Why no long telephoto zoom lenses specifically for cropped frame DSLR's

[richardsperry]

<p>James,</p>

<p>Optically, as you say, a 600mm lens has a 2 foot image circle.<br /> It may, I don't know. A single element 600mm lens may.<br /> A modern 600mm lens is does not actually have a actual focal distance of 600mm. The distance from the first lens element is not 600mm from the film or sensor. There are intermediate lenses which elongate the focal length. But they also reduce the image circle. I am sure that a single element lens of focal length 600mm may have a 2 food image circle, but these single element lenses are not produced.</p>

<p>The Nikkor 600mm F4 is only 445mm long, for example.<br /> http://www.nikonusa.com/Nikon-Products/Product/Camera-Lenses/2173/AF-S-NIKKOR-600mm-f%252F4G-ED-VR.html#tab-ProductDetail.ProductTabs.TechSpecs<br /> <strong>Dimensions </strong><br /> (Approx.)6.5x17.5 in. (Diameter x Length)<br />166x445mm (Diameter x Length)</p>

<p>Even adding in the addition of length between the last element to the sensor or film, that does not account for the difference in 155mm of distance.</p>

<p>Most DX lenses will vignette on a FF camera. The image circles on multi element lenses are very small, smaller than 2 feet.</p>

[richardsperry]

<p>Scott,<br /> "therefore to reproduce a print where the subject is the same size you must have to enlarge them both by the same amount."</p>

<p>I am still quite sure, despite your reassurances to the contrary, that if you take a pic of a bird at the same distance as me, with your D3, and I with my D300 that your bird will be different size, with the same AF-S Nikkor 50mm f/1.4G lens...<br /> http://www.nikonusa.com/Nikon-Products/Product/Camera-Lenses/2180/AF-S-NIKKOR-50mm-f%252F1.4G.html</p>

<p>That our unedited produced images will not look the same. I am sure that my bird will be larger in my image than in your image.</p>

<p>Are we done yet?</p>

[richardsperry]

<p>Edit timed out.</p>

<p>That your bird will <strong>NOT</strong> be the same size.</p>

[scott_ferris]

<p>Sorry Richard, </p>

<p>I thought you understood this stuff and we were talking about the same thing in a different way. It turns out though that you don't know what you are talking about.</p>

<p>First an easy one. A 600mm lens has a focal length of 600mm, that is the primary optic has a focal point 600mm behind it. The term telephoto lens was introduced to describe a lens that was shorter than its own focal length.</p>

<p><em>"There are intermediate lenses which elongate the focal length"</em> No, there are intermediate lenses that adjust the light path but they do not elongate the primary optics focal length, they shorten the light path. This is easy to work out, a 600mm f4 must have an apparent aperture of 150mm, so the front optic of a 600mm f4 has to be no less than 150mm, measure one, it is.</p>

<p>I'll try to explain your other mistakes better as well.</p>

[richardsperry]

<p>Scott,</p>

<p>Explain to me how a lens with a focal length of 600mm is only 445mm long. From rim to mount.</p>

<p>Explain to me how I own a focal length 500mm lens which is only 120mm long on my camera. And produces an image on your FF camera comparable to a 750mm lens.</p>

<p>I r sofa king wee todd id. Splain it to me 2 how i r cun undastan pleez.</p>

<p><em>""There are intermediate lenses which elongate the focal length"</em> No, there are intermediate lenses that adjust the light path but they do not elongate the primary optics focal length, they shorten the light path."</p>

<p>You and I are just destined to disagree, I suppose. If you shorten the light path, as you say, does that not result in a longer elongated equivalent focal length?</p>

<p>I own a 500mm focal length lens that is only 120mm long, to say that you are wrong here Scott.</p>

[scott_ferris]

<p><em>"Scott,</em><br>

<em>"therefore to reproduce a print where the subject is the same size you must have to enlarge them both by the same amount."</em><br>

<em>I am still quite sure, despite your reassurances to the contrary, that if you take a pic of a bird at the same distance as me, with your D3, and I with my D300 that your bird will be different size, with the same AF-S Nikkor 50mm f/1.4G lens..."</em><br>

Not if you enlarge them both by the same amount. Don't forget, my sensor is bigger so my print has to be bigger if we enlarge them the same amount. If we do enlarge them the same amount your image is contained inside my image at exactly the same size.<br /><br /><br>

