Blue Bloating

[AMcD]

Now that I am underway with the QHY268M, I fear that it is revealing the shortcomings of imaging with a relatively fast achromat (my TS152 Individual).  I am seeing significant blue bloating when imaging through the blue filter (even though the Antlia Pro has a lower cut off at approximately 420nm).  Also, although to a lesser extent, with the luminance filter.  I need to undertake further tests on a night without high clouds (such nights appearing almost non-existent at the moment) as I am conscious that the affected subs were taken with some high cloud present, increasing the chance of scatter.  As I understand it however, the following actions may mitigate blue bloating, albeit I appreciate that I am never going to eradicate it entirely whilst I am imaging with an achromat:

(a) Ensure regular focusing.

(b) Image on nights with very good transparency, seeing and no moon.

(c) Seek to reduce the blue bloating in post processing (using the Minimum filter in PS or a masking and star reduction routine in PI).

(d) Employ a minus violet filter in front of the blue filter (albeit the Lumicon minus violet filter also has a lower cut off at 420nm).

(e) Buy a fast(ish) Newtonian 😂 (all suggestions for a new scope gratefully received).

Does anyone have any other top tips?

[DaveS]

With a fast achromat I would stick to NB, as narrow as possible while refocusing between filters, though you may also encounter considerable spherical aberration.

Or buy a slower triplet apo.

[rl]

That's a pretty high end camera that represents a significant financial investment, especially when the cost of the filters are added on. I'd feel inclined to finish the job and get an 80 - 100 mm apo refractor scope...ideally a triplet but there are many good doublets at lower cost. Newtonians can be very good when set up right and with a coma corrector but there is a lot more faffing about compared to the refractor route, and you have to be able to live with the diffraction spikes on bright stars. You may also have back focus issues combining a filter wheel with an off-axis guider and a coma corrector, although some reflectors designed for photography will be a bit more accomodating. Still, refractors generally have much more focuser travel, and the mechanically fixed optics work better with a simple guidescope.