Focal depth / F Stop help (1 Viewer)

[Suffolkringer]

Hi All

Just brought myself a 100mm Canon L IS Macro a few weeks ago. Had little chance to play with it. Please see a couple of images below. Both taken at 1:1 but I would like some advice on depth of field. Clearly not all is in focus. Can someone suggest the sort of F stops I need to reach in order to get everything in focus and is it best to set focus to front or centre of image to achieve the best results.

Hope people can give a newbie macro man some advice.

Thanks in advance.
Jon

 

[SteveClifton]

Hi Jon, these look like a pretty good start to be honest.

By all accounts the 100 L Macro from Canon is one of the very sharpest lenses available for any mount, so while quite sharp already, I would say there is still some room for improvement in your images in terms of absolute sharpness (isn't there always though!)

You didn't give the settings for these two shots, so it's difficult to give exact areas for improvement, but here are a few points that might help.

Depth of field is always shallow at macro distances, and the closer you get, the shallower it gets. For the type of shots you posted, I would say it is unrealistic to expect to get every part of the subject in focus at once. Instead you can aim to get as much of it in focus as possible by reducing the lens aperture, and selectively focus on the parts you want in sharpest focus. Alternatively, you can deliberately use the shallow DOF effect to isolate just the area you want in focus (using a wider aperture) such as an insects head or the stamens of a flower.
The way you position the camera can help to get more of the subject in focus. For example, with dragonflies or damselflies, aim to get them at right angles to the camera body so that the whole subject is roughly at an equal distance from the lens. Even if you do this, you will still benefit from focussing selectively on one area. To do this, forget auto-focus and instead use MF. I find it so much easier to first activate live view and then use the camera's screen to focus. On most Canons you can magnify the image presented on the screen by 5x or even 10x, which makes it even easier to selectively focus on an area. This magnified area can even be 'toggled' away from the centre of the image if necessary. It can be more illuminating to press the depth of field preview button and hold it down while you focus manually. By doing this you will see before you take the shot exactly how much of the image will be in sharp focus in the final picture. Use the camera's self timer or a remote/cable release to reduce vibrations. Using live view is also a benefit as the camera's mirror is already locked up, meaning you don't suffer from 'mirror-slap' at the moment you activate the shutter.

From a practical point of view, in a non-controlled environment (i.e. outdoors, natural light without flash) I always aim for the smallest aperture (highest f-number) that will allow for a fast enough shutter speed to freeze any subject movement. Typically I would aim for somewhere between f9-f16. F16 will give greater DOF than f9, but slower shutter speeds due to reduced light. If the subject is very still and there is no wind, you can get away with a surprisingly slow shutter speed (e.g. under 1/50 second) if the camera is on a tripod. But if there is even a tiny amount of wind/breeze, then movement of the subject can wreck an otherwise good image. Be aware too, that an effect called diffraction can kick in when using very small apertures. This causes reduced image sharpness, and typically begins at apertures smaller than around f16 (it varies from lens to lens).

As I hinted above, I am a firm believer in using tripods for proper macro (1:1 or closer). Some photographers hate using them, but with DOF being so shallow in macro you only have to sway your body a few mm backwards or forwards and the sharpness is lost.

Once you get more confident, then by all means experiment without a tripod, but you will need good light to get your best results. By taking a burst of several shots you increase your chances of getting at least one that is sharp where you want it to be.

One way to ensure that every part of the subject is in focus, is to use a specialist technique called focus stacking. This is something I haven't tried personally, but the principal is to take a series of shots, each with the focus altered slightly so that the nearest and farthest extremities are sharp, then merge them using software such as Photoshop. Obviously, for this to be successful you would need consistent lighting and zero movement of the camera or subject while taking the whole sequence.

Hope some of this was helpful.

 

[Suffolkringer]

This is brilliant Steve, thank you very much indeed...This nice in depth answer does throw up a couple of questions for me.

From the moment I took my first macro picture I have been using it on a tripod. Even with a 7D and IS photographing a moth or flower on a sunny day still will always be easier with three legs!! On the tripod note I was thinking about setting myself up with one of those bendy legs tripods for low down insect work (eventually). I have no previous experience with any of the makes or prices, could you offer a little short advice on this?

Having come from bird photography mostly I have not much experience with using my "liveview" stuff. Could you give me some basic pointers with this? about how to zoom to x5 etc? Also what about a screen shade? I was thinking about buying one if liveview is a helpful feature. Can you make any recommedations?

And lastly, I have also briefly looked at remote releases, some of which looked fairly cheap and nasty. I sort of liked the look of the remote infrared one that Canon do but you seem to need to point this at the front of the camera which I thought might defeat some of the point of having something infront of the lens! Could you offer a little advice on this as well?

Many thanks once again for such a good in depth answer. This is my sort of example of exactly how these forums should be used!

Jon

 

[SteveClifton]

Jon, here is a Youtube video which gives a brief outline of Live view focussing. I think he's using a Canon 40D here, but the principle is the same. Activate Live view (press start/stop button on 7D), use the top right button to see the selected area at 5x. Press again to see it at 10x. Press again and it returns to 'normal view'. You can use the joystick button to move the selected area around the screen. Notice that in the video he has the focus point (centre of the flower) set to the right of centre.

http://www.youtube.com/watch?v=GezrEyQfr00

Once you have live view selected and have chosen your area to focus on, try holding in the depth of field preview button (usually on the left side of the lens mount, on the camera body, under the lens). This should show a much sharper image as it is stopping down the lens aperture before taking the shot. Normally the aperture only closes down for a split second when you press the shutter.

If you continue to hold the DOF preview button, then alter the aperture, you will see the difference in DOF as you stop the lens down. Still holding down the DOF preview button, try manually focussing the lens when it is set at a wide aperture, and you will see the point of sharpest focus move forwards and backwards very noticeably.

Although this method of focussing is indispensible for macro and close-ups, I find it very useful for static birds too, as it allows you to focus on the head or eye. We've all had shots, especially of large birds, where the back end of the bird is in sharper focus than the head!

It can also be very useful to set the back button for AF (instead of the shutter button) then, when you have selected the area to focus on and magnified it to 5x, use AF to focus. AF in live view is generally slower, but often more accurate than normal AF.

As for tripods, I don't think it matters too much, so long as the legs can splay to a wide angle to allow you to get down low. I prefer a ball head for macro, as it allows more easy positioning of the camera than a two-way head, but each to their own.

I have a cheap cable release which cost under a fiver from amazon or ebay. I don't think the brand matters too much, just read the reviews first.

I have never found the need for a screen shade, except maybe for a carefully positioned hand, but by all means try one if you have trouble seeing the screen.

 

[iveljay]

If you want to calculate how much will be in focus this link will help

http://www.dofmaster.com/dofjs.html

For instance a Canon 7D with 100 mm lens focussed at 5 inches at f22 gives .01 of an inch either side of the point of focus.

By and large cheap releases work fine, certainly better than trying to use the camera release and accidentally moving or shaking the camera.

The only screen shade I have used worked well, however, the mount stuck to the back of the camera pretty firmly in order to allow the shade to be unclipped when not in use. The later removal of this glass and metal mount was a bit of a nightmare, so if you go down that route research what you are buying before parting with money.

 

[Suffolkringer]

Improvements

Following your DOF advice and setup advice I have been practicing further and these pics of moths from the garden I think are an improvement.

Still haven't brought a remote release yet!

All the best
Jon