Some explanations on magnification ratios of SLRs and megapixels.

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Some explanations on magnification ratios of SLRs and megapixels.

Last post 03-10-2007 10:44 PM by phughens. 13 replies.

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03-09-2007 6:39 PM

randy25rhoads
Joined on 12-31-2006
Tulsa
Posts 1,503

Some explanations on magnification ratios of SLRs and megapixels.

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There's been a lot of talk about the Canon consumer and prosumer cameras' magnification ratio that occurs when using lenses that are designed for full-frame 35mm sensors because of their smaller sensors. Basically, the reason why your 50mm lens turns into an 85mm lens when using it on the Rebel XTi, XT, 10D, 20D, or 30D is because of the in-camera cropping that occurs. The drawing below explains the basics of it.

A 35mm frame is 36mm wide and 24mm high. An APS-C sized sensor (like all of the digital rebels, 20D, 30D, etc.) is 25.1mm wide and 16.7mm high. Basically, using a lens that's designed for full frame cameras with a camera that has a smaller sensor causes in-camera cropping to occur. Your XTi has turned the 50mm lens into an 85mm lens, that's why you have to scoot back a bit to fit the subjects in the frame. Hope the drawing helps. The dimensions of the sensor sizes aren't to scale but they're close.

There is a way around the magnification though. Canon lenses designed for full-frame cameras are EF lenses. Ones designed for APS-C sized sensors are labeled EF-S lenses. You can use EF lenses on both full-frame and sub-frame cameras, but EF-S lenses can only be used with sub-frame cameras.

There's also a lot of confusion about megapixels, although, I think more people have a firm grasp on this more recently. Another diagram please.

I did the megapixel chart in excel, so the ratios are not exact, but they're fairly close.

I'm a visual learner and when I was learning about all of the technical stuff, I could've used more diagrams.

As always, if any of my info is incorrect, please say so. I pretty sure everything in accurate.

I hope this helps all you visual learners out there!

Michael Harrison

Canon EOS 400D
Apple iMac
Apple Aperture

Harrison Photography

03-09-2007 11:05 PM In reply to

randy25rhoads
Joined on 12-31-2006
Tulsa
Posts 1,503

Re: Some explanations on magnification ratios of SLRs and megapixels.

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Another tidbit of info: I believe that all Nikon DSLRs have a magnification factor of 1.5x. The Canon Rebel XT, XTi, 20D, and 30D all have magnify by factors of 1.6x. Canon's new high-speed camera, the 1D Mark III, and its predecessors, all have factors of 1.3x. The Canon 5D, 1Ds, and 1Ds Mark II have no magnification factor. All three have full-frame sensors, meaning their sensors are the same size as a 35mm film frame. No cropping occurs on these cameras.

Michael Harrison

Canon EOS 400D
Apple iMac
Apple Aperture

Harrison Photography

03-10-2007 12:18 AM In reply to

randy25rhoads
Joined on 12-31-2006
Tulsa
Posts 1,503

Re: Some explanations on magnification ratios of SLRs and megapixels.

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Here are some more diagrams.

These are some common sensor sizes, from cell phone CCDs to medium format 48mm frames.

Here's a visual diagram of some of those sizes. It's hard to get them to scale using excel, but they're very close. The P&S sensors are really smaller than what's represented here. (> P&S)

Michael Harrison

Canon EOS 400D
Apple iMac
Apple Aperture

Harrison Photography

03-10-2007 12:18 AM In reply to

randy25rhoads
Joined on 12-31-2006
Tulsa
Posts 1,503

Re: Some explanations on magnification ratios of SLRs and megapixels.

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Hope this helps. I recently got into a debate with a friend over his 10 megapixel P&S being able to take pictures that are comparable to my 10 megapixel DSLR. Maybe I'll go off on that tangent tomorrow. ;)

Michael Harrison

Canon EOS 400D
Apple iMac
Apple Aperture

Harrison Photography

03-10-2007 8:54 AM In reply to

OHsnap
Joined on 03-03-2007
Posts 6

Re: Some explanations on magnification ratios of SLRs and megapixels.

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Wow, these are excellent! I'm no novice but I still have had a hard time understanding the more detailed and technical aspects of digital camera innards. Your pictures really helped. I also can't believe I'm the first one to comment. You need to compile a whole lot of these lessons into your own website, to help wanna-be camera nerds like me!

"I like rice. Rice is great if you're hungry and want 2000 of something."

-Mitch Hedberg

03-10-2007 9:40 AM In reply to

tommas4
Joined on 05-27-2005
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Re: Some explanations on magnification ratios of SLRs and megapixels.

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Can't help it, I just LOVE the dinosaurus. Big Smile

Tomas

Here is link to my galleries

Here is link to my hotel page

03-10-2007 10:55 AM In reply to

Tom_Steele
Joined on 01-05-2006
Greenville, SC USA
Posts 1,928

Re: Some explanations on magnification ratios of SLRs and megapixels.

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randy25rhoads:
There is a way around the magnification though. Canon lenses designed for full-frame cameras are EF lenses. Ones designed for APS-C sized sensors are labeled EF-S lenses. You can use EF lenses on both full-frame and sub-frame cameras, but EF-S lenses can only be used with sub-frame cameras.

Thanks for the rather imaginative drawings, but I must point out that this appears to be incorrect, unless I am misunderstanding you. If you are saying that an EF-S 17-55 f/2.8 lens does not behave ("magnification-wise") like a 27-88mm lens, then that is incorrect.

The difference with the EF-S lenses is that they have a smaller image area focused on the back sensor. This means that while the EF-S lens will cover the 25mm x 17mm APS-C sensor, it will not cover the full-size (or even the 1D's 1.3 crop) sensor. So you would end up with massive vignetting.

