Maximum sharpness

[miesnert]

Hello everyone,
this will be my first post on the forum.
Since a month I am in the possession of a large format camera.
I am now shooting as much as I can with it to try and familiarize myself with the camera and it's technique.



I have shot this last week and am unhappy with the sharpness in the middle (the part that is furthest away from the lens), it is too soft.
Yesterday I have revisited the location and shot the same image again.
I closed the aperture further down the second time, hopefully I will have everything in the shot sharp this time.
My question is: could I have done anything else to maximize sharpness? If I would use movements, can I then still get everything (left to right, front to back, top to bottom) sharp?
I was wondering because on all sides of the lens there are things close by and far away, all of them need to be sharp.

Thanks,
Sander

[vinny]

http://www.largeformatphotography.info/
scroll down to "taking the picture"

[miesnert]

http://www.largeformatphotography.info/
scroll down to "taking the picture"

Thanks for your reply.
I have read trough the website, but I cannot make out if in this case it will be beneficial to use movements, for instance if I would tilt the lens backwards to get the ceiling and walls sharp, will the floor still be sharp enough? Or, if I would tilt to the left, would the other wall still be sharp? Or is it in this particular case (basically I am standing in a tunnel) the best option to simply stop down?

[Vaughn]

Yes, a difficult situation for using movements. I think the best bet is to just place the plane of focus( w/o movements) in a way that allows for the best use of the DoF as you close down the lens.

You will lose a little sharpness by closing all the way to f64, but depending of the amount of enlargement you hope to do with the image, that loss may not be significant.

[Nathan Potter]

It looks as if your top and bottom are closest to the camera with possibly the edges at some intermediate distance. Using camera movements to increase sharpness at depth will be of little advantage. Swing and tilt will yield only an increase in DOF along a single plane extending out from the camera and anything extending out side that plane will quickly fall out of focus. Rise/fall and shifts does not provide a DOF advantage.

Thus you are left with aperture setting as the main means for maximizing sharpness over all the close and distant features. In cases like this I use a rough hyperfocal focus setting then stop down. To do this I focus sharply on the distant point on the GG and note the setting on a calibrated rail then do the same on the nearest point and note its' rail setting, then set the actual focus point about halfway between. Now as I stop down the (Circle Of Confusion, COC) diameter decreases (sharpness increases) on both sides of the hyperfocal setting.

The sacrifice in such a procedure is that diffraction effects take place at smaller apertures which limits the sharpness (resolution) that you can achieve. The loss is fairly substantial as I show below.

APERTURE COC DIAMETER
f/5.6 7.5µm
f/8 10 µm
f/11 15 µm
f/16 21 µm
f/22 30 µm
f/32 43 µm
f/45 64 µm
f/64 85 µm

Here you can take the COC diameter as what is commonly referred to as one line, so for example, COC of 10 µm would be 100 lines per mm. or 50 line pairs per mm. Also termed as 100 l/mm and 50 lp/mm respectively. A good LF lens can deliver 50 lp/mm or so at f/8. Consideration of the diffraction limit allows you an estimate of the degree of enlargement possible while still retaining a sense of sharpness when viewing a print at normal reading distances.

The other tool you might employ to help with DOF is use of a wider angle lens. For the same Field Of View (FOV) the perspective will change over that of a normal lens but the DOF will increase dramatically. For instance my 75mm Nikon at f/22 with the hyperfocal distance set at about 40 ft. will yield everything in focus from10 ft. to infinity for a COC of about 20 µm. Your most distant object is nowhere near infinity so your hyperfocal setting will bring your nearest object much closer than the above mentioned 10 ft.

Nate Potter, Austin TX.

[C. D. Keth]

I don't even think it's worth mentioning the possibility of changing lenses in this situation. While yes you do gain some depth of field flipping to a wider lens, the gain is almost entirely negated assuming you are also walking in to try to get the same framing. Also, with an interior where we see so many things on both floor and ceiling, angle of view is everything. Suggesting a lens change is essentially saying "take a different photograph."

See this example I just whipped up, changing to the wider lens (150 -> 75) would only get you a couple feet of depth of field at f8.

Attachment 84916

[gliderbee]

, then set the actual focus point about halfway between. Now as I stop down the (Circle Of Confusion, COC) diameter decreases (sharpness increases) on both sides of the hyperfocal setting.

Nate Potter, Austin TX.

Wouldn't it be better to set the focus point at appr 1/3th away from the nearest distance instead of halfway?

Stefan

[C. D. Keth]

Wouldn't it be better to set the focus point at appr 1/3th away from the nearest distance instead of halfway?

Stefan

In that range, it's somewhere between 1/2-1/2 and 1/3-2/3. The closer you come to the lens, the more evenly depth of field is split in front of and behind the plane of focus. As you move further from the lens, it move more toward 1/3 in front and 2/3 behind. Really you just need to ballpark it, stop down, and use your loupe to see if things are sharp that need to be sharp. There's no substitute for using your eyes.

[CP Goerz]

This a focusing situation where a smaller format has the advantage over LF, a 6x9CM thats stopped down would yield a sharper neg in the center.

[E. von Hoegh]

This a focusing situation where a smaller format has the advantage over LF, a 6x9CM thats stopped down would yield a sharper neg in the center.

Agreed. Large format isn't for everything, and sometimes beginners get trapped by the "everything should be sharp" misconception. Sometimes, and this is one of them, it isn't possible. What Herr Goerz suggests is true, using a smaller format will give a better image.
The rule of thumb is that all other things being equal, DOF depends on reproduction ratio.