A7R5: 15 mp vs 61 mp for star tracker astro shots?

[rcreamer]

I was wondering, does anyone knows if the 4x additional memory/processing burden for 61 mp vs 15 mp for high-iso star tracker tracked images is worth it? [A7R5]

Especially since:

• The 15 mp doesn't need Bayer interpolation vs the 61 mp which does

• The inherently lower pixel data value accuracy for low-brightness high-iso images

• The cumulative minor sub-pixel alignment (registration) errors when stacking dozens of noisy images with lens abberations, imperfect polar alignment, etc

• The additional SDXC card, hard drive, memory footprint + the additional CPU burden through all the post processing steps

I'm just getting started with a Star Adventurer GTi and knowing that 15 mp data is essentially as good as 61 mp data would greatly reduce the memory and processing time.

Thanks in advance.

PS: I'm new here so any suggestions on how to improve this posting such as Tags are welcome.

 

[rcreamer]

Update:

About 10 minutes ago I entered a tweaked version of my original post/question below into [Perplexity] [dot] [ai].

Its answer is: go with 15 mp for astro.

I decided not to withdraw my question/post here because it may very well be of interest to other astrophotographers here. Also, I'd enjoy any discussion of this topic here

I recommend pasting the below into Perplexity as I certainly learned a thing or two

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Question text entered into Perplexity:

I was wondering, is the 4x additional memory/processing burden for 61 mp vs 15 mp for high-iso star tracker tracked images is worth it? [A7R5]

Note: this question is not about capturing 61 mp and then downsizing that to 15 mp. It is about capturing 15 mp images natively in-camera using the Sony a7r5's 15 mp lossless compression raw capture mode.

Especially since:

• The 15 mp doesn't need Bayer interpolation vs the 61 mp which does

• The inherently lower pixel data value accuracy for low-brightness high-iso images

• The cumulative minor sub-pixel alignment (registration) errors when stacking dozens of noisy images with lens abberations, imperfect polar alignment, etc

• The additional SDXC card, hard drive, memory footprint + the additional CPU burden through all the post processing steps

I'm just getting started with a Star Adventurer GTi and knowing that 15 mp data is essentially as good as 61 mp data would greatly reduce the memory and processing time.

 

[jacobomerced]

I must admint, i dont know anything about astrophotography.

 

[rcreamer]

In a nutshell, astrophotography is difficult because:

• Stars are very dim.
• Digital sensors' pixel values are very inaccurate for dim pixel values --> noisy images. Plus, high ISO adds more noise.
• It is impractical to "expose to the right" to fix the noise.
• So astrophotographers take many shots and average the pixel values (stack) to reduce the noise.
• Stars make star trails because of the Earth's rotation.
• Telescopes and star trackers can rotate at one revolution per day to counteract the apparent star motion. This enables the capture of many longer-exposure (say 2 minutes) images to stack but you have to aim the mount's polar axis at the north celestial pole very accurately.

 

[iamdlewis]

you have to aim the mount's polar axis at the north celestial pole very accurately.

Equatorial mounts need this but most Motorized heads will use your GPS location to adjust the speed.

 

[rcreamer]

Equatorial mounts need this but most Motorized heads will use your GPS location to adjust the speed.

Thank you! I wasn't aware of this (possibly due to the poor documentation). Also, I was trying to be brief (nutshell).