snubbr.com

Lens focal length.
Hi, Im not sure if this was asked before, hope some masters would help me..

I noticed almost all manufacturers have APC sensor specific lens (Sigma  DC, Canon EF-S, Nikon  DX, etc) on the market now, what confuses me is the focal length..

For example Sigma DC specific lens with 18-125mm. Since this lens is a reduced image circle lens, do I still need to do the focal length multiplier (Canon 1.6x, Nikon & Sony 1.5x) to get the actual FL reading? Or I actually dont need to do so?.

Thanks in advance!..

Comments (23)

YA Tan wrote:.

Hi, Im not sure if this was asked before, hope some masters wouldhelp me..

I noticed almost all manufacturers have APC sensor specific lens(Sigma  DC, Canon EF-S, Nikon  DX, etc) on the market now, whatconfuses me is the focal length..

For example Sigma DC specific lens with 18-125mm. Since this lens isa reduced image circle lens, do I still need to do the focal lengthmultiplier (Canon 1.6x, Nikon & Sony 1.5x) to get the actual FLreading? Or I actually dont need to do so?.

Thanks in advance!.

On interchangable lenses for SLR's, focal length is focal length. A Sigma DC lens set to 50mm on say, a Nikon D80 will produce exactly the same size image as a full-frame 50mm lens on the same camera. The DC lens just doesn't cover a full 35mm frame..

Leonard Migliore..

Comment #1

Apart from what Leonard says - get out of the thinking that you have to multiply the focal length by the crop factor. There is no reason for it. It accomplishes absolutely nothing..

YA Tan wrote:.

Hi, Im not sure if this was asked before, hope some masters wouldhelp me..

I noticed almost all manufacturers have APC sensor specific lens(Sigma  DC, Canon EF-S, Nikon  DX, etc) on the market now, whatconfuses me is the focal length..

For example Sigma DC specific lens with 18-125mm. Since this lens isa reduced image circle lens, do I still need to do the focal lengthmultiplier (Canon 1.6x, Nikon & Sony 1.5x) to get the actual FLreading? Or I actually dont need to do so?.

Thanks in advance!.

Some cool cats that can use your helphttp://www.wildlife-sanctuary.org.

Even if you can't donate, please help spread the word...

Comment #2

IMac, therefore iAm wrote:.

Apart from what Leonard says - get out of the thinking that you haveto multiply the focal length by the crop factor. There is no reasonfor it. It accomplishes absolutely nothing..

Multiplying does accomplish something. It allows you to determine what focal length you'd need on a 35mm camera to capture the same angle of view. It's become a defacto standard..

More useful on digicams though, given the diversity of sensor sizes. If you saw a digicam that only advertised it's lens as "5-15mm", would you be able to quickly determine if the lens met your needs? My guess is you'd look up the sensor size and do the multiplication..

Seen in a fortune cookie:Fear is the darkroom where negatives are developed..

Comment #3

Unless you are used to 35mm cameras, and have those numbers stuck in your head, there is no need to do the conversion. (I mentally convert degrees centigrade to fahrenheit; my children have never heard of fahrenheit). On an APS-C sensor camera, a 'standard' lens, (i.e. that roughly matches the field of view of your eye) is around 30 mm. Less than that is wide angle, more than that is telephoto; that's all you need..

The reason for the conversion factor is the following. A lens will cast an image of a particular size on a screen; that is a fixed property of the lens and it's focal length. Now put a sheet of paper in the middle of the image. If you imagine that the sheet of paper is your film (or sensor), the size of it determines how much you will get in the picture..

Now use a smaller sheet of paper as your film/sensor. You will only capture a smaller part of the image, effectively you have 'zoomed in' a bit. So APS-C cameras, with smaller sensors than full-frame or 35mm film cameras, can take a lens of the same focal length but the field of view is narrower, leading to a telephoto-like effect. So a 30mm lens on an APS-C camera will produce an image on the sensor equivalent to what you would get from a 50mm lens on a full frame camera - but the focal length of the lens is still 30 mm (the image it produces is the same, you are just putting a differently-sized piece of paper behind it)..

Best wishesMike..

Comment #4

Hi, many thanks for your kind explaination and reply. I've better understandings now regarding the multiplier factor..

The reason I ask is because I've came across this:http://www.slrgear.com/reviews/showproduct.php/product/174/cat/31.

If you would see under the Specification tab, it stated the image circle as APS-C, FL 18-125mm, BUT in the same time also include the APS equivalent multiplier factor and FL..

Could it be typo error?..

Comment #5

No, it's not a typo..

