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2x drizzle photo or double the focal length

Equipment Drizzle
3 replies•135 views
Reza Mohammadi avatar
Reza Mohammadi avatar
Hi there
I have a question about drizzled photo quality in a fast image train, in practice if I choose a fast and prefect Newtonian and use drizzle 2x during pre-processing is it almost same as a undrizzled photo of a high quality refractor with the same aperture of the Newtonian and double the focal length in detail and sharpness?

Reza
Médéric Hébert avatar
Médéric Hébert avatar
I'm not an expert far from it and I'm sure they'll shim in soon enough, but my understanding of it is no. The newtonian have a central obstruction so it won't be equal to a refractor of equal aperturea and focal lenght. Drizzling can only get you so far, it is in the end up-scaling your images before stacking to somewhat mitigate under-sampling.
Tony Gondola avatar
Tony Gondola avatar
No, it helps but you can't get something for nothing. By drizzling you are trying to make up for information that simply doesn't exist in the original.
andrea tasselli avatar
andrea tasselli avatar
Reza Mohammadi:
Hi there
I have a question about drizzled photo quality in a fast image train, in practice if I choose a fast and prefect Newtonian and use drizzle 2x during pre-processing is it almost same as a undrizzled photo of a high quality refractor with the same aperture of the Newtonian and double the focal length in detail and sharpness?

Reza

If the newtonian image is significantly undersampled with respect to the seeing you might gain some, possibly large, proportion of the lost resolution back, at the price of some loss of SNR. This cannot compared to a refractor which is well sampling the seeing for its focal length, for both loss of light due to reflective coatings and CO shading and because the refractor (or in fact any equivalent optical system) doesn't need to going through drizzling with the attendant numerical manipulation and loss of SNR.