how deep does my setup go

[teleskopjo]

Hello I would like to know what limiting magnitude stars I am getting with my DSLR.. What software or procedure would you suggest please? One could be loading the image into CdC or equivalent then switch on fainter stars etc.. Any thing easier/faster?

[Knight of Clear Skies]

Interesting question, I've been wondering this as well.

[james_screech]

I used the CdC method as you originally suggested, you may need the Nomad catalogue though. My Modified 500D and 8" SCT (ISO 800, 180 sec exposure) get me down to mag 16-17, and I have bad light pollution. You may be pleasantly surprised at how faint you can go.

James

[Physicist13]

pretty straighforward way is to read off the pixel values of the peak intensity (must be non saturated, non stretched image!) of stars with known magnitudes. Then simply plot magnitude vs pixel value, more the merrier. Read off the average noise level of your image (background noise). Then from your graph read off the equivalent magnitude for this value. This gives the limiting magnitude (SNR=1). Bit more accurate is to take the integrated pixel values of each star, but the methosd is the same.

P

[Ptarmigan]

The excellent freeware IRIS will do this.

http://www.astrosurf.com/buil/us/iris/iris.htm

Quite a steep learning curve but there are lots of tutorials on the web.

It is a long time since I did it so I wont attempt my own guide here, I'd just confuse us both

IRIS will do lots of other interesting things, so well worth the learning curve !

(CdC will work but I found IRIS to be better for me )

[Knight of Clear Skies]

Thanks, I'll give IRIS a try sometime.

pretty straighforward way is to read off the pixel values...

Sounds good but I'm not quite sure I follow that, so I'll give the software method a try first.

[Physicist13]

lol! sorry! software does pretty much what I describe I believe. Good luck.

I keep trying to get people to understand where the noise comes from (read noise or not) as this is pretty impostant in understanding what is limiting the SNR and how to go about improving it.

P

[Ptarmigan]

lol! sorry! software does pretty much what I describe I believe. Good luck.

Once upon a time ( a long time ago when the dinosaurs were young) I noticed that Algol was dim.

Quickly I got out my little camera, perched it on a tripod and proceeded to click away over the next few hours

(yes, even in England it can sometimes happen that we get some hours !)

Then, when it was cloudy and rain etc I learned the format of a BMP file,

I taught myself some C and peeked and poked with the aid of some consol (DosVM was it ? tis long ago now ) progs

(windoze was young and getting away from me )

Thus I constructed some pixel totals,

also I discovered the limited dynamic range of A ) my camera and B ) of 8bit image files,

so ended up counting pixel diameters of over-exposed blobs !

Somewhat later in life (and a bit wiser !) I discovered RAW,

and find it easier to search the web to see if someone cleverer than me has already invented the wheel

Sad, I know !

[Physicist13]

lol! sound like my life!!

[Johanvk]

Not really a software approach, but simple practice: I got a reference field somewhere near M101 (Uma), and imaged it. With a 8" SCT and Canon 450D it got me to a usefull m=16 in 15 minutes.  The weakest star visible is pretty clear to identify. I could use e.g. IAP4WIN which has a straightforward measuring tool. But, if you want to see what lightpollution and foggy skies looks like, come to my place in Leiden (Holland).  There the limiting magnitude is pretty variable from night to night. It does not pay to have a number better than 0.5 m.

[teleskopjo]

thanks for your suggestions

[JRWASTRO]

Some time ago I tried to answer the very same question.  At the time my logic was to take a long exposure image,  process minimally the resulting data and compare the stars in the image with the stars in a star chart with a comprehensive catalogue of stars.  I imaged NGC 247 (very low surface brightness) with a single exposure of about 1000 seconds , used a single dark frame and removed the light gradient due to the city lights 55km to the SW. The optics: 6' Refractor (TOA 150) and the CCD: Canon EOS 350D on iso 400. The resulting image is attached and from my eye ball comparison the dimmest star is around Mag 18. Notice the plethora of dim galaxies starting with the Burbidge Chain of galaxies.