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Cheating with your camera in manual mode


Introduction

Digital SLRs, whatever the make or model normally have 4 key modes; Programme, Shutter Priority, Aperture Priority and Manual. I'm not going to cover the specifics of what each of these modes does as I want to focus on something else; cheating with manual mode.

Everyone agrees that manual mode provides us the best control, we set the shutter speed to control the movement (or lack off) that we want to achieve as well as the aperture to control the depth of field. However, with these two set as you'd desire your exposure is basically controlled by the only other element that you can set, the ISO value. With all 3 fixed, the exposure will also be fixed no matter what the lighting conditions.

Auto-ISO

There is a good cheat that you can use to help reduce the number of badly exposed pictures, most cameras will have an "Auto ISO" setting. With this setting turned on the camera will then apply the required ISO to correctly balance the exposure given the shutter speed and aperture that you have set.

Restrictions

There are some restrictions and drawbacks however, on using this approach. With the shutter speed and aperture set manually, the camera ONLY has the ISO range to adjust in order to correctly expose your images. If you've set the shutter speed slow, with a wide aperture and your outside on a sunny day then the camera just doesn't have necessary controls to stop the picture being over exposed purely by using the ISO. If you'd selected either aperture or shutter priority, then the camera would have been able to adjust two items (the ISO and the setting you didn't fix) in order to correctly expose the image.

On the other side of the scale, if you've selected a small aperture, and fast shutter speed and are taking photos at dusk, then although the camera may do its best by taking the ISO up as high as it can, the pictures are likely to be under exposed still. Additionally, in this situation you're going to end up with a massive amount of noise that would have been introduced through the increased ISO.
Nikon-D5100-ISO-Auto

Working example

So, there are restrictions; however, for some circumstances this cheat works a charm. Let's take a situation where you are photographing outside on an overcast day. You want to have a responsibly shallow depth of field achieved by setting the camera to f4. You have some movement in the image, but not much and hence 1/400 second is suitable. With these 2 settings in place the camera reports the correct exposure can be achieved with an ISO setting of 400. This is a perfect situation to use the auto-iso cheat.

If the image gets a bit darker, then the auto-iso has the ability to increase the exposure slightly without introducing lots of noise, maybe up to ISO800; however, if the sun comes out a bit more and the scene brightens up then the camera can reduce to ISO200 or even ISO100 to compensate. In this situation I would suggest the camera has the ability to compensate for around 2 stops of changes in light, either up or down before noise or over-exposure becomes an issue.

Summary

In this post I've shown how to use Auto-ISO with manual mode to keep control of the depth of field and movement, whilst letting the camera set the ISO in order to correctly expose the image; however, be careful of scenes that require a significant change of settings to correctly expose as there is a risk of over-exposure or excessive noise.

Try it, test it and see how you get on is the best solution. Hope this article was of some interest. If you found this helpful it would be appreciated to show your support by "Liking" my Facebook page TonyHalfordPhotography do so easily by clicking on the Like button, top right.

All the best!

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