DOF & CoC for panoramic 6*17

[Nioukie]

Hello everybody

I'm trying to make some picture with a Shen Hao 617 and a Apo-Symmar 150mm 5,6

Does anyone know where I can find a DOF calculator for that format ? And what is the Coc ?

Thanks

[Emmanuel BIGLER]

......
617 and a Apo-Symmar 150mm 5,6.....

Does anyone know where I can find a DOF calculator for that format ? And what is the Coc ?

hello !

There are two approches to find the proper circle of least confusion (CoC) or the 6x17 cm format

- in a first approach, you may consider that you crop a 6x17 strip from a rectangle which is bigger and less narrow that the 6x17; for example, something of 1:1.5 ratio (like in 35 mm / 24x36 mm photography), for example from a 11x17 cm format
From this you compute the diagonal of the format, about 20 cm.
The traditional value for the CoC, in general for all non-panoramic format, is somehing like 1/1720 of the diagonal, this yields a value of 110 microns.

- in a second approach, you might consider your 6x17 panoramic image like a series of 3 square 6x6 images stitched together. And you wish that each 6x6 portion is as good and sharp as one single 6x6 image. Hence you'll take the diagonal of the 6x6 format, 80 mm and the traditional CoC will be 80mm/1720 = about 45 microns.
The second approach is closer to what the eye actually sees when looking at a panoramic image. However, 50 microns is a very stringent CoC value for large format photography !!

So between those two extreme values, you should experiment with values of the CoC between 50 an 100 microns.
there exist many free DoF calculators available, but once you have your focal length, 150 mm and the value of your CoC, between 50 and 100 microns (in fact the choice depends on the degree of the final enlargement), any DoF calculator will give you the answer.

The formulae are summarised here, it is easy to re-compute them
- first compute the classical hyperfocal distance : H = f^2/(N c)
f = focal langth here : 150 mm
N = f/number 11-16-22-...
c = the value of the CoC, between 50 and 100 microns

From the value of H, the near (p1) and far (p2) distances within which the sharpness is acceptable, for a given distance setting p are computed as !
1/p1 = 1/p + (1/H).(1-f/p)
1/p2 = 1/p - (1/H).(1-f/p)

for far-distant objects beyond about 10 times the focal length, the simplified formulae are
1/p1 = 1/p + 1/H
1/p2 = 1/p - 1/H
derived fro those formulae, the good ol' rule of thumb for landscape is : set the camera to the hyperfocal distance H, and the DoF limits extend from H/2 to infinity. This is the traditional approach at least, no need for DOF tables then ;-)

[Nioukie]

Thanks Emmanuel for this accurate answer !
Next time, I'll write in "la langue de Molière" !

[GPS]

hello !

There are two approches to find the proper circle of least confusion (CoC) or the 6x17 cm format

- in a first approach, you may consider that you crop a 6x17 strip from a rectangle which is bigger and less narrow that the 6x17; for example, something of 1:1.5 ratio (like in 35 mm / 24x36 mm photography), for example from a 11x17 cm format
From this you compute the diagonal of the format, about 20 cm.
The traditional value for the CoC, in general for all non-panoramic format, is somehing like 1/1720 of the diagonal, this yields a value of 110 microns.

- in a second approach, you might consider your 6x17 panoramic image like a series of 3 square 6x6 images stitched together. And you wish that each 6x6 portion is as good and sharp as one single 6x6 image.80mm/

....

derived fro those formulae, the good ol' rule of thumb for landscape is : set the camera to the hyperfocal distance H, and the DoF limits extend from H/2 to infinity. This is the traditional approach at least, no need for DOF tables then ;-)

Well, I have to say that I'm slightly perplex over this answer.
First of all, the Coc is often given very freely, depending on the preferences of the photographer and his intentions regarding the final image size. Speaking about 1/1720th of the diagonal is like saying that a beef steak is normally eaten "well done"...
Apart from that statement to say that you can take a 6x17 image as three 6x6 images has the same value as to say that you can take a 6x17 image as 4.7 images of 24x36 format wishing the same sharpness... You can also take your panoramic image as 2 images of the 6x9 format (and yes, some DOF calculators give you the choice of that format too, instead of the 6x6 format etc.) Or you can take it, with good logic, as a part of 4x5 film format. There you see the freedom in the choice of the appropriate CoC - it all depends on the final print size you're after and the sharpness you like most on it.

On the top of it all, I find the "good ol' rule of thumb" mentioned in the answer as in the same bizarre league - shooting with view cameras focused on the hyperfocal distance is hardly anything typical for a view camera technique. Quite the contrary especially when you use - as often with view cameras - standard movements. Shooting with a camera focused on hyper focal distance is typical for hand held photography not a view camera photography. Not to speak about the fact that having the distant background in the sharp focus is often preferable than shooting with a hyperfocal distance focus, especially in the landscape photography! You will hardly play a "f8 and be there" photographic game with a view camera for landscapes...:)

You can find many DoF calculators on the net, google gives a plethora of them. The same for the Coc size explanation or its value.

