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DPChallenge Forums >> Tips, Tricks, and Q&A >> Digital Cameras vs. Apertures (Question)
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Showing posts 26 - 48 of 48, (reverse)
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02/24/2005 03:10:39 AM · #26
Originally posted by bear_music:

One more thing; the proof of what I'm saying, essentially, is built right into your zoom lenses; notice that when they are zoomed in your maximum aperture may be, say, f:3.5, and when they are zoomed out you will find that the maximum aperture you can accomplish is, say, f:5.6. This is because the physical size of the aperture is not changing, but the focal length of the lens is, and so the ratio is changing, and so is the amount of light that physical aperture is able to deliver to the film plane.

Robt.


Okay, then how does this work with fixed-aperture zoom lenses, like the Canon 17-40 f/2.8 L (or f/4 L)? That's a lens with a fixed maximum aperture along the entire zoom range. I understand what you're saying about fixed openings and changing ratios, but I'm curious how a fixed aperture lens could be built.
02/24/2005 03:14:21 AM · #27
By including a linkage that actually increases the physical diameter of the aperture as the lens is zoomed; expensive but a very nice feature.

Robt.
02/24/2005 03:39:30 AM · #28
Originally posted by bear_music:

DOF is actually independent of focal length. They have nothing to do with each other. DOF is a function of the physical diameter of the aperture in the camera. The larger the physical aperture, the less depth of field.



But the physical diameter of the aperture is in direct relation to the focal length of the lens at any given f/stop. So how is it independent?
02/24/2005 03:43:03 AM · #29
nsbca,

An aperture of a given physical size will always produce the same DOF regardless of what focal length lens it is used on. All that changes is the f:stop descripton of the aperture. See? In other words, a 200mm lens at f:33.33 has the same DOF as a 24mm lens at f:4.0, because each of them is using an aperture of the same 6mm physical diameter.

Incidentally, there's another factor that enters into the equation called "circle of confusion" and it tends muddy the waters somewhat at extremely small physical apertures, but the above description is fundamentally true. I'll leave it to someone with a degree in optics to wade in and explain all this more technically if they're so inclined. But COC is one of the primary reasons lenses have a "sweet aperture" where they are sharpest. DOF is actually a very malleable concept, having to do with how the eye perceives sharpness.

Robt.

Message edited by author 2005-02-24 03:47:21.
02/24/2005 03:56:28 AM · #30
Originally posted by bear_music:

nsbca,

An aperture of a given physical size will always produce the same DOF regardless of what focal length lens it is used on. All that changes is the f:stop descripton of the aperture. See? In other words, a 200mm lens at f:33.33 has the same DOF as a 24mm lens at f:4.0, because each of them is using an aperture of the same 6mm physical diameter.

Robt.


I understand that well. But when working in the field no one is measuring the dia of their aperture. f/2.8 on a 200mm lens is all anyone will see. So at f/2.8 on a 200mm lens you know you have a DOF of X. And at f/2.8 on a 24mm lens you know you have a DOF of Y. The focal length of the lens is in direct proportion to the diameter of the lens diaphram at any given f/stop. So even if it is true that the diameter of the lens diaphram determines the DOF, in usage we measure this diameter as focal length divided by the f/stop.

Message edited by author 2005-02-24 04:13:35.
02/24/2005 04:37:08 AM · #31
Well, sure. For any given lens, the more you stop down the more DOF you get. The point I've been making is that f:4.0 on a telephoto gives less DOF than f:4.0 on a wide angle, and this is a concept that some seem not to understand, so I was explaining why it is so.

Robt.
02/24/2005 04:18:31 PM · #32
Originally posted by nards656:

Originally posted by MeThoS:

Originally posted by damelzakelly:

Apparently when you use a aperture of 2.8 it would give a shallower depth of field than an aperture of 16.0.

The question I have is,
Does that happen with digital cameras, or does the aperture only change the amount of light entering the camera?

The reason I ask is that I have never found that the aperture made any difference to the depth of field in the photos I have taken. I currently own a Nikon Coolpix 8700 with apertures of 2.8 to 8.0


Doesn't anybody know how to use google or pick up a book to find out these very simple questions?


To describe this question as simple is at best condescending. nsbca7 and bear_music are professional photographers, yet they don't exactly agree on this subject, do they? Of course we know how to use google, and we know how to pick up and read books, but that doesn't mean we should be opposed to a simple conversation about a subject that confuses us.

Please don't be so insulting. I was baffled about this for years, and yes, I found my answer on the web, but not on DPC. I'm very glad to see it being discussed here, as this makes it much EASIER for other curious folk to find.

These are open forums. Please don't ever discourage the asking of questions. It's how many people prefer to learn.

Thank you to all who have contributed, even though I disagree with one of you :)


The origianl question was - Apparently when you use a aperture of 2.8 it would give a shallower depth of field than an aperture of 16.0.

The question I have is,
Does that happen with digital cameras, or does the aperture only change the amount of light entering the camera?

