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07/12/2007 09:20:15 AM · #1 |
Hi. Trying to decide on a WA lens and I'm considering either the SIGMA 10-20 or 12-24. The 10-20 is a "digital only" lens, built for the smaller sensor. The 12-24 is conventional or full-frame.
Will the 10-20 be a true 10-20 since it's designed for the smaller sensor?
I would think the 12-24 would need to consider the crop factor and not really be 12-24, more like 18-36?
Thanks. |
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07/12/2007 09:25:33 AM · #2 |
The lenses still state the 35mm equiv even on like Nikon DX lenses and Canon EF-S yada yada and so on. Even my APS film camera it states the 28mm focal length when its equiv of 42mm on APS film!
Message edited by author 2007-07-12 09:26:14. |
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07/12/2007 09:29:06 AM · #3 |
The focal lengths are what they are. Crop factor doesn't change the focal length. Difference between the Digital-only and the standard is that the DO lens throws a smaller image circle and it will not cover a larger sensor. Think of it as the lens doing the cropping for you, effectively.
Between the two lenses, 10mm is substantially wider than 12 mm; 12 mm is 20% longer than 10mm, and the difference in coverage is noticeable.
R.
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07/12/2007 09:30:50 AM · #4 |
| The focal length of a lens is due to its optical properties, it does not depend what camera format is it used on. You always need to take the cropping factor into account. |
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07/12/2007 09:39:21 AM · #5 |
The focal length of a lens does not change when you put it on a camera with a smaller or larger sensor. So, the 10-20mm lens is always a 10-20mm lens regardless of what it's mounted on. The same with the 12-24mm lens, it's always going to have a focal length of 12-24mm
What changes is the field of view. The confusion arises from the so called lens "crop" factor or lens "conversion" factor. This factor tells you the focal length of the lens that has an equivalent field of view for a camera with a "full frame" (24mmx36mm) sensor.
So, the 10-20mm lens on a Canon DSLR (1.6 crop factor) will have the same field of view as a 16-32mm lens on a full frame camera. The 12-24mm lens on the same Canon DSLR will have the same field of view as a 19.2-38.4 mm lens on a full frame camera.
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07/12/2007 09:50:35 AM · #6 |
Originally posted by glad2badad:
Hi. Trying to decide on a WA lens and I'm considering either the SIGMA 10-20 or 12-24. The 10-20 is a "digital only" lens, built for the smaller sensor. The 12-24 is conventional or full-frame.
Will the 10-20 be a true 10-20 since it's designed for the smaller sensor?
I would think the 12-24 would need to consider the crop factor and not really be 12-24, more like 18-36?
Thanks. |
Neither one of those lenses will seem like a "true" 10-20 or 12-24 simply because of the size of the sensor, but yes you can directly compare them even though one is for digital only. I believe the concept behind digital only lenses is that since the sensor crops your image anyway, why not remove all the excess material that is projecting an image on nothing and save some money. They tend to remove the aperture ring too. The downside is that if you ever feel like putting that lens on a film camera body, you'll be in trouble.
I also have the Sigma 10-20 and I really like it. I've heard that it's not as rugged as other WA's out there, but I really baby my equipment, so that wasn't much of an issue for me. If the extra 2mm isn't as important I've heard good things about Tokina's 12-24mm and it's still relatively in the same price range.
Message edited by author 2007-07-12 09:55:42.
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07/12/2007 09:54:23 AM · #7 |
Wow, ok. Glad I asked (I think). :P
So, the FOV is what would be different if I used the 12-24 on a camera with a smaller sensor (i.e. KM 5D)?
I like the 12-24 for future considerations if Sony ever comes out with a full-frame sensor, then I'd be covered.
However, if the 12-24 isn't really that wide on my current KM 5D that would be the deciding factor.
Grrr...works calling. I'll be back. :) Thanks! |
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07/12/2007 10:37:35 AM · #8 |
Originally posted by jpeters:
I believe the concept behind digital only lenses is that since the sensor crops your image anyway, why not remove all the excess material that is projecting an image on nothing and save some money. They tend to remove the aperture ring too. |
There's a matter of optics also; by designing the lens specifically for the smaller sensor, they can optimize performance in that area without worrying about the bigger corners. These digital-only lenses tend to have crisper edge-to-edge performance than their full-frame brethren.
R.
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07/12/2007 10:39:43 AM · #9 |
Originally posted by Bear_Music:
The focal lengths are what they are. Crop factor doesn't change the focal length. Difference between the Digital-only and the standard is that the DO lens throws a smaller image circle and it will not cover a larger sensor. Think of it as the lens doing the cropping for you, effectively.
Between the two lenses, 10mm is substantially wider than 12 mm; 12 mm is 20% longer than 10mm, and the difference in coverage is noticeable.
