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05-28-2012, 10:20 AM   #46
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Alamo5000

one more thing to remember and confuse you a little.

Depth of field has nothing to do directly with sensor size. Depth of field will be the same with a specific lens/aperture/distance for any format, when the same enlargement factor is used. The whole issue evolves around enlargement factor once the image is at the film / sensor depending on the format you enlarge it more or less when viewing,. with todays digital images, DOF is really an issue because the calculators all consider the image acceptably sharp when viewed on an 8inch by 10 inch print, but most of us actually veiw our images much larger than that.

For example I am wreiting this on a 22 inch monitor, which measures 13 x 19. OOPS

05-28-2012, 10:51 AM   #47
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Note also that DOF formulas are just approximations - they give a value for what will be "acceptably sharp" (a subjective determination) based on a "common" print size viewed from a "typical" distance. Don't expect everything in that range to still be completely sharp when pixel peeping.
05-28-2012, 10:52 AM   #48
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Cirlce of Confusion, look it up

Since APS-C always needs to be enlarged X times more then FF it's a constant.

is it 1,5 times?
05-28-2012, 11:40 AM   #49
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QuoteOriginally posted by Anvh Quote
Cirlce of Confusion, look it up

Since APS-C always needs to be enlarged X times more then FF it's a constant.

is it 1,5 times?
Yes it is 1.5 times the FF, assuming both are their respective full frame printed on 8 x 10.

crop in any more, and still enlarge to 8 x 10 or blow it up to a bigger print, from 8 x10 and it is no longer the same, because the definition of acceptably sharp is actually applied to the 8 x 10 print, not the sensor/film and the 20 or 30 microns at that level.

The real definition of acceptably sharp, on the basis of 30 microns CofC on film, is actually ~240 microns or 0.010 inch at the final print when viewed from a hand held type of distance.

regardless of what you do any time a point of light exceeds this, it is no longer acceptably sharp. That means you need to consider as well the 7.5 times enlarging ratio applied to film, or the approximately 12x enlarging ration applied to digital in your equation.

As a result, any depth of field calculator, aside from only being an approximation, is completely useless if you have not yet considered your final crop and enlargement rations.

05-28-2012, 12:32 PM   #50
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QuoteOriginally posted by Marc Sabatella Quote
Note also that DOF formulas are just approximations - they give a value for what will be "acceptably sharp" (a subjective determination) based on a "common" print size viewed from a "typical" distance. Don't expect everything in that range to still be completely sharp when pixel peeping.
Yes!! The calculator I used even says such. The thing I like about that calculator is it gives a rough approximation of what needs to be done..

I have another question which may (or may not) be related to this topic...

http://farm6.static.flickr.com/5164/5220706109_5b95c5179e_b.jpg

If you look at that photo it has almost a 3d effect to it. (found that pic on another thread---taken by poster planedriver)

https://www.pentaxforums.com/forums/attachments/pentax-k-5/77804d1291838124-n...-imgp1805x.jpg

(Another one by schimi76)

Both of those pictures appear almost 3D in effect....

How would one achieve such effect and 'depth' to photographs?
05-28-2012, 12:36 PM   #51
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Some more comments:

* DOF is a distance-range from the camera where image sharpness is acceptable. Bokeh is the quality of OOF (out-of-focus) areas in the image. These aren't necessarily related. DOF and OOF can be calculated; bokeh is subjective and, as mentioned, depends on many factors. There ain't no 'more' nor 'less' bokeh, nor even objective 'better' nor 'worse' bokeh. There's just bokeh we do or don't like. I like smooth bokeh with complex subjects, and itchy bokeh with smooth bland subjects. Your taste may vary.

* DOF is a complex product of photography, presentation, and perception. We *can* control the photographic bits: camera frame size, lens, aperture, distances, etc. We *might* control the presentation bits: where and how the image is displayed, at what size and angle and distance, in what light, with what framing and context. Unless we utilize brain implants or hypnosis, we *can't* control perception: visual acuity, attention span, psychoses, etc. So we do what we can in an imperfect world. Damn, if I ruled the world, everything would look nice...

* Is a straightforward way to handle DOF with MF lenses, especially wider lenses: Read the DOF scale on the lens and adjust by 1+ f-stops. This is ZONE-FOCUS; if the zone extends to infinity, it's HYPERFOCUS. The distance we set to establish the zone is PREFOCUS. Here are a couple examples:

--- I mount my Tokina-made 21/3.8 lens on my K20D. I'm shooting close; I want a DOF zone from 30-40cm, with all else OOF. I set the aperture to f/11 but adjust my reading by 1 f-stop, so I read distances at the f/8 marks. With 30cm and 40cm just inside the f/8 marks, my prefocus is about 34cm.

