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  #1  
Old 07-12-2018, 02:49 PM
raymo
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exposure length question.

I have always noted that some imagers take subs of 3,5,10 minutes, or even
longer. How do they do that? The max I can go before blowing out pretty
much everything is about 100- 120 secs. I have a pretty good sky at Bortle 2 to 3. I had the same limitation when using my 8" f/5 Newt as I now do using just a DSLR and a lens.
raymo
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  #2  
Old 07-12-2018, 02:58 PM
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Atmos (Colin)
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What ISO are you using?
I’m usually ISO200-400 with my DSLRs which allows for 180-300s as a good exposure for most targets.
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  #3  
Old 07-12-2018, 03:24 PM
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Hi Colin, After extensive research and experimentation I found that my 1100D
@ 1600 and my 600D @ 800 gave the best results as far as noise was concerned[which as you would know is the biggest problem with uncooled DSLRs]. The noise gets worse as you depart either up or down from those figures, [with my cameras at least] I didn't believe that until I tried for myself.
So I suppose I'll just have to take very large numbers of subs to bring out the fainter stuff.
raymo
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  #4  
Old 07-12-2018, 05:24 PM
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i use mono which seems to extends it a bit and I also use an IDAS LPS P2 filter, which works very well. I do get a few headaches with colour correction although in the long run it pays off, for me. YMMV.
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  #5  
Old 07-12-2018, 05:43 PM
Startrek (Martin)
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My DSLR capture settings are determined on where Iím imaging from and what object Iím imaging
In Sydney ( bortle 7 to 8 ) Iím currently using lots of short subs ( 30 sec) at ISO 800 on M42 but down at my holiday house 220km south of Sydney ( bortle 2 to 3 ) I used longer subs (60 to 80 sec) at ISO 800 / 1600
I find the ďsweet spotĒ for the Canon 600D is generally ISO800 on a majority of objects
I totally concur that DSLRís were never designed nor do they perform well for long long exposure astrophotography.On 2 to 5 minute subs my DSLRís sensor temperature was reading 45 to 49 degrees which is counterproductive
Cheers
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Old 07-12-2018, 06:39 PM
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Thanks fellas. How does one know what one's sensor temperature is? I have
not seen anything in the 600D's manual concerning this.
raymo
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  #7  
Old 07-12-2018, 07:20 PM
Startrek (Martin)
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Hi Raymo

I run BYEOS to star align, drift align, frame/focus and capture my images
It gives you the sensor temperature ( refer photo attached )
Cheers
Martin
Attached Thumbnails
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  #8  
Old 07-12-2018, 07:49 PM
raymo
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I bought BYEOS but never used it. I'll have to see if it is still on my old laptop.
Thanks
raymo
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  #9  
Old 08-12-2018, 08:01 AM
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Atmos (Colin)
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Quote:
Originally Posted by Startrek View Post
I totally concur that DSLRís were never designed nor do they perform well for long long exposure astrophotography.On 2 to 5 minute subs my DSLRís sensor temperature was reading 45 to 49 degrees which is counterproductive
Cheers
Out of curiosity, what was your ambient temperature when you were getting that?

I've only used a Nikon D7200 & D810 and i am not sure whether Nikon has a temperature readout. I haven't yet done a noise comparison between temperatures but my only gripe has been lack of Ha sensitivity and an unwillingness to mod my every day camera
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  #10  
Old 08-12-2018, 08:57 AM
Startrek (Martin)
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Outside ambient temperature was 18 degrees
Humidity about 50%
Dry north east wind blowing at about 24 k/ hr

