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Setting focus won't affect field angle?
Hi all.I was looking arond on the internet to understand a bit how the objectives work..

As far as the objective is approximated by a single convergent lens, I understand,But then there is something I can't figure out about setting the focus :.

If setting the focus is changing the distance between the lens and the CCD to bring the object's image in the CCD plan, then the vision angle should change slightly when moving the focus. Basically the angle should be greatest when focusing infinitely far (image on the lens' focal point), and get smaller when focusing on a closer object (image further from the lens, beyond it's focal point)..

But in practice the angle seems constant (the image on the display covers exaclty the same area while changing the focus)..

Can someone explain me what happens in a objective regarding that issue? Or tell me where I can find good info on the web (I haven't found any on this specific matter)?.

Thank you very much...

Comments (18)

The field (angle) of view does in fact change as you focus, although it might not be enough to be obvious. But it's hard to generalise because SLR lenses are very complex. They focus not by moving the whole lens in and out, but by moving certain elements. In some of the best lenses the front and rear elements (or groups) are in fixed positions and only the middle group(s) move. As you change focus, the focal length also changes and that changes the field of view..

My EF 100/2.8 Macro has a focal length of 100 mm when focused at infinity, reducing to 77 mm when focused at it's minimum distance of about 30 cm. (Nothing special about this lens, it just happens to be one I've measured.)..

Comment #1

This calculator takes focus distance into consideration when computing angle of view:.

Http://stegmann.dk/mikkel/barnack/.

JimChttp://www.pbase.com/jcockfield..

Comment #2

Aren't the stated focal ranges of lenses based on having focused at infinity? If so then that implies there should be miniscule differences for closer than infinity focusing...

Comment #3

Yes, manufacturers rate their lenses at infinity..

Lens design can play a big role though. Some of the newer internal focus designs from Tamron and others give you a much wider (not narrower) angle of view if you focus on a closer subject because of the way the optical design works (changing focal length with focus distance)...

I see this come up on the forums relatively often ("how come my new lens is only giving me the same angle of view I get with at 150mm with a different lens on the same camera, when it's supposed to be 200mm")..

So, members usually explain that some of the newer Internal Focus designs change focal length with focus distance and the manufacturers assume infinity focus when rating them. They then check their lenses focused on something closer to infinity and see how that works..

JimChttp://www.pbase.com/jcockfield..

Comment #4

Thanks for the reply, Steve..

I am glad that you confirmed my impression, and that you stressed it is a bit more complicated than that in reality..

Cheers..

Comment #5

GearCollector, Jim,thank you both for your input.The Barnack software will be of great help, I'll spend some time on it..

Regards...

Comment #6

Jim Cockfield wrote:.

Yes, manufacturers rate their lenses at infinity..

Lens design can play a big role though. Some of the newer internalfocus designs from Tamron and others give you a much wider (notnarrower) angle of view if you focus on a closer subject because ofthe way the optical design works (changing focal length with focusdistance)...

Not necessarily newer, and not necessarily Tamron!.

The 100/2.8 Macro (Canon, short telephoto prime, 1990-ish design) that I mentioned in my earlier post gets wider by over 20% at closest focus. And my Sigma 18-50/2.8 (Sigma, retrofocus wide angle zoom, 2007 design) also gets much wider..

This discussion made me curious about my other lenses so I checked them all. I have a 50/1.8 Mk1, an old short tele zoom, and a 75-300 zoom (all Canon) and all of them show the same property although the extent is quite variable...

Comment #7

Jim Cockfield wrote:.

This calculator takes focus distance into consideration whencomputing angle of view:.

Http://stegmann.dk/mikkel/barnack/.

Yes, Barnack is the best simulator of photo/optical characteristics around..

My "detector" went off when I read Steve say, "My EF 100/2.8 Macro has a focal length of 100 mm when focused at infinity, reducing to 77 mm when focused at it's minimum distance of about 30 cm.".

