Toronto Photography Meetup Group

Geez, I hate the character-count limit in the subject line!

Here's what I wanted to put:

Will I still be able to get nice shallow depth of field if I switch from 35 mm film to crop-factor digital? (I have been eyeing the Lumix GH1 in particular.)

(A few of us were discussing this after the Jazz fest event, but I'd like to open it up for a broader dicussion.)

Over the years I have taken many photos like these two at the top of my flickr photostream:

http://www.flickr.com/photos/downtowndan

As you know, it's straightforward to achieve shots like this with a 35 mm film SLR; you just select a wide aperture and use a long-ish focal length lens.

What I'm wondering is... will I still be able to get shots like that if I switch to a digital camera that has a 1.6x or (gulp!) 2x crop factor (as with the GH1).

Does it get harder and harder to achieve such shots as the crop factor increases?

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On a more general note, are there other things that I'm gonna miss if I make the switch? (I imagine "not having to wait for the chip to digest the image after long night-time exposures" would be another one. And the ability to make pretty huge enlargements.)

Thanks for any comments!

Hi Dan,

From someone that started out using the Olympus system with the E-300 a few years back, I found it easy to use for having an extended DOF. However, after seeing the shallow DOF from many wedding photographers' work ... I craved the the isolation factor. With the 4/3s system it is a challenge to get that shallow DOF for a couple of reasons. First being that they are very few lenses that are below F/2.8, and those lenses that are ... are very expensive. The second reason is the 2x factor for DOF equivalence of 35mm reference. So the only way to get some great isolation due to DOF is to use zooms at close range. However, that is not always practical or even possible in cramped quarters.

There were a couple of lenses I was looking at which had an F/2 range which were the 14-35mm zoom and the 35-100mm zoom (which in reference to 35mm terms is 28-70mm and 70-200mm both at F/2). Both lenses are over $2K, and are very rare to be seen selling used (probably due to lower volume of sales compared to Nikon and Canon) ... and is still an equivalent to F/4 for 35mm DOF. There is also the Panasonic 25mm F/1.4 prime lens (50mm at 35mm reference), but of course its DOF would equate to F/2.8. All these lenses are great quality glass, I wouldn't question that aspect them at all. I did end up getting an OM 50mm F/1.4 for cheap and practiced using that to get shallow DOF on my E-3. However, when trying to use the lens where light is abundant, and shooting wide open to grab that shallow DOF, I ended up hitting the limit of shutter speed and overexposing.

This led me to a decision to get into Canon FF and I grabbed a 5D classic body. At F/4 on FF, I'm still getting a shallower DOF look than at F/1.4 on 4/3s ... and of course below F/2.8, the 4/3s can't match. One thing I would like to add to is that the bokeh on 4/3s just isn't that pleasing compared to FF. I know there is a discussion around number of blades and rounded blades adding to a more pleasing look, but there must be something around sensor size physics as well ... as I just do not like the bokeh on 4/3s compared to what I can accomplish on the FF.

My recommendation, if you like the DOF that can be had on film, then stick with a FF sensor.

Alan

I don't know about you, but I could, I don't see why not, in fact maybe even better with certain lenses I don't wanna start a heating discussion though

Looking at your squirrel and flower shots, no problem. With the G1 or GH1, you can even mount your old MC/MD glass with a adapter. An MD 50/1.4 will give you a nice short DOF. A 135/2.8 on a m43 body would give you the same FOV and DOF as the combo you had on the SRT with a 2x TC.

The tough part about getting short DOF with a crop sensor is when shooting normal or wide lenses. With longer lenses, DOF is often still razor thin... something that's painfully obvious when you're trying to shoot smaller moving objects like birds or insects.

I have used full frame, 1.3x, 1.5x, 1.6x and 2x crop bodies, and never have problem achieving the thin depth of field that I wanted. I guess a lot has to do with subject distance and the lens. Even on the Panasonic G1 (basically the same camera as the GH1), I don't have any problems with DOF.

Any FourThirds user can tell you that the camera with a 50mm f/4 will have the same field of view and DOF as a 100mm f/8 (on 35mm "full frame") due to the 2x multiplication factor.

If you want to look through tables of numbers, here's one listing the DOF distances for FourThirds lenses (there shouldn't be any difference in numbers for microFourThirds):
http://www.wrotniak.net/photo/tech/dof-43.html

Also you can learn a lot about FourThirds at:
http://www.wrotniak.net/photo/43/index.html

And there's a body-lens matching simulator if you want to check out what certain lenses will look like on a GH1 at:
http://www.four-thirds.org/en/products/ ... index.html




There is no crop factor with FourThirds (or microFourThirds) unless you are using a legacy lens (an older lens designed for 135/35mm cameras)...just like there's no negative crop factor when you use a medium or large format camera. The Lenses designed for FourThirds and microFourThirds are lenses specifically designed for that format and the smaller sensor, so there's no cropping involved.

