I am still somewhat new to astrophotography and I use a DSLR on a star tracker. I started off with a 200mm focal length lens and I have recently upgraded to a 300mm lens. I was wanting to shoot the same targets with the new lens and I was wondering how to integrate the new data with the old data. I don't know if it's possible to combine different data with different focal lengths either by directly stacking them together or blending them after stacking separately. Are either of these methods possible, or are there other ways? I really wanted to get the close-up details from the higher focal length plus the background from the lower.
Processing Different Focal Lengths
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I don't think is going to work the way I think you might think it would work 
You either loose potential resolution by stacking all together using the lower fl image as reference or up-sample the lower fl image thus marring the potential of higher resolution the longer focal length could give using the same process of stacking the two together. This using traditional AP software and processes. A lot depends also on the software you're using and so potentially Photoshopping the two images together might given the answer you're looking for but you'd still need to up-sample the lower fl image, make the two backgrounds identical and clipping away any part of the border that has features in common between the two. It's inelegant but might work for you. Given the choice I'd go for the former route above rather than the latter. It is unlikely that you longer fl image downsampled by a third will actually loose resolution when viewed close-up.
You either loose potential resolution by stacking all together using the lower fl image as reference or up-sample the lower fl image thus marring the potential of higher resolution the longer focal length could give using the same process of stacking the two together. This using traditional AP software and processes. A lot depends also on the software you're using and so potentially Photoshopping the two images together might given the answer you're looking for but you'd still need to up-sample the lower fl image, make the two backgrounds identical and clipping away any part of the border that has features in common between the two. It's inelegant but might work for you. Given the choice I'd go for the former route above rather than the latter. It is unlikely that you longer fl image downsampled by a third will actually loose resolution when viewed close-up.
I‘ve had good success to stack different pixel scale images. I‘ld use one of the higher-resolution ones as reference for registration. But all my subs were oversampled anyway, so I didn‘t lose any resolution. If you‘re undersampled it‘s a different story and it depends on how much more data you can add. If you‘re not at least doubling the integration time, I don‘t think it‘s worthwhile.
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I believe Astro Pixel Processor can integrate images taken with different optics and focal lengths but I haven’t tried it out personally yet.
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Combining Different Focal Lengths with the Same Camera But with the Optolong L-eNhance
Hi all, I am curious to know if it is possible to combine data from different focal lengths taken with the same camera? For example, I am currently re-processing some data I shot of NGC 3372 (Carina Nebula) back in February this year taken through my...
Directly addresses combining data from different focal lengths with same camera.