If you want to see what focal length lens is needed on a 35mm camera for the same angle of view, you still need to use the so called focal length multipliers if you're using a DSLR with an APS-C sensor..

It doesn't make any difference if the lens is designed for an APS-C sensor or not..

Those lenses just don't have an image circle large enough to cover 35mm film..

But, you'll still have a narrower angle of view compared to the same focal length lens on a 35mm camera..

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

Comment #6

IMac, therefore iAm wrote:.

Apart from what Leonard says - get out of the thinking that you haveto multiply the focal length by the crop factor. There is no reasonfor it. It accomplishes absolutely nothing..

The purpose of using the multiplier on cameras with APS sensors is to determine what the equivalent field of view would be compared to a 35mm full frame sensor..

A 100mm lens mounted on an APS sensored camera with a 1.5x crop factor would be equivalent to 150mm. Knowing this allows you to determine the focal lengths you need to accomplish your photography..

The greatest of mankind's criminals are those who delude themselves into thinking they have done 'the right thing.'- Rayna Butler..

Comment #7

I agree with Mike that you only should care about a multiplier if you're a long time 35mm SLR user and you're comparing the field of view. For the many DSLR users who have never used a 35mm, it serves to cause confusion. You need to have a feel for what a given focal length does on your camera. Why would you care what length lens you would need to get the same result on a 35mm? I started shooting an SLR in 1964, so I'm like Mike that I know what a 50mm or 150mm lens does on a 35mm, but a newcomer doesn't, so why confuse them..

David..

Comment #8

GodSpeaks wrote:.

A 100mm lens mounted on an APS sensored camera with a 1.5x cropfactor would be equivalent to 150mm. Knowing this allows you todetermine the focal lengths you need to accomplish your photography..

Isn't that sort of like saying you have to know how many inches in a meter to determine how long a yardstick is ? .

- DennisGallery at http://kingofthebeasts.smugmug.com..

Comment #9

It is indeed true that using the 35 mm field of view is an arbitrary benchmark. But it is still useful, and perhaps essential, to have some common point of reference. A given focal length does not mean the same thing on Canon and Nikon APS-C cameras nor on Olympus and other 4/3rds system cameras. In order to make these comparable it is still useful to "convert" them to 35 m equivalent, even if the user is new to photography. It's just an aid to communication, if nothing else..

Davehttp://www.pbase.com/dsjtecserv..

Comment #10

GodSpeaks wrote:.

IMac, therefore iAm wrote:.

Apart from what Leonard says - get out of the thinking that you haveto multiply the focal length by the crop factor. There is no reasonfor it. It accomplishes absolutely nothing..

The purpose of using the multiplier on cameras with APS sensors is todetermine what the equivalent field of view would be compared to a35mm full frame sensor..

And what good does that do you? Why not figure out what the field of view on a medium format is too?..

Comment #11

The rest of us will be out shooting, and not worrying one bit what lens we'd need on a full frame camera...

Comment #12

IMac, therefore iAm wrote:.

The rest of us will be out shooting, and not worrying one bit whatlens we'd need on a full frame camera..

"full frame camera" is ambiguous. 35mm is less so..

So tell me, when you want to choose a compact camera, does 5-15mm mean anything to you?.

Seen in a fortune cookie:Fear is the darkroom where negatives are developed..

Comment #13

Dsjtecserv wrote:.

It is indeed true that using the 35 mm field of view is an arbitrarybenchmark..

It's not arbitrary at all; it's the frame of reference most photographers understand..

But it is still useful, and perhaps essential, to havesome common point of reference..

For DSLRs, I'm not sure. It's useful to individual photographers to understand what they'll get from a given lens on a new format. For newbies, there's no point in bothering with equivalents (though I agree that newbies are bound to get caught up in discussions with folks who are accustomed to translating). After nearly 3 years with APS-C, I don't need to convert in my head any more; I understand what a given lens is like on APS-C nearly as well as on 35mm film..

Digicams are another matter; nobody can readily grasp what 5mm or 7mm or 14mm on 1/1.8" or 1/2.5" means. I'd still prefer manufacturers express those lenses as % of diagonal ... like a .5X-5X zoom. For two reasons: (1) new camera buyers don't have to understand what 460mm is on 35mm to begin with and (2) I suspect many digicam buyers are already under the false impression that a 10X lens means it offers 10X magnification (like a pair of 10X binoculars)..

A given focal length does not meanthe same thing on Canon and Nikon APS-C cameras nor on Olympus andother 4/3rds system cameras. In order to make these comparable it isstill useful to "convert" them to 35 m equivalent, even if the useris new to photography. It's just an aid to communication, if nothingelse..

