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06-16-2010, 06:59 AM   #676
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2nd pic is a nice close shot Tom! (would've commented last night but posted from my ipod touch and didn't see the pic!)

06-16-2010, 01:51 PM   #677
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QuoteOriginally posted by kacansas03 Quote
About a telephoto lens magnification ability. I have several lenses from 135 mm up. I noticed that some will, as an example, have a focusing range like on one of my 200's that runs up to 200 feet just before being at infinity. I also have a 200 mm that goes up to 50 feet just before infinity. I do not think that this focusing range has anything to do with magnification but I am wondering why the much longer lenses do not go much higher in the distance of the focusing range? Yes, I know infinity is higher than any number on the barrel. I think that the focusing range has to do with placement of elements and this is where the designers come up with the ability of a say 300 mm lens to focus clearly at 2 feet, as an example. I think that same 300 mm lenses(just made it up people) would then have a short, say out to 50 feet, focusing range before reaching infinity. Would that 300 mm have less magnification ability than some 300 mm that had a focusing range out to 300 feet? I know this is confusion in my own head but I am trying to understand plus learn about some of the principles in lens design. Does anyone have an answer that could help me?
Is there another thread where I should post these questions of mine??
06-16-2010, 01:55 PM   #678
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QuoteOriginally posted by Canada_Rockies Quote
The near focus is set by the lens designer, but distance scale has a lot to do with the focal length and the change in depth of field as the focal length increases. For example, a 28 mm lens at f/8 has a hyperfocal distance around 10 feet on 24x36 mm film or sensor - focused at 10 feet with the f/stop at f/8, and 8x10 print will appear sharp from about 5 feet to infinity. On the other hand, the hyperfocal distance for my M 400 at f/45 (that's right 45, out beyond 32) is a bit over 300 feet, and will be acceptable on an 8x10 print as close as 200 feet.

The other factor about the focus scale is the amount of turn the focus ring has. The 400 has a focus turn of somewhere around 270 degrees which leaves lots of room to engrave numbers, so the scale reads all the way up to 300 ft and 100 meters. Another brand of 400mm lens may only have 180 degrees of rotation, which would leave less room to engrave the numbers on it. The 300/100 would run into the infinity mark.

In short, the distance scale needs a lot more numbers at 400mm than at 28mm. I hope this clears the mist up a bit for you.
I guess I was asking why some lenses of say 400 mm say 100 feet as the maximum and others say 500 feet as the maximum on the focus scale. My guess is that some 400 mm lenses are built to close focus while other are built more for distant focus. It could be that is what you were saying in your post but I still wonder about the magnification of say any given 400 mm lens. Will all 400 mm lenses have the same amount of magnification? Does that hold true for 200 mm and 800 mm lenses?
06-16-2010, 02:28 PM   #679
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QuoteOriginally posted by kacansas03 Quote
Is there another thread where I should post these questions of mine??
The Lens Discussion Forum is the right place, I would assume. And if I read the answers correctly, you got the right answers already:

The lettering on the lens barrel for the distances has nothing to do with the optical abilities of your lenses. It has more to do with the available printing space on the tube and it has something to do with the mechanical build of the lens. The focusing threads have different throws and if you have a fine pitched thread, you need to turn the focusing ring much more to span a given distance, than on a coarsely pitched thread.

The finer thread would then invite the lens makers to make a more detailed distance scale, wheras a coarser thread will be accompanied by a matching distance scale, which is not as detailed.

Any normal lens* will focus between its nearest focus point to infinity steplessly, in infinity increments. The distance scale is only a visual aid for the photographer when handling the lens.

Ben

* we will ignore fixed-focus lenses or lenses with only a couple of distinct distance settings, which you may find on cheap compact cameras at times…

06-16-2010, 03:48 PM   #680
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QuoteOriginally posted by Ben_Edict Quote
The Lens Discussion Forum is the right place, I would assume. And if I read the answers correctly, you got the right answers already:

The lettering on the lens barrel for the distances has nothing to do with the optical abilities of your lenses. It has more to do with the available printing space on the tube and it has something to do with the mechanical build of the lens. The focusing threads have different throws and if you have a fine pitched thread, you need to turn the focusing ring much more to span a given distance, than on a coarsely pitched thread.

