nebulosity, poor ISO choices for my DSLR?

[adamphillips]

quick question. my canon 5d mark ii has a good variety of ISO choices, something like 400, 640, 800, 1000, 1250, 1400, 1600.

I just got nebulosity and if I control the camera that way it only lets me choose 400, 800, 1600. or higher or lower.

is there any way around this? just asking because I really liked to shoot in 1250 or 1000 and its kinda bumming me out.

[dph1nm]

Two points:

(1) ISO doesn't change your camera's sensitivity to light, so to some extent there is no point worrying about ISO settings, other than if they are too high you saturate quickly and if you are too low you get quantisation errors.

(2) I think some of these 'unusual' ISOs like 1250 are not real gain changes and are simply created by taking e.g. the ISO1000 data and multiply all the number by 1.25, which you could easily do in software yourself.

NigelM

[adamphillips]

I might just go back to 800 or maybe try some on 1600. im not planning on sticking with the DSLR for too much longer anyways.

people like to sy that the higher you go, you end up with more noise but im not sure how accurate that is. I think as long as you do darks it might be ok.

[lensman57]

thi

quick question. my canon 5d mark ii has a good variety of ISO choices, something like 400, 640, 800, 1000, 1250, 1400, 1600.

I just got nebulosity and if I control the camera that way it only lets me choose 400, 800, 1600. or higher or lower.

is there any way around this? just asking because I really liked to shoot in 1250 or 1000 and its kinda bumming me out.

Nigel has made the point quite well. A DSLR sensor is no different to a CCD and I have yet to see a CCD camera with ISO ( gain ) settings changeble on flight. The sensor' has a fixed spectral response to different wavelengths of light, QE,  and this is detemined by the design of the sensor, the Gain and Offset values are either fixed at the factory or by user after some measurements to make sure that the sensor records the full range of brightness to put it simply. For most Canon cameras this optimal Gain and Offset values are around ISO 800 or 1600 so just stick to these. I have also read that using mid ISO values are of no benefit so just keep to the whole numbers. There is also an off topic point of why the settings have been called ISO values which in terms of a digital sensor is quite meaningless. It is a hark back to the good old days of film cameras and I guess a marketing ploy to assure continuity from film to digital rather than an engineering one.

Regards,

A.G

[Christopher Davenport]

Just a note on the DAC conversion process, if your ISO is to low you will not record the data, when the DAC converts the analogue measurement to digital.

Thus on a lens where you are at F4 say, you could get away with ISO400, but on a F8, you need to be up at ISO1600 to get everything converted.

Going beyond to ISO3200 or higher is just providing a digital stretch and not a analogue stretch, so not worth it.

(unless you are using a 6D or a 7D, these have a much higher sensitivity and the DAC goes much higher before switching to a digital stretch.)

This is just rule of thumb based on experience and some conversations on this forum, so I suggest you experiment with different subjects.