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    Infinite focus - explaination and options
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    Hi,

    I recently got a GH2 and love it. My first lens was the Olympus 45mm 1.8. I love it for the quality and shallow dof.

    I will shoot mainly video, and their will be times when I don't want to worry about the shallow dof and have most/all of the frame in focus.

    I've been researching non-stop for a week, but I must admit that I don't yet fully understand what to look for in an lens to achieve this. I know that setting a higher aperture will increase the dof, but I'm not sure how far you can take it (does a better light rating offer wider dof option I'm guessing) and what other factors affect it.

    I'd really appreciate a more detailed explanation and some suggestions. I'm looking at the 14mm or 20mm Panasonic pancakes as a possible next option, along with some of the more expensive options for better low light performance.

    Thanks.


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    A wide lens along with a stopped down iris (higher number) will give you the most DOF. Those are the only two factors that affect DOF in a lens, though this depends on it's relation to the sensor -- the smaller the sensor, the more DOF you get.

    Whether a lens is fast (has a low f stop rating) is irrelevant in this application, since you'll be stopping down the iris anyway. You'll need plenty of light in order to do this. However, try not to go past an of f stop of 8, because lenses have less resolving power past that point.
    Last edited by Matt Hoss.; 10-14-2012 at 02:41 AM.


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    Thanks Matt. It's interesting. I have the 45mm Olympus and just bought the 20mm Panasonic. With both, I first setup a scene with a person maybe 15 foot from the camera with a high aperture setting which blew out the background. I then took the aperture as low as possible (in steps) and the bokek blurred background wasn't affected noticeably.

    Both times this was indoors with a fair amount of sunlight. I'm sure outside it would be somewhat different, but the results were so far off that I wonder if I could even get what I'm looking for indoors with a high quality 14mm.

    Obviously, this is where video cams shine.


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    Use the GH2 ETC, Extra Tele Conversion mode. It uses a smaller part of the sensor and gives the look of a wider DoF. You need wider lenses though.


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    Senior Member Bruce Foreman's Avatar
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    James.

    I posted this explanation over on the other site, but here it is for anyone who finds it useful.

    Indoors I've found both the 20mm and 14mm to be excellent performers. If you're after deeper DOF (deeper zone of acceptable sharpness) you're going to need more exposure (light) indoors. Two ways to do this:

    Add light with lighting equipment (best quality), or raise the ISO. There will be limits to how far you can raise it without getting potentially objectionable noise.

    When I work indoors and can't (or don't want to) use extra lighting, I try to use the 14mm because even at maximum aperture (f2.5) the wide angle gets me a rather deep focus zone. Working distance with that lens affects the zone of focus also.

    Outdoors you're going to run into another problem. Too much light and without ND filtration you may find yourself having to use an aperture that's too small. Two problem areas with this:

    Your zone of focus may be way too deep for what your want to show, and at minimum or near minimum apertures you begin to run into the "diffraction" effect. This is where the image forming rays begin to "scatter" and "diffuse" to some extent and don't travel in the same straight lines they do at larger apertures.

    The result is the appearance of some diffusion in the image rendering it softer than normal. Edge outlines won't look as sharp as they should and there may be a slight loss of contrast. I got "bit" by this very badly when I forgot to reset my ISO from where I had it the night before. The images took a lot of work in PhotoShop (unsharp mask and contrast adjustment) to make them look normal.

    Solution: ND filters. I keep 0.6ND, 0.9ND, and 1.2ND in the bag (2 stop reduction, 3 stops, and 4 stops respectively). I can't use a hood on the 14mm without some vignetting, I have to use a wide angle hood on the 20mm (it's a "wide" normal field of view), and a deep hood on the 45mm.

    I do avoid the use of variable ND filters as Lumix lenses seem to be very susceptible to internal reflections from filters and the variables are 2 pieces of glass adding FOUR potentially reflective surfaces.


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    Quote Originally Posted by JamesL View Post
    Hi,

    I recently got a GH2 and love it. My first lens was the Olympus 45mm 1.8. I love it for the quality and shallow dof.

    I will shoot mainly video, and their will be times when I don't want to worry about the shallow dof and have most/all of the frame in focus.

    I've been researching non-stop for a week, but I must admit that I don't yet fully understand what to look for in an lens to achieve this. I know that setting a higher aperture will increase the dof, but I'm not sure how far you can take it (does a better light rating offer wider dof option I'm guessing) and what other factors affect it.

    I'd really appreciate a more detailed explanation and some suggestions. I'm looking at the 14mm or 20mm Panasonic pancakes as a possible next option, along with some of the more expensive options for better low light performance.

    Thanks.
    I would strongly suggest you get one the following apps... unless you don't have an iPhone... parish the thought... Toland or pCam, both will allow you to calculate for a given camera such as the GH-1/2, a given lens, such as 45mm, and the calculator will give the Depth of Field for various subject to camera distances.

    There are also 'online' calculators that do this as well... since I've gotten the mobile apps, I've not kept up with the online calculators...

    The thing to remember about f-stops are 1) the markings on the lens for most DSLRs is only a 'hint'... 2) going below 3-4 stops for a given lens will lead to 'diffraction' degradation of the image... 3) the further the subject is from the lens, the deeper the DoF.


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    Senior Member Bruce Foreman's Avatar
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    Quote Originally Posted by j1clark@ucsd.edu View Post
    2) going below 3-4 stops for a given lens will lead to 'diffraction' degradation of the image...
    In a purely practical sense this is going to take place mostly at the minimum aperture or two (depending on the lens). The one time I got "bit" badly by this was when I neglected to reset my ISO after having it set high for a party the night before. Sleepy eyed the next morning I began shooting living history "re-enactors" in bright sunlight with the ISO still set at 1600 (highest that camera would go) and paid little attention to the fact I had to switch to PROGRAM mode to not be fighting camera settings.

    With the 18-55 "kit" lens when I looked at settings displayed on the images I was getting f32 and f22 on a lot of shots and caught the error. The affected images were visibly soft, some had a "dark halo" effect and most had a somewhat diffuse look to them. Fortunately I had started shooting RAW that week and that and Unsharp Mask in PhotoShop saved me.

    I never made that mistake again. But the minimum physical aperture did that.


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    Use a hyperfocal lens to get a large area in focus. The Panasonic 14mm is excellent for this. There are many hyperfocal calculators online, but basically, you will notice a huge difference with a hyperfocal lens, and the 14mm is very sharp as well. Olly 12mm, even slightly better and more hyperfocal. A hyperfocal lens will mop the floor with a tele at the same F stop.
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    Quote Originally Posted by Bruce Foreman View Post
    Solution: ND filters. I keep 0.6ND, 0.9ND, and 1.2ND in the bag (2 stop reduction, 3 stops, and 4 stops respectively). I can't use a hood on the 14mm without some vignetting, I have to use a wide angle hood on the 20mm (it's a "wide" normal field of view), and a deep hood on the 45mm.

    I do avoid the use of variable ND filters as Lumix lenses seem to be very susceptible to internal reflections from filters and the variables are 2 pieces of glass adding FOUR potentially reflective surfaces.
    I started looking at ND filters and was wondering what you are using in terms of brand and model. For instance, I notice Tiffen has 3 different lines of ND filters in the 52mm size.

    Thanks in advance!


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