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Does Canon Long Exposure Noise reduction improve a pic?

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#1 t-ara-fan

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Posted 24 June 2019 - 06:38 PM

Canon Long Exposure Noise Reduction (LENR) is generally considered too time consuming for AP.  If you take a 60" sub, then you have to wait another 60" for the camera to shoot a dark and subtract it from the real image.  It works well, but you lose 50% of your time. So of course people shoot darks at some other time and process that way.

 

My 6D and 7D Mark II (and many other FF Canon cameras) have a nifty feature where if your shoot exactly four images (back to back, 1 sec between images) then wait, the camera will take a single dark and subtract it from the previous 4 images.    You do lose 20% of your time (not 50%) and in return you get dark subtraction with closely matched dark and image temperatures.

 

I have tried this, but have never done a rigorous analysis to see how LENR works compared with shooting a dark library on a cloudy night at the same temperature.

 

Does anyone here use LENR for DSLR AP? 

 

Scientific stuff:  the LENR dark will have plenty of shot noise, because it is a single sub and not smoothed like a stack of 32 darks would be.  But the LENR dark would have all the hot and dead pixels accurately corrected.

 

I have never had the patience for shooting darks with a DSLR.  I now have a cooled camera which is a whole different story. But for travel I think I will use a DSLR. 

 

I have used the "sensor clean, clean now" in conjunction with Adobe Raw Conversion method of killing hot pixels. It works great, but I don't know what it does for other types of noise.


Edited by t-ara-fan, 24 June 2019 - 06:40 PM.


#2 sink45ny

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Posted 24 June 2019 - 06:45 PM

This is news to me and I have both My 6D and 7D Mark II.



#3 Jim Waters

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Posted 24 June 2019 - 06:53 PM

This is news to me and I have both My 6D and 7D Mark II.

Me too...  Will this work past 30 sec?


Edited by Jim Waters, 24 June 2019 - 07:02 PM.


#4 Jim Waters

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Posted 24 June 2019 - 06:54 PM

I only use LENR if I take a SINGLE sub.

 

EDIT - Now it would be real nice if the FW could be modified to take a Light followed by a Dark sub and download them BOTH...  That way you have matching Lights and Darks for later processing.


Edited by Jim Waters, 24 June 2019 - 07:03 PM.


#5 whwang

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Posted 24 June 2019 - 08:04 PM

I don’t believe sensor clean has anything to do with hot pixels.

Costing 20% of time is comparable to taking darks. The difference is darks can be taken during twilights and subsequently put in a library to be used any time later. To me, 20% of night time is still too expansive to pay. The advantage of (almost) exact match in sensor temperature is attractive, but darks can produce almost the same results if they are taken care carefully with some very standard processing techniques.

Overall, the difference between the two approaches won’t be huge.
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#6 t-ara-fan

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Posted 24 June 2019 - 09:33 PM

I don’t believe sensor clean has anything to do with hot pixels.
 

It does.  When using a DSLR, I do the "sensor clean, clean now" once the camera is at a stable temp.  A map of hot pixels is written into each RAW file when taken normally. Conversion of the RAW to something like a TIFF in Adobe Camera Raw removes the hot pixels.  Works with 6D and 7D Mark II. Definitely.  Search for "clean now" on this page.

 

It works like a poor lazy mans darks. 



#7 t-ara-fan

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Posted 24 June 2019 - 09:41 PM

This is news to me and I have both My 6D and 7D Mark II.

 

Me too...  Will this work past 30 sec?

Yes, I have done it at various exposures up to 300".  The trick is you need to trigger the shutter with a remote shutter button / intervalometer, it does not work when you take shots with USB (i.e. BackyardEOS).  You have to enable LENR in the menu. You can take 1-4 shots, then when you stop shooting for more than 2 seconds the camera automatically shoots a dark and subtracts it from the 1-4 shots that are saved on the memory card.

 

With a standard intervalometer you have to set it to shoot 4 shots, then restart the sequence manually after the auto-dark is taken. So I built an Arduino intervalometer to do this.  I am just waiting for the Midnight Sun™ to end to test it out and see how well it works. 


Edited by t-ara-fan, 24 June 2019 - 09:51 PM.


#8 Jim Waters

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Posted 24 June 2019 - 10:01 PM

So what's the benefit of this vs. the standard imaging / processing approach?



#9 bmike-vt

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Posted 25 June 2019 - 04:42 AM

Yes, I have done it at various exposures up to 300".  The trick is you need to trigger the shutter with a remote shutter button / intervalometer, it does not work when you take shots with USB (i.e. BackyardEOS).  You have to enable LENR in the menu. You can take 1-4 shots, then when you stop shooting for more than 2 seconds the camera automatically shoots a dark and subtracts it from the 1-4 shots that are saved on the memory card.

 

With a standard intervalometer you have to set it to shoot 4 shots, then restart the sequence manually after the auto-dark is taken. So I built an Arduino intervalometer to do this.  I am just waiting for the Midnight Sun™ to end to test it out and see how well it works. 

Trying to get this to work today... put an ND filter on, setup for 51 second exposures of the lights in my office.

Have a intervalometer plugged in, but I can never make sense of just how to set it up. Canon 6d Mk2.

Delay to start = 5 seconds

Long (exposure) = 51 seconds

Interval (between shots?) = 2 seconds

Shots = 4

 

With 1 second delay between shots I'm getting what looks like 2 shots to time correctly, but the LENR jumps in and the camera goes to BUSY before it gets the third shot off.  With 2 seconds delay I think I'm getting 3 shots off before the camera goes into BUSY mode


Edited by bmike-vt, 25 June 2019 - 07:25 AM.


#10 Sven_Bortle5

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Posted 26 June 2019 - 03:41 AM

… on my Canon 70D, the LENR does only work when shooting JPGs. The feature is not available for RAWs. Is that different on the 6D and 7D?



#11 Kendahl

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Posted 26 June 2019 - 12:46 PM

I have compared LENR with subtracting darks for my Canon T3i and 350D. LENR is not just dark subtraction. It adds something back so that the resulting image is as bright as one without LENR. It does reduce shot noise but that's all. I didn't find any advantage to LENR over dark subtraction.


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#12 Jim Waters

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Posted 26 June 2019 - 01:49 PM

If only JPEG its of no use.  I will process as normal - Lights, Darks, Flats and BIAS.


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#13 t-ara-fan

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Posted 27 June 2019 - 08:58 PM

  Canon 6d Mk2.

Delay to start = 5 seconds

Long (exposure) = 51 seconds

Interval (between shots?) = 2 seconds

Shots = 4

 

A discussion here.

 

The 6D Mk II does 3 shots, not 4 like the old 6D.


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#14 t-ara-fan

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Posted 28 June 2019 - 12:26 AM

… on my Canon 70D, the LENR does only work when shooting JPGs. The feature is not available for RAWs. Is that different on the 6D and 7D?

I think it only works with RAW on the "single digit"-D cameras. 5D, 6D, 7D etc.



#15 bmike-vt

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Posted 28 June 2019 - 04:31 PM

A discussion here.

 

The 6D Mk II does 3 shots, not 4 like the old 6D.

Thanks! 




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