How do I focus this set up ?

[Dave Tolcher]

Having had a good chat with Joanna and got a better understanding from Merckinger's arcticles I set about a shot which was a little more ambitous than usual for me in the focussing department. I thought I had got it pretty close by laying the plane down the wall but have lost all the underneath and nearly the top of the near stuff. See sections...
Focussed using front tilt with a bit of drop to compensate for he composition. F32 using an 80mm lens.

I couldnt drop the focus any further down the wall or would have lost more of the tops, no further stop down possible....

Was this just too much ?

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Thanks

[du a gwyn]

Dave,have a look on you-tube,there are great articles on it on how to focus large format camera's.
regards.

[Joanna Carter]

Having had a good chat with Joanna and got a better understanding from Merckinger's arcticles I set about a shot which was a little more ambitous than usual for me in the focussing department. I thought I had got it pretty close by laying the plane down the wall but have lost all the underneath and nearly the top of the near stuff. See sections...
Focussed using front tilt with a bit of drop to compensate for he composition. F32 using an 80mm lens.

I couldnt drop the focus any further down the wall or would have lost more of the tops, no further stop down possible....

Dave, how much tilt did you put on? If you tried to make the plane of focus follow the top of the wall, then you more than likely have used too much.

One of the benefits of the "micro-tilt" method that I mentioned to you, is that it gives you a much greater depth of field than large amounts of tilt. I think, as a starting point, I would have done the usual amount of tilt where the back of the bubble on the front standard was only just touching the rear mark on the level, put the near focus coming out of the wall around 8-10ft in front of you whilst setting the far focus at the very top of the distant rock.

Then stopping down should allow you to see if the horizon and the top of the nearest rock were in focus. If the horizon is out of focus, the tilt angle is not enough, if the top of the nearest rock is out then the tilt angle is too much.

Of course, this is all theory and needs a good deal of practice to prove it

Ps - still cant get photos to embed !!

You need to get the URL of the image itself and place that between two img tags; at the moment, you are posting links to the page. You seem to be using a PHP script to show the images, are the images held in a database, or just in hidden folders on the site? Feel free to give me a call if you want to discuss this in more detail.

[Dave Tolcher]

Thanks Joanna, yes too much tilt, I had approaching 20degrees - the classic conundrum of where the theory of tilting to get the plane front to back seems not to be the best answer. The foreground boulder was 1m away and the Nab about 200m. The issue was the height of the boulder relative to the plane and the depth of the floor wrt the line of the wall. I had expected DOF to cover it with an 80mm lens at F32.

I now better understand what you are saying about 'micro tilt' of a small amount, focus at 8-10' away and then tweak based on what happens to the DOF as you stop down. Its interesting how DOF reduces the more you tilt and this would eliminate that problem. I have another example of the challenge with a different subject in the post which I suspect will exhibit the same problems.
Rgds

Dave

[timparkin]

Thanks Joanna, yes too much tilt, I had approaching 20degrees - the classic conundrum of where the theory of tilting to get the plane front to back seems not to be the best answer. The foreground boulder was 1m away and the Nab about 200m. The issue was the height of the boulder relative to the plane and the depth of the floor wrt the line of the wall. I had expected DOF to cover it with an 80mm lens at F32.

I now better understand what you are saying about 'micro tilt' of a small amount, focus at 8-10' away and then tweak based on what happens to the DOF as you stop down. Its interesting how DOF reduces the more you tilt and this would eliminate that problem. I have another example of the challenge with a different subject in the post which I suspect will exhibit the same problems.
Rgds

p.s. You'll never get everything in focus that close to the camera. I would have been tempted to crop out the bottom of the picture and have it starting at the rocks.. If you remember that the focus comes out as a wedge from the hingle line, you have to have almost infinite depth of field to get above and below with a wide angle lens in focus,.

Dave

The microtilt idea has some potential but I think it would probably be dissatisfying when working with something that is this close up. The problem with using depth of field in this manner is that you get everything within your 'circle of confusion' but the really sharp stuff will be at the horizon typically wheras people don't mind if the horizon is a little bit out of focus but will be looking for detail in other areas..

OK - so where would I put the focus? Well, where are people going to be able to notice focus most..

I think people will probably want to look for the detail in the two planes of the big rocks at the front and possibly slightly less along the brick wall..

I think people also notice 'bad focus' across similar surfaces. So for the rock in the foreground, if the bottom is in focus and the top isn't, it will look slightly wierd..

