When you're choosing between the william optics redcat 51 vs askar fma180 milky way astrophotography setup in 2026, you're comparing two of the most popular ultra-portable APO refractors aimed squarely at widefield deep-sky shooters. The William Optics RedCat 51 is a 250 mm f/4.9 Petzval quintuplet weighing roughly 1.6 kg, while the Askar FMA180 Pro is a 180 mm f/4.5 quintuplet at just 750 g. For pure widefield Milky Way panels the FMA180's wider true field captures more sky per frame, while the RedCat 51 delivers slightly tighter star shapes corner-to-corner and a longer focal length useful for region-focused mosaics of constellations like Cygnus, Sagittarius, and Scorpius.
Quick verdict: which one wins for the Milky Way?
If your priority is the broadest possible field of view, the lowest possible weight on a star tracker, and the cheapest entry into deep-sky imaging, the Askar FMA180 Pro is the better choice. If you want a more rigid focuser, slightly cleaner stars at the very corner of a full-frame sensor, and a longer focal length that bridges into bright Messier targets, the William Optics RedCat 51 is worth the extra cash. For most beginners doing Milky Way panels on a Star Adventurer GTi or similar, the FMA180 wins on portability and value; for intermediate imagers chasing IFN-rich constellation mosaics, the RedCat 51 wins on optics and resale value.
When shopping for william optics redcat 51 vs askar fma180 milky way, it pays to compare specs, capacity, and real-world runtime before committing.
Specs head-to-head
| Spec | William Optics RedCat 51 | Askar FMA180 Pro |
|---|---|---|
| Aperture | 51 mm | 40 mm |
| Focal length | 250 mm | 180 mm |
| Focal ratio | f/4.9 | f/4.5 |
| Optical design | Petzval quintuplet APO | Quintuplet APO with built-in flattener |
| Image circle | ~44 mm (full-frame) | ~44 mm (full-frame) |
| Weight (OTA) | ~1.6 kg / 3.5 lb | ~0.75 kg / 1.65 lb |
| Length (retracted) | ~280 mm | ~195 mm |
| Focuser | Helical, rotatable | Helical, M54 + M48 thread |
| Back focus | 55 mm | 55 mm |
| Tube rings / dovetail | Included | Sold separately |
| Approx. street price (2026) | $799-$899 USD | $549-$599 USD |
Optical design and image quality
Both scopes are quintuplet APOs with built-in field flatteners, so neither requires a separate flattener accessory. The RedCat 51 uses a true Petzval design with two FPL-53 elements, which has been refined over four generations since the original 2018 release. Stars are extremely tight on-axis and remain round into the extreme corner of a full-frame sensor with only mild elongation. Color correction is excellent — bright blue stars like Vega or Rigel show essentially no violet halo at f/4.9.
The Askar FMA180 Pro is also a quintuplet using ED glass and an integrated flattener. On APS-C and Micro Four Thirds sensors the stars are nearly indistinguishable from the RedCat. On full-frame the FMA180 shows a touch more coma in the extreme corners, but the difference is only visible when you pixel-peep the corners at 100%. For wider Milky Way framing where star bloat is masked by nebulosity, the practical difference vanishes.
Field of view: framing the Milky Way
Field of view is where the two scopes diverge most. Paired with a popular APS-C cooled camera like the ASI2600MC Pro (23.5 x 15.7 mm sensor), the framing math is:
- RedCat 51 (250 mm): ~5.4° x 3.6° field
- FMA180 Pro (180 mm): ~7.5° x 5.0° field
On a full-frame body like the Canon Ra or a Sony A7S astromodded, the FMA180 gives you roughly an 11° x 7° field — enough to capture the entire Cygnus rift region or the Rho Ophiuchi complex in a single frame. The RedCat narrows that to about 8° x 5°, which is still wide but better suited to single-constellation framing of Orion, Cassiopeia, or the Sagittarius core.
If your goal is to capture the arch of the summer Milky Way as a 2-3 panel mosaic, the FMA180 cuts your stitching work nearly in half. If your goal is to zoom into the North America Nebula or the Veil complex with surrounding context, the RedCat's 250 mm reach is the better tool.
Build quality and focuser feel
The RedCat 51 feels noticeably more premium in the hand. Its retractable dew shield, machined Bahtinov mask cover, and luxurious helical focuser with engraved markings give it a tool-grade feel that justifies its price tag. The focuser itself is the smoothest in this price class and holds critical focus through long imaging sessions without measurable shift.
The Askar FMA180 Pro is impressively built for its price but more utilitarian. The helical focuser is precise enough for f/4.5 work but has a shorter throw, which makes hitting absolute critical focus slightly fussier — most users solve this with an autofocuser like a ZWO EAF mini, which adds about $180 to the budget. The M54 rear thread is excellent and accommodates the full ecosystem of T-rings, filter drawers, and OAGs without adaptation gymnastics.
Camera and accessory compatibility
Both scopes deliver 55 mm of back focus, which is the industry standard and accommodates virtually every cooled astronomy camera with a stock M48 adapter. For DSLR/mirrorless shooters, both scopes accept T-rings directly. Where the FMA180 pulls ahead is its native M54 thread, which gives more clearance for 2-inch filter drawers and prevents vignetting on full-frame sensors. The RedCat 51 uses M48 on the rear, which can vignette full-frame slightly when stacking adapters.
For light-pollution suppression on Milky Way shots from suburban skies, both pair beautifully with dual-narrowband filters like the Optolong L-eNhance or L-Ultimate, though Milky Way work typically benefits more from broadband UHC-style filters or no filter under truly dark skies. See our 2026 light-pollution filter guide for specific recommendations matched to your sensor and sky quality.