Cheers
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  #11  
Old 09-12-2018, 05:27 AM
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NorthernLight (Max)
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Hi Raymo, I think the use of filters changes everything. I’m regularly taking 400-600s exposures. When I used a 2.5x powermate and a UHC Filter I had to go to 15min exposures (on Southern Pinwheel). My camera sensor seems to hold its temperature reasonably well usually at around ambient. It goes up during rapid, short exposures by a degree or 2. Long exposure is not so much an issue, since exposures are delayed by dithering. This allows the sensor to calm down. My batteries are in a power grip not inside the camera chassis. I think the heat from the discharging battery heats up sensors for other people. So I recommend to move to external batteries and allow time between exposures to let the sensor cool.
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  #12  
Old 09-12-2018, 07:30 AM
Startrek (Martin)
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Hi Max
I always use a remote power supply for my Canon 600D as my laptop is 2m away and BYEOS records the sensor temperature at 32degrees for shorter exposures with outside air temperature of 18 degrees
Unless your in colder climates ( < 10deg ) I doubt whether your sensor would get below 30 degrees
I canít see an internal battery causing high sensor temperatures
My 2 cents ....
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  #13  
Old 09-12-2018, 09:16 AM
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Quote:
Originally Posted by Atmos View Post
What ISO are you using?
Iím usually ISO200-400 with my DSLRs which allows for 180-300s as a good exposure for most targets.
Why such a low ISO?
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  #14  
Old 09-12-2018, 10:38 AM
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At ISO 100 the D7200 and D810 have really low read noise, around 2.5e- and 3.2e- respectively. Both also have virtually 14-bit of dynamic range which fits their 14-bit AD converters.

ISO 200-400 has the read noise drop a reasonable amount while keeping a very good dynamic range.

ISO 800 doesn’t have much of a read noise drop so the only thing dropping is the dynamic range. After ISO 800 the read noise stagnates so image quality just goes down hill.
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Old 09-12-2018, 04:08 PM
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Just a note that the temperature reported by the DSLR is NOT the sensor temperature (most likely).

Few of us messed with the cold-finger cooling of the older Canon DLSRs (450D) and got the CCD sensor to sub-zero temperatures (measured by a separate temperature sensor). The temperature reported by the camera was not related to this temperature and, from memory, was always above the ambient temperature.

The conclusion was that the temperature reported by the camera is coming from a temperature sensor on one of the PCBs and not the CCD sensor.
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  #16  
Old 09-12-2018, 05:21 PM
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multiweb (Marc)
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Quote:
Originally Posted by raymo View Post
I have always noted that some imagers take subs of 3,5,10 minutes, or even
longer. How do they do that? The max I can go before blowing out pretty
much everything is about 100- 120 secs. I have a pretty good sky at Bortle 2 to 3. I had the same limitation when using my 8" f/5 Newt as I now do using just a DSLR and a lens.
raymo
Depends on what you're imaging, if it has a brigh core or not, your conditions at the time, windy or not, airplane flight path, etc... then you weigh in the odds of something possibly going wrong in 5, 10, 15 or more minutes, how many beers you had, etc...
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  #17  
Old 11-12-2018, 11:47 PM
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Astrofriend (Lars)
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Hi,

You can use IrFanView to read the exif data from Canon files:

https://www.irfanview.com/

It's free to download.

You find the camera house temperature, not sensor temperature. Canon EOS DSLR from 450D and later have this oportunity and the old Canon 5D.

Here is a good overview of the Canon cameras:
https://ideiki.com/astro/EOS.aspx


When you talking temperatures, is it Celsius or Fahrenheit?

When doing astrophotographing in Sweden where I live in Northern we have from -20 to 0 degrees Celsius, we only have dark nights in the winter.

With my Canon 6D with everything unnecessary shut down it stabilize after a half hour about 6 degrees above surrounding temperature. My older Canon 5D was about 3 degrees above surrounding temperature. If I use my Canon 6D with liveview it could increase the temperture with 20 degrees above the surrounding temperature, not good!

My Canond 6D I normally has the ISO set to 800 or 1600, but lower readout noise at higher ISO settings could sometimes be to prefer. Canon has a pre amplifier before the ADC that makes this thing to work.

See how I used it when I need many short exposures:
http://www.astrofriend.eu/astronomy/...-dynamics.html

Can you see any difference?

Could be useful when photographing fast moving comets or if you have a bad tracking mount.

/Lars
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  #18  
Old 12-12-2018, 10:38 AM
raymo
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Thanks everyone. I thought interest in this thread was finished. I have
irfanview, will look into it.
raymo
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