Landscape focus question

thebigsky · August 26, 2006

I'm travelling to Cornwall next week with the intention of taking some landscape shots. However I'm still grappling with focusing issues with small apertures, hyperfocal and all that.

My question is, what happens when you set an aperture of say f22, point your camera at a scene with foreground detail through to infinity and use autofocus, does autofocus ever get it right?

01af · August 27, 2006

thebigsky wrote:

However I'm still grappling with focusing issues with small apertures, hyperfocal and all that.

Then why don't you simply read what was written about exactly this topic just a few days ago? See this sub-forum, several entries down, a post with exactly the same subject line as yours.

thebigsky wrote:

My question is, what happens when you set an aperture of say f22, point your camera at a scene with foreground detail through to infinity and use autofocus, does autofocus ever get it right?

You mean: Will the auto-focus module inside my camera read my mind? No, it won't. It simply will focus at whatever you point it to.

And at f/22, you will get wide depth-of-field, but hardly anything will be rendered really sharp, thanks to -->diffraction. With APS-C-format D-SLR cameras, better use f/8 or f/11 whenever possible. And don't waste your time on thinking too hard about hyperfocal distance. Focus at whatever constitutes the center of interest in your frame. If there is no center of interest, or if just everything within the frame is 'center of interest,' then you want to shoot something else.

-- Olaf

wxwax · August 27, 2006

Olaf, working on his people skills.

Big sky, there is a thread with an almost identical title in this forum, that you should read.

thebigsky · August 27, 2006

Yes I'm well aware of the other thread, I've even posted in it, maybe I didn't phrase my question correctly but it's not covered in the other thread.

What interests me is what autofocus makes of such situations, good grief, I'm just trying to learn here.

Khaos · August 27, 2006

thebigsky wrote:

Yes I'm well aware of the other thread, I've even posted in it, maybe I didn't phrase my question correctly but it's not covered in the other thread.

What interests me is what autofocus makes of such situations, good grief, I'm just trying to learn here.

Autofocus works by the camera using the lens to see the differnce in contrast between pixels. It will pick the area with the highest difference and choose it as the main focus point. When using a wide angle at a very small aperture, you have a lot of real estate to work with and this is where things get complicated.

Larger pixels will actually be benificial. Sounds weird, but look at the pixel size between the mds mkII and the 20D. The larger sensor not only allows for a higher MP, but also larger pixels. This will mean faster and less error in autofocusing.

This why medium and large format cameras will take such detailed shots. They are able to bring in all the scene in a larger easier to define format. Thus the smaller the format, whether digital or film, the less actual full detail you'll get. Granted, digital has been good at fudging with this, but the overall idea remains the same.

So now, what do you focus on. Like Olaf said, what your want as your subject. Do you want the foreground to play a big part? Focus on it with an aperture small enough to bring the reference point in the background in focus. Don't worry about anything else. Basicly, get out and shoot and learn your camera and your lenses. Experiment, and you'll soon know what apertures on what lenses will give you the results you want.

wxwax · August 27, 2006

f8.

Can you figure out where the focus point was?

I think you just need to shoot landscapes a bit, I believe you're overthinking this a bit.

thebigsky · August 28, 2006

Thanks guys for the detailed information, and that's a beautiful shot by the way. I totally agree with the idea of going out an learning by experimenting, my concern was that with work commitments and a 8 month old baby I don't get the opportunity very often and this trip to Cornwall could provide me with the opportunity to take some nice landscapes. The last thing I want is to return with loads of out of focus shots.

Following the advice gleaned from a book I bought I've been using f22 most of the time, but I gather from what's been said here this isn't necessary and that plenty of DOF is available from f11 onwards.

My use of f22 probably explains why my pictures seem to suffer from fringing and focus issues.

dancorder · August 28, 2006

This is something I've been looking at recently myself. To answer the original question; the camera will focus at the distance of whatever is in the autofocus region you have selected. To use autofocus with hyperfocal distance you need to work out your hyperfocal distance then pick something that far away from you and use the camera's autofocus to focus on that object. Then switch to manual focus to keep the focus where you've just set it and compose your picture.

This link is very good at explaining that method:

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

That said there is a different school of thought that says that the hyperfocal distance isn't that great and you should just focus on the most intersting part of the picture or at infinity.

This link gives a very in depth argument as to why that is (warning it's a very large PDF). You can skip all the maths and still get a good idea of what the author is talking about so don't let that put you off. At the very least you should read the rules of thumb on page 69 and the summary afterwards:

http://www.trenholm.org/hmmerk/TIAOOFe.pdf

wxwax · August 28, 2006

thebigsky wrote:

My use of f22 probably explains why my pictures seem to suffer from fringing and focus issues.

I imagine so. Yes, f11 should be perfectly adequate for most uses, especially with a wide angle lens. If you're using a longer focal length, then you'd be more worried about your depth of field if you had objects near and far.

jfriend · August 28, 2006

Some shortcuts for remembering hyperfocal stuff

thebigsky wrote:

I'm travelling to Cornwall next week with the intention of taking some landscape shots. However I'm still grappling with focusing issues with small apertures, hyperfocal and all that.

My question is, what happens when you set an aperture of say f22, point your camera at a scene with foreground detail through to infinity and use autofocus, does autofocus ever get it right?

dancorder has given you some good thoughts. The direct answer to your question is that the auto-focus system doesn't know anything about the hyperfocal distance. It focuses on the thing you point the focus sensor at, no matter what your aperture. To cause the camera to focus elsewhere, you either have to lock focus when the focus sensor is pointed at a different element of the photo (e.g. with a half press of the shutter) and then reframe your shot while holding that focus. Or, for a more planned shot (often on a tripod), you can switch to manual focus and just dial in the distance you want.