I agree it's useful to know about crop factors and understand that lenses deliver varying FOVs depending on sensor size. Beyond that, conversion to 35mm equivalent shouldn't be something that newbies need to do often, if at all..

- DennisGallery at http://kingofthebeasts.smugmug.com..

Comment #14

YA Tan wrote:.

The reason I ask is because I've came across this:http://www.slrgear.com/reviews/showproduct.php/product/174/cat/31.

If you would see under the Specification tab, it stated the imagecircle as APS-C, FL 18-125mm, BUT in the same time also include theAPS equivalent multiplier factor and FL..

Digicam lenses are typically expressed in 35mm equivalents because they're fairly meaningless otherwise. But interchangeable lenses are labelled with their actual, absolute focal length. The 18-125 you're looking at is 18mm - 125mm. To build such a lens, Sigma reduced the image circle so it just covers the APS-C sensor (at least at the wide end). But the size of the image circle is independent* of the focal length. (What I mean is you can have a tiny 20mm lens that barely covers a digicam sensor; a 20mm lens that just covers APS-C, and a 20mm lens that projects an image circle big enough for a view camera ...



So ... some lenses may be limited to APS-C coverage, but ALL interchangeable lenses, whether designed for APS-C or not, are labelled with actual focal lengths and therefore 'conversion factors' (if you choose to use them) apply to all of them across the board..

- DennisGallery at http://kingofthebeasts.smugmug.com..

Comment #15

Dennis wrote:.

Dsjtecserv wrote:.

It is indeed true that using the 35 mm field of view is an arbitrarybenchmark..

It's not arbitrary at all; it's the frame of reference mostphotographers understand..

But it is still useful, and perhaps essential, to havesome common point of reference..

For DSLRs, I'm not sure. It's useful to individual photographers tounderstand what they'll get from a given lens on a new format. Fornewbies, there's no point in bothering with equivalents (though Iagree that newbies are bound to get caught up in discussions withfolks who are accustomed to translating). After nearly 3 years withAPS-C, I don't need to convert in my head any more; I understand whata given lens is like on APS-C nearly as well as on 35mm film..

Digicams are another matter; nobody can readily grasp what 5mm or 7mmor 14mm on 1/1.8" or 1/2.5" means. I'd still prefer manufacturersexpress those lenses as % of diagonal ... like a .5X-5X zoom. Fortwo reasons: (1) new camera buyers don't have to understand what460mm is on 35mm to begin with and (2) I suspect many digicam buyersare already under the false impression that a 10X lens means itoffers 10X magnification (like a pair of 10X binoculars)..

A given focal length does not meanthe same thing on Canon and Nikon APS-C cameras nor on Olympus andother 4/3rds system cameras. In order to make these comparable it isstill useful to "convert" them to 35 m equivalent, even if the useris new to photography. It's just an aid to communication, if nothingelse..

I agree it's useful to know about crop factors and understand thatlenses deliver varying FOVs depending on sensor size. Beyond that,conversion to 35mm equivalent shouldn't be something that newbiesneed to do often, if at all..

- Dennis.

Dennis:.

I'm not sure whether you are agreeing or not. Using the 35 mm equivalent, rather than, say, the 4 x 5 equivalent IS arbitrary, but my point is that it is a reference that a large number of people can relate to, so I think we are saying the same thing..

Even with DSLRs, some common frame of reference is needed in order for people to communicate about their lenses. If I tell you I used my DSLR and a 50 mm lens to take this picture, you don't know whether the picture has a medium range, "normal" field of view of view or a moderate telephoto. If I tell you it was an APS-C SLR that narrows it down, but you might still be interested in knowing whether it was a 50 mm with a 1.5 or 1.6 crop factor. But if I tell you up front that I used a 50 mm lens (80 mm equiv.) then you quickly have a frame of reference for the field of view I used..

A more accurate and meaningful way to do this would be to reference the angle of view, as in 50 mm (24.5 HFOV), which would tell you directly what "50 mm" means on my camera. But most of us don't relate visually to a field of view number, which kind of leaves the tried and true 35 mm equivalent as the most recognizable frame of reference..

I think we basically agree on all this; I just think it is just as useful for new photographers to be able to relate to a common reference point as it is for those of use who are (ahem) older..

Dave.

Http://www.pbase.com/dsjtecserv..

Comment #16

On behalf of the old gits, could I point out that a lot of us know that 135 mm is normal on quarter plate, and that anything is normal on cut film (say 300 mm on 10" x 8") and 75 or 80 mm on MF but we've no idea at all what is normal on APS? I've never even seen an APS camera, although I have to be wary of the film when buying 35 mm stuff: nothing worse than picking up a bag of APS film and not realising until I get out of the shop..