I agree that the angular FOV changes slightly, but the FL doesn't. A quick pass through Barnack confirms this....

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #8

Chuxter wrote:.

Jim Cockfield wrote:.

This calculator takes focus distance into consideration whencomputing angle of view:.

Http://stegmann.dk/mikkel/barnack/.

Yes, Barnack is the best simulator of photo/optical characteristicsaround..

My "detector" went off when I read Steve say, "My EF 100/2.8 Macrohas a focal length of 100 mm when focused at infinity, reducing to 77mm when focused at it's minimum distance of about 30 cm.".

I agree that the angular FOV changes slightly, but the FL doesn't. Aquick pass through Barnack confirms this....

No, the focal length changes..

I suggest you get your detector fixed...

Comment #9

Steve Balcombe wrote:.

Chuxter wrote:.

Jim Cockfield wrote:.

This calculator takes focus distance into consideration whencomputing angle of view:.

Http://stegmann.dk/mikkel/barnack/.

Yes, Barnack is the best simulator of photo/optical characteristicsaround..

My "detector" went off when I read Steve say, "My EF 100/2.8 Macrohas a focal length of 100 mm when focused at infinity, reducing to 77mm when focused at it's minimum distance of about 30 cm.".

I agree that the angular FOV changes slightly, but the FL doesn't. Aquick pass through Barnack confirms this....

No, the focal length changes..

I suggest you get your detector fixed..

My detector is usually tuned pretty well....

Is your lens the early version or the late (USM) version?.

In simple, thin lenses, nothing in the lens changes as it is focused...just the relationship between the subject, lens, and detector. I'm 100% sure that a lens like this doesn't change it's LF as it is moved to focus..

In compound, multi-element lenses, as all elements are moved as one group to focus, the FL doesn't change either. I'm 100 % sure..

However, in multi-element lenses with 1 or more floating elements, I'm not sure and althought I've spent 2 hours looking for data on line, I can't find much. One reference I found was a sentence on Wikipedia:.

"When the lens is adjusted to photograph objects closer to the camera, the actual focal length of the lens changes.".

But there was no explanation why or information about how much it changes..

I also found this by Peter White, on the photo.net Canon EOS Forum:.

"Changing the focus distance also changes the focal length. The focal length is always the physical distance from the optical center of the lens to the film plane. Another way to look at it is it's the distance that a pinhole would have to be from a film plane to give you the same magnification as you're getting with your lens. So, as you move the lens away from the film plane to focus closer than infinity, you are increasing the focal length. The stated focal length is always the focal length at infinity. The difference between a lens and a pinhole is that "focus" doesn't change with the focal length of a pinhole, and only a lens has a minimum useable focal length, the distance at which it's focused at infinty.".

I believe this is wrong. I got to the 2nd sentence where he said, "The focal length is always the physical distance from the optical center of the lens to the film plane." This is not correct. If you are thinking like Peter, you are 100% wrong..

In the same thread, Alistair Windsor corrected Peter:.

"Moving the lens away from the film plane does not alter the focal length it merely brings a closer object to focus on the film plane. This does not alter the focal length any more than adding extension tubes alters the focal length. A lens has a focal length independent of it being mounted on a camera.".

I 100% agree with what Alistair said..

However, in the next sentence, he said:.

"The Canon 100/2.8 macro also features internal focus and also changes focal length as you focus closer. It is about 70mm at 1:1 reproduction ratio.".

This confirms what you said..

Peter then responded:.

"...if your description is accurate then the lens is technically a zoom; just one that alters it's focal length as you adjust for distance.".

AH! At last, I understand. You have a complicated lens that intentionally changes it's FL during focus operations. It's a zoom lens design, but the FL is not adjustable independently...it's linked to the focus adjustment..

This seems to be a moderately common practice as it reduces the FL as the lens is focused on near objects in order to minimize the amount of extension (this makes the lens smaller) and to control abberations. However, I've not seen data about how many of the "internal focusing" lens designs zoom the FL and by how much..

