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Is there a way to calculate limiting magnitude for EAA?

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#1 Jeff Lee

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Posted 20 February 2020 - 12:46 PM

Since I live in Bortle 6 skies I am wondering how deep I can go. I notice when I had first light with my c5 that http://nova.astromet.../status/3239082 only identified fairly bright stars. One way I guess to print out a sky chart of the same area and match stars. Any one have a formula or site that calculates limiting magnitude for EAA setsup? I know its pretty deep just don't know how, so for now guess I will use the chart method.



#2 nic35

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Posted 20 February 2020 - 07:02 PM

Sharpcap's brain can calculate the faintest observable object - but the results are expressed in e/pixels/second.

 

I'm not smart enough to convert that to magnitudes or surface brightness!

 

j



#3 Jeff Lee

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Posted 20 February 2020 - 08:34 PM

Thank J, I've got the brain setup and will see what that says.



#4 Clouzot

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Posted 21 February 2020 - 02:32 AM

If you saved a capture and know the coordinates, ASTAP could give you an idea of the actual magnitude you reached. But be warned: while powerful, it’s not an easy software to work with
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#5 Clouzot

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Posted 21 February 2020 - 06:27 AM

And here's how to do it:

- install ASTAP with its star catalogs (g17-color in my case)

- launch ASTAP

- open your capture

- tell ASTAP what the object was. To do so, double-click on the object coordinates and enter the catalog name (in my case, a 9-minute stack of M31 I did this summer under an almost full moon, with the C9 Hyperstar and an uncooled ASI183MC, which was running at almost 40°C this night!)

- in the stack window (accessed through the "sigma" button), stack tab, set the FoV to Auto

- press solve, hopefully it will find a solution

- in the Tools menu, choose Calbrate photometry, let it work (it will try and match the stars in your image with the catalog magnitude)

- then choose Magnitude (measured) annotation

- ASTAP will overlay the magnitude for some of the brightest stars (it has some bugs as you can see, mag 97.1 probably means mag 9.71!), but if you hover your mouse on an unmarked star, it will display at the bottom of the window what magnitude it is. In my case, it detected a mag 15.3 star under my mouse pointer, which is consistent with what I get with that setup (mag 17-18 max under those conditions)

 

astap_test.jpg

 

Hope it helps! It's quite interesting to see how our setups can perform, magnitude-wise.


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#6 mclewis1

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Posted 21 February 2020 - 10:16 AM

Jeff,

 

Under my similar skies (mine might get slightly better on a few nights) my C6 with an imx224 camera working at f3.5-4 can easily capture mag15-16 galaxies, and stars in the mag 17 range. My C11 can go a couple of magnitudes deeper but I've never really pushed it to see what the limits might be. I generally don't use filters except for a UV/IR cut and sometimes a Lumicon Deep Sky on extended nebula. Occasionally I also use a 12nm Ha for mono work on strong Ha targets or really bad nights (strong moon, etc.).

 

Generally for EAA work I assume reasonable stellar targets of up to about mag 17, condensed DSOs (small galaxies, planetaries, etc.) up to mag16, and more diffused objects (galactic arms, nebulae, etc.) up to about mag 15. I can push the limits and detect objects in the same classes about a magnitude fainter but only with a lot of work (so not as much observing fun).

 

Oh and be careful of published magnitude numbers. On popular objects it's often a visual magnitude given but on fainter objects it's a "CCD magnitude". A lot of catalog work was originally done with older CCD imagers which were very strong in the blue spectral range (and less so in the red end). So published numbers can vary a bit depending on when the work was done. I generally assume a rounding to the nearest half magnitude. Anything more accurate than that and I think there are too many other variables involved for me to be able to judge things with any more accuracy.


Edited by mclewis1, 21 February 2020 - 10:23 AM.

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#7 Ptarmigan

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Posted 22 February 2020 - 11:53 PM

Jeff,

 

Under my similar skies (mine might get slightly better on a few nights) my C6 with an imx224 camera working at f3.5-4 can easily capture mag15-16 galaxies, and stars in the mag 17 range. My C11 can go a couple of magnitudes deeper but I've never really pushed it to see what the limits might be. I generally don't use filters except for a UV/IR cut and sometimes a Lumicon Deep Sky on extended nebula. Occasionally I also use a 12nm Ha for mono work on strong Ha targets or really bad nights (strong moon, etc.).

 

Generally for EAA work I assume reasonable stellar targets of up to about mag 17, condensed DSOs (small galaxies, planetaries, etc.) up to mag16, and more diffused objects (galactic arms, nebulae, etc.) up to about mag 15. I can push the limits and detect objects in the same classes about a magnitude fainter but only with a lot of work (so not as much observing fun).

 

Oh and be careful of published magnitude numbers. On popular objects it's often a visual magnitude given but on fainter objects it's a "CCD magnitude". A lot of catalog work was originally done with older CCD imagers which were very strong in the blue spectral range (and less so in the red end). So published numbers can vary a bit depending on when the work was done. I generally assume a rounding to the nearest half magnitude. Anything more accurate than that and I think there are too many other variables involved for me to be able to judge things with any more accuracy.