[aduncanson]

GPS,

It is important to understand what Emmanuel is offering. Basically he provides two options for sharpness criteria. The first option, negative diagonal/1720, embeds the assumption that the viewer is at some standard distance (roughly the print diagonal) from the print that allows him to view the entire print at one time. The derivation of this rule of thumb also rests on established values for the typical resolution of human vision. The second option, based on 3 6x6 frames, assumes instead that the viewer is going to get close enough to really view only one third of the panorama at a time.

Both are justifiable assumptions, but as you suggest there are other assumptions that the photographer might make, including that the viewer will walk right up to his near focus limit. In that case the photographer needs to consider the magnification of the enlargement, but in the two approaches offered by Emmanuel, magnification actually falls out of the formula since as the print gets larger the viewer moves back.

- Alan

[GPS]

Alan,
I do understand the point of view in Emmanuel's answer. I just think that his explanation of finding the "proper" (the "well done" beefsteak) Coc value is perplexing - giving an impression of mathematical rules without mentioning the more arbitrary elements that make these Coc values much less religious. A "proper" Coc value is as much a question of a mathematical rule as it is of your personal preferences of the sharpness and of your final print size to mention just some "free" elements.

"As the print gets larger, the viewer moves back" - you say. This rule too - especially with the panoramic format pictures! - is very free. Hopefully I made it clearer to the OP that the Coc is more of a recommendation than a strict mathematical rule. For many and good reasons.

[ic-racer]

Either people who use that format are going to chime in here with their acceptable COC based on experience (none so far) or the OP is going to have discover for himself. I'd use one of the estimations kindly posted above by Emmanuel BIGLER as a starting point and start taking exposing film! :)

[GPS]

Hmm. Sounds good? Now, what is the acceptable sharpness based on experience in your pictures??:)
But I think the OP wanted to know where he can find a DoF calculator...:)
Now, my acceptable (more than that) sharpness from 6x17 film format is very good on 30in prints... So what??:)
My advice to the OP is - choose whatever Coc your calculator gives you for 4x5 format (or 6x9, or 5x7, or 8x10) shoot and be happy. The Coc is not a religion. That is - there is not a "proper" Coc given for a format, just a recommendation for your beefsteak...

[GPS]

Hello everybody

I'm trying to make some picture with a Shen Hao 617 and a Apo-Symmar 150mm 5,6

Does anyone know where I can find a DOF calculator for that format ? And what is the Coc ?

Thanks

If you want to take a DOF calculator with you in the field you can buy a Linus DoF calculator (former Rodenstock type) and use it with the nearest film format value of your choice. Will do.

[ic-racer]

Hmm. Sounds good? Now, what is the acceptable sharpness based on experience in your pictures??:)
But I think the OP wanted to know where he can find a DoF calculator...:)
Now, my acceptable (more than that) sharpness from 6x17 film format is very good on 30in prints... So what??:)
My advice to the OP is - choose whatever Coc your calculator gives you for 4x5 format (or 6x9, or 5x7, or 8x10) shoot and be happy. The Coc is not a religion. That is - there is not a "proper" Coc given for a format, just a recommendation for your beefsteak...


Knowledge of ones own COC is required for interpreting and DOF table or calculation, if one wants to use these tools.

[GPS]

Knowledge of ones own COC is required for interpreting and DOF table or calculation, if one wants to use these tools.

And knowing that there isn't (due to many variables) a "proper" Coc value for a given format, just a reasonable recommendation depending on such variables also belongs to this knowledge...:)

[Lachlan 717]

Just get a lens that covers 5x7", some film and a camera and go shoot...

[Nioukie]

Just get a lens that covers 5x7", some film and a camera and go shoot...

I did and I'll do next week !
But you know I'm just a beginner and I noticied some problems with my previous focusing. Now I'm trying to understand why and to find a solution.

My question is simple : landscape and focus. But the proper way to get it is not so easy

[GPS]

I did and I'll do next week !
But you know I'm just a beginner and I noticied some problems with my previous focusing. Now I'm trying to understand why and to find a solution.

My question is simple : landscape and focus. But the proper way to get it is not so easy

It would help you and us a lot if you say what exactly was the problem you encountered. I'm sure there are a lot of people on this forum knowledgeable and happy to help.

[Nioukie]

Thanks

I have to do panoramic landscapes. I've decided to rent the Shen Hao 617 and a 150mm.

So let's say I have shot a Forest in the morning dawn.

The ground is on focus. The base of the first tree is ok but the bottom of this tree (same distance because it's perpendicular) is out of focus.
Let see the attached pict. I put it in B&W. In green : the focus is ok. Out of the green : out of focus.

So I think I've done some thoughless tilts. Because I'm a new user of view camera, and because I have to do that job, I need to find a proper way to have the largest amount of focus

all the best. Please, would you kindly excuse my "out-of-focus" english...