Given this, I would probably place the hinge line a couple of foot below the camera (maybe about 8 degrees if you were using a 90-110) and place the plane of focus about 30-40 degrees up into the air. I would then add about 3 degrees of swing to help the focus place go from close-botto-right to far-top-left. I'd then stop down to see how much detail I want in the nab (probably 32-45).. You'll end up with a slightly soft nab and horizon but that will add to the 3d recession. (it will just seem like haze blurring to most people)

I'm always very wary if the hinge line ends up close to the camera with a wide angle lens..

Did that make any sense whatseover?

[Dave Tolcher]

Hi Tim, it does make sense. In terms of what isnt in focus in this pic it is the least important element except for the flat rock in bottom left which should be sharper for it to work. I did look at swing and that didnt particularly help because of the requirement for focus on bottom left (which I didnt get anyway !). Try again next visit I think.

[Patrick Dixon]

Ps - still cant get photos to embed !!

[Joanna Carter]

Ps - still cant get photos to embed !!

Patrick, thanks for finding the image files. Did you guess at the directory name or do you know the gallery software?

Anyway, I have removed the links from your post and replaced them into Dave's; thanks again.

[Patrick Dixon]

No problem - no, I just brought up the image, right clicked on it and selected 'Copy image location' (Firefox - pick appropriate option for your browser), and pasted that into the reply with the img tags around it.

Can't really help with the focus though, but having read Merkinger's stuff, I'd probably just put a degree or two of tilt on, focus on the front of the near rock, and stop down to f22 or f32. He says, that the more tilt you use, the less depth of field you get even when stopping down, so with 20 degrees of tilt, you probably don't get much at all.

[Joanna Carter]

No problem - no, I just brought up the image, right clicked on it and selected 'Copy image location'

Well, you learn something new every day

[Charles Twist]

I have read (and results support this) that when tilt is used, the depth of field increases with the distance of the subject from the camera (depth of field is always measured perpendicular to the focal plane). So focus should be very tight in the foreground, but some slop is afforded in the yonder. I agree with Tim (is this a first?) on the importance of focussing on what catches the eye. In this way, the shot mimicks human vision and appears natural. This is the real strength of LF (IMHO). I agree with others that my first instinct tells me to use some swing as well as tilt in this case.
Best regards,
Charles

[timparkin]

Depth of field is wedge shaped starting from the hinge line.

You check the plane of your depth of field limits on the ground glass by focusing forwards and backwards. A good rule of thumb is based on the amount you rack in and out.. .

If it's only a about 1mm you can get away with f22 (max enlargement 10x)
2mm f32 (max enlargement 6x)
3mm f32 1/3
4mm f32 2/3
5mm f45 (max enlargement 5x)
7mm f45 1/3
9mm f45 2/3
10mm + f64 (max enlargement 3x)

For my Ebony, a whole turn of the focus knob is one inch so I have a general rule that says

+/- half a turn needs f/64+
+/- quarter a turn needs f/45
+/- 45 degrees needs f32 1/3
+/- a tweak and I use f/22 2/3
+/- a very small tweak and I might be able to use f/22

Using this method allows you to check the exact plane of focus at the limits of your depth of field..

Tim

p.s. According to Merklinger, with your tilt at 20 degrees, your plane of sharp focus would only be +/- 2.5 degrees ... or with the nab 200 yards away, only 60ft of it will be in focus.. and with the rocks only 2 feet in front of you, the height of the in-focus plane would be 2 inches..

p.p.s. I'll have a crack at working out how micro tilt would have worked... My estimate is that you would have ended up with the stuff closest to the camera at the very limits of your depth of field with sharp focus being about 20-30 feet away. Something else to try out next time we get together

[Joanna Carter]

I'll have a crack at working out how micro tilt would have worked... My estimate is that you would have ended up with the stuff closest to the camera at the very limits of your depth of field with sharp focus being about 20-30 feet away. Something else to try out next time we get together

Just let me know when and where, preferably "up north", and I will gladly share my methods of micro tilt, which, so far, have gotten me some "stonking" images

[Paul Arthur]

Well this is very interesting... circumstances (and certainly what was in your kit bag) may have made this impossible, but theoretically would it be easier to be further away with a longer lens? That way, the area that needs to be in focus is much further in front of your lens than it would be with a wide lens. Since you are so close to it, the amount of tilt you need is increased, which reduces the possible DOF, if you are further away wouldn't that be less of a problem?

I may of course have a fundamental misunderstanding of this all though....

[Patrick Dixon]

But a longer focal length gives less DOF anyway ...