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LENR or taking darks/temp matched dark library

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#1 Dwight J

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Posted 13 September 2018 - 04:18 PM

I have noticed a slight improvement in noise reduction using LENR on my modded Canon T3i as compared to taking a series of darks at the end of the session.  I have not built a dark library of varying temperatures, ISO’s, exposure times yet and I wonder if the time and effort spent doing that would be worth it.  Changes in the sensor over time, say annually, or heavy use may require a library renewal although I do not know enough about that to be sure.  Using LENR certainly lengthens imaging time by 2X so there is that.  It may be the best way to match darks to lights but again I am not absolutely positive.  Taking darks at the beginning, middle or end is what I used to do and this seemed adequate until I saw LENR results.I would appreciate your thoughts on this.



#2 grsotnas

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Posted 13 September 2018 - 04:29 PM

I'd never waste half my time under the stars. Heck - that is just too much. Usually I take darks on the beginning and end of a session (before astro darkness). But my main source is to take them inside the fridge. I monitor the sensor temp with BYEOS, and it usually matches very well with my lights (sensor at 18-25C).

Usually you should match within 2°C.

A library is an excellent idea. I usually take my lights with 2 or 3 exposure settings 120s ISO800, 240sISO800 or 240sISO400 - that way the same darks can be used for several targets. I reuse my darks for about a year and no problems thus far.

Clear skies!

#3 Jerry Lodriguss

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Posted 13 September 2018 - 07:06 PM

Always spend clear dark sky time shooting lights.

 

It is the only way to gather more photons, which make up the signal in the all important signal-to-noise ratio.

 

Shoot darks on cloudy nights.

 

Jerry



#4 B 26354

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Posted 13 September 2018 - 07:15 PM

For the hundreds of you reading this who have no idea what "LENR" stands for, and tried finding it on Wikipedia... it  refers to in-camera Long-Exposure Noise Reduction... as opposed to Low Energy Nuclear Reactions.

 

Let's all please try to remember that astronomy-buff "beginners" don't yet speak the lingo. Please always include explanations of even slightly-obscure acronyms.  waytogo.gif


Edited by B 26354, 13 September 2018 - 07:22 PM.

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#5 ssagerian

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Posted 14 September 2018 - 08:35 AM

Especially if you are doing EAA..lol.gif



#6 mvas

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Posted 14 September 2018 - 09:59 AM

For the hundreds of you reading this who have no idea what "LENR" stands for, and tried finding it on Wikipedia... it  refers to in-camera Long-Exposure Noise Reduction... as opposed to Low Energy Nuclear Reactions.

 

Let's all please try to remember that astronomy-buff "beginners" don't yet speak the lingo. Please always include explanations of even slightly-obscure acronyms.  waytogo.gif

Or you could open a second TAB in your browser, and then Google: what is "LENR" Canon and then start reading.

Is that so hard?

It's not like we are asking you to walk to your local library, find the topic in the Encyclopedia Britannica and then walk home.



#7 B 26354

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Posted 14 September 2018 - 10:53 AM

Or you could open a second TAB in your browser, and then Google: what is "LENR" Canon and then start reading.

Is that so hard?

It's not like we are asking you to walk to your local library, find the topic in the Encyclopedia Britannica and then walk home.

No... but for those of us who spent our formative years doing exactly that, having the author of an article be considerate and purposefully instructive enough to have taken the extra two seconds to type "LENR (Long-Exposure Noise Reduction)" would have been greatly appreciated.

 

Is that so hard?


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#8 sharkmelley

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Posted 14 September 2018 - 11:12 AM

Usually you should match within 2°C.

 

With dark current doubling with every 6 deg Celsius rise in temperature, a dark taken with a temperature 2C too low will remove 80% of the thermal fixed pattern noise (FPN).  A dark taken with a temperature 2C too high will remove 125% of the thermal FPN i.e. it will overcorrect.

 

You may or may not find this acceptable.

 

Mark



#9 mvas

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Posted 14 September 2018 - 11:24 AM

With dark current doubling with every 6 deg Celsius rise in temperature, a dark taken with a temperature 2C too low will remove 80% of the thermal fixed pattern noise (FPN).  A dark taken with a temperature 2C too high will remove 125% of the thermal FPN i.e. it will overcorrect.

 

You may or may not find this acceptable.

 

Mark

In this Canon Camera, the temperature reported, is the temperature of the Digic Processor Chip, it is not the temperature of Image Sensor.

 

When taking images ...

the temperature of the Imaging Chip may, or may not, be the same temperature of the Digic Processor Chip.


Edited by mvas, 14 September 2018 - 11:25 AM.


