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Thread started 10 Feb 2013 (Sunday) 16:55
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Why does FF yield shallower DOF?

 
RDKirk
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Feb 11, 2013 17:55 as a reply to  @ post 15599553 |  #76

Well, dang, I'm back anyway.

Someone please hold me to this. When I get a chance, I'll take test shots clearly showing that sensor size has NO effect on DOF. I will shoot the same subject from the same distance with the same lens and the same aperture, with a 60D and a 5D. Does anyone really think I'll get anything but EXACTLY the same DOF from these shots?

Been there, did that 40 years ago. You clearly did not understand what Skip Douglas said (and I said earlier) about the degree of magnification to the final display size, and you're ignoring issues such as achieving the same framing that others have correctly identified as "how people work in the real world."

You're essentially trying to run the photographic version of a "bar bet."

I doubt Skip will be surprised.




  
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TSchrief
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Feb 11, 2013 17:59 |  #77
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davidc502 wrote in post #15599553 (external link)
Valid points.... Too bad no one really listens....

LOL the word "ridiculousness" <<< You've been watching to much MTV!!

Don't watch MTV. I may have gotten it from the Colbert Report.

Anyway, in reference to my offer to take some test shots to PROVE that sensor size makes no difference in DOF, I make this offer.

I will shoot this twice, just to prove it is not a fluke of the choices I made. Look at my gear list. Choose two different lenses. Choose two different sensor-to-subject distances. Choose two different apertures. YOU define the test. For instance I could shoot the 85 1.8 at 10 feet and f/2.8, then again at 20 feet with f/16. Or the 70-200 at 200mm and f/2.8 from a distance of 20 feet, then again at 50 feet. Keep in mind that I will shoot both sensor sizes using ALL the same settings, in order to show that sensor size has no affect on DOF. I am trying to convince those of you who believe that sensor size affects DOF that you are mistaken. Therefore YOU define the test. I probably won't have time for this until Spring break, the second week of March.

EDIT: Please don't choose an EF-s lens as I can't mount that to my 5D.


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JeffreyG
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Feb 11, 2013 18:01 |  #78

TSchrief wrote in post #15599539 (external link)
This is getting ridiculous. NOBODY thinks like that when they are shooting. NOBODY would think to do that when a change in DOF is desired.

Shooter to self: "Let's see, now. I need switch formats for this shot. I think I'll go back home, get my other (FF/APS-c) camera, mount a different lens, then shoot from the exact same spot, which changes my composition HUGELY, then I'll do a small calculation do determine which aperture I need to get EXACTLY the same DOF out of completely different equipment, for a completely different shot."

Kind-of true. But when I switched from a 30D to a 5D several years ago, after a few months I realized that I was in general using apertures about one stop smaller than I had been.

It wasn't a ridiculous realization like you suggest above, but a natural transfer to continuing to use the same DOF range while adapting to the different format.

So for example, when 'd had the 30D I'd often used various prime lenses at f/2 or so. For a while with the 5D I even toyed with the idea of using just a handful of f/2.8 zooms because I was not needing the f/2 so much. This was especially true for me at 85mm and longer.

This realization is one of the reasons I bother to get involved in threads like this. It's a simple truth that using different formats will affect your DOF, or at least affect your aperture selection to get the DOF you want. I didn't really understand this when I had a 1.6X sensor (only), but it became clear to me a while after I got a 5D.

Sometimes I think that people have trouble acknowledging the (somewhat subtle) differences between 1.6X and FF because the two formats are so close. But if you step back and compare something like a 1/1.8" sensor P&S and then a FF 5D, the DOF effects are obvious. The effects are the same from 1.6X to FF, just they are closer to each other.

People also love to impose totally false premises on the 1.6X vs. FF DOF comparison ("you have to use the same lens, nobody owns two lenses!"). Go to the P&S vs. FF comparison (which is fundamentally the same thing) and nobody suggests that you simply must shoot at 50mm on both an SD120 and 5D and then crop the 5D all the way down to the tiny format of the P&S. This is obviously ridiculous. If you shoot the SD120 and the 5D both with a normal lens and do no cropping, pretty much everyone undestands the SD120 will have much greater DOF at any given aperture.


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TSchrief
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Feb 11, 2013 18:10 |  #79
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RDKirk wrote in post #15599593 (external link)
Well, dang, I'm back anyway.

Been there, did that 40 years ago. You clearly did not understand what Skip Douglas said (and I said earlier) about the degree of magnification to the final display size, and you're ignoring issues such as achieving the same framing that others have correctly identified as "how people work in the real world."

