D.O.F Question?

[mandonbossi]

Hi, I am new to this forum and was hoping someone could help a little with a few questions with regards to D.O.F (or lack of).

Be warned, this may a really stupid, basic question as I am still very new to all of this..

I have a Chamonix 45 and use a Sinar Roll Film back as well.. One that is able to change from 645 format to 612. If you were shooting in a horizontal format is it fair to say that D.O.F is the same across all formats? 67, 69 and 612? And that this only changes when you place the back in a vertical position?

If you were shooting a landscape for example in horizontal format, you could get equivalent sharpness from front to back with say f16 while if you kept the same camera position but changed the back to vertical, then you would need a much smaller aperture (say f32 or so) to obtain sharpness..

Is anyone else able to clarify this? Or am I totally missing something here?

Ok, thanks so much. Look forward to hearing from you. best Mandon

[mandonbossi]

Ooops, the other question I had on a similar front is not so much largeformat related but i hope someone can still help me. I am looking at getting a Makina 67 rangefinder that has an 80mm 2.8 lens. If you were shooting this wide open would it give a similar look in terms of the "lack of depth" to say the Mamiya RZ 110mm 2.8, which is considered the "standard" lens for that camera? or a Hasselblad 80mm 2.8 (I realise this is square format) The images I see with the Hasselblad 80mm 2.8 when shot wide open seems to have a very dramatic drop off but i don't see these examples so much with the rangefinders.. I have to admit that this is only going off things seen on flickr, which is my main reference for examples of the "look" of different lenses..

I was looking at the Mamiya 7 but the 80mm is only a f4 and doesn't have a very dramatic drop off in depth..

Or are rangefinders different somehow?

If anyone has any thoughts or suggestions i would be very grateful for clearing this up.. Ok, thanks a lot. Cheers Mandon

[MIke Sherck]

Hi, I am new to this forum and was hoping someone could help a little with a few questions with regards to D.O.F (or lack of).

Be warned, this may a really stupid, basic question as I am still very new to all of this..

I have a Chamonix 45 and use a Sinar Roll Film back as well.. One that is able to change from 645 format to 612. If you were shooting in a horizontal format is it fair to say that D.O.F is the same across all formats? 67, 69 and 612? And that this only changes when you place the back in a vertical position?

If you were shooting a landscape for example in horizontal format, you could get equivalent sharpness from front to back with say f16 while if you kept the same camera position but changed the back to vertical, then you would need a much smaller aperture (say f32 or so) to obtain sharpness..

Is anyone else able to clarify this? Or am I totally missing something here?

Ok, thanks so much. Look forward to hearing from you. best Mandon

The depth of field is not dependent on film format or orientation. The depth of field will be the same regardless of whether the film is in horizontal or vertical orientation, and for any film format. For example, the depth of field of a 90mm lens at f/8 focused on a subject 20 feet away is exactly the same taking a photo on 35mm film as it is taking the picture on 4x5 film.

The only reason you might need to increase depth of field when changing from a horizontal to vertical composition (or vice versa) would be if the film was not in exactly the same plane as the image from the lens; if the front or back were tilted, for example. Depth of field is solely based on the focal length of the lens, the aperture used, and the focusing distance. Film size or orientation has nothing to do with it.

In a small format camera the film plane and the image plane thrown by the lens are fixed by the camera manufacturer: the film or lens can not be tilted respective to each other. A view camera can tilt the film plane or lens plane relative to each other, and that allows you to do things such as have the bottom of the image in focus and the top out of focus, but you do that by using camera movements. If the film isn't exactly in the same plane as the lens, you may need to increase depth of field in order to get the same apparent sharpness across the entire film, but that's because there's some tilt of either the film or the lens. As the photographer, it can sometimes be easier to correct the problem by increasing depth of field than by using camera movements to get the film and lens planes parallel. This is one reason why some large format photographers prefer cameras with markings which indicate when the front and rear standards are aligned parallel.

Regarding your second question, a shorter focal length lens will, at a given aperture and focusing distance, give a greater depth of field than a longer focal length lens. Thus, at the same aperture and distance, an 80mm lens will give a different look based on depth of focus than a 110mm lens. The difference may not be significant to you, and there are other factors participating in a lens' "look" besides focal length. For example, a lens with fewer or more aperture blades will give a different "look". Also, lenses have different formulas (different number of lens elements, different curves, different types of glass, etc.) which have an effect. The only real way to tell is to try them both and see what you prefer. The best way to tell is by making an enlarged print of the scene with each lens; trying to tell by looking at the negative, even with a loupe, is something that comes with long experience.

Mike

[BetterSense]

The depth of field is not dependent on film format or orientation

Actually it is dependent on film format because different circles of confusion are used for different formats.

