Location: San Bruno, CA
Telescope: Stellarvue SVR 90T with Televue x0.8 reducer on Takahashi NJP-Z Mount
Camera: Qhy9 CCD with Astronomik H-Alpha 12nm Filter
Even with the short focal ratio (f/d 5.6) obtained with the televue reducer, I had to apply 2×2 Binning and take a fair amount of exposure to get details in the Nebulae.
The H-Alpha filter does wonder to combat light pollution, even though the FWHM of this filter is not very narrow (12 nanometers).
Some words about the combination of Stellarvue SV 90T and televue reducer. I had to find the best distance between the CCD chip and the reducer / flattener. Initial trials with a distance of 58mm were not successful. Then 55mm of distance between the CCD chip and reducer/flattener seemed to yield better results.
My tests were done with the Qhy9 having a relatively small sensor (15mm x 19.7mm) – and even with this sensor size stars were not perfectly round on the egdge.
That’s why I am not sure if the televue 0.8x reducer/flattener is a good match with the Stellarvue SV90T for large chips. But at least in my case it turned out fine. On the other hand, the Stellarvue flattener gives perfect flat images with round star till the edge with an APS-C size sensor … but … the F/D is still at 7, making it more difficult to image faint extended objects. That is why I opted for the Televue reducer for this set of images, even though it does not produce a perfect flat field with this telescope optics.