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Post by Randy on Mar 9, 2006 7:21:30 GMT -5
Don't think ill of me folks, but I don't know what the term Prime Lens means. I may own a truck load of cameras and lenses, but I don't know all of the definitions. Anyone want to elaborate on this term?
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Post by kiev4a on Mar 9, 2006 9:23:35 GMT -5
A prime lens is a single focal length lens--as opposed to a multi-focal length zoom.
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Post by John Parry on Mar 9, 2006 9:25:05 GMT -5
Hi Randy
A prime is just a 'normal' fixed focal length lens, as opposed to a zoom. The expressions telephoto and zoom are often used interchangeably (especially on eB@y), but strictly speaking a telephoto is a long focal length prime lens, while a zoom has variable focal length and hence magnification.
Regards - John
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Post by herron on Mar 9, 2006 9:25:54 GMT -5
Randy: If I were to write a definition, it would say, basically, that a prime lens is a lens with a fixed focal length - its field of view cannot be changed - at least, not without the addition of supplemental lenses or teleconverters. I think in the past it was generally considered that prime lenses were sharper and of higher optical quality than zoom lenses. Depending on the lens, that may or may not always be true any more. But you know the common prime lenses used (usually) by 35mm cameras: 28, 50, 85, 100, 135, 200mm, etc.
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Post by herron on Mar 9, 2006 9:28:02 GMT -5
John...looks like you and I posted at the same moment! Wayne, you beat us by a couple of minutes. Probably because I tend to get so darned wordy! Sometimes it takes me several minutes just to say "hi!"
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Post by kiev4a on Mar 9, 2006 12:16:07 GMT -5
John is at a disadvantage. His post has to travel farther
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PeterW
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Post by PeterW on Mar 9, 2006 16:57:28 GMT -5
Hi John,
You wrote:
Er ... not quite I'm afraid, John. That's a little too much oversimplification.
A long focal length prime lens is just that. A lens with a longer focal length than is considered 'normal' for the camera. In the 1960s several companies made cheap long focal length lenses for 35mm SLR cameras. All they did in effect was to take one of their existing lenses, either a triplet or a Tesssar-style four-glass, for a larger format and mount it on the end of a long tube with some sort of provision for focusing. When you looked in the back there was a great big empty space all the way down to the lens groups at the front. They were commonly nicknamed 'drainpipe lenses', and a 200mm lens was quite a long beast, and very front-heavy. They performed reasonably well because they used only the centre part of the lens image, but they were never originally designed to have the definition needed for a good 35mm camera lens.
By contrast, a telephoto lens is a lens which has a negative group, or groups, of glasses somewhere in its construction (some of the better ones have up to 8 or nine glasses in four or five groups) so that it can be made considerably shorter overall than a prime lens of the same focal length. Some of the extra glasses in the groups are used to remove pincushion and barrel distortion to either of which some early cheap telephoto lenses were prone. Lens coating made using multi-elements with little loss of contrast much easier.
Ross and Dallmeyer were making true telephoto lenses of excellent quality in the 1930s to suit 6x9cm and quarter plate reflex cameras.
Early telephoto lenses were of two types, 'variable separation' and 'fixed separation'.
The variable separation type was, in a way, a forerunner of the zoom lens. The focal length could be altered by moving the positive and negative groups closer together or further apart but, unlike a true zoom lens, the whole lens had to be refocused on a ground glass screen each time the separation was altered.
With some of the big ones used on quarter plate cameras you could get a 9x or 10x magnification compared with a 'normal' focal length lens but they took ages to set up and focus. They were also very large. Almost the only people with whom they were popular were wildlife photographers who worked from 'hides'.
With the more popular fixed separation telephoto the distance between the positive and negative groups of elements was fixed (as the name implies) so they worked at only one focal length, but some of them were very compact.
Somewhere packed away I've got a 1930s fixed-separation TeleRoss for a 6x9 format which I got with a 6x9 'Baby Soho'. If I remember rightly, it gives a 6x magnification compared with the normal 5 5/8 inch (roughly 143mm) lens. I think the maximum aperture is about f/5.6, and the whole thing's only about 4 to 5 inches long but quite heavy. In its day it was considered something of a breakthrough, and it was also very expensive when new. It does, though, lack contrast.
With these earlier fixed separation telephotos the makers usually quoted the magnification factor rather than the focal length.
Sorry to go on so long, but the history of telephoto lenses is a fascinating subject. What I've said here barely skims over the top.
Peter
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Post by John Parry on Mar 9, 2006 17:09:28 GMT -5
Peter,
What a polite and erudite way of saying "Shut your mouth Parry" !
Best Regards - John
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Post by herron on Mar 9, 2006 17:18:26 GMT -5
Peter: I think I really knew there was more to it than my simplistic response...and I think I've also come to know that you would know it!