You're essentially trying to run the photographic version of a "bar bet."

I doubt Skip will be surprised.

This may be exactly what you meant. However, it reads as gibberish. You seem to be claiming that I can shoot a 10-22 on APS-c at f/16 and a 200mm f/2.8 at f/2.8, both focused at 20 feet, and the difference in apparent DOF is due to the magnification. Bull-puckee! Your response has to be an EMPHATIC: "No, that is not what I meant. DOF will most certainly be affected by the different focal lengths, apertures and subject distance." Which is my point.

The sensor size plays no role, photographically speaking. If you bore down to the physics of light and perception, which is what the whole 'circle of confusion' thing does, you will see a difference. You'll never see it when comparing two photographs taken on different sensors.


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RDKirk
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Feb 11, 2013 18:11 as a reply to  @ JeffreyG's post |  #80

Sometimes I think that people have trouble acknowledging the (somewhat subtle) differences between 1.6X and FF because the two formats are so close. But if you step back and compare something like a 1/1.8" sensor P&S and then a FF 5D, the DOF effects are obvious. The effects are the same from 1.6X to FF, just they are closer to each other.

Indeed.

Some of us have used different formats--like 35mm and medium format, maybe even large format--for decades. Or using medium format with different sized film backs--"cropping" in the camera with the same lenses.

I've shot with a 4x5 camera using both 4x5 film backs and 6x6 film backs--with the same lenses, as well as medium format with 6x7 and 6x4.5 film backs.

We're well aware of what happens. While the laws of optical physics might have been different at the moment of the big bang, they haven't noticeably changed in the last 40 years.




  
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JeffreyG
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Feb 11, 2013 18:12 |  #81

TSchrief wrote in post #15599539 (external link)
Someone please hold me to this. When I get a chance, I'll take test shots clearly showing that sensor size has NO effect on DOF. I will shoot the same subject from the same distance with the same lens and the same aperture, with a 60D and a 5D. Does anyone really think I'll get anything but EXACTLY the same DOF from these shots?
.

Fine, but I insist on one other thing. I want the same field of view. That's how I actually use my cameras.

I do not automatically frame everything 60% longer on a side when I use FF vs when I use 1.6X. I change my focal length to achieve the same framing no matter what I am doing (unless I'm shooting beyond 560mm, which is the maximum focal length I can reach). But for this comparison let's stick to something in the range of 24mm to 105mm.

This can still be done, just use a zoom lens as your 'one lens' and zoom the lens to a focal length 60% longer when you shoot the FF shot. This is how people actually use cameras.

I mean really.....I once used a P&S with a focal length range of 6mm to 72mm. When I got I 5D I did not waste a lot of time looking for an EF 6-72 to make sure I had the same lens. That would be totally stupid.

For the same reason, I liked a 17-55 kind of range as my everyday walkabout lens for my 30D. But I do not use a 16-35 or 17-40 as a walkabout on a 5D. Nope, I use a 24-105 or 24-70 for this on FF. The larger the format camera I am using, the longer the focal length range of lenses I will select.


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TSchrief
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Feb 11, 2013 18:13 |  #82
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JeffreyG wrote in post #15599605 (external link)
Kind-of true. But when I switched from a 30D to a 5D several years ago, after a few months I realized that I was in general using apertures about one stop smaller than I had been.

It wasn't a ridiculous realization like you suggest above, but a natural transfer to continuing to use the same DOF range while adapting to the different format.

And this has nothing to do with the fact that you were either shooting from a shorter distance, or using a longer lens? C'mon. Distance and focal length affect DOF. It was not the sensor.


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RDKirk
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Feb 11, 2013 18:15 |  #83

TSchrief wrote in post #15599630 (external link)
And this has nothing to do with the fact that you were either shooting from a shorter distance, or using a longer lens? C'mon. Distance and focal length affect DOF. It was not the sensor.

Absolutely nobody has said that distance and focal length do not affect depth of field. Absolutely nobody has said that the sensor was the sole or even the proximate cause of changes in depth of field.

As I said, you're trying to run a bar bet, and some of us have seen enough of them to know it.




  
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Feb 11, 2013 18:24 |  #84

TSchrief wrote in post #15599630 (external link)
Distance and focal length affect DOF. It was not the sensor.

So what? What kind of point do you think you are really making here? It's blindingly obvious that everyone responding to you understands the point you are making, but what we are all continuously telling you is that the point you are making has little practical relevance.

