Quantity of Stars - Forums

Topic starter

8 days ago

Greetings!

I’ve had a few scopes during my life. From a Sears 2” refractor in the 70s to a Celestron 8” SCT to an iOptron RC6. Diving into astrophotography has its own challenges and questions, and I think I have an important and unanswered few. My first question - what is the balance in selecting a scope or equipment in capturing hundreds to thousands of stars and capturing small deep space objects (think ARP)? In other words, selecting a scope depends on the objects planned during an imaging session. I choose either my F/5 APO for a wonderful quantity of stars and larger celestial objects or my RC6 for very small ARP objects (yet only capture a handful of stars - please see my pictures https://app.astrobin.com/u/Kevinito).

—OR—

Is the issue the amount of subs or length of subs? I can easily capture thousands of stars in minutes with my APO (focal length 300mm); however, my RC6 (focal length 1370mm) takes HOURS to capture just a handful.

—OR—

Is the issue my cameras? I have a few: ASI533MC Pro, ASI585MM Pro, ASI585MC Pro Air, ASI183, etc. The reason I selected the 585 is due to the small pixel size (2.9 microns) and the very small imaging window. When I look and compare the 2600Pro, the imaging window is enormous compared to my 585 and I feel like there is no advantage due to the 2600’s larger imaging sensor and larger pixels (3.76 microns). A couple of pictures are included below to see the exactly what I mean.

Finally, is there a scope and camera combination where I can capture ARP deep space objects with a good focal length yet capture thousands of stars? Can I do this with my existing equipment?

ASI585Pro.jpeg

ASI2600Pro.jpeg

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andrea tasselli

Frequent contributor

8 days ago

A larger sensor will capture more stars than a smaller one given that it covers a larger area of the sky. If you are worried about the image scale, don’t. An ASI2600 coupled with the 6” RC has more resolution than you can make use in practical terms.

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K. Wiseman

Topic starter

8 days ago

Thank you, Andrea.

I did seriously look into the 2600 paired to my RC6; however, I saw the word “oversampling” come up on more than one occasion. What does this mean?

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andrea tasselli

Frequent contributor

8 days ago

Oversampling means you sample the FWHM of your average stars with more than 4 pixels, in other words you are wasting signal without any benefit. Whether this is actually the case depends on your integrated seeing, that is your average FWHM (and here average means not only across the frame but across the seasons).

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K. Wiseman

Topic starter

8 days ago

Thank you!

Wei-Hao Wang

Perfect post

8 days ago

Usually, when we image an object, we use a field of view that’s matched to the size of the object. So big objects require big FoV, and vice versa. This means, the FoV for small objects is small, in order to see the details in these objects. Small FoV implies fewer stars. Very naturally, good details on small objects and large number of stars are two goals that go against each other.

May I ask why you care so much about capturing many (thousands of) stars? If you can better explain the reason behind this goal, people can give you more useful advices.

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Paul Larkin

8 days ago

K. Wiseman · Jul 14, 2026, 05:43 PM
Is the issue the amount of subs or length of subs? I can easily capture thousands of stars in minutes with my APO (focal length 300mm); however, my RC6 (focal length 1370mm) takes HOURS to capture just a handful.

Perhaps an additional consideration is f5 for the 300mm vs f9 for the RC6. f9 is around 3.24 times slower than f5. That won’t explain minutes vs hours but it will make a difference to the time required to capture the same amount of light.

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andrea tasselli

Frequent contributor

8 days ago

I shan’t think so.

TiffsAndAstro

6 days ago

My 200mm and DSLR apsc captures many thousands of stars, but galaxies are “small”

My 1600mm C6 and small imx533 sensor captures maybe 50 stars, but the galaxies are much bigger :)

I'm interested in galaxies, so I prefer option 2, however with sampling issues its more complicated than that, but I use what I have.

What are you trying to achieve? :)

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donld

5 days ago

Your RC6 doesn’t look good. You probably want to start by figuring out its potential. How does what you are getting compare to other users here?