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Astrophotography and Sketching >> DSLR & Digital Camera Astro Imaging & Processing

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Rayh
sage


Reged: 08/22/05

Loc: Gilbert, AZ, USA
What ISO to use with T3i
      #5778838 - 04/05/13 12:20 AM

I just purchased a Canon T3i to use for AP. I have doing AP for a number of years with a CCD camera. (QHY8) With that camera the conventional wisdom is to set the gain at 0 or 1 to keep from filling the charge wells so fast, thus maximizing dynamic range. What do I do with the ISO on a DSLR? Use a low number (like 100) to minimize noise and maximize dynamic range, or do I crank up the gain to 3200 or even 6400 to get as much brightness as I can?
Thanks,
Ray


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Falcon-
Post Laureate
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Reged: 09/11/09

Loc: Gambier Island, BC, Canada
Re: What ISO to use with T3i new [Re: Rayh]
      #5778843 - 04/05/13 12:28 AM

There have been measurements made to find the "Unit Gain" (the point at witch 1 unit in the RAW file = 1 electron recorded in the pixel). Shooting at unity-gain would be the way to maximise the dynamic range.

I believe that for most 14bit ADC cameras (such as the T3i) that point was at about ISO400.

(For many 12bit cameras such as my XT/350D and XS/1000D it is closer to ISO1600.)

Edited by Falcon- (04/05/13 12:32 AM)


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Toxic Coolaid
professor emeritus


Reged: 10/01/11

Loc: NorthEast Tennessee
Re: What ISO to use with T3i new [Re: Rayh]
      #5778844 - 04/05/13 12:29 AM

I've found it best to stick with 800 or 1600

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fmhill
sage


Reged: 07/17/12

Loc: Cape Cod, Massachusetts, USA
Re: What ISO to use with T3i new [Re: Rayh]
      #5778854 - 04/05/13 12:37 AM

Hi Ray,
I use a Canon 60Da and from what I understand after months of reading and studying about optimum ISO settings, cause and effect, the earlier Canon DSLR cameras produce lowest noise and greatest dynamic range at ISO-1000, the later models such as the 60Da produces lowest noise and greatest dynamic range at ISO-200... I'm not sure what the major reason for the difference, whether it is the newer sensor, the Digic 4 processor and later, benefiting from the lower ISO, or both together...

And there is a usable range of half to double the ideal ISO that is usable with relatively low noise and high dynamic range slightly less than ideal... With my EOS 60Da, I use 100 to 800 but try to stay on either 200 or 400 and adjust exposure time to compensate image brightness as needed... By keeping the ISO constant for a session makes adding dark frames that match ISO much easier at the end of a session, you are not having to make several sets which is time consuming when you want to get wrapped up and the gear put away...

Edited by fmhill (04/05/13 12:44 AM)


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Falcon-
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Reged: 09/11/09

Loc: Gambier Island, BC, Canada
Re: What ISO to use with T3i new [Re: Falcon-]
      #5778856 - 04/05/13 12:38 AM

If you are interested in the detailes you can see data and analysis on this for *many* cameras at this web page here. Unfortunately the T3i is not in the list of tested cameras so some extrapolation is required but there are a few other relatively recent Canon cameras.

Just brace yourself for info-overload before clicking the link.


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Rayh
sage


Reged: 08/22/05

Loc: Gilbert, AZ, USA
Re: What ISO to use with T3i new [Re: Falcon-]
      #5778891 - 04/05/13 01:22 AM

Thank you for the info everybody. Now I know that I want to start with the lower ISOs. I did not think of the 14 bit vs 12 bit but that does make a difference.
Ray


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SKYGZR
scholastic sledgehammer
*****

Reged: 08/14/09

Loc: Planet Earth, Milky Way Galaxy...
Re: What ISO to use with T3i new [Re: Rayh]
      #5780457 - 04/05/13 08:32 PM

Depending on the target, I'll bounce around..400, 800, 1600..never use higher..too noisy.

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LeCarl
super member


Reged: 03/16/11

Re: What ISO to use with T3i new [Re: SKYGZR]
      #5780722 - 04/05/13 10:03 PM

I tested all of the isos setting... so for me on t3i=
1600, 1600 and 1600, and if not good(burned) ---> HDR


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mmalik
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Reged: 01/13/12

Loc: USA
Re: What ISO to use with T3i new [Re: Rayh]
      #5780826 - 04/05/13 10:42 PM

Quote:

What ISO to use with T3i




Not about T3i per se; here... is some relevant discussion applicable to any DSLR. Regards


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Rayh
sage


Reged: 08/22/05

Loc: Gilbert, AZ, USA
Re: What ISO to use with T3i new [Re: mmalik]
      #5784817 - 04/07/13 09:21 PM

Thanks, mmalik! Based on your link and the Clarkvision article, I can crank up the gain higher than the 400 I was using. At 400 my histograms and images seemed weak.
Ray


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mmalik
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Reged: 01/13/12

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Re: What ISO to use with T3i new [Re: Rayh]
      #5785018 - 04/07/13 11:12 PM

Quote:

I can crank up the gain higher than the 400 I was using. At 400 my histograms and images seemed weak.




