Calculating limiting magnitude

[ScottM]

I hope I'm asking this in the right forum, but I'm wondering if someone can tell me how to calculate the limiting magnitude of a telescope. I've seen a couple of websites that do it out discuss it, but they seem to have different formulas, and I don't know which one I need to follow. Also, since I know it's possible to photograph objects dimmer that what you can actually see, is there a formula to determining limiting magnitude for photography?

[jambouk]

Interesting question. I look forward to the answers.

Jd

[Charic]

ScottM........Hi.  Ive used these two sites before, and depending on how accurate you fill the inputs, they give a similar result for me,   14.2 vs. 14.4 for my 8" skyliner.

http://www.stargazing.net/naa/scopemath.htm

http://www.cruxis.com/scope/limitingmagnitude.htm

Theres a Wiki link explaining more here   http://en.wikipedia.org/wiki/Limiting_magnitude      and from there a link to the cruxis site.

Hope it helps. 

[nmoushon]

From my very limited knowledge on this (so this could very well be wrong so sorry if it is) that for AP the limiting mag is determined by the exposure length. The focal length of a telescope will allow more fainter object to be easily seen because it effects the scale of the object. This is what I thought and I'm not sure if its 100% correct or not so maybe hold off till someone can confirm or deny this lol.

[Charic]

Magnitude is a measurement of the brightness of whats up there in the skies, the things were looking at.

The limiting magnitude is what the telescope is capable of achieving (theoretically) after considerations like your eyesight and observing skills, the optics, weather conditions  ect  are all taken into account?

There would be variables in your measurements, no matter which calculators you use, unless all factors are accounted for.

[ScottM]

I think that's what I was looking for, Charic. Thanks for the help! Based on what I've read on telescope.com about the XT6, I think I could probably get about a 13.0 limiting magnitude with the eyepiece it comes with, it I entered everything correctly.

[Charic]

............give or take .6 ?

Like I said, I do like this calculator. (  http://www.stargazing.net/naa/scopemath.htm  )  It, for me, has often backed up certain suggestions that I've received, and  confirms some of my own calculations. 

[ScottM]

That looks about right. That one said I should have a gain of 6.7 magnitudes and have a theoretical limiting magnitude of 13.6 for stellar objects.