--- Same camera and lens, but I want hyperfocus, with DOF out to infinity. I set the aperture to f/11 again and read distances a bit inside the f/8 marks, say about f/7. This ensures that infinity *will* be in focus! With infinity inside one f/8 mark, I see that 3m is just inside the other f/8 mark, and the prefocus is about 1.7m. So my DOF range is 3m-infinity.

Such zone-focus is tricky with longer lenses, and short-focus-throw lenses; and most AF lenses lack DOF scales. IMHO it's really only useful with wider long-throw MF lenses. Good thing I love those, eh?
___________________________________

* Bokeh (as mentioned) depends on lens design, aperture size and position within the lens, number and shape of iris blades; and also on lens-to-subject and subject-to-background distances, lighting of subject and background, pixie dust, and lunar phases -- or so it seems! But interesting bokeh can be achieved with almost any lens by manipulating distances and light. If a subject is well-lit against a dark bland background, who'll notice itchy bokeh?

* Bokeh monsters! Many of us prize older 'preset' lenses because 1) they have more iris blades giving a more circular opening; 2) apertures may be placed more forward than with auto-aperture lenses; 3) older coatings and fewer optical 'corrections' give certain character to the images; and 4) they feel good. Consider these lens near-twins: I have two CZJ Tessar 50/2.8 lenses. One is a big black M42 auto-aperture guy with 5 iris blades, a common kit lens of its day. The other is a small aluminium Exakta-mount babe, a 1-ring preset aperture with 12 iris blades. Same maker; same optical formula; rather different rendering. The M42 is... nice, average, meh. It usually stays home. The other has 'pop', creamy bokeh, and is with me always.

* A fast wide-aperture lens may or may not have 'better' bokeh. But a wide aperture means more if the image will be OOF than with a tighter aperture. Its bokeh may be more visible. What you *do* with those OOF areas is up to you.

OK, enough of my DOF+bokeh rant for now. Have fun!
05-28-2012, 12:59 PM   #52
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Can't have fun yet. Camera won't arrive until tuesday afternoon.

I will be on a work trip until Friday.

@RioRico please check out the images I included in the post directly above your last post...those '3D' type image... how would one go about creating such an image? In those photos there is NO out of focus areas to speak of but the depth perception in the images is very real...
05-28-2012, 01:22 PM   #53
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Small aperture?

05-28-2012, 01:27 PM   #54
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Perspective is what brings depth in those images
05-28-2012, 02:08 PM   #55
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What I see in those photos:

* Very thick DOF (tight aperture) and
* Wide-normal focal length (24-30mm on APS) and
* Careful attention to light (modeling, to avoid a 'flat' look) and
* Perspective and composition (sufficient separation between near and far)
* Also, contrast seems pumped just a bit, to give some 'pop'

No pixie dust, just attention to detail.