For the OP, the relationship of the lens to the subject and image is defined by a simple equation (for thin lenses):.

1/Focal Length = 1/Dsubject + 1/Dimage.

Note that magnification is Dimage/Dsubject. When any lens (regardless of the FL) is focused at infinity, the magnification is FL/infinity = 0. When the distance to the subject is equal to the distance to the image (regardless of FL), the magnification is 1:1..

The data that Barnack gives is correct for simple lenses (ie, those that don't zoom as you focus). For these complex zoom while focusing designs, the amount of FL change is variable and not well documented. Barnack shows small changes in FOV as the subject gets close to the lens..

BTW, Peter never did "get it". Alistair was unable to explain things well enough. If you want to read the complete thread:.

Http://photo.net/bboard/q-and-a-fetch-msg?msg_id=00I6hq.

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #10

Chuxter wrote:.

My detector is usually tuned pretty well....

Time for an upgrade I guess..

[snip].

I also found this by Peter White, on the photo.net Canon EOS Forum:.

"Changing the focus distance also changes the focal length. The focallength is always the physical distance from the optical center of thelens to the film plane. Another way to look at it is it's thedistance that a pinhole would have to be from a film plane to giveyou the same magnification as you're getting with your lens. So, asyou move the lens away from the film plane to focus closer thaninfinity, you are increasing the focal length. The stated focallength is always the focal length at infinity. The difference betweena lens and a pinhole is that "focus" doesn't change with the focallength of a pinhole, and only a lens has a minimum useable focallength, the distance at which it's focused at infinty.".

I believe this is wrong. I got to the 2nd sentence where he said,"The focal length is always the physical distance from the opticalcenter of the lens to the film plane." This is not correct. If youare thinking like Peter, you are 100% wrong..

Yes, it is wrong, and it is NOT what I said..

Charlie, you need to remember something here. It is you who has spent two hours researching this on the web because you didn't understand it. Not me. Quotes from people who also don't understand it are unlikely to take us forward..

[snip].

For the OP, the relationship of the lens to the subject and image isdefined by a simple equation (for thin lenses):.

1/Focal Length = 1/Dsubject + 1/Dimage.

Note that magnification is Dimage/Dsubject. When any lens (regardlessof the FL) is focused at infinity, the magnification is FL/infinity =0. When the distance to the subject is equal to the distance to theimage (regardless of FL), the magnification is 1:1..

Yes... and? If only you'd followed that through....

1/f = 1/a + 1/b ........ but at 1:1, a=b1/f = 2/af = a/2.

Now, camera focusing distance is (by long established convention) measured from the film plane to the subject, so.

D = a + bd = 2a .................... (at 1:1)a = d/2.

F = a/2 = (d/2)/2f = d/4.

Minimum focus distance of the Canon 100/2.8 Macro MkI is 307 mm (by the focusing scale on the lens) but this is at 1:1 so the focal length is 307/4 = 77mm. QED...

Comment #11

Steve Balcombe wrote:.

Chuxter wrote:.

My detector is usually tuned pretty well....

Time for an upgrade I guess..

Nope. It's still tuned and going off again... .

[snip].

I also found this by Peter White, on the photo.net Canon EOS Forum:.

"Changing the focus distance also changes the focal length. The focallength is always the physical distance from the optical center of thelens to the film plane. Another way to look at it is it's thedistance that a pinhole would have to be from a film plane to giveyou the same magnification as you're getting with your lens. So, asyou move the lens away from the film plane to focus closer thaninfinity, you are increasing the focal length. The stated focallength is always the focal length at infinity. The difference betweena lens and a pinhole is that "focus" doesn't change with the focallength of a pinhole, and only a lens has a minimum useable focallength, the distance at which it's focused at infinty.".

