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What do you mean by an acceptable level of chromatic aberration?
My main visual refractor is a Vixen NA140SS which has superb optics and has well corrected chromatic aberration to the point that I struggle to notice it. It is a superb deep sky instrument.
The only object that shows some noticeable blue wash/fringing that interferes with the sharpness of the image (at high magnification) is the moon. This is easily corrected with a Baadar Fringe killer filter. The faint yellow cast this produces "disappears" after about 10 minutes viewing. I have not tried stopping the aperture down as an alternative but I think if you do the numbers you will be down to about 100 mm aperture to get a long enough focal length. I also have a 103mm APO and I can tell you that I much prefer the views through the 140mm scope to the point that it is my scope of choice for all night sky visual observing. It is gathering twice the light and has noticeably better resolution than the 103. The 103 is now dedicated to solar observing.
Cheers
Steve
PS, your thought of stopping down has me interested to know what the results would be on my scope. I will try making a temporary mask and see what the results are.
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