R. |
My Sigma 18-200 does fit on my EOS 5D, and will work. But not only can you see the edge of the image circle, the edges are distorted. I could use PS and crop the image to an APS-C sized rectangle, but the only reason to use that lens is if I travel light, and there are lighter bodies than the 5D.
Note that some DO lenses project further back into the camera, so they physically cannot be used with a full-frame body (the mirror hits the back of the lens, which may crack the mirror.) |
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07/12/2007 10:52:02 AM · #10 |
Originally posted by Bear_Music:
Originally posted by jpeters:
I believe the concept behind digital only lenses is that since the sensor crops your image anyway, why not remove all the excess material that is projecting an image on nothing and save some money. They tend to remove the aperture ring too. |
There's a matter of optics also; by designing the lens specifically for the smaller sensor, they can optimize performance in that area without worrying about the bigger corners. These digital-only lenses tend to have crisper edge-to-edge performance than their full-frame brethren.
R. |
Ah yes, I do recall reading that now. You are truly a wealth of knowledge, Robert.
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07/12/2007 11:14:10 AM · #11 |
Ok. Now that things have settled down a bit here I've had a chance to reread the feedback that everyone has been so kind to leave...Thanks!
Originally posted by Bear_Music:
Between the two lenses, 10mm is substantially wider than 12 mm; 12 mm is 20% longer than 10mm, and the difference in coverage is noticeable.
R. |
That IS substantial - Thanks!
Originally posted by Spazmo99:
So, the 10-20mm lens on a Canon DSLR (1.6 crop factor) will have the same field of view as a 16-32mm lens on a full frame camera. The 12-24mm lens on the same Canon DSLR will have the same field of view as a 19.2-38.4 mm lens on a full frame camera. |
This is the core of my confusion. The hard part to grasp is if they say the lens is designed/built for the smaller digital sensors, then why wouldn't the 10-20 be a 10-20 on the Canon DSLR you use as an example? The 12-24 being different makes sense since the smaller sensor isn't using all of the lens capacity.
Originally posted by Bear_Music:
These digital-only lenses tend to have crisper edge-to-edge performance than their full-frame brethren.
R. |
Another good to know piece of information. Lord knows I need all the help I can get...crisper sounds better! :)
The 10-20 is sounding like the winner at this point, plus I like the price better too. $$$ IF Sony comes out with a full-frame sensor, and IF I end up buying one, then I can always swap out to the 12-24 at that point. |
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07/12/2007 11:29:06 AM · #12 |
Originally posted by glad2badad:
Originally posted by Spazmo99:
So, the 10-20mm lens on a Canon DSLR (1.6 crop factor) will have the same field of view as a 16-32mm lens on a full frame camera. The 12-24mm lens on the same Canon DSLR will have the same field of view as a 19.2-38.4 mm lens on a full frame camera. |
This is the core of my confusion. The hard part to grasp is if they say the lens is designed/built for the smaller digital sensors, then why wouldn't the 10-20 be a 10-20 on the Canon DSLR you use as an example? The 12-24 being different makes sense since the smaller sensor isn't using all of the lens capacity. |
Let me see if I can explain: on a 4x5 view camera, a 70mm lens gives the same angular coverage as a 24mm lens on a 35mm camera, more or less. It is designed to throw a very large image circle, and it's a big, bulky lens. If you could somehow mount the same lens on a 35mm camera, it would be a moderate telephoto, 70mm, right? And there would be a "crop factor" as compared to the view camera, a very substantial one.
A lens can be designed to throw a very narrow or a very wide image circle at the focal plane. A 70mm lens for an SLR camera is throwing an image circle the size of a 35mm film, not one the size of a 4x5 inch film. See? Optically, there's no reason why ANY lens can't be a wide-angle lens, if it is designed with a large enough image circle and you use a large enough sensor/film to cover that image circle.
So with the digitally optimized lenses, they just narrow the image circle to the size of the sensor for which it is designed, and then they fine-tune the optics for that specific image circle. The thing of it is, lenses don't naturally throw "flat" images; the natural image is curved, so the edges are the same distance from the aperture as is the center. The art of optics includes tweaking the lens to throw that arced image onto a flat surface and have it all be in good focus.
So it stands to reason that if you minimize the area of the potential image projection, you can better optimize performance within that smaller circle, see?
R.
Message edited by author 2007-07-12 13:41:27.
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07/12/2007 11:41:57 AM · #13 |
Originally posted by glad2badad:
Originally posted by Spazmo99:
So, the 10-20mm lens on a Canon DSLR (1.6 crop factor) will have the same field of view as a 16-32mm lens on a full frame camera. The 12-24mm lens on the same Canon DSLR will have the same field of view as a 19.2-38.4 mm lens on a full frame camera. |
This is the core of my confusion. The hard part to grasp is if they say the lens is designed/built for the smaller digital sensors, then why wouldn't the 10-20 be a 10-20 on the Canon DSLR you use as an example?
