Quote from: gostwyck on May 17, 2014, 03:14

Quote from: Beppe Grillo on May 15, 2014, 10:12
Considering a still life, so with no mobile subjects.

When making long exposures the noise tends to increase.
When using higher ISO the noise tends to increase too.

The question: is it better to increase the exposure time or the ISO value?

concretely:
40 sec> 100 ISO
10 sec> 400 ISO
05 sec> 800 ISO

What will give the best result?
Or the results will be identical?

At a constant aperture, increasing the ISO from 100 to 400 will only halve the exposure time, not quarter it as you suggest above.

You can use either method and effectively negate any resulting noise by simply shrinking the image.

isnt going from iso 100 to 400 = 2 stops?  100 - 200 - 400
meaning the corresponding speed will also be 2 stops   = 40 sec - 20 sec- 10 seconds

Quote from: gostwyck on May 17, 2014, 03:14
At a constant aperture, increasing the ISO from 100 to 400 will only halve the exposure time, not quarter it as you suggest above.

I'd love to see a source for this.  Pretty darn sure ISO changes are linear: from ISO 100 to 200 you need half the light, from 200 to 400 half again and so on.  This corresponds to the old ASA film speed system.  According to Wikipedia there's a second ISO standard that corresponds to the old DIN specification; that one is logarithmic rather than linear.

Quote from: gostwyck on May 17, 2014, 03:14


At a constant aperture, increasing the ISO from 100 to 400 will only halve the exposure time, not quarter it as you suggest above.

I don't think you were fully awake when you wrote that, Gostwyck.

Why on earth did Noodle get a vote down when he is correct in everything he says?   

I voted him down by error
Sorry.
Yes, he is right - Corrected the mistake.
(I very rarely vote down, except in cases of offensive posts)


____

Quote from: wordplanet on May 15, 2014, 17:59
It looks like you had sharpening up to 50 - that's very high and could account for the noise. Sharpening at 50 seems really high - with a subject like yours, there should only be a need for very minimal sharpening, IMHO.

On a 25 MPixels camera used at 100 ISO it is not so much.
And of course it depends if the subject has a lot of darker areas or not, or if the image is underexposed or not.

Quote from: gostwyck on May 17, 2014, 03:14
At a constant aperture, increasing the ISO from 100 to 400 will only halve the exposure time, not quarter it as you suggest above.

that is not correct, it will

Use time exposure, your D7100 should have long exposure noise reduction... turn it on! Full Moonrise over Davis exposure 1 sec F5.6 ISO 200