A break in the clouds on the shortest day of the year was all the excuse I needed for a first light image with the new William Optics ZenithStar 73 II APO telescope. I originally had my heart set on a RedCat 51
250mm/f4.9 triplet. But having experienced what the ZS73 is capable of, I’m convinced I made the right choice opting for the bigger scope with the extra reach of 430mm. Despite being only a doublet, the additional 73a field flattener does a great job of keeping the stars in check. Although I do still have a little bit of sensor tilt left to dial out, introduced with the D5500’s astro modification.
One thing I noticed with the narrowband filter is the lack of colour in the stars, with most stars appearing white. I have a plan to deal with this. I’ll attempt to take a sequence of shorter exposures without a filter, using the lowest ISO setting. This should give more dynamic range and hopefully not overexpose the stars. I’ll create a separate stacked image to merge with the main shot of the nebula. I’ll give this technique a try with my next target, once the clouds decide to part!
Image details: Modified Nikon D5500 and William Optics ZenithStar 73 II APO with 73a field flattener at 430mm / f5.9. 38 minutes exposure time (19 x 120 seconds) at iso 800. Using Optolong L-eNhance filter. Tracked with unguided AstroTrac TT320X-AG. Stacked in Deep Sky Stacker with 30 dark / 30 flat / 30 bias frames. Sequenced with N.I.N.A.. Edited with Photoshop and Starnet++