Which refractor ?

[jabeoo1]

I am interested in some advice on buying a final scope (yes I do mean that too folks !), it may be a little way off to really biting the bullet but : 

Currently the 10inch dob is my big guns (Big enough for me), the 4.1inch Astroscan for perfectly simple plonk it down & go, & loved Lunt 50 for Ha Solar.

I would like to buy a decent refractor to complete the tool kit.  Unobstructed diffraction-spike free views are an attractive prospect. 

Would be used for double star observation,  planetary, lunar & some white light solar.  Some daytime wild life viewing when on holiday in remote countryside would also be a bonus.  

Budget of £2000 & not adverse to buying secondhand.

What useful advice can anyone give ? 

Fracs are an unchartered territory for me in the normal visual spectrum.  Terminology such as doublet, triplet, achromatic & apochromatic do not really mean much to me in terms of suitability for my needs mentioned.  What should I expect of these designs in use & what are the advantages of one over the other for my needs?  I do however want a scope that has at least partial corrective measures over the CA.  Can I even afford a scope that is free of CA at this 2K price point?  Do doublets suffer more than triplets....Many ???'s as you can see !

Thanks in advance.

[sbooder]

With that budget, I would separate the astro scope from a birding one.  Get a nice 100mm Apo and a half decent spotting scope.

[sbooder]

Something like this

[sbooder]

And this

[nmoushon]

With this kind of budget you can go down several routes here.

1.) You could spend all of it on the largest aperture you can find. Now this mean going with a achromatic frac but usually at the larger scopes they tend to be slower (F7-9 range) which helps with CA. Also Achro are much better today than they where and are really good at controling CA. Achros dont give a clean of views as Apo but you can get more aperture per dollar.

2.) You could again spend all of it on as much aperture as possible but go with an Apo instead. This will mean you wont get as large of an aperture as you can going with an Achro but CA is no existant and true provides spectacular views.

3.) You can go with Simons suggestion and go with a medium sized Apo scope for astro and then a smaller scope for daytime viewing. Most larger fracs have a lot of FL for daytime viewing. Not that you cant use them just that they tend to be harder to use and find targets with.

Also make sure you have an appropriate mount. An Alt/Az mount is usually the easiest to use for observing. You sig doesnt say if you have one or not so not sure on this so just pointing it out. If you dont does the mount purchse need to fit in this budget as well?

[jetstream]

The optics in my SW120ED Pro are very good and hard to beat for the money. It does show very slight CA on the moon's limb at times, but I think many do not notice it. This scope will go 300x on the planets, with about 240x being a common maximum in good seeing. The 120mm aperture makes splitting stars a dream, and the colors are so vivid. Highly recommended, unless, like some, any hint of CA drives you nuts.

My 90mm APO triplet shows zero CA and is very good, but the aperture is a bit small for the resolution I like, for me 120mm is the minimum aperture that satisfies me well. The 90mm is only about 20" long though and very handy.

I like sbooders idea of separating the spotting scope from the night time frac, myself, I would love to try a C5 sometime, I hear they are good.

How about a TEC 140 + a C5?  

[nmoushon]

Here are a couple scopes that are designed more for observing in mind instead of imaging.

http://explorescientificusa.com/collections/ed-triplet-essential-series/products/127mm-apochromatic-refractor - 127mm Apo triplet

http://explorescientificusa.com/collections/ar-doublet-series/products/152mm-achromatic-refractor - 152mm Achro doublet

Not sure on the availability in GB so prices might differ but should still fit in your budget with the price change from dollars to pounds.

[John]

I'd second the recommendation of a Skywatcher ED120 Pro. You budget is going to need to cover a mount (I assume) so a chunk of it will go on that. 120mm is a pretty good "goldilocks" aperture for a refractor where you have some real performance potential while maintaining a good degree of portability.

My ED120 shows a tiny splash of CA around the brightest stars and Venus but none on the other planets and the lunar limb, when it's at sharp focus.

For visual use I feel that a triplet adds cost weight and cool down time which are not needed. Some of the lower cost triplets show as much if not a wee bit more CA than ED doublets like the ED120.

My ED120 has had it's focuser upgraded to a Moonlite, which is nice but not essential, and it's mounted on a Giro mount:

[Jim Steele]

You could probably get a Secondhand 4" Takahashi for that sort of money; I know thats what I would do, sweet Japanese Glass.

There is also a 130mm WO scope on ABS at the moment http://www.astrobuysell.com/uk/propview.php?view=93543

[ronin]

For decent quality visual you are looking at an ED doublet or an apo triplet.

I will suggest that you try and have a look through at least one of each.

The triplet should be free of CA the doublet may show a small amount.

You may be a person that wonders what all the fuss about CA is and find a small amount to be no problem, equally you may look through one and really dislike even a small amount.

The main reason for this is simply cost. You can get a nice ED doublet for a lot less then a nice apo triplet.

The price difference is quite a jump.

The Explore Scientific scopes mentioned by nmoushon are a good choise at what are reasonable prices. There is an Explore Scientific in Germany that you can purchase from and I believe TS are a main dealer.

Do not get the idea that a 127 apo is not going to be heavy, think about it - there are three 5 inch diameter chunks of glass at the top of that tube, close to a 10 inch mirror in weight.

[mikeDnight]

Takahashi have just brought back an old favourite, The FC100 D, for around £1750.00. That's a bare bones tube assembly, the tube clam shell and 30mm finder will use up your £2000. Optically it is a calcium fluorite doublet with the fluorite lens as the rear element. Its a lightweight tube assembly at around F7.5.