Agree; you may start with 800 and go from there. Another important factor is whether you'll be modifying your T3i or not.


Last but not least, if you have budget and/or if you are able to return T3i, consider getting 60Da... instead for both astro and day imaging. Thx


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Rayh
sage


Reged: 08/22/05

Loc: Gilbert, AZ, USA
Re: What ISO to use with T3i new [Re: mmalik]
      #5787191 - 04/09/13 12:16 AM

At 2x the price and no lenses at all I ruled out the 60da. At least now I have a camera I can use for both AP and regular photography. My Nikon was useless for AP...just too hard to use and no software supported it.
Ray


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Suresh
sage


Reged: 08/05/05

Loc: South India
Re: What ISO to use with T3i new [Re: Rayh]
      #5787384 - 04/09/13 05:08 AM

The ISO is similar to gain in ccd , Jerry lodriguss re commends high ISO at high ambient temperature , stick to 200 ISO in cold climate and even 1600 ISO at temp above 75 f
Suresh


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Mike Phillips
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Reged: 02/21/06

Loc: Swift Creek, NC - 35.682 N, 78...
Re: What ISO to use with T3i new [Re: Suresh]
      #5787779 - 04/09/13 10:36 AM

If I am reading the unity gain charts right, my 7D would gain should be at ISO 1000 ??
I could have used this some time ago, I started shooting with my XTi at ISO 1600 and when I upgraded to a 7D last year, bit into the bigger is better and shot at ISO 6400. BIG MISTAKE! I shoot at ISO400 now and it seems better. I have questions that I'll put into another thread.

Mike


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Mike Phillips
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Reged: 02/21/06

Loc: Swift Creek, NC - 35.682 N, 78...
Re: What ISO to use with T3i new [Re: Mike Phillips]
      #5788159 - 04/09/13 01:49 PM

This is fun!
http://www.dpreview.com/reviews/studio-compare#baseDir=%2Freviews_data&ca...

Mike


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Falcon-
Post Laureate
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Reged: 09/11/09

Loc: Gambier Island, BC, Canada
Re: What ISO to use with T3i new [Re: Mike Phillips]
      #5788226 - 04/09/13 02:07 PM

Quote:

If I am reading the unity gain charts right, my 7D would gain should be at ISO 1000 ??




Actually that is the unity gain scaled to 12bit. The 7D has 14bit ADC however. Roger Clark *has* tested the 7D and the results are listed on a separate page (page found here). 14bit unity gain for the 7D is "ISO 246" according to his tests. The dynamic range numbers and read noise numbers would leave me to say ISO400 or ISO800 are still the best bets. The sample read noise/bias images certainly demonstrate how much higher the read noise is at ISO200 and below!


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mpgxsvcd
Carpal Tunnel


Reged: 12/21/11

Loc: Raleigh, North Carolina
Re: What ISO to use with T3i new [Re: Mike Phillips]
      #5788254 - 04/09/13 02:17 PM

Dynamic range always decreases with increased ISO as long it is a true ISO value and not a simulated or software created "Extended" ISO value.

Everything looks very linear for the Canon cameras that have been mentioned here. Therefore, I would think that your tracking/guiding time and light pollution would be the biggest factor.

Just take exposures for as long as your mount can accurately guide or track and then select an ISO that just begins to show the sky glow.


http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-camer...


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Tonk
Postmaster
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Reged: 08/19/04

Loc: Leeds, UK, 54N
Re: What ISO to use with T3i new [Re: mpgxsvcd]
      #5788328 - 04/09/13 02:37 PM

Na - I'll turn that over. Pick the ISO nearest unity gain for your camera and then select an exposure time that doesn't wash out the background. Thats if your tracking is up to it.

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Campos
Vendor-MonoMods


Reged: 12/26/12

Loc: Portugal
Re: What ISO to use with T3i new [Re: Tonk]
      #5788733 - 04/09/13 05:11 PM

Im my oppionion, crancking the ISO higher then 400 (on my 350D)appart from increasing the noise level to much for my taste, it washes out the colors on the stars. Using lower ISO values like 400 or even 200 and increasing the exposure accordingly is the way to go, the drawback is that for increased sub lenghts you will need to have a very good polar alignment and goos tracking or field rotation starts to creep in your subs...

Cheers,

Lus


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Patrick
Postmaster
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: What ISO to use with T3i new [Re: Mike Phillips]
      #5789329 - 04/09/13 11:06 PM

Quote:


This is fun!
http://www.dpreview.com/reviews/studio-compare#baseDir=%2Freviews_data&ca...





That's an excellent website for seeing the effects of different ISO settings. Thanks for the link!

Patrick


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