Here is a visual example:

The reason for this is that it is much cheaper (and easier and smaller) to make a lens that only has to provide a usable image to the smaller area of the APS-C sensor, so Canon can provide some very good wide angle lenses for the crop sensor cameras at lower cost than if they had to provide that same image (with much of it being wasted on a crop sensor camera) over a wider area.

Another common misconception is that a 50mm lens is "like an 85mm" lens on a crop factor camera. A more accurate way to say that is that a 50mm lens has the FIELD OF VIEW of an 85mm on a crop factor camera. But as the name "crop factor" indicates, you are NOT getting 85mm of pull from a 50mm lens. It is just like if you shot a picture with the 50mm on a full frame camera and then went into Photoshop and CROPPED it down.

-Tom Steele

EOS30D w/580 EX II
EF-S 10-22mm f/3.5-4.5, EF-S 17-55mm f/2.8 IS
24-70mm f/2.8L, 50mm f/1.4, 100mm f/2.8 Macro,
70-200mm f/4L IS, 100-400mm f/4.5-5.6 L IS

Filed under: crop factor, crop sensors, 5d, ef-s, lenses, 30d1d

03-10-2007 11:28 AM In reply to

ProImages
Joined on 10-15-2005
Pittsburgh, Pa.
Posts 3,284

Re: Some explanations on magnification ratios of SLRs and megapixels.

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Thanks Tom,

I didn't feel like going into the detail to explain it the way you did with such great examples.

Randy also did I good job, but your explaination is more accurate.

"Field of View" is the correct term. A 50mm lens is a 50mm lens whether it is on a D20, 1D, or sitting by itself on a table. It does not zoom to 85mm, but is cropped by the smaller sensor.

Good job to both Randy and Tom

Greg

Greg
Nikon D3 and D700
http://proimagespa.com

03-10-2007 11:59 AM In reply to

julieinkc
Joined on 09-19-2006
St. Louis metro
Posts 1,521

Re: Some explanations on magnification ratios of SLRs and megapixels.

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randy25rhoads:
Hope this helps. I recently got into a debate with a friend over his 10 megapixel P&S being able to take pictures that are comparable to my 10 megapixel DSLR. Maybe I'll go off on that tangent tomorrow. ;)

Please do. I've enjoyed your posts very much.

julie

03-10-2007 12:13 PM In reply to

Tom_Steele
Joined on 01-05-2006
Greenville, SC USA
Posts 1,928

Re: Some explanations on magnification ratios of SLRs and megapixels.

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randy25rhoads:

These are some common sensor sizes, from cell phone CCDs to medium format 48mm frames.

You might want to add the 28.7mm x 19.1mm APS-H sensor that is in the 1D series of Canon cameras.

-Tom Steele

EOS30D w/580 EX II
EF-S 10-22mm f/3.5-4.5, EF-S 17-55mm f/2.8 IS
24-70mm f/2.8L, 50mm f/1.4, 100mm f/2.8 Macro,
70-200mm f/4L IS, 100-400mm f/4.5-5.6 L IS

Filed under: canon, aps-h, sensor size

03-10-2007 1:50 PM In reply to

randy25rhoads
Joined on 12-31-2006
Tulsa
Posts 1,503

Re: Some explanations on magnification ratios of SLRs and megapixels.

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Great examples Tom! Thanks for clearing up the field of view. I knew that that the EF-S lenses provide a smaller focused area to accommodate the smaller sensor, but there's one thing that still confuses me. I've seen my 50mm lens' field of view on a film camera, and compared the image that I saw with my XTi, and the image the XTi gave me was about a fourth of what the film camera gave me. The question: If I were to buy Canon's 60mmEF-S marco lens (planning to :) will it have the field of view of a 96mm?

Thanks for all the replies guys!

Michael Harrison

Canon EOS 400D
Apple iMac
Apple Aperture

Harrison Photography

03-10-2007 2:00 PM In reply to

Tom_Steele
Joined on 01-05-2006
Greenville, SC USA
Posts 1,928

Re: Some explanations on magnification ratios of SLRs and megapixels.

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Yes Michael, it would apply to the macro lens as well. Basically, as you correctly illustrated in your drawing, the 60mm would get everything in the bigger box on a full frame camera like film or a 5D. On a 1.6 crop APS-C camera, you get what is in the smaller box. So you get a narrower field of view and it is equivalent to the field of view of a 96mm lens.

In the scheme of things, the crop factor only hurts you when you need to go wide. Like the 50mm in a small studio (an example elsewhere on the forum) is cropping a lot of the image away on an APS-C sensor. Full frame is the ideal way to go, but now with the EF-S lenses, there are several options to get the wide angle back to some degree. I'm sure there are tradeoffs being made though, and as the pricing indicates - full frame is the highest quality. But the APS-C sensor is remarkably good and when zooming it actually works out well. For landscape and wide shots, then the 1.3 and full frame sensors would be better - at least on paper.

-Tom Steele

EOS30D w/580 EX II
EF-S 10-22mm f/3.5-4.5, EF-S 17-55mm f/2.8 IS
24-70mm f/2.8L, 50mm f/1.4, 100mm f/2.8 Macro,
70-200mm f/4L IS, 100-400mm f/4.5-5.6 L IS

03-10-2007 4:51 PM In reply to

bhbphotos
Joined on 09-07-2005
McMinnville, TN
Posts 1,047

Re: Some explanations on magnification ratios of SLRs and megapixels.

formats copy.jpg

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I made this photograph with a 90 year old 8x10 view camera. The normal lens on it is a 300MM. The overlaid lines show what my field of view would be using smaller formats. In decending order, 4x5 film, 6x7 medium format film, 35MM film and final "1.6 crop facter DSLR". This lens could be used on all the formats, with different field of views.