I believe this is wrong. I got to the 2nd sentence where he said,"The focal length is always the physical distance from the opticalcenter of the lens to the film plane." This is not correct. If youare thinking like Peter, you are 100% wrong..

Yes, it is wrong, and it is NOT what I said..

Good, But I didn't say that was what you said. In fact, I was ASKING if you THOUGHT that way! Note that I have difficulty determining what you are thinking, at times.  .

Charlie, you need to remember something here. It is you who has spenttwo hours researching this on the web because you didn't understandit. Not me. Quotes from people who also don't understand it areunlikely to take us forward..

Quit preaching. I admitted that I had never seen a lens like your macro. This exercise was informative. Note however that I also included quotes from Alistair, who DID understand. You snipped all his quotes so you could lecture me, I guess..

[snip].

For the OP, the relationship of the lens to the subject and image isdefined by a simple equation (for thin lenses):.

1/Focal Length = 1/Dsubject + 1/Dimage.

Note that magnification is Dimage/Dsubject. When any lens (regardlessof the FL) is focused at infinity, the magnification is FL/infinity =0. When the distance to the subject is equal to the distance to theimage (regardless of FL), the magnification is 1:1..

Yes... and? If only you'd followed that through....

It was for the OP, not you. I said so..

1/f = 1/a + 1/b ........ but at 1:1, a=b1/f = 2/af = a/2.

Now, camera focusing distance is (by long established convention)measured from the film plane to the subject, so.

D = a + bd = 2a .................... (at 1:1)a = d/2.

F = a/2 = (d/2)/2f = d/4.

Minimum focus distance of the Canon 100/2.8 Macro MkI is 307 mm (bythe focusing scale on the lens) but this is at 1:1 so the focallength is 307/4 = 77mm. QED..

I wonder if the OP learned anything from your equations?.

I'm getting the idea that you didn't MEASURE the FL of your lens at 1:1, but calculated it as above? Hmmm...I thought you said you had "measured" it? Yes, I see at the end of your 1st post, you said (in part), "...Nothing special about this lens, it just happens to be one I've measured." Not only did you say that you had measured the FL, you also said that your wierd macro lens was "nothing special"!.

I think that you are a terrible influence on this, the "Beginners Questions Forum"..

The OP asked a really good, simple question. You referenced your strange macro lens that zooms while focusing as if it was common! If the OP had told us that he had a lens like yours or even a similar lens, then there would be justification for your ploy. If you had said that most lenses don't work like your lens, then explained how it works, that too would be OK. But to simply imply that all lenses work in that strange way is wrong. It doesn't educate the OP and other people who read but don't post (ie, the silent majority)..

If you will recall, your first post said (in part), "...it's hard to generalise because SLR lenses are very complex. They focus not by moving the whole lens in and out, but by moving certain elements. In some of the best lenses the front and rear elements (or groups) are in fixed positions and only the middle group(s) move. As you change focus, the focal length also changes and that changes the field of view.".

That snipped paragraph has massive problems. Let me take them one by one:.

1. Some SLR lenses are very simple. Some are very complex. There are both kinds.2. Some SLR lenses focus by moving the COMPLETE lens group as a unit!.

3. Some of the best lenses only keep the FRONT group fixed and move everything else. There are many different ways to focus a lens!4. In MOST lenses the focal length DOES NOT change as you focus..

5. The FOV changes as you focus, but not for any of the reasons you talked about. The FOV changes as a function of focus was what the OP asked about. I suspect his lens (what ever it is) doesn't zoom as it's focused. You ignored the OP's question, except for your first comment: "The field (angle) of view does in fact change as you focus, although it might not be enough to be obvious." That was a great reply. You probably should have stopped there?.

I also think your assumption that the OP had a dSLR was presumptious. He never gave you any reason to think that. Why not speak about lenses in general, instead of trying to impress us?.

You are NOT much help teaching beginners about photography! KISS....

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #12

Chuxter wrote:.

Steve Balcombe wrote:.

