That's not a planet

The previous image description stated, that more focal length would be required for galaxies. This is not entirely true, we better evaluate the field of view and angular resolution per pixel.

Combining a focal length of 580mm with an APS-C size sensor the field of view is about 2.3 degrees, and the 3.76µm pixels give a resolution of about 1.3 arcseconds per pixel.

To obtain a small object larger into the frame, we may either increase the native focal length of the telescope, do a crop, trading some resolution or use a smaller sensor with smaller pixels.

The image above was taken with the same focal length of 580mm but a sensor with tiny pixels of 1.45µm, an ASI715MC. This results in an angular resolution of about 0.5" per pixel. In addition, as the sensor is significantly smaller than APS-C, we only image half a degree at once.

In fact this setup operates in oversampling, as the optical resolution of the telescope is only about one arcsecond, the size of a bayer group.

As the optical resolution primarily depends on the aperture of the telescope, I imaged the same object using my fast 360mm reflector for comparison:

M51, ASI715MC Gain 100, 360mm, 110x90s, 2.75h

Due to the shorter focal length the galaxy is, of course, smaller within the frame. In fact its resolution is slightly higher as the telescope has a larger aperture. And with a similar exposure time the faster optics collected about four times the photons compared to the APO.

The ASI715MC is in fact a planetary camera, optimized for higher sensitivity and frame rate to collect as many frames as possible in a short timeframe so the stacking software than will only use the best frames.

Jupiter: ASI664MC Gain 252, 580mm, 2x Barlow, 5.5mSec, 15% of 11000 frames

For this image the ASI664MC with larger pixels in combination with a 2 times barlow lens was used, effectively the same resolution per pixel as with the ASI715MC. Only 1500 of the collected 11000 frames were finally stacked using Autostakkert. It is still a crop, though.

M81: ASI715MC Gain 100, 360mm, 167x90s Mix, 4.2h

The larger galaxies from Messier's catalog can be imaged with such a setup quite nicely, like Bode's Galaxy, or Messier 81.

I had experimented with various gain settings and exposure times to find a sweet spot to make best use of the typical 12 Bit ADC in planetary cameras. While higher gain settings allow for shorter exposure times, the fainter parts are easily hidden in increased noise.

M106: AS715MC Gain 35, 580mm, 85x300s, 7.1h

For Messier 106 a lower gain setting was used and each sub exposed for five minutes. A rather long time for relatively bright galaxies.

Somewhat easier targets are starclusters, like Messier 3:

M3: ASI715MC Gain 35, 360mm, 94x120s, 3.1h

At a focal length of 360mm the starcluster perfectly fits on the sensor of the ASI715MC. And with its tiny pixels the stars are nicely resolved.

Faster optics are advantageous when hunting deep sky objects with a planetary camera to accomplish reasonable exposure times. Using the ASI664MC with its larger pixels we may collect sufficient photons to even image brighter planetary nebulae like the Owl Nebula Messier 97 along with the galaxy Messier 108:

M97+M108: AS664MC Gain 50, 360mm, 130x120s, 4.3h

Of course there are significant limits with such a setup, in particular when imaging any type of nebulae.

M97: ASI715MC Gain 100, 580mm, 229 Subs 180-300s Mix, 14.75h

The planetary nebula M97 seems to be a rather bright object, but its surrounded by a quite quite faint hull of O3. I could not resolve this using the relatively slow APO even with nearly 15 hours of integration time.

In addition uncooled planetary cameras are not designed for long exposure times and tend to generate some static pixel pattern which require dithering per sub and still degrade the background noise. After many experiments I took some hours of darks with the camera placed in the refrigerator at about +8°C (46°F).

You'll find some more information on this topic here: Deepsky with a planetary camera

It is much simpler to use these planetary cameras for their intended purpose, imaging brighter objects like planets or the moon and using short exposure times:

Mond: ASI715MC Gain 100, 360mm, 1.0mSec, 75% of 400 Subs

The obtained resolution can be kind of impressive for this comparable small setup.