It is not just magnitude, it is also distance. I have seen APM 08279+5255 and TON 618 and they are well over 10 billion light-years. cool.gif



#8 Hobby Astronomer

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Posted 06 March 2020 - 12:33 PM

Here is an easy and intuitive way to do this.

 

I know this sounds funny but if you shoot an image as deep as you are limited to and next open stellarium to see how deep you have gone. Find your target in stellarium and then do the star comparison between stellarium and your image. Stellarium will show stars to 17.99 mag.

 

Very useful.

 

HA



#9 GaryShaw

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Posted 06 March 2020 - 12:40 PM

You can upload an image with a variety of faint stars and/or DSO's to Astrometry.net and they'll identify what's in the image and you can look up the magnitudes. Doing this is in 'excellent' and 'average' seeing conditions would give a good idea of the 'ideal' and 'typical' magnitude limits of your gear.

Gary

 

https://nova.astrometry.net/upload

 



#10 Noah4x4

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Posted 06 March 2020 - 04:16 PM

Calculate the limiting magnitude? Easy.

 

If I take my glasses off, I can see nothing on my screen. lol.gif


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#11 Ptarmigan

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Posted 08 March 2020 - 03:16 PM

I use ASTAP.

http://www.hnsky.org/astap.htm

 

I also use Astrometry.net and it links to World Wide Telescope.

 

I use NASA/IPAC Extragalactic Database (NED).

http://ned.ipac.caltech.edu

 

I have seen fuzzy objects that are not identified on ASTAP and Astrometry and use NED. I get many objects that I have never heard of.


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#12 Stargazer3236

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Posted 22 March 2020 - 06:15 AM

I once did Astrometry with my old Nexstar 8SE and ASI224MC camera about 3 years ago. I was imaging M57 and the surrounding area. I was at F/10 and and pointed straight up at zenith and go very clear skies and little atmosphere to look through.

 

I managed to bag 18.3 magnitude stars with lots of 17th and 16th magnitude stars as well. As far as nebulous objects, your limiting magnitude is limited by the overall size of the objects you are looking for and the surface brightness per square arc minute of size. So if your object is a large nebulous objects, like a faint planetary nebula, it will all depend on where the object is located in the sky, atmospheric deviations, seeing and transparency. Also, if you are trying to image a faint object low near the horizon and within 20 degrees of the horizon, atmospheric extinction will also limit your ability to image said object.

 

When you want to image a particular object, do your research on the object. Check with Reiner Vogels website: http://www.reinervog...et/index_e.html or Alvin Huey's website: http://www.faintfuzz...ingGuides2.html and get some of his PDF catalogs loaded onto your computer. Read through the catalogs and get insights as to how big the object is, its surface brightness, diameter in arc seconds or arc minutes and calculate how big of a field you will have to view or image this object. Use the Astronomy.tools website: http://astronomy.too.../field_of_view/ and go to FOV calculator and then either Eyepiece mode or imaging mode to find out what you size viewing area you will have with your telescope and camera.

 

By reading up on the catalogs, you will find out how deep you can see. In most cases, using a broadband or narrowband filter will bring out more detail, make the object a bit brighter and nearly eliminate the background light pollution to make it easier to see the object you are looking for.


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#13 Ptarmigan

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Posted 22 March 2020 - 10:41 AM

I once did Astrometry with my old Nexstar 8SE and ASI224MC camera about 3 years ago. I was imaging M57 and the surrounding area. I was at F/10 and and pointed straight up at zenith and go very clear skies and little atmosphere to look through.

 

I managed to bag 18.3 magnitude stars with lots of 17th and 16th magnitude stars as well. As far as nebulous objects, your limiting magnitude is limited by the overall size of the objects you are looking for and the surface brightness per square arc minute of size. So if your object is a large nebulous objects, like a faint planetary nebula, it will all depend on where the object is located in the sky, atmospheric deviations, seeing and transparency. Also, if you are trying to image a faint object low near the horizon and within 20 degrees of the horizon, atmospheric extinction will also limit your ability to image said object.

 

When you want to image a particular object, do your research on the object. Check with Reiner Vogels website: http://www.reinervog...et/index_e.html or Alvin Huey's website: http://www.faintfuzz...ingGuides2.html and get some of his PDF catalogs loaded onto your computer. Read through the catalogs and get insights as to how big the object is, its surface brightness, diameter in arc seconds or arc minutes and calculate how big of a field you will have to view or image this object. Use the Astronomy.tools website: http://astronomy.too.../field_of_view/ and go to FOV calculator and then either Eyepiece mode or imaging mode to find out what you size viewing area you will have with your telescope and camera.

 

By reading up on the catalogs, you will find out how deep you can see. In most cases, using a broadband or narrowband filter will bring out more detail, make the object a bit brighter and nearly eliminate the background light pollution to make it easier to see the object you are looking for.

I found larger nebula (Abell 31, IC 405, etc.) or face on spiral galaxies (M33, M101, NGC 2403, etc.) more difficult than distant galaxy clusters or quasars. Distant galaxy clusters and quasars are smaller and light is more concentrated.




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