Cropping Images

Cropping of an image to produce the final magnified view is often better than using other options to obtain higher initial image magnification, and is an easy option with digital photography that can often prove beneficial for several reasons. Done well cropping can help to improve any image, to provide better image balance, or to draw the viewers attention to the main intended subject or aspect of the shot.

One of the main drawbacks with high magnification image taking is that as MR rises depth of field becomes an ever greater issue, becoming ever smaller, and accurate focusing plus small apertures are needed, the later giving rise to the use of ever slower shutter speeds or higher ISO's. Even then getting sufficient DOF often proves to be a major challenge, and images which look fine at small sizes can turn out to be less than satisfactory once viewed on screen at larger sizes up to 100%.

In this respect digital photography proves to be of huge advantage since you can take as many shots as the subject and memory card space will allow and discard all but the best later when reviewing them. Whilst we have never been users or advocates of the 'machine gun' type of photography that some use, just shooting away at a camera's maximum fps frame rate in the hope that something useful will result, this is a slightly different scenario. It doesn't really matter whether you are using AF focusing or Manual focusing because the focusing distance is so critical that the smallest difference, the slightest movement, can mean an image easily goes from being in-focus to out of focus at the point needed. Using a cable release or self-timer here - especially with a mirror-up option - can help because just pressing the shutter button can often be enough to cause a difference.

Taking an image from a greater distance can help to offset this to a certain degree as DOF becomes larger the further away you are and so focusing becomes less critical. But taking a series of shots at the same settings and focus distance often proves to be valuable and time well spent because almost invariably we find that some shots will be better than others even though they might at first look almost identical.

If you are already at the maximum level of magnification that it is possible for you to obtain, but the particular subject or section of it that you want to feature isn't as large as needed, then cropping to increase the view is the only option left. This might be for any number of reasons. You couldn't get any closer, or the magnification used was the maximum the camera/lens combination could supply. Even though this means a lower resolution image it isn't as crucial an aspect as it might sometimes appear. Often a lower resolution doesn't detract from the image because of the subject matter it contains, which is of more interest and greater significance than the outright image quality.

There is only really one negative aspect to this, or lets say that needs to be kept in mind. And that is that the lowest ISO possible should be used. High ISO images taken in good light levels can often be very acceptable, but high ISO rates tend to be used as light levels fall, and under these circumstances crops, especially tight ones, can often prove less than ideal in that the level of detail isn't as good or as visible as that obtained when a lower ISO is employed.

In order to illustrate this let's first return to an image used on a earlier page. The hoverfly taken with our 3mp Epson digicam at ISO100 and a magnification nearly the equivalent of 1:1 ratio from a 35mm full frame DSLR. 

Below is a crop which helps to show a bit more of the detail. There's not any more, it's just a bit more visible at a larger size. Not too bad from what many would today deem a low resolution digital camera, and although no doubt a higher resolution would have been beneficial here, it's not quite as vitally important as is often assumed.

Now we'll turn to our 10mp Canon 400D used with the EF-S 60mm macro at 1:1 ratio. The subject here is something a bit different and helps to illustrate once again the use of macro photography to produce an image of something not really visible either with the naked eye or even with a magnifying glass unless it's an extremely powerful one, and where cropping of an image has benefit.

It's a record deck stylus/needle, used of course for the playing of vinyl records. The shot on the left is at 1:1 and reflects the small size of the subject which is roughly 10x15mm. You can see the metric steel ruler under it for some kind of size comparison. On the right is a crop of the actual needle head which is roughly 0.5mm diameter. Looks quite crude at this magnification doesn't it? But it's quite clean actually. These were taken at ISO400, 1/5th sec, f8.0

Below are a couple of cropped views of the needle before cleaning. It also shows the worth of cropping, the dirt and hairs are quite visible. Scary to think this is used to play vinyl records isn't it? The biggest laugh though is that it's virtually brand new, so we hate to think what the old one looked like at this magnification. These two crops were from shots taken in higher light levels, ISO100, 1/200th sec, f5.0 on the left, and ISO100, 1/320th sec, f5.6 on the right.

And just for comparison here is one taken at ISO1600, 1/20th sec, F8.0 in lower light. The full size 1:1 image on the left doesn't look much worse than the other one pictured top left at ISO400. But look at the crop on the right which is at about the same angle as the ISO100 crop above left. It's actually quite good compared to many other digital cameras at this ISO level, (Canon have always been ahead in this area and remain so despite Nikon catching them up recently), and is far better than any film image taken at the same ISO. However it's not really good enough for severe crops when high levels of detail are the main requirement as we hope you can now see, and sticking to the lowest ISO's is always the best option where this is possible.