While the whole concept of hyperfocal tables can seem fairly complicated to learn and memorize, I use a few shortcuts. Here's my logic:

First, if there's a central object in the photo that needs to be sharp, I just focus on that and make sure my aperture is appropriate for the amount of depth of field I need.
Then, I examine whether it's most important to have near things or far things in focus. I've learned the hard way that near things that are blurry are usually more distracting than far things that are blurry, but that's just a guideline - it can still vary by the content of your image. So, based on this, I decide where to bias my focus.
If I decide that far things should be clear, then I'm looking for the hyperfocal focus distance that will be the best compromise from infinity in. For this, I just memorize the following points that correspond to my wide angle equipment:
#1: 17mm at f/5.6 - For your camera (which I think from your gallery is a Canon 5D), the hyperfocal distance for this combination is 5.6 feet (let's round up to 6 feet). Since I rarely shoot wide at an aperture larger than this, that means that at 17mm, focusing on a point 6 feet away will get me everything from 4.5 feet to infinity at any aperture from f/5.6 to f/22. At f/16, the hyperfocal distance is only two feet, but usually focusing on 6 feet will work just fine for f/16 too so that's why I just try to remember this one number for 17mm. Anything wider than 17mm just has so huge a depth of field that unless you are shooting wide open at f/4 or f/2.8 or trying to perfect the maximum depth of field, you can use this same rule in the field.
#2: 25mm at f/8 - From the dofmaster calculator, the hyperfocal for this combination is 8.6 feet (let's call it 9 feet) which captures everything from 6 feet to infinity. Usually this is plenty, but I know that you can go to f/22, still focus on the same 9 foot point and get even closer things in focus.
#3: 35mm at f/8 - Hyperfocal distance is 17 feet which captures from 9 feet to infinity. At f/22, with the same focus point, it will bring things in focus from 4 feet to infinity.
I picked these focal lengths because these are interesting focal lengths (to me) for landscapes. If you have different equipment or focal lengths you like to shoot landscapes with, then you can pick your own small set of representative ones yourself. You can even look through your own photos to see what you shoot.
At 17mm, you have a ton of DOF at any reasonable aperture (often more than you need), so you just need to remember one good focus distnace.
At other longer focal lengths, you start to lose DOF fairly quickly, but I try to remember at least a few points to go with as a guideline. As always, if you are trying to maximize the effect, you will want the exact settings for your particular scene, but in my experience most of the time you only really need to get close and err on the safe side.
You could also put a hyperfocal table in in your camera bag and be able to consult it in the field before any planned shot, but you'll still want to memorize a few guidelines so you can apply them in the cases where you can't consult a table.
Lastly, go back to the first two points I make and be sure that you are assured that the most important things are in focus no matter what you do. If your central subject is on the edge of a hyperfocal focus situation so that infinity can be fairly sharp, you'll probably wish you'd optimized more for the central subject and let inifinity be less than perfect.

thebigsky · August 29, 2006

Thank you all so much for all this wonderful information, I went out and experimented yesterday and got a lot of things clear in my head (as well as my shots) that were fuzzy before.

I downloaded a DOF guide for my PocketPC which is really useful in the field and I tried loads of combinations most of which were successful.

Using f-11 to f-16 resulted in much crisper shots all round than f22 which I was using all the time before. Overall I feel much more confident that, weather permitting, I should return from Cornwall with some good shots.

Now comes the real problem, how to fit myself, wife, baby and dog, suitcases, pram and camera equipment in the car?

Swartzy · August 30, 2006

thebigsky wrote:

Now comes the real problem, how to fit myself, wife, baby and dog, suitcases, pram and camera equipment in the car?

Ha, that's simple...leave wife, baby, dog at home ???? JK

This was a great thread and I learned some new things. Yes, I too have found trying to shoot at an F/stop higher than high teens to 22 never seemed to work right. I think every lens has a "sweet spot" or range that it performs best. Thanks for the thread and have a wonderful trip.

thebigsky · August 30, 2006

Swartzy wrote:

Ha, that's simple...leave wife, baby, dog at home ???? JK.

Don't tempt me

What's probably more likely is that it will either rain all week or I'll get there and realise I left some vital piece of equipment at home, like my camera

pathfinder · August 30, 2006

Does anyone here use the Depth of Field Preview button on your camera at the time of shooting, rather than fretting with hyperfocal tables??

I tend to use the Depth of Field preview button and examine the image at the time. It seems dark at first, but if you give your eye 30 seconds it will adjust and you can then evaluate the DOF through the viewfinder realltime.

wxwax · August 30, 2006

pathfinder wrote:

Does anyone here use the Depth of Field Preview button on your camera at the time of shooting, rather than fretting with hyperfocal tables??

I tend to use the Depth of Field preview button and examine the image at the time. It seems dark at first, but if you give your eye 30 seconds it will adjust and you can then evaluate the DOF through the viewfinder realltime.

I guess I have never been patient enough to let it work. The few times I have tried it, I gave up in frustration.

So no, I do not.

thebigsky · August 30, 2006

pathfinder wrote:

Does anyone here use the Depth of Field Preview button on your camera at the time of shooting, rather than fretting with hyperfocal tables??

I do if the subject is well lit, but most of the time I just can't see enough to determine focus.

dancorder · August 31, 2006

pathfinder wrote:

Does anyone here use the Depth of Field Preview button on your camera at the time of shooting, rather than fretting with hyperfocal tables??

It's the one thing that almost tempted me to pay the extra for a D70s, but I didn't so I can't.

Landscape focus question

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