The finer thread would then invite the lens makers to make a more detailed distance scale, wheras a coarser thread will be accompanied by a matching distance scale, which is not as detailed.

Any normal lens* will focus between its nearest focus point to infinity steplessly, in infinity increments. The distance scale is only a visual aid for the photographer when handling the lens.

Ben

* we will ignore fixed-focus lenses or lenses with only a couple of distinct distance settings, which you may find on cheap compact cameras at times…
So the Magnification ability of a given focal length is the same no matter what the markings? Such as 400 mm = 8 power magnification no mater what the brand or scale of distance numbers?
06-17-2010, 01:32 AM   #681
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QuoteOriginally posted by kacansas03 Quote
So the Magnification ability of a given focal length is the same no matter what the markings? Such as 400 mm = 8 power magnification no mater what the brand or scale of distance numbers?
Yes - for any given lens-camera combination.

For a Pentax DSLR figure about 3x of magnification for every 100mm of lens focal length. Thus on a Pentax DSLR a 400mm lens would give you about 12x magnification.

There is a simple direct linear relationship between FL and magnification.

FL is magnification for all practical purposes.

Last edited by wildman; 06-17-2010 at 03:34 AM.
06-17-2010, 03:30 AM   #682
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QuoteOriginally posted by kacansas03 Quote
So the Magnification ability of a given focal length is the same no matter what the markings? Such as 400 mm = 8 power magnification no mater what the brand or scale of distance numbers?
The "magnification" is just a convenience tool. It has no real meaning. If you say, the 400mm lens has an 8x magnification, you would compare it to a 50mm standard lens on 24x36mm film format. On APS-C you could base the magnification factor on a standard lens of 30mm and would get something like a 13x magnification or you would simply use the crop factor of 1.5x, as wildman did and get 12x magnification.

And is you use the 400mm lens on a 645 camera where a 80mm lens is the standard lens, you would only have a 5x magnification lens.

So the "magnification" is somewhat arbitrary and wholly dependent on the calculation base, i.e. the standard lens you use as the base.

I personally never used that "magnification factor", as it has really no meaning. THe real measure is the focal length of the lens.

Ben
06-17-2010, 03:41 AM   #683
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QuoteOriginally posted by wildman Quote
Yes - for any given lens-camera combination.

For a Pentax DSLR figure about 3x of magnification for every 100mm of lens focal length. Thus on a Pentax DSLR a 400mm lens would give you about 12x magnification.

There is a simple direct linear relationship between FL and magnification.

FL is magnification for all practical purposes.
Ah-ha! Would the FF formula be +/- 2(FL/100mm) then?

06-17-2010, 03:51 AM   #684
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QuoteOriginally posted by Ben_Edict Quote
The "magnification" is just a convenience tool. It has no real meaning. If you say, the 400mm lens has an 8x magnification, you would compare it to a 50mm standard lens on 24x36mm film format. On APS-C you could base the magnification factor on a standard lens of 30mm and would get something like a 13x magnification or you would simply use the crop factor of 1.5x, as wildman did and get 12x magnification.

And is you use the 400mm lens on a 645 camera where a 80mm lens is the standard lens, you would only have a 5x magnification lens.

So the "magnification" is somewhat arbitrary and wholly dependent on the calculation base, i.e. the standard lens you use as the base.

I personally never used that "magnification factor", as it has really no meaning. THe real measure is the focal length of the lens.

Ben
But it's a useful way to expressing an important optical characteristic across formats, isn't it?
06-17-2010, 04:47 AM   #685
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QuoteOriginally posted by dadipentak Quote
Ah-ha! Would the FF formula be +/- 2(FL/100mm) then?
Yes.

Or, more directly, 2x1=2x mag.

So a 400mm lens on a FF would simply be 2x4=8x mag.

If we use the convention of a "normal" lens defined by the diagonal of the image plane of the camera than more precisely we would get 43mm/100mm or 2.33x of magnification per 100mm of FL.

Thus a 400mm lens on a FF would be 2.33x4=9.32x of mag.

and...

On a Pentax DSLR 28mm/100mm=3.6x mag per 100mm of FL.
So on a 400mm lens it would be 3.6x4=14.4x of mag.