Chuxter wrote:.

For the OP, the relationship of the lens to the subject and image isdefined by a simple equation (for thin lenses):.

1/Focal Length = 1/Dsubject + 1/Dimage.

Note that magnification is Dimage/Dsubject. When any lens (regardlessof the FL) is focused at infinity, the magnification is FL/infinity =0. When the distance to the subject is equal to the distance to theimage (regardless of FL), the magnification is 1:1..

Yes... and? If only you'd followed that through....

It was for the OP, not you. I said so..

I saw that. I didn't interpret it as "nobody else is to respond to this"..

[snip].

I wonder if the OP learned anything from your equations?.

Quite possibly, yes. They are very simple. But I'm surprised you commented on that, because it was you who introduced that equation into the discussion, I just took it somewhere useful..

In any case, my guess is that Cedrik0s will have no problem at all with a few simple equations - the original question implied a level of understanding that most 'beginners' wouldn't have. If Cedrok0s didn't learn from the equations it is because he already knew of them, and the result which followed..

I'm getting the idea that you didn't MEASURE the FL of your lens at1:1, but calculated it as above?.

I measured it myself - there was a discussion about it quite recently which you will find in my posting history. But it is also stated on the lens, and in the specifications on Canon's web site..

... Not only did you say that you had measured the FL,you also said that your wierd macro lens was "nothing special"!.

I repeat, it is nothing special. It is common for complex SLR lenses to change focal length as they focus. The reason I used my macro lens as an example is that I could provide actual numbers to back it up. My Sigma 18-50/2.8 exhibits the same property but I don't have the numbers..

The fact that Jim Cockfield said something similar (and he was not referring to the EF100/2.8 Macro that you claim is weird) doesn't seem to have convinced you, so perhaps nothing will..

[snip].

1. Some SLR lenses are very simple. Some are very complex. There areboth kinds.2. Some SLR lenses focus by moving the COMPLETE lens group as a unit!.

Some, yes. I think my 50/1.8 probably does. But telephoto lenses typically don't, zoom lenses don't, and retrofocus lenses can't. Which doesn't leave many, does it?.

3. Some of the best lenses only keep the FRONT group fixed and moveeverything else. There are many different ways to focus a lens!.

Yes, rear focusing is pretty common too. Not sure how that contributes to your case, since it is another example of complexity..

4. In MOST lenses the focal length DOES NOT change as you focus..

5. The FOV changes as you focus, but not for any of the reasons youtalked about..

The FOV change which occurs in a simple lens (the one shown in the Barnack calculations) is a narrowing of the field of view at very close focusing distances. However, what we typically observe in SLR lenses is a widening of the field of view. It *cannot be* caused by the effect shown in Barnack, and shows that the focal length must be changing..

You ignored the OP's question, except for your firstcomment: "The field (angle) of view does in fact change as you focus,although it might not be enough to be obvious." That was a greatreply. You probably should have stopped there?.

So what you are saying is that the first thing I did was to answer the OP's question correctly. And then I went on to state that real SLR lenses are complex, which is obviously true, and relevant. I then expanded on that point by giving the data on one of my own lenses. It is hard to see how that could be - what was it you said? - "a terrible influence on the Beginners Forum"..

I also think your assumption that the OP had a dSLR was presumptious.He never gave you any reason to think that..

True, and very remiss of me. I should never darken the doors of this forum again..

You are NOT much help teaching beginners about photography! KISS....

That is a real jerk remark to finish with...

Comment #13

Steve Balcombe wrote:.

Chuxter wrote:.

[snip].

It was for the OP, not you. I said so..

I saw that. I didn't interpret it as "nobody else is to respond tothis"..

[snip].

I wonder if the OP learned anything from your equations?.

Quite possibly, yes. They are very simple. But I'm surprised youcommented on that, because it was you who introduced that equationinto the discussion, I just took it somewhere useful..