[GPS]

Could be a bulging film. Did you use a cut sheet film or a roll film holder? Forget the worry about your English ;-) The reason you mention for the out of focus area could also be a probable cause. Go and take another one... ;-)

[Brian Ellis]

Knowledge of ones own COC is required for interpreting and DOF table or calculation, if one wants to use these tools.

Maybe we're thinking of different kinds of depth of field tables but I've been using Linhof's depth of field table for years and I don't have the foggiest idea what my acceptable COC is or why I'd need to know it.

[Nathan Potter]

Thanks

I have to do panoramic landscapes. I've decided to rent the Shen Hao 617 and a 150mm.

So let's say I have shot a Forest in the morning dawn.

The ground is on focus. The base of the first tree is ok but the bottom of this tree (same distance because it's perpendicular) is out of focus.
Let see the attached pict. I put it in B&W. In green : the focus is ok. Out of the green : out of focus.

So I think I've done some thoughless tilts. Because I'm a new user of view camera, and because I have to do that job, I need to find a proper way to have the largest amount of focus

all the best. Please, would you kindly excuse my "out-of-focus" english...

Yes, I think you've done some thoughtless tilts. It appears that you have encountered the limitations of the Scheimpflug rule. Tilting provides an in focus condition, at maximum aperture, only in a single, horizontal plane from near to far. Any subjects that project out of that flat horizontal plane will be out of focus. The further away from that plane then the more out of focus (thus the larger the COC). You will need to stop down, (reduce the diameter of the aperture, as well as tilt judiciously) in order to bring other elements of the scene into better focus (reduce the diameter of the COC). Your situation may be an extreme example of obtaining full frame sharpness so I would guess you'll need a very small aperture. The very small aperture will also limit the overall sharpness due to diffraction effects but it will be the best you can do short of using heroic technology solutions such as multiple images with stitching, etc. :)

Nate Potter, Austin TX.

[Nioukie]

Could be a bulging film. Did you use a cut sheet film or a roll film holder? Forget the worry about your English ;-)

I use a roll back, I first thought it might come from it. It might not press the film enough. But the others pictures present different "focus bulging"

Brian said "Any subjects that project out of that flat horizontal plane will be out of focus."

So, if I understand for that kind of pictures (not so far or horizontal subject) I should forget about titling and be carefull about stopping down. Sounds ok for you ?

I'm going to shot again next week (rent the Shen Hao, drive a few hours, leave the children home etc) so I want to be more precise and come back with acceptable pictures...

[Lachlan 717]

You need VERY little tilt on these cameras. You're using a much smaller section of the image circle for the vertical portion of a panoramic shot, so front to back is also limited. It is not like shooting 4x5/8x10 in vertical with foreground interest and infinity at the top.

In fact, the only time I use tilt is for wide angle lenses (72mm and rarely 90mm).

All othe times, I use f16-f32.

I do use swing quite often.

Remember with movements, less is generally enough in landscape work.

[GPS]

I use a roll back, I first thought it might come from it. It might not press the film enough. But the others pictures present different "focus bulging"

...

If you have the other pictures with "different bulging" it is possible that you had the film not tightly wound (some roll film holders allow for that more than others). Try (if possible) to wind the film regularly or tighten it before the exposure.
Other possibility is that you forgot to tighten a standard after tilting it.

[Nioukie]

Lachlan, thanks for your answer. I'll try to pay attention about swinging and have very light fingers on my camera's movements

GPS, I think it's not possible to tighten the film before exposure because there's no stop on the Shen Hao roll-film the shop rent to me. (I mean something like a notch to stop the film from a 617 view to the next one).

By the way, because you're very patient with me ( thanks for that) one more question : do you use the f-stop (focus spread) method which explained here http://www.largeformatphotography.info/fstop.html#result2

All the best

[GPS]

...

GPS, I think it's not possible to tighten the film before exposure because there's no stop on the Shen Hao roll-film the shop rent to me. (I mean something like a notch to stop the film from a 617 view to the next one).

By the way, because you're very patient with me ( thanks for that) one more question : do you use the f-stop (focus spread) method which explained here http://www.largeformatphotography.info/fstop.html#result2

All the best

I'm not familiar with the Shen Hao roll film holder but perhaps you can tighten the film by holding one knob firmly while trying to wind the other (like it is possible with Fotoman cameras)?
And no, I'm a bad boy and I don't use the mentioned method. For landscape photography I look at the gglass, use some movements if necessary and do that without math in my head taking away the concentration. I'm too full of the composition I need and do the rest (even the exposure measuring) like in a trance. But I've been in photo business the last 30 years and there was a time that I did a lot of math with my pictures too.

Your scene is not difficult and shouldn't need any math. I think you had some unwanted tilt on your standard and if you take the scene again with more care you'll get it right. Either that or the film was somehow out of the rails or so.