So, how would you focus this?

[Patrick Dixon]

90mm/F6.8 Angulon 4sec @f22

[dave_whatever]

I don't think i'd use any tilt, just stop down. Probably focus using a conventional DOF scale type approach and stop down accordingly.

[Nigels]

Agree with Dave_w - Tilting won't gain you anything. I'd be using my 80mm and using my DOF calculator reckon I can focus from 94.9cms to Infinity at f/32. (calculator is DoF Plus app on the iPhone)

[Joanna Carter]

Hi Patrick

Well, I would try two different approaches, depending on the focal length of the lens.


If you look for the red marks on the image, you can always try using front forward tilt, focusing from just below the heads of the flowers in the foreground to either halfway up the tree trunk on the left or halfway up the thin tree just right of centre, then stopping down, ensuring that the ground in the dip after the main carpet of flowers is in focus.

If you look for the green marks on the image, they are meant to, approximately, represent the plane of focus you would get if you put on the tiniest possible amount of front forward tilt. And I do mean as little as is humanly possible to achieve, theoretically 0.006°. This should give you a depth of field of around 80+°, which you need to centre around a plane of of focus at around 40° from the horizontal. The plane of focus should leave the ground around 2-3 metres in front of you (represented by the green mark about 6 flowers back) and then rising to somewhere in the middle-distant canopy.

This latter "micro-tilt" technique is very effective at giving you a very large wedge of focus but it does take some time getting used to imagining the angles and finding the best angle to ensure that neither the ground in the distance nor the top of the foremost trees lose focus. You can usually get away with around f/22 to f/32 instead of having to stop right the way down to f/45 to f/64.

[Patrick Dixon]

Thanks.

I actually used something close to Joanna's red mark approach ... but maybe the green would have been better. I don't think no front tilt would have worked that well because the closest flowers were only about 30cm from the lens ... and I don't have an iPhone.

I'm reasonably happy with the focus, but the limb stump at the top of the right hand tree is obviously not in focus (jpg & small images cover a lot of sins), so it could be better.

The light was fading quite quickly so I didn't have a lot of time to play around (this was the only shot). I was actually only casing the joint, but wanted to capture the last light through the trees on the left and on the patch of garlic in the middle of the frame. The neg looks very thin but scans right in the middle of the epson range - so I think it's just low contrast. I haven't really got my head around the +/-1 stuff and it requires film/dev testing ... which all sounds rather boring and wouldn't really work with my mottly collection of out-of-date film.

[Thingy]

That's interesting Joanna and Patrick. Looking at the image I had assumed that you have tilted the back down a squidgen to get the upper part of the front trees in reasonable focus whilst sacrificing the resolution of the wild garlic by the hedge. It must be an optical illusion, but I thought the lower part of the two closest tree trunks were marginally wider that the upper parts of their trunks. It's probably the angle you used to take the image and the use of the wide angle Schneider.

[dave_whatever]

The microtilt idea is good, IF you can nail it. If you overtilt and end up with something out of focus then the risk is that will stick out like a sore thumb, whereas a global slight loss of resolution due to diffraction is never really noticable to the viewer unless they've got something to compare it to.

[David Evans]

Agree with Dave_w - Tilting won't gain you anything. I'd be using my 80mm and using my DOF calculator reckon I can focus from 94.9cms to Infinity at f/32. (calculator is DoF Plus app on the iPhone)

I could well be be wrong with this (but I did run it past Tim Parkin a couple of weeks ago!), but my understanding is that the DOF calculators are generally set for the appearance of in focus with an 8"x10" print viewed from 25cms by someone with 2020 vision. I've just checked using DOFMaster and with setting the format to 4x5, lens 80mm, aperture F/32 I get the near limit at hyperfocal distance at 104cms. A little different from 95cms, but in the same area approximately.
With the hope of getting in focus prints at up to 40" longest length from a 4x5 negative, I would set the format on my calculator to 35mm, which changes the hyperfocal near focus to 337cms.
With a 90mm lens the near limit is 426cms.
This is a good resource on depth of field http://www.cambridgeincolour.com/tutori ... ulator.htm

[dave_whatever]

I think you're right, the "standard" that manufacturers use for DOF, as used on lens scales etc I believe is for a print viewed from the distance equal to its diagonal. So that's a 10x8 from a foot away. I'd want to stopdown a stop or two if you want to get anything approaching critical sharpness. Similarly, if your eyesight is crap, open up a stop.

[timparkin]

Hi Patrick

Well, I would try two different approaches, depending on the focal length of the lens.


If you look for the red marks on the image, you can always try using front forward tilt, focusing from just below the heads of the flowers in the foreground to either halfway up the tree trunk on the left or halfway up the thin tree just right of centre, then stopping down, ensuring that the ground in the dip after the main carpet of flowers is in focus.

If you look for the green marks on the image, they are meant to, approximately, represent the plane of focus you would get if you put on the tiniest possible amount of front forward tilt. And I do mean as little as is humanly possible to achieve, theoretically 0.006°. This should give you a depth of field of around 80+°, which you need to centre around a plane of of focus at around 40° from the horizontal. The plane of focus should leave the ground around 2-3 metres in front of you (represented by the green mark about 6 flowers back) and then rising to somewhere in the middle-distant canopy.