<em>"That our unedited produced images will not look the same. I am sure that my bird will be larger in my image than in your image."</em> </p>

<p>Yes our unedited images look different, I have a lot more information than you, and if we view them at the same size, mine is enlarged much less than yours so the subject <strong>appears</strong> smaller, but they were both recorded at the same size, yet again, <strong>your image is being enlarged much more</strong> than mine to fill your screen, so of course your bird looks bigger. Look at it this way, how could a lens know, or project differently, onto a ff sensor or a crop sensor, it can't, it projects the image at the same size onto any sensor with the same registry distance. </p>

<p>Try thinking like this, in James' scenario the bird is reproduced on the sensor at 24mm high, that fills your sensor, now do a 20x enlargement and your bird is 480mm tall, or 19" odd, a good sized print. Now enlarge my full capture 20x my print is a whopping 720mm tall, 28". But the bird is a smaller portion of that 28", how much? Well 9"! Yep the bird ends up being 19" tall in my print too, when it is enlarged the same amount as your smaller capture and smaller print.</p>

<p><em>"Are we done yet?"</em></p>

<p>I don't know, do you understand yet?</p>

[scott_ferris]

<p>It would appear you don't!<br>

<em>"Explain to me how a lens with a focal length of 600mm is only 445mm long.</em>" <a href="http://en.wikipedia.org/wiki/Telephoto_lens">Because it is a telephoto lens.</a></p>

<p><em>"If you shorten the light path, as you say, does that not result in a longer elongated equivelent focal length?"</em> No.</p>

[richardsperry]

<p>"Don't forget, my sensor is bigger so my print has to be bigger if we enlarge them the same amount."</p>

<p>I asked you what your max resolution size was, Scott.</p>

<p>What is it?</p>

<p>"...so the subject <strong>appears</strong> smaller"</p>

<p>That's what I said over and over again. The word apparently, which I have used properly over and over again, means what something <strong>appears</strong> to be. They are derived from the same meaning. They even look the same.</p>

[scott_ferris]

<p>Resolution is still irrelevant when talking about reproduction ratios.</p>

<p>Oh, it seems my Wiki link supports your shorter focal length position, funny because that is not what I was taught. Never mind I did get the telephoto meaning right and I also understand projected image size and reproduction ratios whereas you obviously don't.</p>

[richardsperry]

<p>Scott,</p>

<p>You are either obtuse or intentionally argumentative for argument sake. I am done.</p>

 

[scott_ferris]

<p>I think I give up. You are not a beginner, I am not helping you, you have some strong opinions that are incorrect and you just don't understand. I have failed you, sorry.</p>

[James G. Dainis]

Let us resort to math. I am going to round all numbers off to avoid irritating decimals.

 

The D3 sensor is 36 x 24 mm and has a resolution, image size, of 4256 x 2832

 

The D300 sensor is 24 x 16 mm and has a resolution, image size, of 4288 x 2848 mm.

 

 

Take a shot of the bird using the same lens on each camera and at the same distance such that the bird is 24 mm long from beak to tail on each of the sensors.

 

On the D300 (24 x 16mm sensor) the bird will just fill the sensor, the beak touching one side, the end of the tail touching the other side.

 

On the D3 (36 x 24 sensor) the bird will have 6mm of space between its beak and tail and the sides of the sensor.

 

Take the image captures to a printer and tell him you want a 12 x 8 inch print made of each one.

 

He will print them at 360 ppi.

 

D3 = 4256/360 by 2832/360 = 12 x 8 inches.

 

D300 = 4288/360 by 2848 = 12 x 8 inches

 

On the 12 x 8 inch print made from the D300, the bird's beak and tail will each be touching the side of the photo.

 

On the 12 x 8 inch print made from the D3, there will be a 2 inch space between the bird's beak and the side of the print and a 2 inch space between the bird's tail and the side of the print.

 

The D3 owner doesn't like that. He wants the beak and tail touching the side of the print. So he crops out a 2876 x 1920 section so the beak and tail are on the edges of the crop. He tells the printer to make a 12 x 8 inch photo from that.

 

The printer prints it at 240 PPI

 

2876/240 by 1920/240 = 12 x 8 inches.

 

That photo now looks the same as the photo made directly from the D300 sensor but with a slight loss in depth of field.