The reason I ask is that I have never found that the aperture made any difference to the depth of field in the photos I have taken. I currently own a Nikon Coolpix 8700 with apertures of 2.8 to 8.0


High school photo classes teach the answer to this question, which inded is very simple. What the others talk about is a more complex issue. And my point was, try to find the answer out for your self first before just asking...
02/24/2005 05:00:34 PM · #33
Originally posted by nsbca7:

Originally posted by nards656:


To describe this question as simple is at best condescending. nsbca7 and bear_music are professional photographers, yet they don't exactly agree on this subject, do they?


Just a note:

I'm an amatuer.

Added note: I do agree with the rest of what you posted. (so far)


Aren't you the guy with several thousand images on one of the stock agencies? If not, I apologize. My definition of professional is more in line with the one the state fairs use - do you make money off of your photography? Didn't mean to put you in a class you didn't want to be in :)

Okay, here's the deal. If a camera has a small sensor, the lens will have a shorter focal length than it would for a large sensor, assuming that the field of view is kept the same. nsbca is correct that focal length is involved in depth of field. It is also correct that aperture is involved.

The basic fact of digital life - regardless of the optical laws involved - is that if your digicam has a small sensor, which they typically do for cost reasons (1/1.8" or 2/3" are common, while 35mm film is something like 1.4 inches) it will normally have short focal length lenses, which will result in exceptionally large depth of field.

As the sensor becomes larger, the appropriate lenses will have much greater focal lengths, which will result in much narrower depth of field across the board. A 200mm @ f/2.6 (effective focal length of 200/2.8=71.4) will have MUCH less depth of field (ie easier to blur backgrounds) than a 9mm@f2.0 (effective focal length of 9/2=4.5).

So yes, sensor size is usually the culprit, even though it is not what optically causes the problem. I contend that sensor size IS directly related to the real world problem.
02/24/2005 05:05:20 PM · #34
Originally posted by MeThoS:



High school photo classes teach the answer to this question, which inded is very simple. What the others talk about is a more complex issue. And my point was, try to find the answer out for your self first before just asking...


Oh, that's classic. "Don't raise your hand and ask a question until you've wasted three hours in the library looking for it yourself because I don't have time to fool with you..." What's the problem with someone asking a question, my friend? No one has required you to read it or respond, so surely they've not purposely imposed on your time. Sure, it might be easy to find somewhere else, but why would someone be doing us a disservice by asking a question? I think questions are great, and I hope everyone feels free to ask them.

I've learned quite a bit more than I knew before, and I personally appreciate the original poster asking the question.
02/24/2005 05:13:00 PM · #35
Originally posted by nards656:

Originally posted by MeThoS:



High school photo classes teach the answer to this question, which inded is very simple. What the others talk about is a more complex issue. And my point was, try to find the answer out for your self first before just asking...


Oh, that's classic. "Don't raise your hand and ask a question until you've wasted three hours in the library looking for it yourself because I don't have time to fool with you..." What's the problem with someone asking a question, my friend? No one has required you to read it or respond, so surely they've not purposely imposed on your time. Sure, it might be easy to find somewhere else, but why would someone be doing us a disservice by asking a question? I think questions are great, and I hope everyone feels free to ask them.

I've learned quite a bit more than I knew before, and I personally appreciate the original poster asking the question.


I wonder what else they would of come across in the library looking for their answer? I'm guessing they would of stumbled across much more info then just asking a question. Questions are great, but so is finding out the answer with out having to ask.
02/24/2005 07:03:26 PM · #36
Originally posted by MeThoS:

Doesn't anybody know how to use google or pick up a book to find out these very simple questions?


What a ridiculous thing to say.

Yes, sure they can, and a google search will turn up forums such as this. If nobody however discussed it then all you would find are more formal articles. However, often far more can be learned from discussion, questions and answers etc on a forum such as this.

So what, DPC should not bother to discuss something if it can be found elsewhere?

The biggest attraction of this site for a lot of people is being able to ask questions, get answers, debate issues etc. To decide that the questions should not be asked if they can be found elsewhere is contrary to what this site stands for imho.

Also remember that what is a "simple question" to most, may not appear simple at all to a newcomer.
02/24/2005 07:08:56 PM · #37
someone wrote the book that has the answer. someone else figured out originally what the answer was. lots of people have asked the question.
if no one asked, nothing would ever get figured out...

no time to copy and paste author of the quote.

Originally posted by :

I wonder what else they would of come across in the library looking for their answer? I'm guessing they would of stumbled across much more info then just asking a question. Questions are great, but so is finding out the answer with out having to ask.



02/24/2005 07:13:24 PM · #38
I would like to add that alot of research data found online is written by professionals or engineers that many people have trouble understanding. What I have seen of the folks on this site (I'm fairly new) discuss things that are understandable and further respond if something is not understood.

I haven't read a book yet that answered me if I didn't understand it, which led me to another publication! Nothing wrong with research, but I see this site as research and learning site.

