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03-29-2014, 09:04 AM   #16
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QuoteOriginally posted by ElJamoquio Quote
This is one of the best reasons to get used to the idea of equivalent lenses.

Equivalent focal length, equivalent aperture, equivalent ISO, you get the same DOF, SNR, and view. It's the same picture with two different size sensors.
What is one of the best reasons? It is good to know (in general, knowledge is good), but in practical terms when does it ever come up? Who is walking around with two kits of different format and "equivalent" lenses to match? I am WAY more interested in how the same lens (one that I've got in my bag) will perform on a different format...

03-29-2014, 09:06 AM   #17
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QuoteOriginally posted by vonBaloney Quote
What is one of the best reasons? It is good to know (in general, knowledge is good), but in practical terms when does it ever come up? Who is walking around with two kits of different format and "equivalent" lenses to match? I am WAY more interested in how the same lens (one that I've got in my bag) will perform on a different format...
I was editing as you were writing.

I said 'this thread's topic'.

In practical terms it comes up when people are deciding what to buy.

FYI I am walking around with two different formats. There's some overlap and I sure as heck use the equivalence ratio when I'm going from one body to the next. You would be too, with the same set of lenses and two different formats.

Last edited by ElJamoquio; 03-29-2014 at 10:10 AM.
03-29-2014, 09:06 AM   #18
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QuoteOriginally posted by amoringello Quote
Appearance of DOF, is not DOF!
And that is your primary misconception. DOF is a perceptual measure only, that is founded on the notion of acceptable blur.
In reality, it does not exist.
There is only one point of focus regardless of aperture, focal length, etc. and if you look closely enough (pixel peep), all photographs have zero DOF. But the final viewer of our images does not pixel peep, so we are allowed to put the quirks of physics and the limits of human vision on our side to give the illusion of focus where none exists.

Truly, I suggest that you find a good camera store that sells medium and large format cameras and do a little hands-on look-see through the viewfinder (or groundglass) of a system with truly limited DOF. There is a reason why view cameras have movements and medium format portraits have that certain "look" and why "fast" lenses basically don't exist for media larger that than 35mm film. A little experiential learning is a good thing.


Steve

(...was truly shocked the first time working with 6x7 and 4x5 formats...gimme that f/64 and give it to me NOW!)

---------- Post added 03-29-14 at 09:19 AM ----------

Perhaps it is time to dig up the example images I posted on this site back in about 2008 that illustrate identical DOF for equivalent compositions at 1:1 and 50% crop.


Steve

Last edited by stevebrot; 03-29-2014 at 09:13 AM.
03-29-2014, 09:55 AM   #19
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QuoteOriginally posted by stevebrot Quote
I won't comment on your lengthy note, but I think you need to go back to the drawing board. DOF is truly based on three factors,* but not the ones you listed. They are:
  • Absolute (not relative) aperture
  • Magnification required for final image size**
  • Viewing distance for final image
Focal length, taking distance, capture media frame size, and post-exposure crop all factor into magnification.

For a given composition and aperture, available DOF varies according to the media frame size. This behavior is readily demonstrable. Just ask anybody who shoots medium or large format. If you disagree, I suggest that you prepare a series of example images proving otherwise.


Steve


* There is also a fourth (assumed) factor, that being the notion of acceptable blur.
** Any doubts about magnification? Simply compare the DOF of my avatar image to the original: https://flic.kr/p/5SzM3k

Post exposure crop? Really?
No need to go any further, other than to say you may wish to read up on how DOF works.

Example photos...
Take a photo, bring it into Photoshop. Crop the image.
Does DOF change? There's your answer about FF v.s CF sensors.
PERIOD.


True, DOF is somewhat used an a term of "acceptable sharpness" and it isn't 100% cut and dry.
But you need to throw out subjective issues up to and including how well a person sees... When you do and stay with consistent and definable terms, there is a specific amount of fall-off based on those three physical properties.

Other issues affecting "acceptable sharpness" include circles of confusion, refraction, signal-to-noise, high ISO noise and others...
BUT NONE OF THOSE are specific qualities to full frame v.s crop frame.
A crop frame may have smaller or larger circle of confusion based on the pixel density, among other factors.
A crop frame may have more or less high ISO noise than a full frame camera (depending on age, model, type of sensor)
A crop frame camera may have more refraction or glare based on a host of issues including lens, angle of light, etc...
All affect perceived sharpness, but none have anything to do with DOF.