[scott_ferris]

<p>James,</p>

<p>I was with you until <em>"That photo now looks the same as the photo made directly from the D300 sensor but with a slight loss in depth of field."</em> There is no difference in DOF, the two images are identical. The different DOF figures for crop cameras and ff ones is due to an assumption of an unequal enlargement to achieve the same print size, but if you enlarge both captures the same ratio, the DOF is identical.</p>

<p>An image shot with crop and ff cameras from the same place with the same lens and then printed so the subject, not the print, is the same size (and if you then trim off the excess from the FF one) are identical.</p>

[James G. Dainis]

Scott, You are right. I thought a bit about that last sentence of mine but decided to put it in anyway. I forget why.

[joseph_wisniewski]

<blockquote>

<p>First an easy one. A 600mm lens has a focal length of 600mm, that is the primary optic has a focal point 600mm behind it. The term telephoto lens was introduced to describe a lens that was shorter than its own focal length.</p>

</blockquote>

<p>Actually, the "primary optic" of a 600mm telephoto is considerably shorter than 600mm. The negative lenses behind it increase the focal length and decrease the aperture. Google "Peter Barlow" or "teleconverter" if you want to understand a bit more about this.</p>

<blockquote>

<p>I'll try to explain your other mistakes better as well.</p>

</blockquote>

<p>Pot meet Mr. Kettle. Mr. Kettle, the right honorable Mr. Pot.</p>

[scott_ferris]

<p>James,</p>

<p>Thanks, nice to know I am not completely mad :-)</p>

<p>Joseph,</p>

<p>The difference between the pot and the kettle is that I admitted when I made a mistake, indeed I posted that I had before anybody picked up on it. I have made several mistakes in my multi thousand posting history here on Photo.Net over the last 8 or so years, on each occasion I have tried to add a correction. Not many do. In fact I think I can count on less than one hand the posters I know who do.<br>

Now Mr Kettle, how about you give a less condescending explanation of how one piece of 100 iso film is more sensitive to light than another piece. Because my flawed understanding of photography taught me that the iso rating was the only measure of its sensitivity, what you do to it, or how much you enlarge it post capture, is irrelevant.</p>

[joseph_wisniewski]

<blockquote>

<p>Now Mr Kettle, how about you give a less condescending explanation of how one piece of 100 iso film is more sensitive to light than another piece</p>

</blockquote>

<p>Sorry, Mr. Scott. I mean Pot... That's not at all what I said, and you know it. It's pretty obvious that you don't bother to acknowledge what people really say, and instead just post your own twisted interpretations of it. I'm not going to play that game.</p>

[scott_ferris]

<blockquote>

<p>James Dainis - Sensitivity doesn't vary with sensor (or film) size.....<br>

Joseph Wisniewski - Of course it does. <br>

Scott Ferris - how about you give a less condescending explanation of how one piece of 100 iso film is more sensitive to light than another piece<br>

Joseph Wisniewski - That's not at all what I said</p>

</blockquote>

<p>That is about the quality of correction I am more used to here, ever thought about a career in politics Mr Kettle?</p>

[joseph_wisniewski]

<blockquote>

<p>That is about the quality of correction I am more used to here,</p>

</blockquote>

<p>Well, if you communicated your numerous errors more clearly, people would correct you more clearly.<br>

Like I said, early on</p>

<blockquote>

<p>Les, that's only true if you hold the ISO constant. Given equal sensitivity, a FF is 2 stops more sensitive than 4/3. So, it's absolutely false that "the rest will not". Every single thing varies with the sensor size.</p>

</blockquote>

<p>And</p>

<blockquote>

<p>I've always been amazed at how many experienced photographers seem to forget all their shooting experience when they start making those "you can't change the ISO" arguments. It's like they never shot fine grained film on a 35mm and Tri-X on a 8x10.</p>

</blockquote>

<p>Interesting how much more actual information is conveyed when quotes aren't so deliberately taken out of context, isn't it, Mr. Pot?</p>

<p>Now, while it is possible that you are so inexperienced in photography that you've never noticed that people tend to use a different range of ISO films with different formats, so you really, honestly did not understand what I said, I think it's much more likely that you are simply being deliberately indigenous. Are you sure you're not already a full time politician?</p>

[joseph_wisniewski]