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I'll answer this two different ways.
1. The 10-20 IS a 10-20 on a DSLR, but that still only describes its focal length, NOT the field of view. What determines the field of view for any given focal length is the size of the imager.
2. The better answer is that a lens's focal length doesn't have to be directly related to the size of the image it projects. What makes the 10-20 a "digital" lens is that it projects a smaller image--just enough to cover an APS-sized sensor. The focal length is still 10-20mm, with the same resulting FOV that that implies (i.e., the same field of view as a 16-32mm on a 35mm SLR).
Think of it this way--on a medium format camera, say a 6x6 Hassie, an 80mm lens is a "standard" lens. That 80mm lens has to project an image that covers 60mmx60mm. If you were able to take that same lens and mount it on a 35mm SLR, you would get the same field of view as, well, an 80mm lens on a 35mm camera--the only difference is that the Hassie lens projects an image that is larger than the imaging area if the film--the 35mm flims "crops" the Hassie lens, and you have a slight telephoto, NOT a normal lens anymore. A made-for-35mm 80mm lens would project an image that would only cover the 35mm frame, but the field of view would be exactly the same as if you mounted the Hassie lens, with it's larger projection, on the 35mm body. You could say that the made-for-35mm lens is a "24x36" lens but that doesn't change the fact that it's still a slight telephoto and NOT a normal lens just because the projected image from the 35mm 80mm lens is smaller than the projected image from the medium format 80mm lens.
Maybe that was more confusing. If so, sorry. :-)
Message edited by author 2007-07-12 11:46:36. |
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07/12/2007 11:56:30 AM · #14 |
There's a nice graphic in the Wikipedia article on "Crop Factor" that helps illustrate the descriptions made by others here.
//en.wikipedia.org/wiki/Crop_factor |
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07/12/2007 12:08:27 PM · #15 |
Originally posted by glad2badad:
Ok. Now that things have settled down a bit here I've had a chance to reread the feedback that everyone has been so kind to leave...Thanks!
Originally posted by Spazmo99:
So, the 10-20mm lens on a Canon DSLR (1.6 crop factor) will have the same field of view as a 16-32mm lens on a full frame camera. The 12-24mm lens on the same Canon DSLR will have the same field of view as a 19.2-38.4 mm lens on a full frame camera. |
This is the core of my confusion. The hard part to grasp is if they say the lens is designed/built for the smaller digital sensors, then why wouldn't the 10-20 be a 10-20 on the Canon DSLR you use as an example? The 12-24 being different makes sense since the smaller sensor isn't using all of the lens capacity.
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I think you have focal length confused with field of view.
Focal length is a property of the optical system. It has nothing to do with the sensor/film size.
The field of view does change with the size of the film/sensor. If you're looking through a camera & lens at a flat wall and you mark 2 diagonally opposite corners of the image, then, if you were to take string from each point back to the center of the lens, you would have an angle between those strings. That angle is the field of view for that lens/camera combination. With a smaller sensor, that angle will be narrower than it would be on a camera with a larger sensor, just as it would with a longer focal length lens on the camera with the bigger sensor. |
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07/12/2007 01:10:00 PM · #16 |
Originally posted by Spazmo99:
I think you have focal length confused with field of view. |
I do (did?). :P
What makes it more confusing at times is references made by the manufacturer themselves. Going directly to Tamron, Sigma, etc...you see this.
Tamron site, SP AF11-18: "...provides the extended focal length covering 17mm (when converted to 35mm format)...".
Sony site, Sony 11-18: "...and its 35mm-equivalent zoom range of 16.5mm to 27mm gives you wide latitude in framing and composition."
Back to FOV...
Sigma 10-20 is 102.4 - 63.8 degrees.
Sigma 12-24 is 122 - 84.1 degrees.
Tamron 11-18 is 103 - 75 degrees.
Sony 11-18 is 104 - 76 degrees.
According to the angle of coverage, the Sigma 12-24 looks like the widest of the four listed. However, it's the only one of the group listed that isn't "digital", meaning it's full-frame sensor sized. What is it's real angle of coverage on the smaller sensors?
Maybe I should just buy one, slap it on the camera, and call it good - eh? :D |
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07/12/2007 01:25:30 PM · #17 |
I remember reading somewhere that non-digital lenses are better than digital only on digital SLRs with a crop factor.
Logic being that since all lenses perform less well at the edges, with a normal lens you 're not using the edges of the glass.
Is that true? We 're probably talking test-chart differences, I would assume.
