ISO Invarience?

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 The Lemming 19 Sep 2020

While wandering through Youtubes on astrophotography and the illusive desire to get good exposure, I came accross ISO Invarience.

Any of you Digital Ninjas heard of this and does it do what it say's on the tin?

 james mann 19 Sep 2020
In reply to The Lemming:

As someone who does quite a bit of landscape Astro, I’m not totally convinced of the value of this. I think that better results are possible with fast lenses and low iso. If you are stacking for star trails, exposure time is of no consequence. The use of noise reduction and sharpening in post using a plug in like topaz would likely give better results. For non Astro applications in low light it may work.   I’ve never tried it.

James

OP The Lemming 19 Sep 2020
In reply to james mann:

What is frying my little brain, is knowing how to get good exposure settings for an image of the Milky Way.

What should I look for to get good exposure?

Do I use intuition or the histogram?

I'm on holiday, with one more potential night of clear sky's ahead of me. I have a wide 15mm (Full Frame equivalent lens) at f2 but what do I try to achieve because I don't want to got too far and mess things?

Do I use the 500 rule and expose for 33 seconds or be more conservative at 20 seconds?

At 20 seconds I have virtually no movement but at 30 seconds, there is obvious movement. Have I answered my question and the only variable is ISO?

Questions, questions, questions.

In reply to The Lemming:

The difference in exposure time here is less than 1 stop. It probably makes very little difference on your camera changing between ISO 800 and 1600 (1 stop) or whatever you are using to keep the exposure constant. You could achieve the same effect on your computer later, especially if you use raw files.

If you get a sharper picture at 20 seconds, use that, I think you answered your own question! 

Pictures are cheap for things that don't change quickly like the night sky, take several with different settings and review them afterwards and see which you like.

If you want to see some of the tradeoffs in taking very long exposures of very faint objects (of which the Milky way is not really one) and stacking images then this webpage and other chapters is very technical but informative. It has some relevance to the star trails you were trying before. Personally I use a low ISO for my images, not to make the images less "noisy" but because it's less likely to saturate on bight stars, but then I stack the images afterwards to get much longer exposures with less noise.

https://clarkvision.com/articles/astrophotography.and.exposure/

This second page gives some processing tips.

https://clarkvision.com/articles/night.photography.image.processing/

Enjoy your holiday!

Post edited at 23:38
In reply to The Lemming:

I recall 10 seconds being the limit for zero movement.  After that, it depends what your word 'virtually' includes.

T.

 wintertree 19 Sep 2020
In reply to The Lemming:

If in doubt, take images over the full range of ISOs and exposures - it’ll take you half an hour - and answer your own question by looking at the resultant images in post.  Given your short time window for taking data, and the much longer window for post processing, this seems like the way to go.  Then you’ll find out what works best for your setup, ready for your next holiday...

For about 15 years now I’ve been intending to build a barn door tracker to get better long exposure night sky images.

> have a wide 15mm (Full Frame equivalent lens) at f2

Is that the Sigma f2.8 or is it one with proper optics?

OP The Lemming 20 Sep 2020
In reply to wintertree:

> Is that the Sigma f2.8 or is it one with proper optics?

Its a 7.5mm Laowa lens.

Is the sigma a dudd?

Post edited at 08:38

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