<p>... it's much more likely that you are simply being deliberately <strong>disingenuous</strong>.</p>

<p>Sorry about that, spell checker got the better of me.</p>

[scott_ferris]

<p>Well if you can put your sarcasm and derision aside for a minute the wording of yours that I just can't get my head around is this <em>". Given equal sensitivity, a FF is 2 stops more sensitive than 4/3"</em> I'm sorry, you just haven't explained what you mean there. The words do not make sense. If it is equal, it is equal, if it is 2 stops more sensitive, then it is not equal sensitivity.</p>

<p>If, what you are trying to say, is that to get a similar sized print with the same characteristics from different sized formats, then, as your capture medium size increases you need to use a longer focal length to maintain the same fov and because of that, you have to stop down more to regain lost dof, but, you can gain that loss back by enlarging it less so you can use a less sensitive medium, if, you are not prepared to increase your shutter speed, well that is a very perverse way of looking at the mediums use. And is not, truthfully, a sensitivity issue any more than an aperture or shutter speed one. It certainly doesn't make an 8x10 piece of film 4 times more sensitive than a piece of 4x5 film. To connect iso to film size is as disingenuous as saying 1/2 sec on 8x10 really equals 2 seconds on 4x5. It doesn't. A length of time is a length of time (assuming you are not going to take proximity to strong gravitational forces and relative speeds into account :-) ). An aperture is an aperture, whilst you might consider it an arbitrary ratio, it is a mathematical constant, like shutter speed. And sensitivity is sensitivity, it is measurable, and size is not a factor in its measurement. To assume you want an equal result from different sized sensors is, as I said, a perverse way of looking at real world use anyway, and is not any measure of sensitivity.</p>

<p>The reason it is a perverse way of looking at capturing images? If you look at it like that there is no image quality advantage to using a larger format, myself, and everybody I know who uses medium format and larger, is doing so for the sole reason of increased image quality, so they use the same film or iso. What would be the point of carrying a 6x9 if it gave no better results than a 4/3? It also ignores one of my real world examples regarding FF and crop camera use. If you use the same lens on different sensor sized cameras and want to end up with a same sized subject in a print, rather than same sized print, you use exactly the same exposure settings and exactly the same enlargement ratio.</p>

<p>So, is that what you are trying to say? And please, leave the sarcasm at your house.</p>

[studio460]

<p>Is Joseph's argument somehow related to the optical property of reflecting telescopes, where telescopes with larger mirrors, are in fact, gathering more photons, and are therefore "brighter?"</p>

[studio460]

<p>[However, from what I just read, I believe that the size of the mirror on a reflecting telescope is analogous to the aperture on a lens.]</p>

[James G. Dainis]

Joseph's argument is that a larger film or sensor has more silver or photo cells than a smaller film of sensor so it is more sensitive to light. This is convoluted logic. I can, and have, cut down 8x10 sheet film to use in a 4x5 reducing back on my 8x10 view camera. The 4 x 5 film now has less total silver than an 8 x10 film but it still has just as many grains of silver per square inch and is just as sensitive. I have shot both on the same camera with the same lens in the same lighting and have used the same exposure settings and ISO. I didn't have to open up 2 stops with the 4 x 5 film. After developing, the densities of the negatives were identical. Believe me, I would have known if I underexposed anything by 2 stops.

 

Most photographers are familiar with the Sunny 16 rule:

 

On a sunny day set aperture to f/16 and shutter speed to the reciprocal of the ISO film speed or ISO setting for a subject in direct sunlight.

 

I always have that in the back of my mind as a check on my incident light meter. If I am shooting 100 ISO film I set the aperture to f/16 and then shutter speed to 1/100 sec and am fine no matter what size film I am using. Joseph would argue that if the Sunny 16 rule works for 8x10 inch film then with the smaller 35mm film, one would have to open up 8 stops more since 100 ISO 35mm film is less sensitive than 100 ISO 8x10 inch film.

[scott_ferris]

<p>Thanks James,</p>

<p>Of course the failure of that argument is it takes four times more photons to expose an 8x10 sheet as it does a four times smaller 4x5 sheet, so by that weird logic you could argue that an 8x10 is two stops slower than a 4x5! Neither view is helpful or correct.</p>

<p>But thanks for taking the time to help my understanding of Joseph's argument.</p>