#10 calypsob

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Posted 14 September 2018 - 12:47 PM

I have noticed a slight improvement in noise reduction using LENR on my modded Canon T3i as compared to taking a series of darks at the end of the session.  I have not built a dark library of varying temperatures, ISO’s, exposure times yet and I wonder if the time and effort spent doing that would be worth it.  Changes in the sensor over time, say annually, or heavy use may require a library renewal although I do not know enough about that to be sure.  Using LENR certainly lengthens imaging time by 2X so there is that.  It may be the best way to match darks to lights but again I am not absolutely positive.  Taking darks at the beginning, middle or end is what I used to do and this seemed adequate until I saw LENR results.I would appreciate your thoughts on this.

I also find that lenr gives me superior results. It is painful to waste clear sky time, but the results do not lie. Still though I take darks at the end of my session. Recently I realized that I can mimic summer mountain temps using the air conditioning controller in the rear of my suv. This lets me shoot darks while driving home and maintains a stable even temperature. Id say it is the next best thing. 



#11 Dwight J

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Posted 14 September 2018 - 08:29 PM

Well, I am going to do some imaging tonight if the sky holds.  I will be debating the points made in my head all the way to actually starting the exposures.  Currently I am still leaning LENR way slightly.  I arrived there originally after attendeding a lecture by Alan Dyer who demonstrated a noticeable difference using it over other dark taking methods. He also poopooed bias frames but in both cases he was using a late model 6D Mk11.  My older digic processor, sensor, etc may and very likely does perform differently.  That is the other part of the discussion in my head.  It may be all moot as the forecast low is 4 C and taking any darks less important.  We’ll see.



#12 mvas

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Posted 15 September 2018 - 09:45 AM

I'd never waste half my time under the stars. Heck - that is just too much. Usually I take darks on the beginning and end of a session (before astro darkness). But my main source is to take them inside the fridge. I monitor the sensor temp with BYEOS, and it usually matches very well with my lights (sensor at 18-25C).

Usually you should match within 2°C.

A library is an excellent idea. I usually take my lights with 2 or 3 exposure settings 120s ISO800, 240sISO800 or 240sISO400 - that way the same darks can be used for several targets. I reuse my darks for about a year and no problems thus far.

Clear skies!

You cannot measure the Sensor Temperature with BYEOS.

There is no temperature probe attached to Image Sensor.

The temperature probe is inside the Digic Processor - the "CPU" Chip.

Whenever you use the Digic Processor, it gets hotter and hotter.

The temperature of the Image Sensor, is not the same temperature as the CPU chip.

 

You are matching your Dark Library to the temperature of the Canon Digic Processor Chip, not the Image Sensor.



#13 Dwight J

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Posted 15 September 2018 - 04:04 PM

Well I stayed with LENR last night.  I was using only 120, 90, and 60 sec exposures so the exposure time semed to accumulate fast enough for me.  Since it was high ISO 3200 and 6400 I thought that I could use all the noise reduction I coukd get.  I haven’t stacked and processed them yet and will post them up when I do.  Here is M57 from my last session with the C14, 66 min total of 2 min subs at F11, unguided on AP1200 mount.  ISO 1600.  

DE8D47AF-E4B4-4D17-B34E-4F2A92A45E50.jpeg


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#14 Dwight J

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Posted 15 September 2018 - 11:39 PM

And from last night, M27 taken with a mix of 120 sec subs at ISO 1600 and 90 second subs at 3200 for a total of 80 minutes on a C14 at F11.  I processed it in photoshop and Carboni’s Astro Tools.  If I get another clear night (forecast for yhe next 7 days is poor) I will take the same image but take separate darks for a comparison.  

 

AC844543-F6B0-43F1-8D78-8565E41EF9E1.jpeg

 



#15 Der_Pit

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Posted 16 September 2018 - 03:49 AM

I'd be interested to hear whether you do take flats, too, and if they work.

I have recently taken data using LENR, and then additonal flats and flat darks, because for the short exposure time of the flats LENR doesn't kick in. But applying the flats to my data results in an overcorrection :(



#16 jgraham

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Posted 16 September 2018 - 03:14 PM

I have used both libraries of dark frames and LENR. I even spent about a year taking a close look at the LENR function and decided that for me it was the way to go. I have used it ever since and I am delighted with how well it works. it has now been some 5 years and I still use it when I use my DSLRs. I have also found that it has had zero impact on my productivity since my imaging is driven by when an object climbs above the trees and when it reaches the meridian, not by how many subs that I take.

 

LENR, I use it, love it, won't image without it, taken a lot of flack over it, don't care. It is my secret sauce. smile.gif

 

One quick example...

 

M27 (8-12-2015)-2j.jpg

 

Telescope: Meade SN10, Orion Atlas EQ-G
Camera: Baader Modified Canon 550D (Rebel T2i)
Filter: Orion Imaging Skyglow Filter
Guide scope: Williams Optics 50mm, Meade DSI Pro II, PHD
Exposure: 64x30sec, ISO 1600 saved as RAW
Darks: Internal (Long Exposure Noise Reduction On)
Flat: 32x1/20sec, ISO 400 taken with an LED tracing tablet
Average Light Pollution: Red zone, good transparency
White Balance: Deep Sky Stacker Automatic
Software: Backyard EOS, Deep Sky Stacker, Nebulosity, Photoshop

 

 


Edited by jgraham, 16 September 2018 - 03:20 PM.

