OVL Field Flattener

OVL Field Flattener

  (24 Reviews)
✓ 2 year warranty


3x in stock shipped 1-2 working days

About this product

Model:  skywatcher_field_flattener
Part Number:  20225

A high-quality, non-focal-reducing Field Flattener optimised for DSLR imaging on refractor telescopes with focal ratios around f/5.5 to f6.0. 

Will also provide much improved results on refractors with focal lengths narrowly outside this optimised f/range.

Integral T-Ring adaptor thread. High quality CNC machined body with gloss black anodised finish.

Features standard 2" push-fit barrel for use with 2" focusers.  Threaded for 2" filters.

Customer reviews

Average Rating (24 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
18 March 2023  | 

Muy bien con el 72 ed gracias.

Rating (max 5):  
Brilliant Accessory
13 June 2022  | 

I purchased this flattener a few months ago and due to bad weather could only test in the past few weeks. I was pleasantly surprised by the excellent quality and look of this flattener, the glass looks superb. Tested on some single shots using a Skywatcher 72ED, adjusted back focus slightly on my ZWO 294MC PRO and the did a 2 pane mosaic of the Carina nebula. perfectly focused stars up to the edges, no noticeable aberrations. Definitely a good purchase for the price!

Rating (max 5):  
Great advice from FLO staff
19 May 2022  | 

Acquired a SW 72ed refractor & needed parts to attach my camera. A quick email response from Alex meant that I could quickly order the flattener, T ring & adapter which meant I had a solid imaging train & the correct backspacing for my camera. Just need a clear night to try it all out. I continue to be impressed by the service from FLO & it has become my one stop shop for all my astrophotography needs. Great stuff

Rating (max 5):  
More information
30 April 2022  | 

I bought this field flattener for my skywatcher Evostar 72 ed and I didn't even try it because my sky is cloudy since 2 weeks, and it's going ti be so for other 2 weeks. In my order there were 3 products: the flattener, an adapter ring and clouds. Can I give back clouds as written in the return terms? Sorry for my bed english.

Rating (max 5):  
not really a good FF for my refractor
25 March 2022  | 

I bought this FF last summer. I have a skywatcher 72ED with an astro camera Altair 269c (aps-c). I didn't succeed to get the right back focus (55 mm or 56 mm or something else). Thus the FF gives me some halos around bright stars.
I do not recommend to buy this equipment. I don't use it anymore and i lost 80 pounds for nothing.


Sorry to hear the flattener wasn't a good match for your 72ED and Altair camera (we don't stock Altair cameras so are unable to advise) but your purchase was covered by our 30-day return policy, so you were able to return it for refund :-)

Rating (max 5):  
OVL Field Flattener
24 March 2022  | 

A realy good product. Works great with SW Evostar 72ED. Front thread for filter installation. Overall good build quality. When attached to the scope fit well and doesnt move at all. A good alternative to the reducer/flattener from SW.

Rating (max 5):  
OVL flattener
06 January 2022  | 

Brilliant service from FLO and the flattener does everything it should do on my Skywatcher ED72. Plenty of focus tube travel, lovely flat field as compared to when not using the flattener. It is also well machined and feels quality, but also pretty light and takes 2 inch filters in the nosepiece. The nose piece holds firmly with the upgraded FLO ED72 two inch compression adapter Superb.

Rating (max 5):  
Great product
13 April 2021  | 

I tested the product on my Skywatcher 72ED and was very satisfied with pinpoint stars up to the edges paired with the ASI294MC. Highly recommended.

Rating (max 5):  
OVL Flattener Field Test
31 March 2021  | 

I bought this FF in the hope of using it on my SW 72ED as it was the recommended FF for this scope and reviews were positive. The FF arrived the day after being ordered form FLO. After the customary period of cloudy skies following recent arrivals of astro kits I went in earnest to test the FF. The easiest way is to point it to Polaris on a tripod with any alt-az head on. Test were carried out with a Nikon D5100 and UV/IR Cut filter. I shot a sequence of 60 5s exposures for the tested configuration and the reference configuration (no FF but just UV/IR Cut filter). Post-processed (calibration and stacking) the two sets in PI. The resultant field is 3deg8' wide x 2deg4' high. The useable field in the reference configuration (that is, without FF), where elongation is no more the 1.5x the width of the PSF, is about 2 degrees (i.e. the full hight minus a strip about 100 pixels wide at the top and bottom) and the remainder is dominated by astigmatic field curvature. The OVL FF improved the extent of the corrected field to the full height of the frame (2 deg 4') at the price of introduction of coma (seagull shaped aberration). The remainder of the field shows a less pronounced field curvature but with the introduction of comatic shape to the PSF so that at the overall PSF spread is reduced but the radial elongation is about the same. The FF also shifted the centre of the corrected field to one side by about 1/4 os its width, which is kind of annoying. Overall the result of the field test shows that while in the strict optical sense the overall amount of curvature was reduced, most noticeably toward the edges, the increase in useable field is minor at best (around 7%) which is further compromised by the introduction of detectable coma already within the the corrected field. The OVL Field Flattener was returned to FLO.

Rating (max 5):  
Exceeded my expectations
19 March 2021  | 

As usual the service from First light Optics was ecxeptional. Regarding the product I fitted this to a F5 skywatcher startravel150(750 mm focal length) . Some very strange deformed stars became apparent when i used the afore mentioned scope with optolong l extreme pointed at the bright sttars in the flame nebula. The diifference made with this field flattener was dramatic.That particular target brought my attention to the no so flat field from that scope as i guessed it i geared more towards visual use.

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