Deminishing returns.....

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

thinker wrote:

Thank you for the information!

When OP uses [1a] an Optolong L-eNhance filter which I understand is a duo narrowbandfilter, and what you say [1b] about lower read noise would help with narrowband filter, wouldn't higher ISO help OP? Or is Optolong L-eNhance not narrow enough? (filter curve below)

With his camera, higher ISO produces lower read noise.

Lower read noise lets you use shorter exposures to reach a sky-noise limited exposure.

Narrowband filters don't let in much light, so to reach sky-noise limit for the sky background (not the nebula lines which the filter are passing) you need really long exposures.

The L-enhance bandpasses are narrow, but not as narrow as a true narrowband filter.

With a lot of light pollution, all of this becomes moot.  The sky noise totally overwhelms readout noise so you can use a lower ISO with a high readout noise.

Once your exposure is sky-noise limited, increasing the ISO only reduces the dynamic range.

So with bright skies, where you don't have to worry about being sky-noise limited, you should use a low ISO to get as much DR as you can.

There is an alternative argument to use a higher ISO for exceedingly faint objects, but I won't get into there here.

Combining this (above) with the fact that OP uses LENR [2a] with your [2b] statement about adding noise in each dark shot in camera, wouldn't this suggest that using, say, ISO3200 and avoid using LENR lead to OP having potential for much improved result with his gear? (the subject of this thread)

No. As I mentioned, all you would be doing would be sacrificing dynamic range. You don't need extrememly low read noise in bright skies. I certainly recommend not using LENR. And I recommend a lower ISO if you are guiding and can track accurately.

Sorry, not my intention to nag you, I'm an (eternal) beginner ..

No problem.

Jerry

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