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Old 04-07-2020, 02:00 AM
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Kurt is offline
Join Date: May 2013
Posts: 8
Advice: Sharpstar 100Q II v Sky Rover 115 ED APO

Hi team,

Iím in the market for an APO Refractor around the 550mm - 700mm Focal Length for astrophotography and am tossing and turning on either of the below, and could really use some varying points of view.

Sky Rover ULT 115 ED Glass Triplet 115mm APO

Sharpstar 100Q-II

I donít have any experience with APOs, but have done a tonne of reading these past few months, enough to do my head inÖ but plenty to understand the gist. Iím a regular photographer with DSLR gear and have been using a SIGMA 150-600mm, and others, on a HEQ5 Pro with both a 7D I and 5D IV, guided; but am now looking to upgrade to my first APO and dedicated focal length in what I would traditionally refer to as a prime lens, but for far less cost in comparison. Iíd also like to buy local.

I like the idea of wide field, though prefer that 600mm-700mm range for Nebule etc, with something acceptable weight wise that would still suit my HEQ5 pro, and then ease of use with my Full frame 43mm sensor DSLR.

Will look into dedicated cooled astro CCD later on, baby steps, and minister of financial affairs approval etcÖ

I know thereís a few things to consider with a nice APO, price, weight to suit mount, double v triple v quadruple design and quality, flatteners v inbuilt for the quad, resulting FL, flat field and ease of use etcÖ

Iím also aware through these forums and others that the Sharpstar is re-branded and sold under other aliasís all over the world, but similarly with the Sky Rover 115, there arenít a huge amount of reviews singing their praises, but not trashing them either, so itís actually been difficult to make a decision. Plus, Iíve even considered the SW 100 Esprit, it gets some really great reviewsÖ but is that APO just a more ďpopularĒ choice, not superior? Iím still researching a lot, but thought Iíd throw it on the table for a few more opinions if thatís ok.

Weight wise the SW 100 Esprit clicks in at 6.3kg, so that added with guiding equipment, filters and DSLR, weíre now loading up the HEQ5 Pro payload, but I have read about others who use this setup just fine and get great results, so that sounds promising. It averages around $3500.00 in Oz and itís a triplet (or doublet with a field flattener) with an FL of 550mm at f5. Itís on the shorter FL end out of the three Iím considering, but acceptable. It comes with a D Losmandy type bar, so would need an ADM bracket or similar plate to allow it to fit on my vixen head for the mount.

The Sharpstar 100Q II (second version of this variant) clicks in at 5.2kg, which gives me a little more headroom on the HEQ5. I can get it around $3800.00. Itís advertised on Testar as an Petzval quadruplet, but on Sharpstar it says itís an quartette doublet air-space design (I assume thatís the same) as in the ďcorrectorĒ or ďflattenerĒ is inbuilt, so itís a more of a plug and play APO without having to worry too much about spacing in the imaging train compared to a triplet where backspacing accuracy is required!? The 100Q II FL is 580mm at f5.8 with a FF flat field of 44mm, perfect for the 43mm 5D IV sensor. Testar also details that the objective lens includes one FPL53 Ohara glass, whereas the Sharpstar website only mentions ďspecial ED lensĒ. Not sure if that is the same thing? In addition, Sharpstar website says you can use a F4.3 full-frame reducer lens (but Michael Fong from Sharpstar confirmed that there actually isnít a reducer for the 100Q II yet) so Iím not sure why thatís advertised. I may or may not use one anyway, but would be cool to have the versatility.

The Sky Rover 115 APO is a triplet which clicks in at a similar 5.1kg, so thatís also nice for the HEQ5 and comparable to the Sharpstarís 5.2kg which for my setup with guiding, filters and DSLR seems to make sense. Price at $3000.00 sounds great, especially for the native FL at 805mm at f7. It would be reduced with the 0.8x reducer/flattener to an astrophoto flat field of 42mm FL of 644mm at f5.6, also perfect for the 5d IV 43mm FF sensor. So the way I see it, the Sky Rover 115 APO gives me the greatest focal length and decent aperture at the cheapest price and it's the lightest. I just wonder if the advertised ďPremier Japanese Triplet ďEDĒ Extra Dispersion glass lensĒ is on par with the others FPL53?

So I really like the price and extra FL of the 115 APO and definitely the added flexibility being able to use it at 805mm for visual and then 644mm for FF flat field Astro, so I like that versatility. Itís supplied with a vixen dovetail so that will mount straight onto my HEQ5. Iím just not sold on ease of use though compared to the 100Q II Quad, and instead having to use the flattener and getting correctly spaced for focus etc. (Only because I have no experience doing this).

(I may also not really need to benefit from the 115 APOís 805mm for visual though anyway, as I already use a Celestron C5 at 1250mm for some visual fun in that arena, albiet at f10Ö)

I also really like the sound of the Sharpstar 100Q II too, mainly because of itís ease of use, flat field for 43mm Full Frame sensor straight out of the box, plug and play basically, I like the top handle for Guide-scope placement and it too ships with a vixen dovetail bar for mounting, plus itís locally bench tested here in oz and itís a comparable price against the SW Esprit 100, but itís the most expensive out of the three.

The Sharpstar price compared to the 115 APO confuses me a littleÖ.. would there be $800 worth of quality difference between the Quad compared to Triplet? Is ease of use worth $800? Am I missing something? Or perhaps thatís really the only decision I have to make?

All three seem to list good focusers with 360 rotation for image composition, so thatís handy too. Form factors between the 100Q II and Esprit 100 are all pretty similar, the 115 APO comes in a little longer.

At the end of the day, there may or may not be a right answer here, and maybe I canít really go wrong for amateur astrophotography between either of these three, which is ok, but I would really appreciate some thoughts or your experiences on the above, which for me, might give just a little more comfort in the decision I take in the end :-)

Thanks muchly
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