Thanks for the lesson! ;D
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Post by kamera on Mar 9, 2006 19:30:08 GMT -5
Geee, Geeoly...some of the replies make me laugh. OK...let me play devils advocate...a prime lens is one used more than others!!! ;D ;D...! Oh wow...Krazee Ronnee is back! Ron Head Kalamazoo, MI
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Post by Randy on Mar 9, 2006 19:34:05 GMT -5
So it's safe to say that most SLRs come with Prime lenses. I take it all lenses that do not Zoom, that is cannot change focal length are Prime? I have a long lens that changes from 90, next 105, 135, 180, 200, to 230, and that is a Zoom but not Prime?
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Post by kamera on Mar 9, 2006 19:50:18 GMT -5
Randy,
Basically as I understand photographic jargon...a 'prime' lens is strictly a single focal length lens as opposed to a 'zoom' lens. And, at least in past times, produces better quality pics than a zoom lens, although many of today's zoom lenses get a high rating even from the pros.
IMHO...both are very usefull within their quality parameters.
Ron Head Kalamazoo, MI
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Post by paulatukcamera on Mar 10, 2006 3:02:04 GMT -5
Probably one for Peter, but all comments are welcome.
When I first bought my Nikon FE in 1979 it came with the almost universal 50mm. Then I read somewhere that if I really wanted to take better pictures of my children I should buy a "portrait lens".
This I did (an 85mm) and I found I soon was using this lens more than the standard.
Two years ago, when Nikon lens prices crashed, I bought a 105mm and now I find this adorns the front of my camera as often as the 85mm
I have never been keen on a 135mm as it just seemed "over the top" for portraits.
I digress from the question. What constitutes a traditional (presumably Victorian) portrait lens? Is it different in construction from a telephoto?
My 85mm must be a portrait lens, but is the 105mm? Where does the term "telephoto" start? I understand that a 200mm is a telephoto, but is a 135mm?
Paul
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PeterW
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Post by PeterW on Mar 10, 2006 6:43:22 GMT -5
Oh my, Paul, don't get me started on lens history or I'll never stop! What was the 'traditional' Victorian Portrait lens? For years and years this was a lens of Petzval, or modified Petzval design. Right back in the days of Dageurrotypes photographers wanted a faster lens to cut down the exposure and avoid the strained 'hold still for half a minute' look of portraits. Petzval designed a four-glass lens with the then unheard of maximum aperture of f/3.7. Its focal length was usually about twice the diagonal of the plate is was made to cover. The sharp definition was limited to to a relatively small centre circle and then fell of quite rapidly towards the edges. This didn't matter for portraits as the photographer focused on the sitter's eyes, and the lens gave a 'soft focus' effect the further from the eyes you got - quite flattering for female sitters. The lens was modified by later designers like Dallmeyer to give either a wider centre circle of definition or. sometimes, a smaller one which gave the dreamy 'feminine' ethereal look to portraits where only the eyes were really sharp. This was not very popular with male sitters who thought it looked a bit 'pansy' . They generally preferred the sharp all over look of the Petzval modified to give a larger circle of sharp definition. Generally, Petzval or modified Petzval lenses were in use in some studios right up to the 1920s but were displaced by anastigmats, the Tessar being a firm favourite. Petzvals were used only for head or head and shoulder portraits, usually vignetted on printing. For full length studio shots with lots of props, photographers used first the ubiquitous Rapid Rectilinear with a maximum aperture of f/8 and later anastimats at around f/4.5. Shorter exposure times were taken care of by faster emulsions. Modified Petzval designs are still made, but pretty well only as lenses for cheap slide projectors where they give a wide aperture and a bright screen. The term 'portrait lens' for 35mm cameras came into general use to mean a prime lens with a focal length of about twice the diagonal of the film frame, usually about 90mm to 105mm focal length which filled the frame with a head and shoulder portrait without having to go in close and get an over-emphasised perspective. It was reckoned to give a more 'natural' look than a 50mm. Whether or not a lens is a telephoto depends on its construction, not its focal length - see my earlier posting. Not sure if this is of much practical help, but there are a lot of terms used so loosely nowadays that they seem to have lost their original meaning. Peter
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PeterW
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Post by PeterW on Mar 10, 2006 8:38:29 GMT -5
Hi all, TELEPHOTO LENS PRINCIPLE As there still seems to be some confusion over what the difference is between a prime lens and a telephoto here's a very much simp-lified diagram of the principles of the two: Top is a prime, bottom is a telephoto. This is diagramatic only. In practice the single glasses would be replaced by groups of glasses, with possibly some intermediate groups as well, but it shows how including a negative group can increase the image size without building a massively long lens. The distance C, the back focus, is the same in each case, and the tele is only a little longer than the prime but gives an image three times the size. Peter
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