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Which Apochromatic Refractor ?

badgers

By badgers
in Imaging - Discussion

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badgers

badgers

Posted
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Hello People,

I'm seeking an apochromatic refractor to complement my 6" Newt for wide field astrophotography.

Ideally this would be:

  • Between 60 and 100mm aperture
  • Fast, i.e. less than f/6 (either with or without a reasonably priced reducer)
  • Good quality optics.
  • Cost less than a grand, although I'd be willing to go a bit more if it made a big difference optically.
  • Can carry the weight of my imaging kit (Atik 460 + Filterwheel + OAG + lodestar)

I'm happy to buy whatever corrector/reducer is needed and to upgrade the focuser if that's whats needed to make it work.

So far I've looked at:

  • Skywatcher 80ED DS Pro
  • Williams Optics Zenithstar ZS70
  • Williams Optics Zenithstar 80 DDG
  • Williams Optics GTF81
  • Williams Optics Megrez 90
  • TS Triplet Apo 80
  • TS Quadruplet Apo 65
  • Vixen ED80SF
  • Takahashi FS-60CB (maybe too wide...)
  • Altair Wave Series 80 F6 ED Triplet APO

I've no feel yet for refractors and quality of optics and coatings, so any feedback on the different models for astrophotography would be much appreciated.

The alternative option I have is to buy an ASA corrector reducer (£700ish ) which would take my 6" Newt and make it wide-field and f/3.65... i.e. very very fast...

Any advice much appreciated!

Anton

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nmoushon

nmoushon

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If you can afford it I'd go with one of the 80Triplets + reducer. You wont regret it. Doublets are cheaper but if your willing to pay for a triplet do it!. I have an equinox ED80 with .72x reducer (which brings it from f/6.25 down to f/4.5 which is quite fast) and I can frame the entirety of M31,M32,M110 easily in the entire FOV. And plenty of room to spare so I think its very nicely framed. I wouldn't go anything less that an 80mm because I think by the time you put a reducer on it you just get to wide and lose a lot of the discernible detail. I'll post a pic when I get home from work so you have a clearer idea of what I'm talking about.

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nmoushon

nmoushon

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The one thing thats nice about the ES 80 is it comes with some extra gear and most others are OTA ONLY. I cant help you compare the quality between them all(since I've only owned 1 scope) but I haven't heard any horror stories about any of them so I guess the quality of the build is very comparable between them all. Someone might say other wise that has some experience but like I said I havent hear anything horrible. So I guess its down to what you think looks nicer than the others lol. If you've made a decision for an 80 Triplet.

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nmoushon

nmoushon

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The only thing that comes to mind that would make one stand out above the rest is if their stock focuser can handle the load of your imaging gear. Again can't give much insight into that but that would be the one thing that would help you make a decision for one over another. Unless your planning to upgrade to a Moonlight then it doesnt really matter.

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Sirius Bizness

Sirius Bizness

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If I had a grand to spend on a refractor for imaging I would go for the Tele Vue 85 that's on ABS right now (no affiliation). Yes its only a doublet but I have read good things about it and so far the TV premium has fulfilled my expectations on the EPs i have used. Native it's slower than you want at f/7 but a reducer could help.

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ollypenrice

ollypenrice

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If I had a grand to spend on a refractor for imaging I would go for the Tele Vue 85 that's on ABS right now (no affiliation). Yes its only a doublet but I have read good things about it and so far the TV premium has fulfilled my expectations on the EPs i have used. Native it's slower than you want at f/7 but a reducer could help.

You'd need the flattener but this is exactly what I'd do as well without a shadow of doubt, assuming it's in good nick. It has a simple but superb R and P focuser and lovely optics. It'll last a lifetime. You can improvise a fine focuser by adding a wand or lever to the knob.

The 60 quads were berated for getting pinched in cold weather (or sometimes just in any weather) and the little FS60 does struggle to control blue stars.

The Altair 80 seems good, too. I had some trouble with corner stars when testing it for imaging but it seems I was given the wrong flattener so no surprizes there!! It gave a great visual star test, confirmed by Ralf Ottow, an optics professional.

But for me, the second hand TV would be number one if it's a good one.

Olly

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badgers

badgers

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Thanks for the feedback.

The orion optics newt is nice... But I'm already imaging on a corrected f/5 newt with a moonlite focuser and optically it is performing very well.

It's worrying to hear about the pinching on the TS scopes.

I spotted the TV85 yesterday on ABS..... But it seems to be gone now :(

I'll keep an eye out for more of them coming up... 2nd hand

I'll also try and find some more reviews on the Altair wave series.

Thanks again,

Anton

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badgers

badgers

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I'm gutted about the TV85.....

However, I'm reading nice things about the Lightwave 80 triplet.

With the 0.8 reducer flattener it would come in at f/4.8 and it looks like it has a very solid 3.5" focuser.

I might go over to visit them sometime soon and talk to them directly. I'm always happier if I can actually talk to the manufacturers/designers directly.

Thanks,

Anton

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badgers

badgers

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Thanks Capricorn,

I've seen Olly's review of the Altair 115 Triplet in Astronomy now and I'm hoping the 80 Triplet is optically similar.

Due to visit Altair astro tomorrow morning and have a look in person.

I think I'll bring my imaging kit too so I can check spacings while I'm there.

Between my pimped out f/5 Skywatcher Newt and the 80 Triplet running at f/4.8 I figure I'll have the best of both worlds this winter.

I can't wait!

Anton

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badgers

badgers

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The reviews from Craig stark and Sky and Telescope Magazine suggest the 101ED has a little chromatic aberration and distortion on the edges of the field.

Whether or not this would show up on my sensor, I don't know.... but I worry about this slightly....

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badgers

badgers

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The problems some people reported with pinched optics worry me about the TS Triplets, although a lot of people love them.

Whats the verdict on a Takahashi Sky90 for imaging ? I'm seeing one or two 2nd hand that are almost in reach.

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badgers

badgers

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That's a nice find earl, thanks. Ohhh christ it's another one to add to my list!

Those 80mm super apo's with the LOMO objective seem to get great reviews.

That seems very cheap, I've seen identical looking scopes with regular glass I'll have to check its LOMO.

Anton

Edit: I guess it's cheaper because it's coming with no case and the stock focuser, the more expensive ones have the feather touch.

This might be a winner for price/performance?

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johninderby

johninderby

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The early WO 80 Lomo scopes were actually not that good. They had problems (bad design) and WO had to resort to masking the aperture down by a few mm to reduce CA to an acceptable level. Of course that begs the question as to why a "Lomo" objective would have CA problems. Best stick to the later improved ones with the re-designed tubes and lens cell.

BTW got the above from the optics expert hired by WO to sort the problem out.

I had an early WO Lomo that I thought was good until I tried a TMB. Sold WO and got TMB.

John

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badgers

badgers

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The Borg is too pricey for my budget its more than the cost of a new Televue 85.

I've tried to query APM about the LOMO, especially considering John's comment.

I phoned this morning and tried out my broken german....

Q: "Sprechen sie English ?"

A: Nein

Q: "Gibt es andere leute da konnen Englisch Sprechen"

A: Nein

I've caved in and asked my wife to phone them... She's german but not fluent in optical speak, so we'll see what happens

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