ZWO ASI1600MC-Cool colour cam­era


Sky at Night Magazine - - CONTENTS - WORDS: PETE LAWRENCE

SKY SAYS… Is this the ul­ti­mate astro cam­era? Well, it does tick a lot of boxes and can be used across the board...

We have re­viewed a num­ber of cam­eras re­cently that have pushed at the bound­ary be­tween So­lar Sys­tem and deep-sky astropho­tog­ra­phy. ZWO’s cooled, one-shot-colour (OSC) ASI1600MC-Cool is an­other. How­ever, un­like its pre­de­ces­sors, which have nipped at the heels of mid-res­o­lu­tion cooled as­tro­nom­i­cal CCD cam­eras, this CMOSbased de­vice has a 4656x3520 pixel (16 megapixel) sen­sor that takes a se­ri­ous swipe at cooled large­for­mat OSC CCD de­vices and DSLRs.

Its full res­o­lu­tion is best suited for deep-sky imag­ing and its large for­mat sen­sor cer­tainly gives a DSLR-like ex­pe­ri­ence. Shoot­ing the Orion Ne­bula through a 130mm f/3.3 as­tro­graph, we had no dif­fi­culty in fit­ting the en­tire sword re­gion on chip in one go. De­spite the cam­era’s rel­a­tively small 3.8µm pix­els, we found its sen­si­tiv­ity to be ex­cel­lent, as was its colour ren­di­tion. It was as ca­pa­ble of cap­tur­ing the hy­dro­gen-al­pha reds in the Orion Ne­bula as it was the lovely blues of the reflection ne­bula that per­me­ates the Pleiades open clus­ter.

Us­ing the whole sen­sor area re­stricts the cam­era’s peak frames per sec­ond (fps) value to 23fps in 10-bit mode, or 14fps if us­ing the in­creased tonal range of its 12-bit mode, which is fine for large deep-sky ob­jects. Ex­po­sures can range from 32 mi­crosec­onds up to 2,000 sec­onds, and typ­i­cally we found our­selves work­ing in the 10- to 60-sec­ond range while imag­ing deep-sky tar­gets. With the low noise char­ac­ter­is­tics of a cam­era such as this, short ex­po­sures will de­liver a good sig­nal to noise ra­tio, which is ideal. Noise is fur­ther kept at bay via ac­tive cool­ing, en­abled by con­nect­ing an op­tional ex­ter­nal power sup­ply. This is very ef­fi­cient and can drop the tem­per­a­ture of the sen­sor to be­tween 40 and 45 de­grees be­low the am­bi­ent tem­per­a­ture. In our tests, we timed a drop from 15°C to –20°C as tak­ing five min­utes.

The clear ben­e­fit of cool­ing

The dif­fer­ence be­tween hav­ing the cool­ing on and off was dra­matic when we com­pared a –20°C cooled 900-sec­ond dark frame against a non-cooled one. It was only af­ter a se­vere stretch that we could see any back­ground noise in the cooled ver­sion, in­clud­ing a cou­ple of re­gions of amp glow. Stretch­ing the much nois­ier, non-cooled im­age by the same amount made it ap­pear pure white.

For the plan­ets, the full 4656x3520-pixel ar­ray is overkill; in­stead you would typ­i­cally de­fine a re­gion of in­ter­est (ROI) to re­duce the num­ber of ac­tive pix­els. With re­duced data over­head, the peak frame rate limit in­creases. Imag­ing Jupiter at f/28 through a 14-inch Sch­midt-Cassegrain with a ROI of 344x300 pix­els

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