If you want to check the math, go to any Depth Of Field calculator and see what happens. There are plenty of them out there.
CoC is included, but again does not apply strictly to FF vs CF sensors so its a moot point unless you give a specific brand and model as well.

03-29-2014, 10:08 AM   #20
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QuoteOriginally posted by amoringello Quote
does not apply strictly to FF vs CF sensors so its a moot point unless you give a specific brand and model as well.
As exceedingly-commonly-defined, the CoC only relates to the magnification of the sensor. Full frame will always have a larger CoC than APS-C, and the ratio between the two will be (surprise!) the equivalence ratio.

We're at the point where pixels are small enough not to matter. Brand/model do not matter as long as the sensor size is maintained. You might be confusing Canon's 1.6 E.R. and Sigma's 1.7 E.R. for 'megapixel' differences.
03-29-2014, 10:12 AM   #21
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QuoteOriginally posted by ElJamoquio Quote
As exceedingly-commonly-defined, the CoC only relates to the magnification of the sensor. Full frame will always have a larger CoC than APS-C, and the ratio between the two will be (surprise!) the equivalence ratio.

We're at the point where pixels are small enough not to matter. Brand/model do not matter as long as the sensor size is maintained. You might be confusing Canon's 1.6 E.R. and Sigma's 1.7 E.R. for 'megapixel' differences.
Sensors do not magnify anything. They accept light.
CoC deals with pixel size and spacing.

Circles of confusion are often measured in hundredths of a millimeter. Until your sensor gets that small, your sensor size won't really matter. Light does not change its physical properties based on size of the sensor, sheet of paper, projector screen, etc...
03-29-2014, 10:33 AM   #22
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QuoteOriginally posted by amoringello Quote
Sensors do not magnify anything. They accept light.
indeed.

QuoteOriginally posted by amoringello Quote
CoC deals with pixel size and spacing.
That's wrong, though. CoC as most commonly defined has nothing to do with pixel size.

QuoteOriginally posted by amoringello Quote
Circles of confusion are often measured in hundredths of a millimeter.
Pixels are measured in thousandths. So the pixel size is not the limiter.

QuoteOriginally posted by amoringello Quote
Until your sensor gets that small, your sensor size won't really matter. Light does not change its physical properties based on size of the sensor, sheet of paper, projector screen, etc...
Pixels are that small. Light doesn't change, but the magnification of aberrations does. Luckily, for practical applications, it all works out mathematically back to the equivalence ratio.

Suggest you learn more about the CoC....


https://en.wikipedia.org/wiki/Circle_of_confusion
03-29-2014, 10:59 AM   #23
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QuoteOriginally posted by amoringello Quote
Post exposure crop? Really?
No need to go any further, other than to say you may wish to read up on how DOF works.

Example photos...
Take a photo, bring it into Photoshop. Crop the image.
Does DOF change? There's your answer about FF v.s CF sensors.
PERIOD.
If you are going to make the same size print from your crop that you would have from an uncropped image (which assumes same viewing distance with either), then YES it did change because now you are going to enlarge it more and what might have fallen within the boundaries of acceptable sharpness with the uncropped image may no longer be within those boundaries. So while a post-crop of an image isn't quite the same as using different sized sensors (because the pixel density is also likely different between sensors), the principle is the same. But note that the change here is actually opposite of what is normally claimed -- the DoF has actually gotten thinner with the smaller format (or crop), not larger. Confusing, eh?