Tight aperture (maybe f/11-16) with a wide-normal lens hyperfocused for thick DOF makes the image details crisp, especially a slight increase in contrast. Wide-normal focal length makes the distant just a bit small, separating fore- and back-ground planes. Light from the side 'models' roundness|thickness, heightening a sense of dimensionality. Yes, these are careful shots.
05-28-2012, 02:21 PM   #56
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Hey there. I see you're a little confused, so I'll try and share my 2c worth of information.
Don't get into this assumption that bigger is better, larger aperture, longer tele, wider wide, longer zoom, etc. Each lens was designed to its own purpose, and few others really beat it at that. You can't judge a lens purely by numbers (or a camera, for that matter).
That being said, you won't be able to find all focal lengths you're looking for with an f/1.2 aperture (actually you could, but not for 35mm film/APS-C digital, those are CCTV lenses). Aperture is actually the focal length of a lens assembly divided by its diameter at its optical center. Being a multiple of focal length, and transmittance not being dependant on it, aperture is noted as "f/#". Aperture(f) stops commonly run from 1, and go by multiplying with the square root of 2 (approx. 1.4) - hence the series 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 etc. The reason is the definition of an f-stop difference as the light required to double the light captured. You could a) halve shutter speed, b) double film/sensor sensitivity, c) double lens area. We will concentrate on alternative c, although a) and b) are sometimes more practical. Doubling lens area means multiplying radius by 1.4 (think A = pi * r^2). As I said, finding all your favorite focal lengths in a nice, big aperture isn't always possible, because, let's say you need a f/2 300mm telephoto lens. That means you need a lens that has glass 15cm in diameter, and I'm not even talking about the barrel. However, a vast majority of lenses float around the same aperture value, so I'll mention some of these values so you have a reference when shopping around. I'll only be talking prime lenses, because that's what I use and what I think gets best results for least money.
- 24mm and wider - things can get expensive, so I'd rather buy a 28mm and wait for a full-frame to get really wide images from it. In this wide section, every mm counts.
- 28mm - f/2.8 is the norm, though f/3.5 is also OK. Finding faster usually commands for more money.
- 35mm - here it depends. You'll see some 35mm lenses have "just" f/3.5, the norm is again f/2.8. Lenses covering full 35mm format usually stop at f/2.8, but there were also expensive ones that went to f/2. Now, 35mm is a popular focal length for APS-C DSLRs (it isn't wide anymore), it kind of tends to replace the 50mm focal length. You will see 35mm f/1.4, but those only cover this smaller frame for digital, because lenses with smaller image circles are easier to produce.
- 50mm - the most common focal length you'll find on film bodies. Looking through them, you'll quickly understand why - normal perspective. f/2 is COMMON (I certainly wouldn't buy a 50mm lens slower than f/2, if only there would be something special about it, like macro or small like the Industar 50-2). f/1.8 or 1.7 is fine, in my experience you don't NEED f/1.4 or f/1.2, you just want it.
- 80-85mm - this is the "portrait" focal length. I tried to skip these, because they're expensive. f/2 is the norm here, faster than that is very sought after.
- 135mm - the most common telephoto lens in the film era. It's actually a short telephoto, if you think you're going to spy your neighbours with this. f/2.8 is the norm, f/3.5 is also common; faster than f/2.8 is going to get you some HUGE glass (and some serious weight lifting), which can also be difficult to control in terms of optical performance (prone to flare, chromatic abberation, softness, etc). Not recommended. The focal length itself is nice and I personally recommend getting one of these for portraits.
- 200mm - f/4 is the norm, these are a little slower and bigger, thus harder to shoot handheld (require more light, and are more sensitive to shake). f/2.8 is considered FAST among these lands, I think f/2 is unheard of.
- 300mm and above - I have no clue myself, because these are impractical for my style of shooting - would require a tripod.
Also, something you'll surely have to deal with later, although now is kind of theoretical. Depth of field increases with (the square of?) the distance at which the lens is focused. being virtually infinite at infinity. This has two important consequences. First, this is exactly what makes macro photography difficult. Secondly, it means you can't get a nice, clean shot with blurry background with your subject at any distance from you. That's why all "bokeh" shots are close-ups.
In a nutshell, as long as you get a K-mount lens and it fits the above criteria, you should be good to go. Don't spend a fortune on super-fast glass, you'll soon find that you don't use it wide open that often. Sorry for the long post, I tried to be helpful, but it seems I got beyond myself

Last edited by kcobain1992; 05-28-2012 at 02:43 PM.
05-28-2012, 05:51 PM   #57
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My opinions, mostly about MF primes:

* With FE's (fisheyes) and UWA's (ultrawides) shorter than 16mm, speedy wide-aperture lenses are mostly rare, costly, and unnecessary. Such short focal lengths have immense DOF, and the 1/FL rule shows we can shoot with fairly slow shutter speeds. I *do* love my Zenitar 16/2.8! But f/3.5-5.6 are sufficient for much FE/UWA shooting. And legacy FE's in the ~15-21mm range aren't really fishy on APS-C. Most glass around 10mm are modern AF zooms. That's life...

* Wide lenses (WA's) in the ~16-24mm range are great for 'context' (including a subject's surroundings) and some 'scapes. Faster and wider ones aren't cheap. The DA18-55 is actually a great bargain! Lenses around 20/4 may not cost too much. A 24/2.8 may not cost much; a 24/2 will cost MUCH more. But my 24/2 is just what I need for shooting squirmin' vermin (my grandkids) in a less-than-bright room.

* Normal (28mm) or wide-normal (~25-30mm) are very common and inexpensive at f/2.8-3.5, and not necessarily too costly at f/2-2.5. My 28/2 and 28/2.5's were bargains! A decent 28mm gives a view as seen by one human eye, and has minimal distortion. Slower (f/3.5) glass in the 25-30mm range can be VERY sharp. Because 'normal is not an extreme view, it can be challenging to compose interesting shots. Meet the challenge!

* Long-normal (35-40mm) is popular, like pre-cropping a normal view. Fast (f/2-2.5) can be fairly expensive; slower (f/3.5-4.5) can be pretty cheap and VERY sharp. This range is good for full- or 3/4-body portraits, for showing subjects without too much context, etc.