[Nathan Potter]

Well yes, sort of. Different lenses are generally used for different formats and the tolerable COC is usually specified by the user. But to keep it simple, Depth of Field is a function of the lens only. Makes no difference whether vertical or horizontal format as long as the lens covers the format.

You can compute the Depth of Field of a lens using a simple equation well known to photographers.

DoF =2u^2NC/f^2 where u = object distance
N = f number
C = Circle of Confusion diameter
f = lens focal length

BTW if you are not a math freak, u is squared and f is squared.

keep all units the same - mm., in., ft., etc.

Nate Potter, Austin TX.

[rdenney]

Depth of field depends on how large a print you want to make and the viewing standard for that print.

If you want to make 16x20 prints, for example, and you want the viewer to be able to see what appears to be a sharp image at minimum viewing distance, then you will need to resolve about 5 lines/mm on the print. That corresponds to a circle of confusion of about 0.2mm on the print.

Then, you divide that print circle of confusion by the enlargement ratio. I'll compare two roll-film formats that have the same shape, because changing shape requires you to decide which dimension is the important one in terms of print size. So, let's compare 645 to 6x7, which are similar enough. 645 printed to 16x20 is a 10x enlargement. So, if you set 0.2mm as the print standard, you must use a 0.020mm circle of confusion for your depth of field calculation.

For 6x7, you need a 7.5x enlargement to make a 16x20. So, the circle of confusion you need for that image is 0.026mm.

(For 6x12, the width is around 112mm, and if you print the width to 20", you need a 4.5x enlargement. The needed circle of confusion would therefore be 0.044mm.)

Then you can plug these circle of confusion values into your favorite depth of field calculator. I use DOFMaster, but I calculate my own circle of confusion. My print standard is 16x20, and DOFMaster standardized on 8x10. Thus, I need circle of confusion values that are half of what they use.

Just to provide some examples using the above circles of confusion:

For a 645 camera with 75mm lens focused at 20 feet, the depth of field at f/16 is 15.5 feet.

For a 6x7 camera with a 105mm lens focused at 20 feet, the depth of field at f/16 is 9.53 feet.

For a 6x12 camera (printed to 20" in the long dimension) with a 125mm lens focused at 20 feet, the depth of field at f/16 is 11.9 feet.

The calculations above are from DOFMaster. There are alternative calculations, but these are fine as long as you go in with your own circle of confusion standard.

If you want to make bigger prints, the larger enlargement ratios will result in smaller circles of confusion and less depth of field. If you are happy with smaller prints, the reverse is true.

(I can't resist a bit of reductio ad absurdum. Let's compare a 15x23 APS-C digital sensor to an 8x10 camera, both printed to 16x20. The enlargement ratio for 15x23 (printed to the long dimension) is 22x. The target c of c at the sensor is therefore .009mm. With a 28mm lens at f/16--with the acknowledgment that diffraction might overwhelm the effect--the depth of field at 20 feet will be infinite, from 9.5 feet to infinity. But the lens and sensor will have to deliver 22x5=110 lines/mm. Good luck with that one.

For 8x10, the enlargement ratio is 2x, so the c of c will need to be 0.1mm. A 300mm lens at f/16 will provide only 4.2 feet of depth of field to that standard. But the lens and film would only have to deliver 2x5=10 lines/mm. All life is a trade-off.)

Remember that the image is only really focused on the focus plane, no matter what your aperture. The smaller aperture reduces the size of the blurred rendering of a point away from the focus plane. If it reduces it small enough so that it looks like it is focused in a print, we say that it is within the depth of field. The boundary between just inside that limit and just outside it may not be visible in many cases. In any case, that boundary is not a law of physics--it sits right where you put it.

Rick "who has DOFMaster on his iPhone, but selects c of c rather than film size when using it" Denney

[Brian Ellis]

Depth of field is affected by three things and only three things: focal length of lens, aperture used, and distance from subject. How the resulting depth of field appears in a print is affected by the size of the print, the distance from which the print is viewed, the lighting on the print, the viewer's visual acuity, and other similar variables. There have been many discussions of depth of field here, if you search using that term you'll be able to learn more than you likely want to know about the subject.

[Jack Dahlgren]

I have a Chamonix 45 and use a Sinar Roll Film back as well.. One that is able to change from 645 format to 612. If you were shooting in a horizontal format is it fair to say that D.O.F is the same across all formats? 67, 69 and 612? And that this only changes when you place the back in a vertical position?

Yes, the depth of field at the film plane is the same regardless of what film is sitting there. However when you enlarge the film, the situation changes. I have no idea what you are talking about in horizontal and vertical. It makes no difference. Lenses are generally symmetrical around the center axis.



