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
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
hello !Originally Posted by Nioukie
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 ;-)
Thanks Emmanuel for this accurate answer !
Next time, I'll write in "la langue de Molière" !
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.
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
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.
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!
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...
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.
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.
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