<p>It's the magnitude where the average signal-to-noise ratio (I assume that's what j_snr represents) is 3.</p>

CC BY-SA 4.0
2020-10-12T07:19:39.800Z
Is this possible to calculate from j magnitude and their error?
GHC
CC BY-SA 4.0
2020-10-12T10:30:37.613Z
@GHC No. And notice that magnitude uncertainties are generally non-linear and asymmetric, particularly when large.
ProfRob
CC BY-SA 4.0
2020-10-14T10:16:20.033Z
May I ask that what the different if I need to get the depth in 5sigma/2arcsec? So I can plot the SNR and get the SNR to 5, but what the meaning of 2arcsec.
GHC
CC BY-SA 4.0
2020-10-11T17:36:12.390Z
2020-10-11T17:36:12.390Z
ProfRob
<p>I saw that some survey said that their depth is 27.5 magnitudes.</p>
<p>May I ask that if I have a dataset with magnitude and their errors, for example I have J band <code>j_m</code>, <code>j_cmsig</code>, <code>j_msigcom</code>, <code>j_snr</code> from Sextractor.</p>
<p>How can I derive the 3 sigma magnitude depth in this fields to compare with the other survey.</p>

<data-analysis><photometry><magnitude>
How to derive the depth in my image (limit Magnitude )?
GHC
# How to derive the depth in my image (limit Magnitude )?

(Asked by: username_0 on 2020-10-11)

I saw that some survey said that their depth is 27.5 magnitudes.

May I ask that if I have a dataset with magnitude and their errors, for example I have J band `j_m`, `j_cmsig`, `j_msigcom`, `j_snr` from Sextractor.

How can I derive the 3 sigma magnitude depth in this fields to compare with the other survey.

**Tags:** data-analysis, photometry, magnitude

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## 1 answers

### Answer by username_1 on 2020-10-11. Score: 1

It's the magnitude where the average signal-to-noise ratio (I assume that's what j\_snr represents) is 3.

> **Comments:**
> **username_0**: Is this possible to calculate from j magnitude and their error?  
> **username_1**: @GHC No. And notice that magnitude uncertainties are generally non-linear and asymmetric, particularly when large.  
> **username_0**: May I ask that what the different if I need to get the depth in 5sigma/2arcsec? So I can plot the SNR and get the SNR to 5, but what the meaning of 2arcsec.  

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