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#17 t-ara-fan

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Posted 19 September 2018 - 12:00 AM

   Using LENR certainly lengthens imaging time by 2X so there is that. 

My 6D has a mode where it will take 4 lights, then one dark, and apply that dark to the previous 4 lights.  So that is only a 20% loss in light gather time, better than the 50% that some cameras offer.   I believe some 5D models, and the 7DMark II also do this.    The lower end crop sensors do not offer this feature.

 

From what I know, you have to shoot the sequence of 4 shots back to back, with perhaps a 1 second delay in between them.  The 4:1 lights:darks does not work if you trigger the shot by USB. You have to use an intervalometer.

 

I tried it just shooting 5min subs with the lens cap on, it definitely works. Will try in the field when I get a chance. 


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#18 calypsob

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Posted 19 September 2018 - 10:04 AM

My 6D has a mode where it will take 4 lights, then one dark, and apply that dark to the previous 4 lights.  So that is only a 20% loss in light gather time, better than the 50% that some cameras offer.   I believe some 5D models, and the 7DMark II also do this.    The lower end crop sensors do not offer this feature.

 

From what I know, you have to shoot the sequence of 4 shots back to back, with perhaps a 1 second delay in between them.  The 4:1 lights:darks does not work if you trigger the shot by USB. You have to use an intervalometer.

 

I tried it just shooting 5min subs with the lens cap on, it definitely works. Will try in the field when I get a chance. 

does it work if you are using magic lantern as the intervalometer? 



#19 t-ara-fan

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Posted 19 September 2018 - 03:16 PM

I don't know about Magic Lantern.

#20 B 26354

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Posted 19 September 2018 - 03:39 PM

I don't know about Magic Lantern.

I use an Olympus E-M1, and I know absolutely nothing about Canon cameras... but Magic Lantern for Canon EOS cameras looks pretty cool (and it's free):

 

https://magiclantern.fm

 

...so it might be worth looking into for you.

 

And thanks for liking my post!  waytogo.gif



#21 Jon Rista

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Posted 20 September 2018 - 12:55 AM

High sensor temp of 46C. Without LENR using other darks taken after the fact with mismatched temps:

 

xK3PX2g.jpg

 

With LENR:

 

YmmBPCv.jpg

 

This is an extremely high sensor temp, what you might get with live view focusing on a very warm night. 

 

LENR will usually deliver much better calibration than regular darks. Depending on how bad your dark current is, even though you lose sky time with LENR, the results could potentially be better when using LENR, because the dark signal will be corrected better, with far less remnant FPN. It is a judgment call whether LENR would be valuable on a given night or not. But on warm nights, it is worth at least giving a try on an object to see how things go.

 

It should be noted, if you have high LP, then the LENR may not really help much, as LP can muck with the signal as much as dark current or more so. LENR could be pretty useful at a good dark site on a warm night, though. 


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#22 Jon Rista

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Posted 20 September 2018 - 12:56 AM

To note, 46C is pretty extreme. Even 6C lower (a little more than the doubling temp for my DSLR), LENR produces an almost perfect frame:

 

uD622vc.jpg


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#23 Dwight J

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Posted 20 September 2018 - 09:16 AM

That's an eye opening finding Jon.  What is to bad is not having the capability of what the 6D does on crop sensor cameras.  Perhaps one conclusion is that the warmer it is (sensor and ambient) the more benefit LENR brings.  



#24 B 26354

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Posted 20 September 2018 - 09:23 PM

I never use the LCD's "Live View" function on my mirrorless OM-D E-M1 at all. Its Electronic ViewFinder (EVF) is much higher resolution, and its ability to magnify the EVF image by as much as 14X has so far proven sufficient for achieving critical focus.

 

I always keep the LCD's brightness turned down to minimal visibility, and as an added measure to keep whatever small amount of heat the LCD might generate away from the camera body, I also always pull the LCD about 1/4" away from the back of the camera. During programmed exposure sequences, the LCD remains completely dark until the end of the sequence.



#25 Alen K

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Posted 21 September 2018 - 07:05 AM

I always keep the LCD's brightness turned down to minimal visibility, and as an added measure to keep whatever small amount of heat the LCD might generate away from the camera body, I also always pull the LCD about 1/4" away from the back of the camera. During programmed exposure sequences, the LCD remains completely dark until the end of the sequence.

FWIW, the self-heating effect of the sensor (edit: depending on how long the exposure is) is likely far higher than any heat generated from the LCD, especially in the case of an articulating display where the camera has insulating plastic between the LCD and the camera innards. But there's no harm in taking all precautions. I always keep the LCD turned down as well but just to conserve the battery. And all cameras I know of turn off the LCD during a bulb exposure, probably also mostly to save power.

Edited by Alen K, 21 September 2018 - 08:16 PM.

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