Message edited by author 2005-02-24 19:15:02.
02/24/2005 07:18:40 PM · #39
Originally posted by nards656:

Originally posted by nsbca7:

Originally posted by nards656:


To describe this question as simple is at best condescending. nsbca7 and bear_music are professional photographers, yet they don't exactly agree on this subject, do they?


Just a note:

I'm an amatuer.

Added note: I do agree with the rest of what you posted. (so far)


Aren't you the guy with several thousand images on one of the stock agencies? If not, I apologize. My definition of professional is more in line with the one the state fairs use - do you make money off of your photography? Didn't mean to put you in a class you didn't want to be in :)



Amatuer:enthusiastic pursuer of an objective [French, from Latin amtor, lover, from amre, to love.]
02/24/2005 07:41:08 PM · #40
I'm with nards656, the size of the sensor does still matter. although nsbca7 put forth that sensor size means nothing, according to Bear and the idea that it's the physical size of the aperature driving the DOF more than anything else, it seems that sensor size still is a factor. If it's a matter of ratio driving the f-stop (and also partially the focal length) then if you are dealing with the very small sensors in consumer digicams then the physical size of the aperature is greatly forced down. Then in a round about sense it would hold true that the sensor size will affect it...indirectly.

My experience regardless, is that when I increased my sensor size by getting the 10d I've dramatically changed the way I shoot and my ability to manipulate my DOF. So the answer I've found to creating a shallor DOF is if I have a consumer DigiCam, I need to start looking to get into a larger sensor/Prosumer/professional digital camera/SLR
Cheers to all
02/24/2005 08:40:54 PM · #41
Originally posted by ericsuth:

I'm with nards656, the size of the sensor does still matter. although nsbca7 put forth that sensor size means nothing, according to Bear and the idea that it's the physical size of the aperature driving the DOF more than anything else, it seems that sensor size still is a factor. If it's a matter of ratio driving the f-stop (and also partially the focal length) then if you are dealing with the very small sensors in consumer digicams then the physical size of the aperature is greatly forced down. Then in a round about sense it would hold true that the sensor size will affect it...indirectly.



I won't disagree with that. But when it is put forth as the size of the sensor causes an increase in the focal length of a lens by adding "reach" when in effect all that has been done is to crop the image I will argue the point. This concept was originally put forth by the camera manufacturers to delude the public into thinking there was some obvious advantage to having a smaller sensor.

The size of the sensor is not the direct cause of DOF effects that vary from those of a full frame sensor, but it is the smaller apertures and shorter lenses that are (purposely mislabeled) used with these smaller sensors that are the physical cause.

Message edited by author 2005-02-24 22:37:44.
02/24/2005 09:02:14 PM · #42
wow iam impressed with how much i jus learned in about 3 paragraphs!
02/24/2005 10:41:05 PM · #43
Let's get this all in one set of statements:

1. DOF is solely dependent on the physical diameter of the lens aperture (not its ratio, or f-stop number).

2. The smaller the physical diameter of the aperture, the more DOF the image will have.

3. The longer the focal length of the lens (in absolute terms), the larger must be the physical diameter of the aperture to deliver a given amount of light to the film plane/sensor.

4. For this reason, on a given camera platform, longer lenses have shallower DOF at a given f-stop than shorter lenses do.

5. "Angle of coverage" is what determines, in practical terms, whether a lens in considered "long", "normal", or "wide angle".

6. The smaller the film/sensor size, the narrower is the angle of coverage for a given focal length of lens.

Therefore, in practical terms, if you want more "control" over your DOF (if you want to be able to isolate one plane of the image by its focus, blurring everything in front of and behind that plane), you must use the largest film/sensor size you can afford. In practical terms, the typical point-and-shoot digital camera has unlimited DOF, and you have to go up to "pro-style" imaging systems to begin to get serious control of your DOF in wotking conditions.

For those of us who can't afford dSLR bodies and their very expensive glass, or choose not to use them because we prefer portability and ease of operation, there's always Photoshop and a judicious combination of selection tools and gaussian blur :-)

Robt.
02/24/2005 10:46:40 PM · #44
And I think that with that, we have almost come to a peaceful resolution and explanation of the subject. Thanks to bear, nsbca, and all the rest of you!

I'm not the guy who originally asked the question, and I basically knew the answer, but I think it should be a lot clearer for everyone now.

And that is good.
02/25/2005 07:07:24 PM · #45
I wish some one could jus sumorize everything to confusing to follow
02/25/2005 07:11:39 PM · #46
Originally posted by LEONJR:

I wish some one could jus sumorize everything to confusing to follow


I think Robert did that about three posts before this.
02/25/2005 07:18:14 PM · #47
man, school is tough... ;}

Message edited by author 2005-02-25 19:18:33.
02/25/2005 07:19:26 PM · #48
Ohhh yes i see there were jus so many posts i got lost thanks
Leon
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