I gave him a tool. You took that tool and gave him an answer about YOUR lens. See the difference? I doubt the OP was interested in YOUR lens... .

In any case, my guess is that Cedrik0s will have no problem at allwith a few simple equations -.

[snip].

You may be right. I also got the impression that he was curious and competent. I suspect that our "discussion" has chased him away. His post that started this thread was his 2nd ever on DPR. He resposted twice in this thread and then disappeared...{snip].

...it is also stated onthe lens, and in the specifications on Canon's web site..

I looked at the Canon site and looked at the specs. I saw nothing about variable FL or variable angle of view:.

Http://www.usa.canon.com/...hSpecsTabAct&fcategoryid=155&modelid=7400.

Is there another specification?.

... Not only did you say that you had measured the FL,you also said that your wierd macro lens was "nothing special"!.

I repeat, it is nothing special. It is common for complex SLR lensesto change focal length as they focus. The reason I used my macro lensas an example is that I could provide actual numbers to back it up.My Sigma 18-50/2.8 exhibits the same property but I don't have thenumbers..

This is a good discussion...finally. I understand that many current ZOOM lenses have 1-2 floating internal lens groups. But that's a different animal. I'm not aware that many fixed FL lenses do this. And especially I'm surprised that they vary the FL as it's focused! I'm very interested in this development. Like, does Nikon do this with their 105/f2.8? I've read several reviews and so far never seen anything imply they do.[snip].

1. Some SLR lenses are very simple. Some are very complex. There areboth kinds.2. Some SLR lenses focus by moving the COMPLETE lens group as a unit!.

Some, yes. I think my 50/1.8 probably does. But telephoto lensestypically don't, zoom lenses don't, and retrofocus lenses can't.Which doesn't leave many, does it?.

Zoom lenses are not a part of this discussion. All my old Nikkor lenses move all the lens elements as one group. I have measured them. I think most of my Nikkor lenses are retrofocus designs? I think you are wrong here. I think it is a reasonably new design paradigm (to make fixed FL lenses change FL)..

The FOV change which occurs in a simple lens (the one shown in theBarnack calculations) is a narrowing of the field of view at veryclose focusing distances. However, what we typically observe in SLRlenses is a widening of the field of view. It *cannot be* caused bythe effect shown in Barnack, and shows that the focal length must bechanging..

Yes, I agree...now. But, go back and read the OPs original post. He was OBVIOUSLY asking about the narrowing of FOV as a result of the small geometry change:.

"...If setting the focus is changing the distance between the lens and the CCD to bring the object's image in the CCD plan, then the vision angle should change slightly when moving the focus. Basically the angle should be greatest when focusing infinitely far (image on the lens' focal point), and get smaller when focusing on a closer object...".

When you answered his question, you answered the WRONG question. You were centered on YOUR lens and took the thread off in a weird direction. The OP even replied and thanked you for this! I hope by now he has read some more of his thread and has seen that most prime lenses don't work that way..

What you should have done, if you are really trying to help Beginners, is to FIRST answer their question in a simple and basic way. THEN, say that it can be more complicated...that SOME lenses, with multiple internal moving lens groups, actually zoom the FL as the lens is focused. Then explain why..

You ignored the OP's question, except for your firstcomment: "The field (angle) of view does in fact change as you focus,although it might not be enough to be obvious." That was a greatreply. You probably should have stopped there?.

So what you are saying is that the first thing I did was to answerthe OP's question correctly. And then I went on to state that realSLR lenses are complex, which is obviously true, and relevant. I thenexpanded on that point by giving the data on one of my own lenses. Itis hard to see how that could be - what was it you said? - "aterrible influence on the Beginners Forum"..

I think, in hindsight, that you were trying to do what I stated above. I appologize for thinking you were a marplot. I guess you were too terse for me to understand? I didn't detect the break between your first sentence and the rest..

I also think your assumption that the OP had a dSLR was presumptious.He never gave you any reason to think that..

