big-guy Loc: Peterborough Ontario Canada

Correct me if I am wrong but to my understanding when using an APS-C sensor, the apparent focal length changes but the effective aperture setting remains constant. In other words, f 8 is f 8 whether on FF or APS-C but the DOF changes to coordinate with the apparent focal length. Correct? (it's the aperture I am questioning, not DOF)

DOF calculated results:
-FF 100mm at f 8 focused at 20' gives a DOF of 4.47' (near 18', far 22.5', total DOF 4.47', hyperfocal distance 178.6')
-APS-C (Canon 1.6) 100mm at f 8 focused at 20' gives a DOF of 3.68" (near 18.3', far 22', total DOF 3.68', hyperfocal distance 216.2')

Screamin Scott Loc: Marshfield Wi, Baltimore Md, now Dallas Ga

The only thing that changes is the Field of View (FOV)of the lens when used on an APSC sensor camera.

Armadillo Loc: Ventura, CA

Scott,

:thumbup: :thumbup:

It is similar to taking a 35mm film camera and it's 100mm lens with a single 35mm chip of film, then replacing the 35mm film with a 16mm film chip.
On the 35mm chip you project the image from the outlet lens of the 100mm lens onto the 35mm film chip. The only change when the 16mm film chip is used is a smaller recording of the same field of view from the 100mm lens. The projected image is still the same physical size, only the physical size of the film chip has been reduced.

Consider this option. Take a 35mm slide projector with no slide in the projector. Place the projector 5 feet away from the wall and turn on the projector. Now focus the white rectangle on the wall so the rectangle edges are sharply focused.
Assume, for the moment, the rectangular projection is 3 feet horizontal x 2 feet vertical. Allow that to represent a full frame digital sensor. Now take a sheet of blue, standard, paper measuring 8.5" x 11". Place the paper into the projected white rectangle on the wall. This represents the APS-C crop sensor and what it can record of the original scene projected by the lens.
There is no change in focus, or Depth of Field. The only change is the perceived enlargement of one section of the original scene by the smaller sensor.

Michael G

tinplater Loc: Scottsdale, AZ

What bothers me about this is people speak of the "extended reach" of a telephoto on a cropped sensor lens, when in reality you achieve the same effect by cropping the image on a full frame camera. If there really was greater true telephoto effect, the tinier the sensor the more powerful your lens becomes.

Linda From Maine Loc: Yakima, Washington

Not everyone can afford a full frame camera and long lens, or has the ability or desire to carry around that kind of weight. Bridge cameras such as the Canon SX-50 are a wonderful alternative. I think most folks understand they give up some image quality, but price and ease of use make it well worth it.

Screamin Scott Loc: Marshfield Wi, Baltimore Md, now Dallas Ga

That is correct, but the upside of using an APS-C sized sensor camera is that there is no loss of pixels as cropping a full frame sensor would entail. Other than teles & macro lenses, there is no other advantage of the smaller sensor. I shoot a lot of macro & even with the smaller senor, I crop a lot as many of my subjects (insects) are only about 6mm long. If i had to use a full frame camera, the final crop would wipe out any gain from the larger pixels.

Screamin Scott Loc: Marshfield Wi, Baltimore Md, now Dallas Ga

What to use really depends on any number of factors, some of which you touch on. Remember that you are also giving up on features (like fast apertures for subject isolation) that the bridge cameras don't possess. I used to use a bridge camera but found the feature set didn't meet my needs.. If you are only posting images online, then yes, it doesn't always pay to have a DSLR. As for cost, buying used helps a lot.

Beercat Loc: Central Coast of California

Incorrect .........

A 100mm on a FF set to F/8 at 20' gives you 5' 10"

A 100mm on a APS-C 1.6X acts like a 160mm lens, set to F/8 at 20'
gives you 13"

Or ........

If you actually have a 100mm EF-s lens setting, set to f/8 at 20' gives you 3' 8"

big-guy Loc: Peterborough Ontario Canada

What are the numbers you refer to?? FF = 5' 10" vs APS-C = 13" and why the HUGE difference. My numbers were derived from a DOF app based on a Canon camera. Please explain.

big-guy Loc: Peterborough Ontario Canada

Then why does my DOF app give me different results? Results that seem to coincide with the 1.6 factor.

Tried on 2 other DOF apps and got the same results.

Screamin Scott Loc: Marshfield Wi, Baltimore Md, now Dallas Ga

As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance). This is because larger sensors require one to get closer to their subject, or to use a longer focal length in order to fill the frame with that subject. This means that one has to use progressively smaller aperture sizes in order to maintain the same depth of field on larger sensors. The following calculator predicts the required aperture and focal length in order to achieve the same depth of field (while maintaining perspective).
This was copied from this website...
http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

Beercat Loc: Central Coast of California

I use the site most go to for calculating DOF. Make sure you use the right camera.

For full frame I would recomend the Canon 5DII/III. For APS-C use the 7D which is 1.6X

dsmeltz Loc: Philadelphia

I am interested in this topic, but is a lot more complex than it appears. There is an difference in DOF between APS-C and FF with the same lens at the same aperture and distance. I am not really good with the rather complex reasons for this, but I am sure someone will enlighten us soon.

This is where the techies come in.

big-guy Loc: Peterborough Ontario Canada

My error, your error, but neither addresses the original aperture question. I inadvertently clicked on the 1D MII which is not FF but is actually an APS-H sensor size. However, your readings for an APS-C are way off. 13"? Really?
What might the site that "most go to" be? DOFMaster.com?

The cameras now used for my calculations are the Canon 1Ds MII for FF and the 50D for APS-C (1.6 crop factor)

Using your suggested cameras I get
5DII 5.88' DOF vs. 1DsII 5.88' DOF (same)
7D 3.68' DOF vs. 50D 3.68' DOF (same)

I also get the same results using http://www.dofmaster.com

Beercat Loc: Central Coast of California

oops 17"

I'm getting old, my eyes are not the best, thank goodness our cameras have adjustments to deal with it.

Canon 7D is a 1.6X crop ;-)