There is a multiplication factor IF you want to think in terms of 135/35mm equivalence, but as you use FourThirds you stop thinking in terms of 135 format, even if you use a legacy lens; when I switched to 135 after years of using 6x6, I didn't think, "what would this 135 lens be on my 6x6?" I did learn on 135 what "normal" focal length (FL) was, what portrait FL was, wide and super wide, and from then on I stopped thinking in terms of my 6x6.

FourThirds users will probably rue that statement since most put up with the misused term "crop factor" from Canon and Nikon users, but since you are trying to learn about the format you might as well learn the reality.




If you have noise reduction turned on, with long exposures the camera will take a "black image" after it takes the photograph to use to subtract the noise from the photo...this will take more time, but can be disabled; I never used it myself unless I plan to take VERY long exposures (as in minutes), which I've never done. If there is noise I'll just use one of the noise plug-ins to get rid of it.

Wouldn't a crop sensor have a smaller "circle of confusion" (who came up with that term?) than a full-frame sensor? And if so, wouldn't the same focal length, same aperture, and same subject distance therefore give you a shallower DOF on a crop sensor than a full-frame sensor?

I think this site will be quite useful; even better would be a graphical presentation of the data, but if you plug in several values and play with it, you'd see that there should be no problem in getting the crop sensor cameras to give thin DOFs, just that the parameters required are different, and as others have mentioned, it would probably be easier to get thinner DOFs if you use a full frame or larger sensor.

As for the circle of confusion business, I think a good place (for me at least) to read about it is here, although it might appear a bit threatening to the tech/math/physics-averse...

No, just the opposite...with smaller sensor you'll have a deeper/wider depth of field.

For instance, with my tiny sensor ultra zoom here are two images, the top one at equivalent of 38mm (5.9 actual) and the bottom 380mm (59 actual):
http://img.photobucket.com/albums/0803/Mikefellh/OlyC700stuff/dof.jpg

Note that the background of the 380mm is not that blurred...that's because the actual focal length is 59mm, and even wide open that shot would have the equivalent DOF of f/22 instead of the actual f/3.5.

This link might be of interest to some:

http://www.cambridgeincolour.com/tutori ... -field.htm




So the smaller the sensor the larger it has to be blown up to reach 8x10" Another consequent of a smaller sensor is the need of the optics to resolve the same number of lines projected over a smaller area.

This gets real complicated really quickly take a pinhole it has infinite DOF but poor resolution so A little better is my P&S not terribly sharp but because the optics are wide angle to get a normal equivalent 50mm FOV it's hard to without getting very close to get a good background blur. Dof of field can be more or less calculated for lens aperature sensor combination yet DOF does not seem to be what Dan is looking at finding an answer to. It's seem to be the look and feel of a good shallow DOF shot. This is a combination of sensor size, sharpness, point spread function and Bokeh not just DOF. The smaller the sensor the more constrained you are at getting the type of shot he is looking to get.

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That is correct.

Notice that this is true for the "same focal length" rather than "same field of view".

The more you enlarge, the more obvious focus errors become, so for the same focal length, aperture and subject distance, you're basically enlarging more with a crop sensor than a FF35 sensor.

If you change the equation to same _FOV_, aperture and subject distance, then DOF increases instead.

The circle of confusion (CoC) is dependent on the lens (especially spherical aberration) and aperture designs, and not the sensor. Based on these factors, the same lens on two sensors, one large and one small, with the same pixel count, the smaller sensor would have a higher pixel density, and therefore more of the 'blur region' is resolvable, leading to a deeper apparent DOF.

To elaborate somewhat, the CoC is due to imperfections; in idealised optics, a point light source will be focussed to a point on the sensor (film/retina/CCD/CMOS) by the lens. However, the in the real world, lenses can never do that, thus there is a region around the central spot where there is a smear of light, and this smear is not necessarily circular (for a point source), but is affected by the aperture design and optical diffraction. This smeared out circle can be thought of as the CoC (for our discussion), although it is defined differently depending on who's using it.

Actually the perfect len has a COC what you are describing iswhat is happening when the point is at the correct distance to be projected onto the focus plane. This is more closely related to resolution. The COC is related to what happens to the point as you move it away from the focal plane. This point however good or bad starts to expand. An analog is the shape of the middle of an hour glass. The COC is a simple number to describe a complex process. It might be counter intuitive but COC could be equal for a sharp and a not so sharp lens.

I suppose this is what I get for learning my terminology from the internet

When I wrote "circle of confusion" I mean "the size of the circle that you get from a point being out-of-focus at which the out-of-focusness becomes noticable". (I called it "circle of confusion" because that's what the online DOF calculator called it.) What would you call that?

Thanks... hmmm... there is much to chew upon here!

Why don't you just organize a meet up and bring a couple of CF cards with you. Try out an Olympus camera and a FF camera (obviously shoot in JPEG) and review the images when you get home. Shallow DOF is no problem when you're outside and using longer lenses, but doing the comparison indoors with short focal lengths ... and that's where it will make or break which system fits your current desires.

Alan

Check out Gummiebear's shot using a f0.95 c-mount lens in the f1.2 thread for shallow DOF with a G1 and short focal length lenses.