtonian was on an EQ mount. That can require some gymnastics to get your eye to the EP, and can be a bit of a pain to set up. A dob tends to be easier in both respects.

Yes. It was a Beacon Hill mk 2 EQ mount. Dreadful eyepiece height most of the time and should really have been on a 2 - 3 foot pillar. It just wasn't particularly portable, but at the time was a great used bargain.

P

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