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Mineral PhotographyISO setting for minerals

24th Oct 2014 16:22 UTCHoward Heitner

The Nikon S8000 has the following ISO choices: Auto, Fixed range auto, 100, 200, 400 800.


I am usually using daylight from a skylight and some daylight fluorescent bulbs for lighting.


Any advice on choosing the best setting?

24th Oct 2014 17:52 UTCEugene & Sharon Cisneros Expert

Lower ISO settings will produce the best results, assuming that you have enough light. Higher ISO relates to higher sensor light sensitivity. The physics of the sensor is such that higher sensitivity also results in greater noise in the image. For that reason, a lower ISO setting is preferred. Use the lowest ISO setting that you can, while maintaining a reasonable aperture setting and shutter speed. I would stick to ISO 100 or 200. A reasonable aperture is about two stops up from wide open, usually around f8. Shutter speed should be high enough to prevent blur from movement. If you are using a tripod and use a shutter release or timer, you can get away with a few tenths of a second if necessary. However, it is always best to have enough light to begin with.

24th Oct 2014 23:15 UTCOwen Melfyn Lewis

To add to Gene's wise remarks, test the results that *you* obtain with various low-light subjects. Sensors and their firmware differ. I use a Canon 600D that has a max ISO of 12800. I find I can use ISO 400 with no observable diminution of image quality compared with lower ISO settings and ISO 800 is often OK, subjectively. Even then, I frequently work with exposure times as long as 2-4 seconds because I do a lot of photomicrography (camera on a microscope). As one (linearly) doubles the image magnification, so the subject illumination reduces as a square root.


What is ample illumination at, say, x20 mag, often leaves one screaming for more light if one raises to magnification to, say, x160. As a rule of thumb, magnification above x40 causes subjects to start to dim noticably to the eye as opening of the pupil can no longer fully compensate. Raising the ISO setting of the camera sensor plate is one way of coping in photography. Another is to increase the light flux - but that usually requires a different and stronger light source.

24th Oct 2014 23:36 UTCRonald J. Pellar Expert

<< subject illumination reduces as a square root >>


Owen,


The illumination is proportional to the inverse square of the linear magnification, i.e., increasing linear magnification by x2 decreases the illumination by 1/4.

25th Oct 2014 00:35 UTCOwen Melfyn Lewis

'By 1/4' - or to 1/4? Not the same thing. With the latter, increase the mag to x4 and the illumination flux reduces to 1/16. or 1/256th at x8. Assuming that a subject is sufficiently illuminated for correct photography at x20 linear mag, by how many stops must one increase the exposure for the same level of brightness/sensitivity at x160 mag? I.e. this is as per my first post.


Have it your way and quadruple the magnification and the illumination is reduced only 'by 1/16' (i.e. negligible, as 15/16ths then remains) - and the higher the one takes the mag the the more vanishingly small the diminution of illumination will become - a nonsense as all microscopists know.


I know, I know.... it's all to do with the rules of language that some insist do not exist in English. But grammar rules OK? :)-D This is a fair example of where a grammar rule is critical to meaning. Sorry to drag this in here but it's a good example.

25th Oct 2014 01:09 UTCHoward Heitner

OK folks, thank you for your suggestions, however my camera is very different from what you are describing. There is no manual setting of either aperture or exposure time. There is a through the lens light meter that makes all these decisions. The metering can either be matrix (everything on the screen) or center weighted. The ISO setting in this case obviously means something different. I did two test shots with all the other settings the same, with ISO on auto and 200. After some very slight tweaking of brightness and color temperature, they looked the same.

25th Oct 2014 02:09 UTCEugene & Sharon Cisneros Expert

My first post does apply to your, or any, camera. Since yours only has an auto mode, you can coerce it into doing the best that it can. Just make sure that you set to ISO no higher than about 400. Lower is still better. Use good lighting to force the camera to close down the aperture at the expense of slower shutter speed. Play with the lighting to get the best results. You should be able to get very good results with practice.

26th Oct 2014 00:53 UTCOwen Melfyn Lewis

Howard Heitner Wrote:

-------------------------------------------------------



> I did two test shots with all the other settings

> the same, with ISO on auto and 200. After some

> very slight tweaking of brightness and color

> temperature, they looked the same.


Why did you not also try the ISO 400 and 800 settings, to see for yourself what any difference might be?

26th Oct 2014 02:40 UTCEugene & Sharon Cisneros Expert

Howard Heitner Wrote:

-------------------------------------------------------

> I did two test shots with all the other settings

> the same, with ISO on auto and 200. After some

> very slight tweaking of brightness and color

> temperature, they looked the same.



I suspect that is because you have sufficient light and the auto mode was setting ISO to some low value. For educational purposes, you can try reducing the light and set ISO to auto and you should see what a noisy image looks like.
 
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