Table showing ave. object magnitude you can see with various size Telescopes

[Flyhigh7]

Is there a table that shows for the various size telescopes what the lowest or should I say highest magnitude object that size scope should be able to find?

Astronomy magazine is great as far as telling us what cool objects are out there each month and what magnitude it is in a dark sky. I'd like to use that info to decide what objects are going to be too faint for me to bother finding with a specific size Telescope.

Example: If I buy a Nexstar 8SE, I think, this Telescope should be large enough to hunt objects that may only be of a 13 or 14 magnitude in a dark sky. But that is just a guess and that's why I'm looking for a table that might give this information.

Thanks in advance.

[pakarinen]

Yes, there was one posted to Cloudy Nights. I downloaded a copy but deleted it, I think.

Edit: I guess I didn't delete it. There's probably a clearer version out there if you Google a bit.

[JayTee]

I've never seen that graphic before -- nice!

I'll try to find the original, it looks worth having.

[Thefatkitty]

There is also this:

telescope-calculator/

You need to scroll down a bit, but hopefully it helps

All the best,

[OzEclipse]

The graphic posted by Olen is unrealistically optimistic based on my own observing experience. The calculator posted by @Thefatkitty agrees much more closely with my visual observations but this is only for stars. In the late 1970's and early 1980's, I used to do visual searches of star fields in galaxies in searching for supernovae. This was done with my 6" f7 and when my eyesight was excellent. The reference charts of each galaxy had stellar magnitudes marked or indicated. I also assisted the author of the supernova search charts in that I was one of a number of observers involved as a chart checker. This involved checking all the relative visual magnitudes to see how the charts matched the visual experience. So I was able to test the limiting visual magnitude of the instrument from my parents suburban back yard and a Bortle 1 site, Mt Tamborine Observatory where I was a regular guest of the owner. Mt Tamborine now has quite poor skies but in the early 80', the skies were truly excellent.

An observer with good eyesight 8” scope can nominally see a mag 14-14.5 star. But this limit is affected by the observers eyesight, light pollution, seeing and transparency.

Extended objects are objects with an observed angular diameter. These are objects such as nebulae, planetary nebulae, clusters or galaxies but also includes brighter solar system objects. Integrated Visual Magnitude is the object brightness of an extended object (nebula, cluster or galaxy) expressed as if all the light were concentrated into a single starlike point. This is a useful way of recording the overall brightness of objects but is neither a good indicator of whether an object is visible (with detail) or detectable without detail (as a faint smudge)

Deep sky objects vary greatly in size so you might be able to see one compact object eg planetary nebula of say mag 13 but not another large object of magnitude 9 because the light is spread across a much bigger area. A good example is comparing the visibility of two magnitude 9 objects, the Ring Nebula (M57) and the Rosette Nebula (NGC2244). The Ring nebula is approximately 4 x 4 minutes while the Rosette is about the same all over brightness but 1.3 degrees diameter some 400 times bigger in area. The Ring nebula is an easy object, visible in a 50mm finderscope under a dark sky whereas the Rosette is very challenging due to it's low surface brightness.

The visibility of an extended object is a factor of:-
The surface brightness rather than the overall magnitude
The losses of brightness due to sky transparency
The contrast of the object brightness against any light pollution in the background surrounds.
The sensitivity of the eyesight of the observer.

If the surface brightness after losses with transparency is brighter than the sky taking light pollution into account, then you will be able to detect it.

Last year I embarked on a project, adding a relative surface brightness column to the digital NGC catalogue. But I had to get the NGC data from multiple sources that were each formatted differently and I soon found that it was more work than I had time to do. If I ever complete this, I’ll make it available.

My intention is that:-
you will be able to sort the catalogue on the basis of surface brightness.
Find your own observing limit by testing observations and finding an object that is barely visible
Colour code objects that are easily visible; barely visible, not visible
Resort the catalogue back to NGC number

Any observer will then have a colour coded NGC catalogue colour coded for their eyesight and a particular instrument. If you have multiple instruments, you can easiily have multiple copies of the catalogue coded for each telescope.

Joe

[Flyhigh7]

Thanks guys! This is excellent information.

