Deminishing returns.....

Started 3 months ago | Discussions thread
Astrozoid Contributing Member • Posts: 846
Re: Deminishing returns.....

thinker wrote:

Astrozoid wrote:

Kemo-sabe wrote:

Astrozoid, you are correct in your analysis. The images were shot in Bortle 9 sky and consist of 193 5 minute subs with a Canon FD 800mm f5.6l lens with a Canon 5D MKIII at iso400 incorporating an Optolong L-eNhance dou-band 2" drop-in filter. My guide scope consist of a DIY Canon FD 300mm f4.0l lens coupled to a QHY5LII-C guide camera. The Mount is an iOptron CEM25P with ADM side by side saddle and iPolar scope for polar alignment. I have Pegasus power distribution for the mount/equipment and dual Pegasus focus controllers for remote focusing the primary optics and guide-scope.

I am a newbie to processing astro images. It has has taken me more than 1 year to automate and dial-in the hardware software aspects of astro imaging and learn the nuances of the system.

However, astro processing is another story. I was to embarrassed by my pitiful results to post such a sad image in the light of so many awesome images that I have seen on this forum. Pride is a terrible thing.

My son suggested that I post the image to see if I could get some advice and input on what I am doing wrong in my processing workflow. Or, is this the best that one might expect from Bortle 9 skies with the optical equipment I am using or a combination of both?

I am using Clarke's methodology of in camera dark frame extraction for the subs. Using Clarke's Methodology the subs actually take 10 minutes to shoot per sub. I use Sequator and/or DSS for stacking. PS RC-Astro filter GradientXterminator to remove gradients. Then RNC stretch or PS to stretch. StarTools or DxO PhotoLab4 Post Processing.

I have been experimenting with Canon's DPP4 RAW processor to process and convert the RAW subs to TIFF prior to stacking with varying results. In an attempt to pull more fine detail from the subs.

Post a link to the raw, linear stack and we'll see if there is more there to be brought out in processing.


Could you please comment on the use of ISO400 with 7.8 electrons read noise vs ISO3200 (2.4 electrons) or even ISO6400/ISO12800 (with his filter)?

And the use of in-camera dark frame subtraction, as a misunderstanding of Roger's "On-Sensor Dark Current Suppression Technology", besides doubling imaging time?

A lower read noise would only help you if you were shooting under truly dark skies or with a narrowband filter.

Once your exposure is sky-noise limited, and not read-noise limited, you can pretty much totally forget about read noise, it is trivial.

With a really bright sky, you don't have to worry about read noise, so use a low ISO. Just expose so the peak of the histogram on the back of the camera is 1/3 of the way over from the left. Then turn off LENR and shoot as many frames as you can. Dithering will also help tremendously.

Personally, I have never recommended LENR - except for single frames.

Photons are only recorded when the camera is open to the sky. Photons are the only thing that make up the signal half of the signal-to-noise ratio. There is no other way to improve the signal. But you could have recorded twice as many photons and doubled your signal if you had shot lights continusously instead of wasting half of your clearsky time shooting LENR in-camera darks.

So I advise to shoot darks on a cloudy night in your garage under similar temperatures. Then you can shoot darks all night long and create a really good master dark frame.

When you use LENR you get a double whammy hit because not only have you lost half the signal you could have recorded, you are adding noise in each dark that you shoot in the camera. You would add a lot less noise with a good master dark.

LENR is not the same thing as on-sensor dark suppression technology.

And, most importantly, dark suppression technology is not removing thermal signal. It just removes the artifacts, like bright pixels, from thermal (dark) signal. It does not remove the shot noise associated with the dark signal. The only way to deal with this is by collecting more photons to improve the signal half of the signal-to-noise ratio.


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