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How to figure out the readout noise for Canon cameras


I have a Canon T1i (body only) which I use to do astrophotography with. I just purchased a program to control all my equipment and am trying to enter all my camera specs for my camera. One of the entries it is asking me which I have no idea what it is or how to get it is Readout Noise. Does anyone on here know how to figure this out or know what the Readout Noise is for the Canon T1i?








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What software are you using?  I do astrophotography and have a variety of applications which help both control equipment as well as process the data, but I don't think any of my equipment asks for a 'value' for read-out noise.


Typically what software wants are 'bias' frames...


The idea is that the process of merely powering up the camera sensor and performing a read-out ... without actually exposing any light ... will result in a frame that has non-zero data in it.  To capture bias frames, just leave the lens cap on, set the camera to whatever ISO you plan to use, and then take a couple dozen shots using the shortest possible exposure time (e.g. 1/2000th sec).  


The software takes those bias frames and builds a statistical model that includes the information needed.


The same is done for 'dark' frames except those frames are exposed for the same amount of time as the 'light' exposures to determine how much noise will build up over time.



Tim Campbell
5D III, 5D IV, 60Da

Hey Tim


I have purchased SGPro to help automate my whole setup. In the Equipment Profile Manager under the camera tab, it ask for Pixel Scale and Readout noise. I know the Pixel Scale for my camera is 1.29 but don't know what the Readout Noise is. I don't even know if I have to enter any value for that. I have other software to which I can use but I didn't purchase those. I purchased SGPro though. 

The SG Pro docs say it’s an optional value — you can safely ignore it.


Sequence Generator Pro says it can use it to find the ideal exposure time.  Since the focal ratio of the telescope is fixed (ignoring focal length reducers/multipliers) the only adjustments you can make are exposure time and ISO sensitivity.


It turns out Canon cameras use a combination of both analog amplification (“upstream gain”) prior to the analog-to-digital conversion (ADC), but at some point it hits dimishing returns and switches over to using digital amplification (“downstream gain”).  


The reason you care about this for astrophotography is because digital gain simply multiplies the values at each pixel but a computer has a maximum value that it can store (in the case of these camera’s it’s based on the 14-bit depth of the RAW image) you’re really just losing dynamic range.  “Upstream” gain loses very little dynamic range compared to “downstream” gain.   So you want to find the magic point where you get to apply as much “upstream” gain as possible before it flips to downstream gain.


For your T1i... that magic ISO is 1600.




I would set the camera to ISO 1600 for all long exposure astrophotography images and then just alter the exposure time.


For certain objects (e.g. the Orion Nebula) you need to do HDR images anyway (bracketed exposures) so there’s really no single ideal exposure time.



Tim Campbell
5D III, 5D IV, 60Da

Thanks for the info Tim! 


So far I've only shot at ISO 800, never tried 1600 yet, and the images have been coming out great(at least for me). 

For the Gain setting, I'm not sure what to put either. So far I've left it blank but may try setting a value for 1x1 say 1

just to see what happens.


The weather has been horrible over here for this entire month so I haven't been out for awhile to shoot. Plan on getting back out soon as we have some clear days coming up!