Orion with 135mm mosaic

tradesmith45 wrote:

elgol20 wrote:

Hi,

since I had servere break downs due to cold ice I just could do some lighttrack photos the old way with a Sigma Art 135mm lens, here a 3 panel mosaic, total ca. 90min at f/2.2 using a modded D800E. Missed the complete Barnard loop, next time...

This is a wonderful image. It would help me if I knew the FOV of this mosaic. I'm using APSc & have 90 & 56 & 50mm. So I'm trying to figure out if one of them would give a similar FOV as your 3x 135mm. I could do a mosaic or single frame.

Since you did not get the answer you wanted, I would suggest using your 56mm with the camera in portrait orientation to get a similar field of view on APS-C. At any particular f-ratio, your 90mm lens will have a larger aperture than the other two you listed.  So if you were to do a three-panel or even four-panel mosaic (the latter with more overlap) of the area with the 90mm in landscape orientation, you would capture more light and fainter stars in the same total exposure time.

But unless your camera is modified to be more sensitive to the h-alpha wavelength, you won't be capturing quite as much of the light from that as elgol20 did here. With most stock cameras, you would need to expose much longer to compensate. But the resulting image won't emphasize the red quite as much. OTOH, the image would actually have a more natural color balance.