But for real world practical use out in the field just 3x(per 100mm of FL) is all you really need for your Pentax DSLR.

Out in the field I don't say this a shot for my 15x mag glass but this is a shot for the 500mm.
06-17-2010, 08:12 AM   #686
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QuoteOriginally posted by dadipentak Quote
But it's a useful way to expressing an important optical characteristic across formats, isn't it?
I simply do not know, whether anybody finds this helpful. I for once have never used that and I have very, very rarely seen any reference to that "magnification" in photographioc books ar mags. Magnification is a term much more related to visual observations with binoculars or telescopes. In binos it is indeed part of the specs, wheras I have seen it only a handful of times mentioned in photographic lens specs during the last three decades.

I find focal length in mm much easier to understand. But as with many other things, this is a personal preference.

Ben
06-17-2010, 08:44 AM   #687
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QuoteOriginally posted by Ben_Edict Quote
I simply do not know, whether anybody finds this helpful. I for once have never used that and I have very, very rarely seen any reference to that "magnification" in photographioc books ar mags. Magnification is a term much more related to visual observations with binoculars or telescopes. In binos it is indeed part of the specs, wheras I have seen it only a handful of times mentioned in photographic lens specs during the last three decades.

I find focal length in mm much easier to understand. But as with many other things, this is a personal preference.

Ben
When asked by non-photographic people, I have equated the "power" of a lens to the binocular equivalent: "It's a 400 mm lens, about like a pair of 8x binoculars", or now with APS-C format, "...l a pair of 12X binoculars". It does give the layman an idea of how much closer the subject will appear.
06-17-2010, 09:39 AM   #688
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QuoteOriginally posted by wildman Quote
Yes - for any given lens-camera combination.

For a Pentax DSLR figure about 3x of magnification for every 100mm of lens focal length. Thus on a Pentax DSLR a 400mm lens would give you about 12x magnification.

There is a simple direct linear relationship between FL and magnification.

FL is magnification for all practical purposes.
Thank You very much. I thought that was the case but I started questioning it because of the variable differences from various 200 and 300 mm lenses. I realize that it was DOF which is a function of a lens largest open aperture. So I have it all straight again. Thanks again.
Alan.
06-17-2010, 10:51 AM   #689
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QuoteOriginally posted by Ben_Edict Quote
I simply do not know, whether anybody finds this helpful. I for once have never used that and I have very, very rarely seen any reference to that "magnification" in photographioc books ar mags. Magnification is a term much more related to visual observations with binoculars or telescopes. In binos it is indeed part of the specs, wheras I have seen it only a handful of times mentioned in photographic lens specs during the last three decades.

I find focal length in mm much easier to understand. But as with many other things, this is a personal preference.

Ben
About the only time I've seen a "magnification" factor is on P&S cameras - as in: 8x optical & 4x digital. Doesn't seem to have any real relevance on a DSLR or SLR. YMMV
06-17-2010, 02:13 PM   #690
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"Magnification" as I understand it and how I use it - for what it's worth.

I'm very image centered. So , for instance, I use a lens on a box out in the yard. It's real dimensions is 20" wide by 10" tall. When I look at the image of the box on the screen I find that it's screen dimensions is 2000x1000 pixels.

Than I change the lens and take another picture at the same distance. I find that with this lens that the screen dimensions are now 4000x2000 pixels.

What ever the original mag of the first lens I know that the second lens has given me a 2x increase in magnification and that therefore the second lens has a real or effective FL twice that of the first lens.

In other words, for me, magnification has everything to do with the scale of the subject within the frame of the image. I shoot mainly small birds half the size of a man's fist and ideally I would like the length of the bird to be about 1/3 to 1/2 the width of the image frame and sometimes larger. This requires very long glass. My 500mm is at the bottom of my useful range for instance.

I have four different FL of glass and I pretty precisely know when a bird is within range of a particular FL to give me the image scale I want. Image scale is a function of magnification. But my sense of "magnification" is intuitive rather than analytical. I know that if a little Warbler get's much beyond 25 feet it's out of range for the 500mm for instance.

One was taken at 1000mm and the other at 560 - can you tell which is which?

Last edited by wildman; 07-30-2010 at 07:23 PM.
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