Nobody....absolutely nobody changes format sizes and then continues to shoot absolutely everything at the same focal length while having a completely different field of view with the new format. While it's technically true that this will give essentially the same DOF, this comparison also makes absolutely no sense. Why would I buy a 60% larger (on a side) format camera just to shoot the same focal length and then crop off 60% of the sides of every picture. That's nutty.

When normal photgraphers ask about DOF and format (like in this forum) they are usually interested in the practical aspects of photography. And practically speaking, this means they are interested in scenarios where the photographer adjusts the focal length along with the format size in order to achieve the same field of view.

So to be pedantically correct, larger formats lead to shallower DOF (at constant aperture) because photographers must use longer focal lengths in order to achieve the same field of view.

It would seem that you understand this, but you have some bizarre goal to be technically correct in a narrowly defined sense that has little interest to anyone who would ask this question in the first place. If that's your goal, well done.


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Feb 11, 2013 18:37 |  #85

TSchrief wrote in post #15599539 (external link)
This is getting ridiculous. NOBODY thinks like that when they are shooting. NOBODY would think to do that when a change in DOF is desired.

Shooter to self: "Let's see, now. I need switch formats for this shot. I think I'll go back home, get my other (FF/APS-c) camera, mount a different lens, then shoot from the exact same spot, which changes my composition HUGELY, then I'll do a small calculation do determine which aperture I need to get EXACTLY the same DOF out of completely different equipment, for a completely different shot."

This may or may not work. Not my point. The ridiculousness of anyone actually doing this defies the imagination. Any particular f/stop, on a set FL, whether on APS-c, full-frame, or 8x10 for that matter, will yield the same DOF when shot at the same distance. Who cares what FF aperture yields the same DOF as APS-c at a completely different distance? You will shoot what is in your hands AT THE MOMENT.
.

Of course nobody thinks like that, and changes DOF by switching bodies, you just change the aperture. Nobody has suggested any different. Just because we have been discussing what the difference is between the bodies, does not mean you need to use it to control DOF. It's just a matter of knowing how it differs.

Yes, of course you shoot what is in your hands at the moment, but what you have in your hands affects the focal length you will use to get the shot you want, and that will affect the DOF. Besides, what you have in your hands "at the moment" may have been specifically chosen because of the DOF you can get from that particular camera. I use a bridge camera (about 5x crop at a guess, maybe more) for shooting my product shots for ebay. I have small items, and often need several in one shot and they need to be sharp. The heavy crop on the sensor means I can shoot with really short focal lengths and get enough DOF. Using my 1.6x crop DSLR doesn't get the job done because I cannot get enough DOF without standing so far back that the items are way too small in the frame, and my FF DSLR is even worse.

TSchrief wrote in post #15599539 (external link)
DOF is affect by:
Focal length, aperture and sensor (film) to subject difference. Note that sensor size is NOT in that list. Sensor size WILL affect your choice of lens. It does NOT directly affect DOF.

I fully agree. I think everybody who has answered in this thread fully agrees. Nobody is saying any different. All of those who say that using a FF camera gives you shallower DOF than using a crop camera agree with this.

Nobody is saying that the FF sensor alters the DOF. They are saying that when you frame the shot you want, you will be using a longer focal length with a FF camera and that will reduce your DOF.

TSchrief wrote in post #15599539 (external link)
Someone please hold me to this. When I get a chance, I'll take test shots clearly showing that sensor size has NO effect on DOF. I will shoot the same subject from the same distance with the same lens and the same aperture, with a 60D and a 5D. Does anyone really think I'll get anything but EXACTLY the same DOF from these shots?

SkipD, stay tuned. You are in for a surprise.

No, nobody thinks you will get anything but the same DOF (it won't be exactly the same unless you also show the 60D shot at a smaller size to keep enlargement the same).

Go ahead, do the test, we all know you will get the result you want (in terms of DOF). SkipD won't be surprised at all.

However, you will be showing two very different images. If you nicely frame the subject with the 60D, then there is going to be a lot of dead space around the subject in the shot from the 5D. As that dead space isn't wanted as part of your composition, you will need to crop it away to get back to your desired composition (and guess what, that makes the 5D the same crop factor). Alternatively, you can nicely compose your image with the 5D, then switch to the 60D, but "oh, no" you've cut off your subjects head, or feet, because you can no longer get them all in.