This latter "micro-tilt" technique is very effective at giving you a very large wedge of focus but it does take some time getting used to imagining the angles and finding the best angle to ensure that neither the ground in the distance nor the top of the foremost trees lose focus. You can usually get away with around f/22 to f/32 instead of having to stop right the way down to f/45 to f/64.

Hi Joanne,

Totally with you on the micro-tilt idea but 0.006 degrees is way, way too small..** for a 90mm lens, to get an appreciable increase in depth of field, you'd have to use a tilt of around 0.1 degrees

I have a plotting tool I've written that shows the layout of depth of field for different lens tilts and bellows extensions which I'm hoping to blog about soon.

I would have focussed on the green line with a tilt of about 0.1 degrees in this case and stopped down to about f/22 2/3

Tim


** (I'm wondering if strange things are happening on Merklingers charts at small values of alpha as if you follow the trend of these charts, for alpha tending to zero, you should have infinite depth of field everywhere - I think not)

[Patrick Dixon]

I doubt the front and rear standards are aligned to 0.1 degree (or better) ... so it all seems a bit academic.

I don't want to end up looking like Tiger Woods at the Open, with books and charts to consult and a caddy to advise and carry all the stuff, so I guess it's just a matter of picking two points and trying to get them in focus at the same time.

[Joanna Carter]

I doubt the front and rear standards are aligned to 0.1 degree (or better) ... so it all seems a bit academic.

I don't want to end up looking like Tiger Woods at the Open, with books and charts to consult and a caddy to advise and carry all the stuff, so I guess it's just a matter of picking two points and trying to get them in focus at the same time.

The trick with micro-tilt is to check, with no (official) tilt, whether you have "normal" focusing or whether you can make out a tilted plane. If you can already see that "line" of focus, then you may already have enough tilt on the front standard, just check that it is forward tilt, not backward.

I can understand Tim's scepticism about Merklinger's charts but, in the end, I can't tell exactly how much tilt I am putting on at that minute level. When I was teaching last year's workshop in France, I told people to use « le poil de chien » (the hair of a dog) as a guide to how much tilt to apply; in English, we might say a gnat's ***** In any case, whatever the exact measurement, the technique really works but it is far more down to experimentation and experience than to any real calculation.

Patrick, forget the charts, get out there and start playing with as small a tilt as you can manage to apply, look for where the plane of focus lies and try to get it around 40° from the horizontal by altering the bellows extension. Then stop down whilst watching the distant lowest point and the foreground highest point. If the distant lowest point won't focus, then lower the angle by extending the bellows; if the foreground highest point won't focus, shorten the bellows to raise the angle.

[timparkin]

I doubt the front and rear standards are aligned to 0.1 degree (or better) ... so it all seems a bit academic.

I don't want to end up looking like Tiger Woods at the Open, with books and charts to consult and a caddy to advise and carry all the stuff, so I guess it's just a matter of picking two points and trying to get them in focus at the same time.

There is a good point to take from Merklingers stuff though... The depth of field above and below the plane of focus is proportional to the distance below the camera that the hinge point lies. i.e. if your pivot point is one meter below the camera and you then decide to change your focus so your pivot point is four meters below the camera, you now have four times as much depth of field above and below the focal plane...

So - the hopefully, the general rule that most of you know as "it's better to apply less tilt than more tilt" can be understood a bit better..


For the visual among you, the following graph shows how the depth of field bounds change with tilt..

blue 1 degree
orange 0.5 degree
green 0.1 degree
yellow 0.001 degree

The scale is in meters and is for a 90mm lens at f/22 with a typical circle of confusion (0.06)



One of the other interesting things that comes out of this is seeing how the bounds of the depth of field rotate around the 'normal' depth of field limits (look where the thin lines coincide).

So, you can use a 'standard' depth of field application (or rule of thumb) and then you can just draw an imaginary line from your hinge line to these bounds to visualise your depth of field bounds.

I'll write some more about this on my blog and hopefully have a little javascript widget for you to play with

Tim

[Patrick Dixon]

Hmm.

What Tim's diagram says to me, is that I have no chance of focusing this scene @f22!

If my near focus point is <1m and close to the ground, and I also need to cover about 4m high 4m away, but still have ground level at infinity covered - I need more, rather than less, tilt.

If I used 1deg (blue), but pulled the focus point in, I'd probably be OK for the first two, but the ground level beyond a couple of meters would OOF.

Is this why everyone just goes with a rock in foreground and a mountain & sunset in the upper third then?

[Joanna Carter]

Hmm.

What Tim's diagram says to me, is that I have no chance of focusing this scene @f22!

If my near focus point is <1m and close to the ground, and I also need to cover about 4m high 4m away, but still have ground level at infinity covered - I need more, rather than less, tilt.

If I used 1deg (blue), but pulled the focus point in, I'd probably be OK for the first two, but the ground level beyond a couple of meters would OOF.

Is this why everyone just goes with a rock in foreground and a mountain & sunset in the upper third then?

Tim's diagram seems to show the DOF at a fairly large aperture. When you get to around f/22, you actually start to see a much larger angle.



If my rubbish diagram isn't good enough for you, then take a look at this image



This was taken using « le poil de chien » front tilt. The boat is less than 3 metres away and yet it is perfectly sharp, as is the water from under the boat to the horizon. And that was the challenge here - to place the hinge point low enough that the foreshore, the front of the boat and the water all the way to the horizon were all sharp. It's a bit like your picture but with the camera about 6 metres above the "ground" and the boat where your front trees would be.