03-29-2014, 11:04 AM   #24
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The idea of "greater DOF control" is about having the ability to use less DOF.
In basic terms, given the same FOV and the same aperture, a camera using a larger image format will have less DOF.
Steve is right though, DOF is more about "appearance of DOF" than a definable, measurable depth.
Magnification is the primary factor in DOF, both in camera and final image size.
Here's a good article
DOF2
03-29-2014, 03:20 PM   #25
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QuoteOriginally posted by amoringello Quote
True, DOF is somewhat used an a term of "acceptable sharpness" and it isn't 100% cut and dry.
But you need to throw out subjective issues up to and including how well a person sees... When you do and stay with consistent and definable terms, there is a specific amount of fall-off based on those three physical properties.
Steve already gave you the list of things that affect it. 1. Focal length, 2. distance from subject, 3. Fstop. maybe you need an example.
1. Focal length.
Take a photo with a 50mm lens on K-5. If you want to take THE SAME COMPOSITION with a full frame camera you need to use a 75mm lens. This is because putting the 50 on full frame will place some other objects in the picture which were not there before. i.e. the 50 is wider on full frame than on crop frame. 75mm will give you shallower depth of field. To understand this, think how much subject separation can you achieve with a super wide lens. Almost none. The wider the lens the bigger the depth of field. Try that with your DOF calculators.
2. Distance from subject.
Take a picture with your K-5 with a 50mm F1.4 lens. Take the lens off and put it on your K1000 (Full frame film camera). You realize that if you dont physically MOVE you have a bunch of additional stuff in the picture which you now are able to see. This is because you now see more of the lens image circle. How do you take THE SAME composition with a K1000. You move in closer so the additional material in the photo goes away. When you mover your DOF will change. This is one of the three things which affect it. Once you are closer your background will be more "blurred out" i.e. your depth of field fell.
3. I feel like this is pretty self explanatory and photography 101 but not related to the type of camera you shoot with.

seriously, i dont mean to be rude but you need to read up on this...
03-29-2014, 03:41 PM   #26
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QuoteOriginally posted by oxidized Quote
Steve already gave you the list of things that affect it. 1. Focal length, 2. distance from subject, 3. Fstop. maybe you need an example.
1. Focal length.
Take a photo with a 50mm lens on K-5. If you want to take THE SAME COMPOSITION with a full frame camera you need to use a 75mm lens. This is because putting the 50 on full frame will place some other objects in the picture which were not there before. i.e. the 50 is wider on full frame than on crop frame. 75mm will give you shallower depth of field. To understand this, think how much subject separation can you achieve with a super wide lens. Almost none. The wider the lens the bigger the depth of field. Try that with your DOF calculators.
2. Distance from subject.
Take a picture with your K-5 with a 50mm F1.4 lens. Take the lens off and put it on your K1000 (Full frame film camera). You realize that if you dont physically MOVE you have a bunch of additional stuff in the picture which you now are able to see. This is because you now see more of the lens image circle. How do you take THE SAME composition with a K1000. You move in closer so the additional material in the photo goes away. When you mover your DOF will change. This is one of the three things which affect it. Once you are closer your background will be more "blurred out" i.e. your depth of field fell.
3. I feel like this is pretty self explanatory and photography 101 but not related to the type of camera you shoot with.

seriously, i dont mean to be rude but you need to read up on this...
Not rude at all but I think you misread the wrong name or what I stated.
It sounds a lot like what I originally said several pages back. :-)

It is pretty simple, but different (incorrect??) uses of different terminology is getting in the way for much of this thread.

Last edited by amoringello; 03-29-2014 at 04:23 PM.
03-30-2014, 03:02 AM   #27
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QuoteOriginally posted by Swift1 Quote
The idea of "greater DOF control" is about having the ability to use less DOF.
In basic terms, given the same FOV and the same aperture, a camera using a larger image format will have less DOF.
Yes, that is understood. I was just not sure if the term "greater DoF control" had some theoretical/scientific backing or no as it stands and now it's verified it has none. It's a "colloquial term" for one half of the picture ("more maximum subject isolation") and in the meaning of the way it's used it fits while still being plain wrong in the original sense of the words. I let people use the term as it is and translate it in my head.
And it's confusing if you are reading theory stuff where every word counts. But now I am more robust in my understanding.

QuoteOriginally posted by ElJamoquio Quote
You speak of a hypothetical lens that only has an aperture range of F/4 to F/16. Such a lens would be exceedingly rare, the aperture range would only be four stops! That doesn't happen in practice.
I just wanted to make the example easy. And as I was referring to theory I did not care about "practise". Practise makes all things difficult and in many time overrides theory. In practise people usually have budgets. If your budget is $600 for new equipment this will change the result of the "more DoF contest" a lot...
So I first try to understand the theory completely and worry about practise separately later.

QuoteOriginally posted by ElJamoquio Quote
So in equivalent lens terms there is no difference between capability of the lenses.
Yes, that took me a while to understand in the past as well. Until I took it the easy way: "equivalent" = "same" and what difference would anyone expect to get out of comparing two same items?