It might also help if I add that we used to think in terms of the format and still do. So I can swop quite easily from MF film to 2/3" CCD without once stopping to do sums. Although the fact that I think in terms of normal (75 or50), wide (50/35) and portrait (150/90) helps..

In any event it helps if you frame the subject and look at the viewfinder/screen rather than think in terms of "about 45 needed but allowing for the format say... " etc..

Just my 2d worth..

Regards, David..

Comment #17

Even with DSLRs, some common frame of reference is needed in orderfor people to communicate about their lenses. If I tell you I used myDSLR and a 50 mm lens to take this picture, you don't know whetherthe picture has a medium range, "normal" field of view of view or amoderate telephoto. If I tell you it was an APS-C SLR that narrows itdown, but you might still be interested in knowing whether it was a50 mm with a 1.5 or 1.6 crop factor. But if I tell you up front thatI used a 50 mm lens (80 mm equiv.) then you quickly have a frame ofreference for the field of view I used..

Dave:.

So if I use a 30mm lens on a DSLR with a 1.5 crop factor, should I consider this a medium range, "normal" field of view, Or should I think of more it as a cropped wide-angle image because the relationship of objects in the subject, or am I trying to over-analyze this?.

Brian..

Comment #18

Remymartn wrote:.

Dave:.

So if I use a 30mm lens on a DSLR with a 1.5 crop factor, should Iconsider this a medium range, "normal" field of view, Or should Ithink of more it as a cropped wide-angle image because therelationship of objects in the subject, or am I trying toover-analyze this?.

Brian.

Well, it's equivalent to 45 mm in 35 mm format, which most people would regard as the "normal" range. (The definition of "normal" itself is controversial and I have no intention of entering that fray!) The relationship of objects in the subject will always be exactly the same for any given field of view. It won't make any difference whether you use a 45 mm on a full-frame camera, a 30 mm on a 1.5 crop camera, or a 9 mm on a 5x crop point-and-shoot. So in that sense you could be overanalyzing it..

Davehttp://www.pbase.com/dsjtecserv..

Comment #19

Ahhh. Thank you! This simplies the whole therad. I did need that answer...

Comment #20

It's just a silly argument you have. Most people know that a good portrait focal length is 85-100 mm on a 35 mm camera. But my camera has 6.2-66.7 mm. What focal length should I use?VictorBucuresti, Romaniahttp://s106.photobucket.com/albums/m268/victor_petcu/..

Comment #21

Baloo_buc wrote:.

It's just a silly argument you have. Most people know that a goodportrait focal length is 85-100 mm on a 35 mm camera. But my camerahas 6.2-66.7 mm. What focal length should I use?.

Get back to about 2 meters a zoom to what you like. It will probably be about 50 to 60 mm. ;^).

DavidPentax K100D..

Comment #22

I just wanted to outline that you need a reference. For my camera the focal length should be 19-25 mm for a portrait.VictorBucuresti, Romaniahttp://s106.photobucket.com/albums/m268/victor_petcu/..

Comment #23

Click Here to View All...

Sponsored Amazon Deals:

1. Get big savings on Amazon warehouse deals.
2. Save up to 70% on Amazon Products.


This question was taken from a support group/message board and re-posted here so others can learn from it.

 

Categories: Home | Diet & Weight Management | Vitamins & Supplements | Herbs & Cleansing |

Sexual Health | Medifast Support | Nutrisystem Support | Medifast Questions |

Web Hosting | Web Hosts | Website Hosting | Hosting |

Web Hosting | GoDaddy | Digital Cameras | Best WebHosts |

Web Hosting FAQ | Web Hosts FAQ | Hosting FAQ | Hosting Group |

Hosting Questions | Camera Tips | Best Cameras To Buy | Best Cameras This Year |

Camera Q-A | Digital Cameras Q-A | Camera Forum | Nov 2010 - Cameras |

Oct 2010 - Cameras | Oct 2010 - DSLRs | Oct 2010 - Camera Tips | Sep 2010 - Cameras |

Sep 2010 - DSLRS | Sep 2010 - Camera Tips | Aug 2010 - Cameras | Aug 2010 - DSLR Tips |

Aug 2010 - Camera Tips | July 2010 - Cameras | July 2010 - Nikon Cameras | July 2010 - Canon Cameras |

July 2010 - Pentax Cameras | Medifast Recipes | Medifast Recipes Tips | Medifast Recipes Strategies |

Medifast Recipes Experiences | Medifast Recipes Group | Medifast Recipes Forum | Medifast Support Strategies |

Medifast Support Experiences |

 

(C) Copyright 2010 All rights reserved.