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07/12/2007 01:31:55 PM · #18 |
Originally posted by hsolakidis:
I remember reading somewhere that non-digital lenses are better than digital only on digital SLRs with a crop factor.
Logic being that since all lenses perform less well at the edges, with a normal lens you 're not using the edges of the glass.
Is that true? We 're probably talking test-chart differences, I would assume. |
I've heard that also...but can't remember the source. Kind of makes sense. Most testing of lens that I've read have some verbiage about fall off at the edges, etc... |
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07/12/2007 01:32:18 PM · #19 |
Originally posted by glad2badad:
Originally posted by Spazmo99:
I think you have focal length confused with field of view. |
I do (did?). :P
What makes it more confusing at times is references made by the manufacturer themselves. Going directly to Tamron, Sigma, etc...you see this.
Tamron site, SP AF11-18: "...provides the extended focal length covering 17mm (when converted to 35mm format)...".
Sony site, Sony 11-18: "...and its 35mm-equivalent zoom range of 16.5mm to 27mm gives you wide latitude in framing and composition."
Back to FOV...
Sigma 10-20 is 102.4 - 63.8 degrees.
Sigma 12-24 is 122 - 84.1 degrees.
Tamron 11-18 is 103 - 75 degrees.
Sony 11-18 is 104 - 76 degrees.
According to the angle of coverage, the Sigma 12-24 looks like the widest of the four listed. However, it's the only one of the group listed that isn't "digital", meaning it's full-frame sensor sized. What is it's real angle of coverage on the smaller sensors?
Maybe I should just buy one, slap it on the camera, and call it good - eh? :D |
Using the Canon APS-C sensor dimensions, I calculated the FOV for the Sigma 12-24 to be 97.3 degrees at the 12mm end |
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07/12/2007 01:38:31 PM · #20 |
Originally posted by Spazmo99:
Using the Canon APS-C sensor dimensions, I calculated the FOV for the Sigma 12-24 to be 97.3 degrees at the 12mm end |
:) Thanks! |
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07/12/2007 01:40:00 PM · #21 |
Originally posted by glad2badad:
Originally posted by hsolakidis:
I remember reading somewhere that non-digital lenses are better than digital only on digital SLRs with a crop factor.
Logic being that since all lenses perform less well at the edges, with a normal lens you 're not using the edges of the glass.
Is that true? We 're probably talking test-chart differences, I would assume. |
I've heard that also...but can't remember the source. Kind of makes sense. Most testing of lens that I've read have some verbiage about fall off at the edges, etc... |
No; the center of the full-frame lens is less optimized than the center of the digi lens, all other things being equal, because it has to make greater compromises viz the edges. The narrower the field of view of the lens, especially in extreme WA, the easier it is to optimize the entire field with no corner sacrifices.
By that logic, the 4x5 90mm lens would be a better 35mm telephoto than a 90mm designed for 35mm work, and it isn't. Not by a long shot.
R.
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07/12/2007 10:11:11 PM · #22 |
| Ok. One Sigma 10-20 on the way! :D |
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07/17/2007 02:04:11 PM · #23 |
Originally posted by glad2badad:
Ok. One Sigma 10-20 on the way! :D |
It's here, it's here!!! :)
One minor problem - I'm an hour away at work. :/
I think I'll volunteer to feed the horses tonight, with camera in hand of course. :P |
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08/03/2007 09:52:55 AM · #24 |
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08/22/2007 09:32:54 AM · #25 |
After reading about the "sweet spot" of a full-frame lens I wanted to revisit this. Any thoughts/feedback on this statement published in Popular Photography Magazine in a recent lens review?
(Best Buys: Lenses - see the section on the Tokina 19-35mm)
PopPhoto.com: "And remember that you're shooting through the central sweet spot of the lens with such DSLRs, so your shots will be even sharper."
Originally posted by Bear_Music:
Originally posted by glad2badad:
Originally posted by hsolakidis:
I remember reading somewhere that non-digital lenses are better than digital only on digital SLRs with a crop factor.
Logic being that since all lenses perform less well at the edges, with a normal lens you 're not using the edges of the glass.
Is that true? We 're probably talking test-chart differences, I would assume. |
I've heard that also...but can't remember the source. Kind of makes sense. Most testing of lens that I've read have some verbiage about fall off at the edges, etc... |
No; the center of the full-frame lens is less optimized than the center of the digi lens, all other things being equal, because it has to make greater compromises viz the edges. The narrower the field of view of the lens, especially in extreme WA, the easier it is to optimize the entire field with no corner sacrifices.
By that logic, the 4x5 90mm lens would be a better 35mm telephoto than a 90mm designed for 35mm work, and it isn't. Not by a long shot.
R. |
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