Noob question about lenses & full frame

[salils]

So since this camera is full frame does that mean that I can shoot with slower lenses to get a similar depth field to smaller sensor cameras? ie: f4.0 on 5dmk2 ~ f2.8 on Nikon D90. I don't know the exact difference but is that how it would work? I don't really like to shoot wider than an f2.0 on my non full frame DSLR usually. So does this mean I should be ok buying glass that's a stop or 2 slower for my full frame camera and still have a similar depth of field?

 

[squig]

jah, f/2.8 D90 is roughly half a stop between f/4 and f/5.6 on the MKII for a comparable DOF.

 

[Emanuel]

That's why these FF35 options (options?) are a whole different world.

 

[KeithAndrews.TV]

You can use a slower lens with a FF camera and acheive the same DOF of a smaller sensor camera, but then again you can also use a fast lens with a high aperture and achieve the same results.

Now, just as a FF camera can give you shallower DOF as compared to a smaller sensor camera shooting at the same focal length and same aperture, the opposite is true for larger DOF with a smaller sensor. A smaller sensor camera shooting at the same focal length with an aperture of lets say f/11 or f/16 is going to achieve larger DOF than the FF counterpart can achieve shooting at the same focal length and same aperture. Make sense?

Take a look at this visual explanation:

http://www.clarkvision.com/photoinfo/dof_myth/

 

[morgan_moore]

I disagree that one can keep a look through large variation of chip size in day to day use when aperture must also be used to control light, and small apertures are affected by diffraction

check this

http://www.sammorganmoore.com/smmcom/format_test/index.html

IMO it is showing that to get a similar look you have to be comparing f8 to f2.8 which means you pretty quickly run out at either end



S

 

[KeithAndrews.TV]

True as you say about running out at either end. Wikipedia explains it pretty well:

DOF vs. format size

To a first approximation, DOF is inversely proportional to format size. More precisely, if photographs with the same final-image size are taken in two different camera formats at the same subject distance with the same field of view and f-number, the DOF is, to a first approximation, inversely proportional to the format size. Strictly speaking, this is true only when the subject distance is large in comparison with the focal length and small in comparison with the hyperfocal distance, for both formats, but it nonetheless is generally useful for comparing results obtained from different formats.

To maintain the same field of view, the lens focal lengths must be in proportion to the format sizes. Assuming, for purposes of comparison, that the 4×5 format is four times the size of 35 mm format, if a 4×5 camera used a 300 mm lens, a 35 mm camera would need a 75 mm lens for the same field of view. For the same f-number, the image made with the 35 mm camera would have four times the DOF of the image made with the 4×5 camera.

In many cases, the DOF is fixed by the requirements of the desired image. For a given DOF and field of view, the required f-number is proportional to the format size. For example, if a 35 mm camera required f/11, a 4×5 camera would require f/45 to give the same DOF. For the same ISO speed, the exposure time on the 4×5 would be sixteen times as long; if the 35 camera required 1/250 second, the 4×5 camera would require 1/15 second. The longer exposure time with the larger camera might result in motion blur, especially with windy conditions, a moving subject, or an unsteady camera. Adjusting the f-number to the camera format is equivalent to maintaining the same absolute aperture diameter.

The greater DOF with the smaller format can be either an advantage or a disadvantage, depending on the desired effect. For the same amount of foreground and background blur, a small-format camera requires a smaller f-number and allows a shorter exposure time than a large-format camera; however, many point-and-shoot digital cameras cannot provide a very shallow DOF. For example, a point-and-shoot digital camera with a 1/1.8″ sensor (7.18 mm × 5.32 mm) at a normal focal length and f/2.8 has the same DOF as a 35 mm camera with a normal lens at f/13.

I found another great article online with good visuals and lots of explanation:

http://toothwalker.org/optics/dof.html

 

[salils]

So in some sense Panasonic's GH-1 might actually be better in low light unless you plan to pull focus with an inch of depth of field which isn't practical.

 

[KeithAndrews.TV]

It depends on what you mean by "better in low light." From a low light performance perpective, the 5D Mark II will be a better choice due to it's larger sensor and low noise performance. Match it with a fast EF lens and you will be very impressed with the low light, low noise capabilities of the camera. It will be a more expensive investment however.

From an operational perspective, the GH-1 will reproduce greater depth of field at the same aperture when compared to the larger sensor 5D Mark II, which in turn would make racking focus easier in most cases. It all depends on what you are comfortable working with and what kind of look you are going for. In my opinion it's going to come down to budget, period.