True, and very remiss of me. I should never darken the doors of thisforum again..

Actually, that was what I was thinking last night..

You are NOT much help teaching beginners about photography! KISS....

That is a real jerk remark to finish with..

Yep. I think I have learned more than Cedric. I guess that makes me a Beginner? .

Have a good day and try to write better in the future....

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #14

Chuxter wrote:.

What you should have done, if you are really trying to helpBeginners, is to FIRST answer their question in a simple and basicway. THEN, say that it can be more complicated...that SOME lenses,with multiple internal moving lens groups, actually zoom the FL asthe lens is focused. Then explain why..

I will be sure to run my answers by you in future, so you can correct my presentation..

It really is hard to believe that someone who has had to admit so many mistakes in one thread is *still* trying to tell me how I should have answered the OP's question, and then telling me I shouldn't be here at all..

Amazing...

Comment #15

Steve Balcombe wrote:.

Chuxter wrote:.

What you should have done, if you are really trying to helpBeginners, is to FIRST answer their question in a simple and basicway. THEN, say that it can be more complicated...that SOME lenses,with multiple internal moving lens groups, actually zoom the FL asthe lens is focused. Then explain why..

I will be sure to run my answers by you in future, so you can correctmy presentation..

No! Just don't "bristle" when I try to correct what you said. Even if I'm misreading what you said...even if I'm wrong...that gives you a chance to refine HOW you are communicating and to perhaps expalin things better..

It really is hard to believe that someone who has had to admit somany mistakes in one thread is *still* trying to tell me how I shouldhave answered the OP's question, and then telling me I shouldn't behere at all..

The difference is that I was willing to admit my mistake (singular). I simply didn't understand that you were saying that most lenses DON'T zoom as the focus ring is twisted and that a few, "weird" lenses do this..

Also, you (correctly) read into two of my sentences that I was THINKING that it would be nice if Steve Balcombe stayed off the Beginners Questions forum. However, I never told you to do this. I just said:.

"I think that you are a terrible influence on this, the Beginners Questions Forum" and "You are NOT much help teaching beginners about photography!".

But I've mellowed out. Sleep and then coffee....

Amazing..

You sure are! .

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #16

Well thank you all for the discussion..

I am sorry it's getting hot between some of you..

Anyway it might show that my question was not as simple as I thought it was. .

I am not yet into photography, really, as I only own a compact camera (which I enjoy though). I am informing myself on the subject before I get a good camera..

I like to get the "why's" of things. And as I had studied lenses basics when I was younger, I came to the conclusion that the fov should change as the focus changes (in the case of a single thin lens). But I could neither see this effect on my camera neither on friends' cameras which I could only manipulate for a short time..

I regularly encounter new questions as I think of those things... but they are questions of someone that doesn't even have an objective in his hands. So maybe the questions will seem weird... you may see on future posts  ..

Anyway now I know more, thanks to you guys..

Thanks...

Comment #17

Cedrik0s wrote:.

Well thank you all for the discussion..

I am sorry it's getting hot between some of you..

Thanks for posting again. I was afraid we had chased you off! I'm sorry the discussion between Steve and I got so far off topic..

Anyway it might show that my question was not as simple as I thoughtit was. .

I am not yet into photography, really, as I only own a compact camera(which I enjoy though). I am informing myself on the subject before Iget a good camera..

That's an excellent approach..

I like to get the "why's" of things. And as I had studied lensesbasics when I was younger, I came to the conclusion that the fovshould change as the focus changes (in the case of a single thinlens). But I could neither see this effect on my camera neither onfriends' cameras which I could only manipulate for a short time..

As Steve correctly said, the effect is small. Nothing to worry about..

I regularly encounter new questions as I think of those things... butthey are questions of someone that doesn't even have an objective inhis hands. So maybe the questions will seem weird... you may see onfuture posts  ..

I hope so. I like weird questions, as I invariably learn something!.

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

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