* Short-tele (45-60mm) is fully populated with TONS of great legacy glass, from the days when these were the kit.lenses for 135/FF cameras. On APS-C they're great for isolating subjects from their contexts, for head-&-shoulders portraits, for florals and still-lifes etc. The fastest Fifties (f/1.2-1.4) can grab otherwise-impossible shots. For great sharpness wide-open, get an M50/1.7; or just stop-down a Faster Fifty a little.

* Mid-tele (70-105mm) tend to be costly, with few legacy bargains -- unless you're lucky. Cheap bastards like me may thread screw-on tele adapters onto Fifties to reach this range. For cheap sharp glass, try a ~75-90-105mm enlarging lens on a small bellows or focusing helicoid. Or adapt an Enna Tele-Sandmar 100/4.5, likely costing under US$20.

* Long tele (120-210mm) are a mixed bag. Legacy 135/2.8's and 200/4's are abundant and cheap. Faster long teles are bigger and often a bit costlier, and zooms in the ~70-210 range can almost anywhere in size, cost, quality. Fast long lenses are indispensable for action, sports, snooping, etc. And schlepping them around is good exercise, eh? But some 200/3.5's aren't too big nor costly.

* Ultra-tele (240mm and up) are another mixed bag, from cheap slow long.lenses (long tubes with glass at one end and a mount on the other) to overwhelmingly expensive monsters favored by birders and Olympics shooters. If you have a need for speed, you'll pay for it.
_______________________________________

At any focal length, wide apertures serve three purposes:
1) grab more light;
2) use a faster shutter;
3) get thin DOF.

Wide (short focal length) lenses also have three aspects:
1) get a larger FOV (field of view) and shrink the background;
2) use a slower shutter (the 1/FL rule);
3) get thick DOF.

And three points of longer lenses:
1) get a tighter view;
2) get thin DOF, to isolate subjects from surroundings;
3) stay a safe distance away!

There are a couple basic guidelines for DOF:
* For thicker DOF, use a shorter focal length and/or tighter aperture and/or more subject distance.
* For thinner DOF, use a longer focal length and/or wider aperture and/or closer subject distance.

We can compare (but not measure) the DOF of different lens setups with the FL/AP rule, dividing FL (focal length) by AP (aperture). A larger FL/AP number means thinner DOF. A 50/1.4 lens has the same FL/AP as a 100/2.8 or 200/5.6; their DOFs will be similar. Compare an expensive 85/2 lens (FL/AP= 42.5) with a cheap 135/2.8 (FL/AP= 48.2) -- the 135's DOF is thinner!
_______________________________________

Now let's put this stuff together. You want ultra-thin DOF? Get a fairly cheap 200/3.5 (FL/AP= 57.1) and shoot from as close as possible. You want sharp undistorted landscapes? Get a cheap 28/2.8, stop-down to f/8, and use a tripod. You want barrels of fun? Put a cheap (US$20) 0.25x fisheye adapter on your DA18-55 kit lens and shoot full-circle fisheyes. You want other possibilities? Read my other posts; I must go cook dinner now. (Tonight: chiles rellenos de RioRico and chicken tamales de Trader Joe. C'y'all soon!

Last edited by RioRico; 05-28-2012 at 05:59 PM.
05-28-2012, 06:23 PM   #58
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@RioRico
You made some mistake regarding the bokeh, really read this, it should interest you.
http://toothwalker.org/optics/bokeh.html

He also wrote about DOF
http://toothwalker.org/optics/dof.html
05-28-2012, 08:06 PM   #59
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QuoteOriginally posted by Anvh Quote
@RioRico
You made some mistake regarding the bokeh, really read this, it should interest you.
OK, I read those. I'm not sure what you object to. Is bokeh *not* the quality of OOF areas? Is DOF *not* a complex product of photography, presentation, and perception? Can DOF *not* be compared between lenses? Please specify. Please don't just send me fishing for clues. Thanks.
05-29-2012, 08:25 AM   #60
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* Bokeh (as mentioned) depends on lens design, aperture size and position within the lens, number and shape of iris blades
If you're talking about OOF then yes you're correct but not when we talk about Bokeh.
It's in the first 2 chapters and i can present you with more studies if you want.

* A fast wide-aperture lens may or may not have 'better' bokeh. But a wide aperture means more if the image will be OOF than with a tighter aperture. Its bokeh may be more visible. What you *do* with those OOF areas is up to you.
You're forgetting so much here but you corrected that later so no comment there but i thought you would find for example Figure 4. very interesting.
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