If you were shooting a landscape for example in horizontal format, you could get equivalent sharpness from front to back with say f16 while if you kept the same camera position but changed the back to vertical, then you would need a much smaller aperture (say f32 or so) to obtain sharpness..

Is anyone else able to clarify this? Or am I totally missing something here?


You are totally missing something. Or, rather you have something extraneous which is untrue and I don't know where it came from.

Large format has the advantage of generally being able to change the film plane to allow the focal plane to either match your subject (think of a field stretching out or a flat building) or to not match it (giving a selective focus). If that is what you are thinking about, I'd recommend getting your camera out and looking through the ground glass and see what happens when you tilt the front in different ways.

[Jack Dahlgren]

I am looking at getting a Makina 67 rangefinder that has an 80mm 2.8 lens. If you were shooting this wide open would it give a similar look in terms of the "lack of depth" to say the Mamiya RZ 110mm 2.8, which is considered the "standard" lens for that camera? or a Hasselblad 80mm 2.8 (I realise this is square format) The images I see with the Hasselblad 80mm 2.8 when shot wide open seems to have a very dramatic drop off but i don't see these examples so much with the rangefinders.. I have to admit that this is only going off things seen on flickr, which is my main reference for examples of the "look" of different lenses..

I was looking at the Mamiya 7 but the 80mm is only a f4 and doesn't have a very dramatic drop off in depth..

Or are rangefinders different somehow?

If anyone has any thoughts or suggestions i would be very grateful for clearing this up.. Ok, thanks a lot. Cheers Mandon

Rangefinders are different in that your focusing is based on the rangefinder so getting a narrow depth of field just right is harder. You don't see what the image is going to look like. Because of this I'd expect that fewer rangefinder photographers chase that look, or don't use a rangefinder for it. They are safer stopping down a bit and get better resolution as well. Rangefinders can do it, but they are not the optimum tool for that sort of work.

If you are looking for dramatic drop off in DOF, use some tilts on LF with a fast lens or do what many digital photographers do and add it in Photoshop.

[rdenney]

I am looking at getting a Makina 67 rangefinder that has an 80mm 2.8 lens. If you were shooting this wide open would it give a similar look in terms of the "lack of depth" to say the Mamiya RZ 110mm 2.8, which is considered the "standard" lens for that camera? or a Hasselblad 80mm 2.8 (I realise this is square format) The images I see with the Hasselblad 80mm 2.8 when shot wide open seems to have a very dramatic drop off but i don't see these examples so much with the rangefinders.. I have to admit that this is only going off things seen on flickr, which is my main reference for examples of the "look" of different lenses..

I don't recall if the Mamiya 7's have shutters in the lenses or a focal-plane shutter in the camera. I suspect the former, which does constrain the maximum size of the aperture in some cases, especially with longer lenses. Also, the limits of the rangefinder accuracy suggest a smaller maximum aperture to allow a modicum of depth of field to cover any slight mistakes.

But if you want less depth of field, use a longer lens in addition to a wider aperture. The f/2.8 maximum aperture on most 80mm-100mm normal lenses for medium format is not really that fast. Mamiya makes an f/1.9 lens in that focal length range for their 645. Pentax's 105 normal for the 6x7 is an f/2.4--a third of a stop faster than usual. But another option is to keep the same aperture ratio but use a longer lens. Here, the shutters in the lenses are a constraint. Most longer lenses for cameras like the Hasselblad are at least f/4, just as with the Mamiya rangefinder.

Carl Zeiss Jena (East German in the communist days) made a 180mm f/2.8 Sonnar lens for the Pentacon Six line of cameras. It will also work on the Exakta 66 and the Kiev 60. I would not recommend any of these for non-tinkerers. But it can be adapted pretty easily to both Mamiya and Pentax 645 cameras. At 180mm, f/2.8 is pretty quick indeed, especially for medium format. Zeiss (West German) made a 180/2.8 Sonnar for the Hasselblad 2000 and 200-series camera. It has no shutter and must be used on a camera with a focal-plane shutter.

Without tilting the lens, this is about as narrow as one can get. There are very fast lenses for small format that emulate the look, but at high prices and with more limited enlargement capability. And with very large format, it doesn't take that low an f-number to narrow up the depth of field to a greater extent. But then you have to deal with the inconvenience of the large format.

Rick "who maintains Pentacon Six-mount systems just to have access to the Arsat fisheye and the CZJ 180/2.8 Sonnar" Denney

[Jack Dahlgren]

Without tilting the lens, this is about as narrow as one can get. There are very fast lenses for small format that emulate the look, but at high prices and with more limited enlargement capability.

There are a number of fast cheap 35mm format lenses. You can pick up a manual focus Nikkor 55mm f/1.2 for a few hundred $US. Only the new fast lenses or exotic old ones are expensive. The thing is that they do start to get soft all over when wide open.