Charles Hagen:
LLMs (ChatGPT, etc.) are not astrophotographers, they do not know anything about astrophotography. They will regurgitate the mean of the information commonly available on the internet blindly and indiscriminately. There is zero point asking it technical questions or about technical concepts for which it has no real knowledge.
Given the VERY wide range of responses, often conflicting, any AP question to real people gets, isn't a 'mean' of that information possibly useful? LLM's can be wrong, but I'm not sure any randomly chosen answer from the community has a higher likelihood of being right.... As a quick test, I asked CGPT for acquisition suggestions given my location and gear (response below). I give it a B. It didn't recommend binning, and at my image scale and seeing that would be pretty standard, M42 is only available for about a half hour between dark and 30deg and M57 doesn't rise above 30deg until 2:30am, so the target list isn't great, and the fifth suggestion for exposure balance is muddy. On the other hand, the most useful part of its answer, the exposure length suggestions, is pretty spot on. So, not the best response possible, but I wouldn't call it totally bereft of any AP insight.
So, still buyer beware, but same as seeking answers anywhere else.
Cheers,
Scott
Below is a set of suggestions tailored to your equipment and local conditions. Of course, each target can behave differently, so treat these as starting points to be refined by your own tests.Recommended DSOs
Given Jackson’s dark (Bortle 3) skies, your moderate aperture, and 3″ average seeing, you have a wide range of options. Consider targets such as:
[*]
M42 (Orion Nebula):
A bright, well‐defined nebula that works well with LRGB. Its high surface brightness may even allow for slightly shorter exposures.
[*]
M57 (Ring Nebula) or M27 (Dumbbell Nebula):
Both planetary nebulae offer fine structure. They’re forgiving on a 9.25″ scope and provide a good testbed for color balance in LRGB.
[*]
M51 (Whirlpool Galaxy):
A fainter galaxy that benefits from longer integrations; its spiral structure can be teased out by stacking many subframes.
Other targets—such as open clusters (e.g., the Beehive) or even portions of larger nebulae like the Rosette—can also be rewarding, but the above are excellent starting points given your setup.Suggested Exposure Lengths
Your exposure times will ultimately depend on your camera’s dynamic range and the brightness of the target. As a general guideline:
[*]
For Luminance (L) Frames:
• 300 seconds per subframe is a good starting point.
• For very bright targets (like M42), consider trying 180–240 sec subframes to avoid saturation.
[*]
For Color (R, G, B) Frames:
• 300 seconds per subframe works well in many cases, providing a balanced SNR across channels.
• If you’re imaging a fainter galaxy (like M51), you might extend these to 300–600 seconds per subframe—but always check that stars remain tight given your 3″ seeing.
Keep in mind that these are per-subframe times. You’ll likely want to acquire a series (say, 15–30 subframes per filter) to later stack and increase your overall signal-to-noise ratio.Additional Acquisition Techniques
To make the most of your imaging session:
[*]
Calibration Frames:
• Darks, flats, and bias frames are essential to correct for sensor noise, vignetting, and other artifacts.
[*]
Dithering:
• Introduce small offsets between exposures. Dithering helps reduce fixed-pattern noise and improves the final stacked image.
[*]
Accurate Focusing:
• Use a Bahtinov mask or your camera’s live view to ensure sharp stars; even small focus errors can be critical when stacking many subframes.
[*]
Autoguiding:
• Even though the iOptron CEM70 is capable, autoguiding can further ensure that your exposures (especially those longer than 5 minutes) remain perfectly tracked.
[*]
Experiment with Exposure Balance:
• If you find that your luminance frames are giving you too much detail compared to the RGB channels (or vice versa), adjust the exposure times to balance the dynamic range. Some imagers even opt for a slightly longer integration on the luminance channel for extra detail, while keeping color exposures in check.
[*]
Software Considerations:
• Use stacking software (such as DeepSkyStacker or PixInsight) to align and combine your subframes. Techniques like “drizzle” can help improve resolution in post-processing.
These guidelines should get you started on a productive night of imaging. Remember that the key is to experiment a bit—the optimal settings can vary by target and by the specific sky conditions on any given night. Happy imaging!
