Portraiture apertures in 6x7

[alex_z]

Well, yet me again. :-)

Reading through online resources on MF I realize that DOF-aperture

relationship in MF differs from that of 35mm in terms of actual DOF at

given aperture. For instance, at any given aperture the DOF in MF is

more shallow then in 35mm at the same aperture and this is going

further with bigger formats (6x4.5, 6x6 and 6x7).

 

The question is related to portraiture, where DOF si improtant.

If say, in 35mm, I do portraits in the range of f/2.8-f/5.6 (mostly

f/2.8-f/4) using my 70-200/2.8 lens, what would be the equivalent

aperture to achive similar DOF shallowness in 6x7 ? (so far I have

100mm standard lens only, but plan to expand my line by 200mm soon

(equivalent to about 100mm in 35mm format))

What are the most useful apertures for portraiture in 6x7 from your

experience ?

 

Besides the direct interest in this issue, I also try to figure the

implications of this to flash photography given manual, auto-aperture

flash utilization. Most of teh flashes of this kind offer very limited

apertures range (usually f/2, f/4 and f/8, sometimes also f/11).

I intend to acquire Sunpak 383 unit, but its range is f/2, f/4 and

f/8, so a suspision has raised in my mind that available apertures

choice may not be enough for a flexibility in portraiture to control DOF.

 

What do you say ?

 

Regards, Alex

[jbq]

Approximately, for a given distance, angle of view and print size, the depth-of-field is related to the diameter of the aperture (i.e. a 200/5.6 on 6x7 will have about the same depth-of-field as a 100/2.8 on 35mm). If you focus very close or very far, this isn't quite true and the bigger film has less depth-of-field.

[joey]

Depth of field is dependent on focal length, aperture, and focusing distance. The film format has nothing to do with depth of field. A Canon 200mm lens at f/8 will have the same depth of field as a Mamiya 200mm lens at f/8. The difference in focusing distance is negligable in the case of most portraits.

 

There is an apparent difference in depth of field between the two formats because to get a "normal" framing with 35mm you'd use a 50mm lens, but with 6x7, you need a 90mm lens. The 90mm lens has less DOF than the 50mm, therefore the appearance of the larger format having a shallower depth of field.

 

For head/shoulders and 3/4-length portraits, I usually use f/5.6 or f/8 with my 90mm lens (on 6x7). This setup works well for me, although f/5.6 is pretty shallow so you need to be careful with your focusing.

[steven_muncy]

Like many people who started with 35mm photography, I keep translating when using a

different format. This is probably not the best way, but I can't seem to get away from it.

 

I use lenses in the 50-135mm range in 35mm and very similar angle of view for larger

formats. Most of my images are portraits at typical distances. Infinity and very close focus

I'm sure go outside this "rule of thumb". (more technical photographers will point out the

problems).

 

The normal lens is:

35mm = 50mm

645 = 70mm

67 = 90mm

4x5 =150mm

 

divide the 35 normal into the new format - decrease the aperature by that amount in

stops.

35mm = no change

645 = 1.5 stops

67 = 2 stops

4x5 = 3 stops

 

This works for me with any lens in that format. So when I use a 90mm at f/4 in the 35

format, I get a similar image with a 180mm at f/8 in 67 format.

 

Best wishes

[john_stockdale2]

For the same angle of view and same shooting distance and same print size, the MF lens will have to be stopped down about 2 stops to achieve the same DoF.

 

I don't know much about auto-aperture flash. I wonder if you can alter the effective range of set apertures by altering the film speed on the flash.

[vijay_nebhrajani]

My understanding is that DOF for a lens of given focal length at a given aperture at a given print size <i>increases</i> with format area.

<p>

This is simple to deduce: for the same focal length and the same aperture, the size of the circle of confusion will have exactly the same relationship with the deviation from actual plane of focus. In other words, the increase of diameter of the circle of confusion as the subject moves away from the plane of focus is exactly the same for two 50mm lenses at say f/8, one for 35mm and one for 6x7. Since the 6x7 has to be enlarged less to achieve the same print size, it will show greater depth of field.

<p>

I know this seems counterintuitive but it is true nonetheless. Just compare the barrel markings for a 35mm lens and a medium format lens of the same focal length.

[russ_britt1]

F/8 on a 150mm lens on a hassey will have the same depth of field as F/8 on a 150mm lens on a 35mm camera. You will get a different field of view on the two formats. The lens will work the same ,it does not care what size of film is behind it.You will probally be using a longer lens on the hassey to get the same field of view and thats where the difference happens.

[bueh]

Hey Alex, I use this neat program for all my depth-of-field calculations: <b><a href="http://tangentsoft.net/fcalc/">f/Calc by Tangentsoft</a></b>. Free, quick and easy.

[john_stockdale2]

and when you're calculating DoF, remember that the circle of confusion is arbitrary and you need to test to see if the criterion meets *your* criterion of sharpness. As is often said, DoF markings on lenses can be very optimistic, and fine for postcard-sized prints

[helenbach]

Apart from close up, depth of field varies linearly with the size of the circle of confusion (ie double the diameter of the circle of confusion (CoC) and you double the depth of field) and inversely with the square of the focal length (ie double the focal length and you quarter the depth of field).

 

In general this means that, at any given aperture:

 

a lens of a given focal length will have more dof with MF than with 35 mm (because the CoC can usually be larger), and

 

a lens having the same angle of view will have less dof with MF than with 35 mm (because the change in focal length more than outweighs the change in CoC).

 

Best, Helen

[russ_britt1]

The best way to learn photography is to take pictures, not do math! As I said in an earlier post the lens does not care what film is behind it, it works the same if using the same focal length from the same distance. You usually use longer focal lengths from closer distances with larger formats. That is what causes the depth of field to be different, not a math formula or film size.It is easier to correct a lens for a smaller format so some of the 35mm lens are better corrected. To answer your question when I shoot portrats with my 150mm on my Hassey I usually shoot around f5.6-f8 which is about the same as what you said you ar doing with a 35mm with the same focal length lens.

[helenbach]

Russ, an understanding of optics (which needs a little, very basic, maths) does not prevent you from learning from practical experience and combing the two in a greater understanding of what is going on.

 

However, I suspect that if you had understood what I wrote, you would see that we are saying similar things in terms of using the same focal length at the same aperture on different formats.

 

To answer the original question: in 6x6 and 6x7 portraiture I tend to use my lenses wide open - so it's f/2.8 with a Rolleiflex, Makina or a Mamiya Press, and f/4 or 4.5 with a Rolleiwide, Tele-Rolleiflex or Mamiya 7.

 

Best, Helen