Alternatively, you could go for a SW 100 ED PRO and buy a SW Equinox ED 80. The first for your astro needs and the ED 80 for your birding and as a grab and go astro scope. And you'll be in pocket.

Personally I'd get the Equinox ED 120 as a serious astro scope and the Equinox ED 80 as a grab and go. I say this because I've put my moneywhere my mouth is and done just that. A brilliant combination! You may even have some change to buy a finder scope or two.

Mike :-)

[rwilkey]

My doublet has never shown CA, and I therefore don't see the point of spending extra money on a triplet when you can get good results cheaper, coupled with some quality eyepieces.

[jabeoo1]

 If you dont does the mount purchse need to fit in this budget as well?

I currently have a Vixen Porta 2. It has a 6.8Kg / 5 Ib payload capacity, I use this with my Lunt 50.  The budget set is for an OTA only, the other accessories can be added on as extra if needed.  All eyepieces are sorted for now too.

[jabeoo1]

Thanks to everyone for all the responses so far.  I am making my way through them all & there are some excellent points being made, exactly what I hoped for, people who use this gear with honest views on it.  This forum is awesome !

Thanks everyone, I will digest this stuff and no doubt bounce some more questions around when I have taken it in.

[John]

I currently have a Vixen Porta 2. It has a 6.8Kg / 5 Ib payload capacity, I use this with my Lunt 50.  The budget set is for an OTA only, the other accessories can be added on as extra if needed.  All eyepieces are sorted for now too.

The Porta 2 will limit the scope to a 100mm of around F/7-ish. 120/127mm refractors tend to weigh 7kg and upwards and the longer tubes put more stress on the mount.

[jabeoo1]

Some daytime wild life viewing when on holiday in remote countryside would also be a bonus.  

Second thoughts I will use my current binoculars on their small tripod for the birding/wildlife stuff. 

I would rather optimize the one purchase.

[A40farinagolf]

Altair Astro 130mm APO - Father Christmas brought one for me and so far it's a great bit of kit - not too heavy at 8Kg.

F7 as std but F5 with dedicated focal reducer - beautifully engineered and they come with individual test certs - mines at Strehl 0.968 which takes some beating for £2k

Ian at Altair Astro will help you out.

[mikeDnight]

The Equinox ED 120 on a sturdy and very portable altazimuth fork mount (Helix Hercules Mount). Mike

[jetstream]

jabeoo1 you are actually close with your budget to one of these http://www.apm-telescopes.de/en/telescopes/refracting-telescopes-ota/apochromates/apm-doublet-ed-apo-152-f-7-9-ota.html The mount would have to be more substantial for sure. These scopes review well and once bought that would satisfy most people, myself included. The big tube will get the ooohs and ahhhs as a bonus. As you can tell I want one

[ollypenrice]

Your solar white light viewing my lead you to a Herschel wedge (if you're not already there). They beat front end filters but should not be used on oil spaced objectives. This rules out the TEC140, as does even an optimistic second hand price. Some lovely AP scopes are also oil spaced. Bear this in mind.

A good triplet does, in my experience, beat a good doublet but by very little in many cases, visually. A more traditional design with long focal length and slow f ratio, with colour correction not aimed at CCD imagers, might well fit your needs.

Olly

[John]

The Equinox ED 120 on a sturdy and very portable altazimuth fork mount (Helix Hercules Mount). MikeIMG_20150119_113838.jpg

Don't see many of the Helix Hercules on this side of the pond Mike - nice set up

I had a 10" Hercules a while back with a 6" F/8 on board.

[Piero]

Would be used for double star observation,  planetary, lunar & some white light solar.  Some daytime wild life viewing when on holiday in remote countryside would also be a bonus.  

To me you have different targets here. In the first sentence you are looking for resolution, whereas in the second one for wide field. 

As you wrote, I understand that you are not necessarily interested in astro wide field.

If so, I would go for a very good doublet 100-120mm for double stars, planetary, etc, and a spotting scope (~70mm?) for wild life observing. 

If the doublet is good, you won't see aberrations (at least with my eyes). It is also lighter, cools down faster and less expensive as John and others already said. 

120mm is a very powerful beast, 100mm more portable. I would consider also weights of the scope, portability factors, and mount you plan to use. 

With those targets in mind:

If I were you (and had a car), I would possibly go for the SW 120ED DS-PRO and spend the rest in a giro mount. 

If I were you (, had a car), already had a good mount AND could spend all those money (without worrying) on ONE FINAL telescope... I would go for a second hand Takahashi TSA102S 

[perfrej]

Totally off topic... Your signature, "pdp10", as in "DECSystem-10"?

/per

[sbooder]

I think from reading everyone's input and with the budget you have, you are in a good position to take your time and read as many reviews as you can.  Most of the Apos out there are pretty good and some makes will be cheaper giving you the option for a larger aperture.

But I see you have a Dob, do you already have a mount that will take a frac?  Worth remembering that this may take up some of your budget.

[A40farinagolf]

Mount Mount Mount  is to astronomy what location, location, location is to house buying- this has been said many times before and I totally agree.

It's more important to get a top notch mount than it is to get top quality optics - balancing a jelly on a rubber band is not recommended.

Reasonable optics on a brill mount will render better images than brill optics on a dodgy mount.