Widefield refractors: the silver standard?

[hunterknox]

Hi All,

I'd like a nice, portable, widefield refractor for imaging.

I've figured out that the Televue NPs and Takahashi FSQs are pretty much the gold standard, but I don't have 4 grand to spend, so my question is: what's the silver standard? Is there anything that's nearly as good at say, half the price? Quarter the price?

Any suggestions welcomed...

[brianb]

William Optics FLT (available in several sizes: 98mm, 110mm, 132mm, 158mm ....) Brilliant for imaging but you need the optional field flattener to cover a sensor bigger than APS-C size (and maybe for APS-C as well if you're picky).

The various ED 80mm semi-apos can be quite good, too, but usually don't have the same quality focuser and, despite the doublet design using ED glass, there is still some tendency to "blue bloat". A lot cheaper though.

The Skywatcher MN190 is reputed to be pretty good for widefield imaging but it's HEAVY.... quite reasonably priced but you're going to need a real man of a mount to get the best from it.

[John]

The Stellarvue ED scopes seem to get a lot of positive comments on forums. The SV 102mm ED is an F7 which should provide a nice blend of wide fields and decently corrected optics. I believe they retail for a bit over £1K.

John

[Peter Drew]

Don't overlook s/h, premium refractors are usually very well looked after. I bought a Sky 90 in mint condition for 1K and they are well thought of for wide field imaging.

[Whippy]

What sort of budget have you got in mind?

Tony..

[hunterknox]

Thanks to everybody for your responses so far.

Tony: I'm thinking under 2 grand, preferably closer to one.

I ask because the top end of the market seems pretty well defined (quadruplets from people beginning with 'T') and there's plenty of good stuff at the lower end (Equinoxes, smaller WO scopes et al.) but the middle just seems kinda sprawling.

Sky 90 seems a good option (especially 2nd hand!), but can a perfectly engineered doublet really compete with a triplet from the likes of WO or TMB? How about the smaller Televue doublets for that matter?

[alfi]

hi

how about a meade triplet?

alfi

[Whippy]

Sky 90 seems a good option (especially 2nd hand!), but can a perfectly engineered doublet really compete with a triplet from the likes of WO or TMB? How about the smaller Televue doublets for that matter?

There's a question! I guess it depends on how demanding you are.

Until recently I was the proud owner of a WO FLT98, a really nice scope. Unfortunately I had to sell it for financial reasons and replaced it with the much cheaper Skywatcher ED80. So far, I've really been quite impressed with it and it'll do the job that I'm asking of it. I'm using a mono CCD camera with a small(ish) chip so I don't need a wide flat field, nor colour correction that's the equal of the very best APO refractors around because I can re-focus in between each colour filter to counteract the scopes' lesser colour correction. If you're using a DSLR or a 'big chip' CCD then I'm sure you'd notice the difference between a cheap scope and a more expensive one.

For your budget, IMO the FLT98 would be a contender although you may have to budget for a flattener.

Tony..

[John]

hi

how about a meade triplet?

alfi

The price is fantastic for those - but is it realistic to expect consistant quality in a triplet manufactured to hit that price point

Personally I think I'd probably go for a FPL-53 doublet - the chinese seem to have got the production of those off to a pretty fine art now.

Jon

[SteveL]

How about a nice Borg?

[Doc]

Or a Pentax.

[hunterknox]

Out of interest I know the pentaxes use 3 lenses, but I got the impression that this is two at the front and an in built flattener somewhere further down the tube, rather than 3 in one cell. Is that right?

[RobH]

The meade triplets are excellent from all accounts, and quality control is good.

My WO 80MM flourite doublet takes some beating until you get into the Tak range. No issues with blue bloat, and I'm pretty picky.

Cheers

Rob

[Marmite]

...but can a perfectly engineered doublet really compete with a triplet from the likes of WO or TMB?

In a word, yes. In some cases, easily. A well-designed and executed doublet will equal or better a mediocre-to-good triplet.

For instance, there are many posts and threads on sites like CN detailing how the Equinox or EON 120 (or any of the equivalent Synta ED models) is considered by many to be optically superior to any of the 127mm triplets hitting the market recently.

Others have stated their belief that only the most expensive of triplet designs can best Takahashi's older model flourite doublets. It takes a TOA or FSQ to get the better of those, it seems.

Excellent triplets are harder to make than doublet designs. Tests of some newer triplet optics have demonstrated that manufacturers of quality doublets may have difficulties manufacturing quality triplets. (See Rohr's tests of the WO FLT-132 triplet for example.)

Don't discount a doublet simply because it's a doublet, and don't assume a triplet will be better just because it's a triplet. Theory isn't everything.

[brianb]

Out of interest I know the pentaxes use 3 lenses, but I got the impression that this is two at the front and an in built flattener somewhere further down the tube, rather than 3 in one cell. Is that right?

Which model? At least one of the Pentax scopes is a Petzval design, with a doublet at the front (as usual) and another doublet towards the bottom of the tube. Works well as a wide field scope but not easy to construct or collimate.

A field flattener will be a compound device with four or maybe five elements.