[Lady Fraktor]

https://telescopenights.com/star-bright ... t-to-know/

[KingClinton]

Great advice so far! I basically suck at math and figures so it makes my head swim real quick trying to do all those calculations.
I take a slightly different approach. Your mileage may vary.

In your telescope literature there should be a mention of the "Limiting stellar magnitude or limiting visual magnitude". This is the theoretical maximum magnitude of stars your scope should be able to resolve under the right conditions.

For my XT8 this is 14.0
So I should under the right circumstances be able to see stars to magnitudes of 14.
Now factor in light pollution and the maximum magnification you have.
With experience I have learned that most DSO(not stars) over 8th magnitude are going to be impossible to see from my current backyard location. There are also other factors like surface brightness that can affect the views, again this also comes with a bit more experience at the eyepiece.
As for the stars(you may want to see a double or open cluster) I have seen some down to 13th magnitude under excellent conditions.

So I can quickly decide what is worth adding to my observing lists and what I will probably struggle with.

Not a very scientific or mathematically correct method but it works for this old goat in Africa.

Keep getting out there every time you have a clear night and soon a clearer picture of your scope capabilities and your observing skills will become apparent, have fun and keep looking up!

[OzEclipse]

I don't know how bad your light pollution is but I think you may be limiting yourself too much.

Some deep sky objects like planetary nebulae or galaxies are quite small and have quite decent surface brightness.

An 8" telescope can easily observe some mag.10 galaxies eg NGC 1316(Mv9.7) and NGC 1365(Mv 10.3). I can easily observe them in my 6" f7 reflector.

Don't forget that the entire Messier catalogue was discovered using a 3" refractor and James Dunlop discovered all the southern objects in his catalogue using a 3" refractor and later a homemade 9 inch f12 reflector.

Joe

Great advice so far! I basically suck at math and figures so it makes my head swim real quick trying to do all those calculations.
I take a slightly different approach. Your mileage may vary.

In your telescope literature there should be a mention of the "Limiting stellar magnitude or limiting visual magnitude". This is the theoretical maximum magnitude of stars your scope should be able to resolve under the right conditions.

For my XT8 this is 14.0
So I should under the right circumstances be able to see stars to magnitudes of 14.
Now factor in light pollution and the maximum magnification you have.
With experience I have learned that most DSO(not stars) over 8th magnitude are going to be impossible to see from my current backyard location. There are also other factors like surface brightness that can affect the views, again this also comes with a bit more experience at the eyepiece.
As for the stars(you may want to see a double or open cluster) I have seen some down to 13th magnitude under excellent conditions.

So I can quickly decide what is worth adding to my observing lists and what I will probably struggle with.

Not a very scientific or mathematically correct method but it works for this old goat in Africa.

Keep getting out there every time you have a clear night and soon a clearer picture of your scope capabilities and your observing skills will become apparent, have fun and keep looking up!

[KingClinton]

Joe, light pollution here sucks!
As the crow flies I am within a few kilometres of the city centre, even closer to a major harbour(once rated busiest in Africa) and for good measure only a few kilometres from a major oil refinery.
Sodium lights are still all the rage here.

On a overcast night I could stand outside and browse the paper without any additional lighting. Get a nice satisfying orange glow from the clouds.
Clear nights here always have a slight orange tinge to them.
Some planetary nebula are visible but purely as a small fuzzy circle, similar to seeing Neptune or Uranus.
I can count all the galaxies I can see from here on one hand! Only the brightest objects need to apply here, no chancers!
I learned long ago to accept the limitations beyond my control and focus on and enjoy what I can.
And that in turn makes dark sky trips even more valuable!

Thanks for your excellent advice and input as always Joe.

[jrkirkham]

I find the posted limiting factors on various telescopes to be useful in comparing telescopes. I also find them to be somewhat helpful in narrowing my expectations down to something more realistic. Those things are important for deciding if the telescope you are looking at can accomplish what you want to do with it. But, as everyone mentioned, there are so many variables these only serve as guidelines,

Another variable for me is slapping a camera on your tube. How far can that extend your range? Even if you don't try to make a beautiful picture you can up the ISO, take a string of 30 second exposures, and enter a whole new world. I always use a camera if hunting Pluto or asteroids. Following dim comets is another place where a camera helps.

I would like to have a guess how far a person can reach with short exposures and high ISO through various aperture sizes.