$1000 OTA and flattener budget
Posted 07 July 2020 - 04:50 PM
Posted 07 July 2020 - 07:07 PM
“Nothing over 80mm”
I assume that a reflector will not be considered? A 6” F4 Newt Astrograph weighting at 13lbs might be a nice wide field option and well below your budget..
Posted 07 July 2020 - 07:07 PM
There's plenty of great options in the 60-80mm apo doublet or triplet class within that price range, you can't really go wrong. And they are all light enough to be a good match for your mount. In many cases, different brands carry essentially the same scope e.g, in the 60mm class: AT60ED, WO61, Apertura 60, Altair60; in the 70mm class: AT72ED, WO7, Apertura 72, Altair72; in the 80mm class AT80, Orion 80ED, Skywatcher 80 - you get the picture. In many cases they are likely made by the same supplier, just re-branded. Sharpstar makes 61EDPH & 76 EDPH, which are slightly faster (so different designs).
Among Petzval type scopes (with built-in correctors), Sharpstar have recently come out with the Askar 400mm/72mm flat-field refractor that is just slightly above your budget at ˜$1100. The Meade 70 quad is $1200 new but occasionally shows up for sale used for ˜$800-$900. And of course the very popular Redcat 51, about $750, but hard to find in stock.
It all comes down to price, brand preference, customer service, mechanics. Check the forums for user experience. Astro-Tech mechanics and quality control are excellent, and so is their customer service. Also you get a CN member discount. All good reasons to make AT your first choice.
Check out the FOV calculator for the focal length and camera combo over a range of targets: https://astronomy.to.../field_of_view/
If you are looking to buy new, the challenge these days is finding these in stock, as the supply chain has been disrupted by Covid. Or you'll find the scope in stock but not the flattener. The good news is that used copies of these scopes and flatteners come up for sale regularly in the classifieds.
I would look for:
1) Color correction: FPL53 or FCD100 will tend to have better color correction than FPL51/FK61/FCD1. Triplets tend to have better color correction than doublets - a doublet with FPL53 will likely have comparable performance to a triplet with FPL51.
2) Focuser: 2-2.5inch R&P focuser with 10:1 micro-focus is better for imaging than a Crayford (which can tend to slip with a heavy camera).
Posted 07 July 2020 - 07:37 PM
I only covered refractors in my prior post as (a) this is the refractor forum and (b) the standard advice for beginners is to start with a 60-80mm apo for astrophotography.
Fast Newts such as a 6in f/4, with a coma corrector can give excellent results in the right hands but at 13+lbs will be at or above the recommended weight limit for your mount (for astrophotography, you should divide the stated capacity by a factor of 2 - not that good results are not possible if you break these guidelines, but getting consistent results can be a challenge). Also, they are very sensitive to collimation and this can be frustrating for some. They also tend to have longer focal lengths, so less forgiving of tracking errors and not really widefield.
I would avoid a Ritchey-Chretien (despite the association with Hubble). Too heavy, too long a focal length and too slow. And sensitive to collimation.
Posted 07 July 2020 - 08:25 PM
I would like a stellarvue but out of reach of my wallet. I've been looking at Williams optics and astrotech. Have not heard of sharpstar. I will check them out.
You guys don't think I'll see much difference between an fpl53 doublet or triplet? That would save alot of money. I've never looked through a triplet before.
Posted 07 July 2020 - 09:14 PM
For the same aperture and focal ratio, an FPL53 doublet will be better corrected than an FPL51doublet. An FPL51 triplet should be roughly comparable to an FPL53 doublet. FPL53 triplets will have the best color correction but are significantly more expensive.
As always, it's a cost vs. performance trade-off - and only you can decide what you like. These days FPL-53 doublets are both cheap enough & good enough that there is not much reason to go for anything else, unless other considerations (cost, mechanical quality, desire etc) come into play.
For instance the AT80ED is an FK61 (equivalent to FPL-51) doublet, but is very well made and cheap at ~$400 and gets great reviews. It costs less than the Orion 80ED which uses FPL-53, but the AT80ED has a better focuser which for some people would be a good tradeoff. Or you could split the difference and get the AT72ED for ~$470 and it has both FPL-53 glass and the better focuser, and it's faster so better suited to astrophotography. This scope and it's little brother the AT60ED are terrific choices but hard to find in stock (unlike the AT80ED which is in stock), though you can get these scopes in other brands (Apertura, Altair etc) if you look around.
Edited by RajG, 08 July 2020 - 08:45 AM.
Posted 09 July 2020 - 05:58 AM
Askar 72mm f/5.6 Quintuplet Petzval Flat-Field Astrograph
What do you all think? I looked on astrobin and compared some of the images with some of the different scopes you all recommend and this one peaked my interest the most.