QuoteOriginally posted by ElJamoquio Quote
In theoretical-practical, owning-one-lens terms there is a difference. Most of us don't have one lens, and if you only plan on owning one lens then I would suggest a psychiatric forum!
Considering the mood in a forum sometimes and considering that probably the huge majority of people out there actually only buy a single kit lens I do wonder who would need psychiatric help or actually an anti-aggression training. I read too many forums lately. In real life there would need to be bullet-proof glass between the people discussing...

QuoteOriginally posted by ElJamoquio Quote
On the contrary, it is often the case that users want shallow DOF.
At least the ones whose voice can be heard on the net seem to trend that way, yes.

QuoteOriginally posted by ElJamoquio Quote
That's why enthusiastic users who've studied the +/-'s go FF before they go to expensive lenses.
I personally think it's smarter to go buy good glass before go change a body (assuming the body is generally well covering feature and sensor requirements of the user and not completely obsolete). But that is a personal taste discussion I would not want to bring in here.
03-30-2014, 08:21 AM   #28
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QuoteOriginally posted by HavelockV Quote
Hi,

I read a lot of funny material on the basics of photography and always when I feel I understood I find some things in a forum which challenge this.

Now my question:
Lets say I have two lenses lying around:
  • 20mm F4, which can be stopped down to F16
  • 40mm F4, which can be stopped down to F16
Both are FF-compatible and I have a FF-senor camera and a mFT camera with adapter, so I can use both lenses on both cameras.

Why would anyone say using the FF camera he get's "more DoF control" using any of the lenses?

Doesnt he gain less DoF on the small FNumber side but loose the exact same DoF control on the large FNumber side?
You are actually correct here. The DOF 'control' you gain on the high end (low f-stop) you effectively lose on the low end (high-fstop.) However, the vast majority of non-landscape shots folks take are f/11 and higher (f/1.2 to f/11,) and so this 'loss' up past f/16 is largely theoretical. If you use your cameras primarily in portraiture or low-light applications, this 'loss' is almost entirely theoretical - you only see the gain.

There are some landscape applications where 'DOF control' is negated, because those shots are taken at f/16, f/22, whatever, but aside from that type of shooting you will see, effectively, 'more DOF control' with larger sensors.

In other words, in the most common shooting scenarios you will probably find yourself in, you can always stop down the larger sensor to match the smaller one's DOF - can't always go the other way, because they (generally) don't make the lenses that would allow it. Smaller is a subset of larger. That's the 'more DOF control'.

(also, note that it's not really about the sensor size - it's about the lenses, or the linear aperture available at that FOV for that focal length. To put it succinctly: they don't make lenses for m/43 with large enough maximum apertures, because they can't.)

(note II: 'more DOF control' is not a judgement on smaller formats' ability to isolate subjects enough for any given shooter - don't take it that way.)

.

---------- Post added 03-30-14 at 09:48 AM ----------

QuoteOriginally posted by amoringello Quote
Post exposure crop? Really?
No need to go any further, other than to say you may wish to read up on how DOF works.
Actually, Steve was right.

QuoteQuote:
Example photos...
Take a photo, bring it into Photoshop. Crop the image.
Does DOF change? There's your answer about FF v.s CF sensors.
PERIOD.
DOF does change in that example - the act of enlarging that crop to the same display size as the original image is what does this.

The only way the DOF does not change there is if you don't enlarge that crop - for example, if you crop a 5x7 out of an 8x10 image and leave it at 5x7. If you enlarge the 5x7 image to the 8x10 dimensions (before framing or whatever,) you will change the DOF in the resulting image.

.

Last edited by jsherman999; 03-30-2014 at 08:49 AM.
03-30-2014, 08:59 AM   #29
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OP, do you own a manual lens with distance scale and aperture ring?

Just by looking at how those 2 work will make you understand this "more DOF control".
03-30-2014, 10:20 AM   #30
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QuoteOriginally posted by HavelockV Quote
I personally think it's smarter to go buy good glass before go change a body (assuming the body is generally well covering feature and sensor requirements of the user and not completely obsolete). But that is a personal taste discussion I would not want to bring in here.
It's definitely smart to buy good glass! Unfortunately 'good glass' is a bit of a subjective statement, and can end up costing thousands more on smaller format sensors.
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