As a photographer, do you compose your shots? Frame them the way you like? avoid lots of uninteresting, empty space? If so, then you will do what most of us do and fill the frame with the subject (when possible, it isn't always with birds etc).

So, when you have done your test keeping all the variables the same, and produced one nicely composed image and one where the subject is lost in the middle, how about doing another test. Take your 60D, and compose a nicely framed scene in it, leaving out anything that doesn't add to the image (you know, the way photographers actually work) and take the shot. Then, recreate the composition and perspective with the 5D, same framing, without all the wasted empty space you had last time. You will need to use a longer focal length of course. You may be surprised to see that you now DO have shallower DOF, unless you stopped the aperture down more, to compensate and keep the DOF the same.

It is all very well stating that "if you don't change the variables, DOF will stay the same", that much is obvious and doesn't need pointing out. However, in order to create the image you have in your mind, you need to change the variables according to whether you are using a FF or crop camera, and therefore the DOF will change.

Why is that so hard to grasp?




  
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Feb 11, 2013 18:48 |  #86
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RDKirk wrote in post #15599634 (external link)
Absolutely nobody has said that distance and focal length do not affect depth of field. Absolutely nobody has said that the sensor was the sole or even the proximate cause of changes in depth of field.

As I said, you're trying to run a bar bet, and some of us have seen enough of them to know it.

OK. I concede. On one condition. You take two shots with the same lens, same aperture, same sensor to subject distance. One shot on APS-c, the other on full-frame. YOU are claiming DOF will be different. Please show us.

Edit:
The only sense I can make out of this thread is that we are all saying the same things, while using different words. What, essentially IS the debate about? OP asked why is FF DOF shallower. Has that been satisfactorily answered?


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Feb 11, 2013 18:56 as a reply to  @ sandpiper's post |  #87

:lol: :lol: :lol:

People get a little cabin fever this time of year and just love to argue topics that are rather simple and hashed out a million times before. I wonder how long we could power a lightbulb with the energy put into the keyboards so far. :lol:

I fully expect a snarky argument tossed my way as well just for mentioning something that can be argued. :p


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Feb 11, 2013 18:59 |  #88

Canon_Lover wrote in post #15599781 (external link)
:lol: :lol: :lol:

People get a little cabin fever this time of year and just love to argue topics that are rather simple and hashed out a million times before. I wonder how long we could power a lightbulb with the energy put into the keyboards so far. :lol:

I fully expect a snarky argument tossed my way as well just for mentioning something that can be argued. :p

Well now that depends.........are you talking AC power or DC? How long did that take - about 2 minutes?:lol:


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Feb 11, 2013 19:06 |  #89

TSchrief wrote in post #15599748 (external link)
OK. I concede. On one condition. You take two shots with the same lens, same aperture, same sensor to subject distance. One shot on APS-c, the other on full-frame. YOU are claiming DOF will be different. Please show us.

What's the point? We all know the DOF won't be different. He isn't claiming DOF will be different in that scenario, nobody is for goodness sake. What we are saying is that the scenario has little relevance as it creates two very different photographs. To create the same photograph (or as near as is possible) you will run into different DOF as you need to use a longer lens on the FF camera.

TSchrief wrote in post #15599748 (external link)
Edit:
The only sense I can make out of this thread is that we are all saying the same things, while using different words. What, essentially IS the debate about? OP asked why is FF DOF shallower. Has that been satisfactorily answered?


Yes, of course it has been answered. The OP got it right himself in the opening post of the thread. The DOF is shallower when using a FF camera because you have to use a longer lens to take the same picture.

Either you are trolling, or you are unable to understand the most basic concept of photography, which is to take a specific image that meets your requirements, including perspective, composition and framing. Not to take an image that is very badly framed, just to give you the DOF that you would have got if using a different format sensor, which is what you are trying to do.




  
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Feb 11, 2013 19:14 |  #90

TSchrief wrote in post #15599748 (external link)
OK. I concede. On one condition. You take two shots with the same lens, same aperture, same sensor to subject distance. One shot on APS-c, the other on full-frame. YOU are claiming DOF will be different. Please show us.

DOF will be different, you get LESS dof with a APS-C camera in your situation, not more.

Try it - photograph a ruler at a 45 degree angle, same lens, same aperture, same distance to subject, and then output at the same size.

The APS-C camera photo will be more magnified showing LESS dof than the FF image.

I'm not trying to confuse things even more, but in the above situation, FF has MORE DOF than a Crop camera


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Why does FF yield shallower DOF?
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