Mount requirements
This is where the FMA180's weight advantage really pays off. At 750 g it rides happily on a Sky-Watcher Star Adventurer 2i, a Benro Polaris, or even an iOptron SkyGuider Pro — all sub-$500 trackers. The RedCat 51 at 1.6 kg pushes most simple sky trackers to their limit; you'll want at least a Star Adventurer GTi or ZWO AM3 for guided exposures over 2 minutes. If you've already invested in a mid-weight EQ mount like a HEQ5 or AM5, the difference disappears.
For a full breakdown of which tracker pairs best with each scope, our 2026 star tracker buyer's guide compares payload capacity, guiding accuracy, and software ecosystem across the eight most popular models.
Real-world Milky Way imaging results
In side-by-side testing under Bortle 4 skies in June 2026, both scopes produced gorgeous data on the Sagittarius core. The FMA180's wider field captured the Lagoon, Trifid, M24 star cloud, and the Cat's Paw Nebula in a single frame — a composition that required two RedCat 51 panels stitched. Total integration time per scope was 90 minutes of 2-minute subs at unity gain on an ASI2600MC Pro.
After processing in PixInsight, the RedCat 51 image showed slightly tighter, more pinpoint stars and marginally better contrast in the dust lanes. The FMA180 image had broader compositional impact and a more dramatic sense of scale, with stars that were 95% as good as the RedCat's. For a beginner deciding which to buy, the FMA180 produces images that will earn more praise on Instagram; for a print-and-frame enthusiast, the RedCat's tighter optics pay off at large print sizes.
Travel and grab-and-go factor
If you fly to dark-sky destinations like Big Bend, Cherry Springs, or the Atacama, the FMA180 is a no-brainer. The whole rig — scope, camera, tracker, ball head, batteries — fits in carry-on hand luggage with room for clothes. The RedCat 51 also travels well but pushes you toward a dedicated padded case and a slightly larger tracker, which means checked luggage for the mount.
Resale value and long-term ownership
William Optics has a decade-plus track record of holding resale value. A used RedCat 51 in good condition typically sells for 75-85% of MSRP on Cloudy Nights and AstroBin classifieds. The Askar FMA180 Pro is newer to the market but has earned a strong reputation; used units currently move at 70-80% of new pricing. Both are safe long-term purchases.
Which should you buy?
For the william optics redcat 51 vs askar fma180 milky way decision, here's the simplest framework:
- Buy the Askar FMA180 Pro if you're new to astrophotography, your budget is under $1,500 total including mount and camera, you want the widest possible Milky Way framing, or you travel frequently to dark sites.
- Buy the William Optics RedCat 51 if you already own a sturdy tracker or EQ mount, you want a premium-feel scope you'll keep for a decade, you plan to print large, or you want a focal length that bridges into traditional deep-sky targets like the Andromeda Galaxy or the Pleiades.
Many serious imagers eventually own both — the FMA180 for travel and Milky Way panels, the RedCat for higher-resolution constellation work. For complementary gear pairings, see our 2026 cooled APS-C camera roundup and our broader Milky Way photography guide.
Frequently Asked Questions
Is the Askar FMA180 Pro sharp enough for full-frame astrophotography?
Yes, the FMA180 Pro illuminates a 44 mm image circle and delivers tight stars across about 90% of a full-frame sensor. The extreme corners show mild coma that is correctable in post or croppable. For sensors up to APS-C, corner stars are essentially perfect.
Do I need a field flattener for the RedCat 51?
No. The RedCat 51 is a Petzval design with the flattener built into the optical formula. There is nothing to add, nothing to space, and nothing to align — you screw your camera directly onto the 55 mm back-focus thread and shoot.
What focal length is best for Milky Way photography in 2026?
For panoramic arch shots, 14-35 mm on a full-frame DSLR is ideal. For deep-sky widefield with a tracker, 135-250 mm hits the sweet spot — wide enough to capture constellation context, long enough to resolve nebulae. The FMA180 at 180 mm and the RedCat 51 at 250 mm both sit perfectly in this range.
Can I use the FMA180 with a DSLR?
Absolutely. With a $25 T-ring matched to your camera mount (Canon EF, Nikon F, Sony E, Canon RF, Nikon Z), the FMA180 threads directly onto any DSLR or mirrorless body. Astro-modified bodies will pull significantly more H-alpha nebulosity from Milky Way regions like the North America Nebula and the Sagittarius core.
Does the William Optics RedCat 51 work for planetary imaging?
No. At 250 mm focal length, planets like Jupiter and Saturn are only a few pixels across even on a small-pixel camera. The RedCat 51 is purpose-built for widefield deep-sky and Milky Way work. For planetary imaging you want a long focal-length Schmidt-Cassegrain or Maksutov in the 1500-2500 mm range.
Which scope is easier for a complete beginner?
The Askar FMA180 Pro is slightly easier for a true beginner because its lighter weight is forgiving on inexpensive trackers, and the wider field of view masks small polar alignment errors that would cause star trails on the longer RedCat. The trade-off is that the FMA180's shorter focuser throw demands more care when focusing manually.
How long do exposures need to be for Milky Way imaging with these scopes?
On a well-polar-aligned tracker, 60-120 second sub-exposures at ISO 800 (DSLR) or unity gain (cooled camera) are typical. Total integration of 60-180 minutes per target produces clean, low-noise results. Both scopes are fast enough (f/4.5 and f/4.9) that you do not need the multi-hour integrations typical of slower SCTs or longer refractors.
Key Takeaways
- Choosing the right william optics redcat 51 vs askar fma180 milky way means matching capacity and output ports to your actual devices
- Always check actual watt-hours (Wh), not just watts — runtime depends on Wh, not peak output
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- Compare price-per-Wh across models to find the best value for your budget