(please help) expain crop factor for ASPC camera

[lesch2k]

i'm looking into the Canon XS / XSi but i dont understand when to apply the corp factor.


Rephrased question:

Does the 1.6 x magnification factor also apply when using an EF lens? If i have an ASP-C sensor do i just multiply every lens distance by 1.6

My first question was answered. The 1.6 x magnification / crop factor applies to the EF-S lenses when using an ASP-C Sized sensor.


What are the best way to spend $300-$400 on lenses for maximum versatility.

 

[corkyg]

The printed ratings of EFS lenses do not take into account the crop factor.

Why is somewhat of a puzzlement since the EFS lenses cannot be used on a full frame EOS camera.

But - that's the way it is.

 

[lesch2k]

edited above with follow on question.

 

[lesch2k]

new question added: Does the 1.6 x magnification factor also apply when using an EF lens?

Is the 17-85mm EF-S lens very similar to the 28-135mm EF lens?

 

[Madwand1]

Originally posted by: lesch2k
new question added: Does the 1.6 x magnification factor also apply when using an EF lens?

Is the 17-85mm EF-S lens very similar to the 28-135mm EF lens?

Here's a link briefly illustrating crop factor:

http://www.millhouse.nl/digitalcropfactorframe.html

If you're trying to understand this, then you should understand that the crop factor is just due to a smaller sensor size. The magnification of the lenses doesn't really change. 50mm focal length is 50mm focal length, regardless of the lens and branding, etc.. From this perspective, the 17-85 and 28-135 are very different lenses, as they have different focal length ranges.

What changes is the field of view due to the sensor size differences, and implicitly, the amount of magnification needed on the image in post-processing to fill the same size of print. In other words, if you take an image with a small sensor, then to have that image fit the same size of paper as an image taken with a larger sensor, you have to magnify the small-sensor image more. This leads to an apparent increase in magnification due to the small sensor, but is just a consequence of the crop in post-processing, not an actual increase in magnification.

In other words: If you took an image with a full-frame camera, and then cropped it in Photoshop by a factor or 1.6 in length and width, you would have essentially the same image that you would have gotten with a crop format camera using the same lens. Note that a common next step after the crop would be to increase the image to fit the window -- this is the magnification, an aspect of post-processing, and this step leads the images to seem to have greater magnification.

The 17-85 is not very similar to a 28-135 when put on a cropped DSLR. However, if you're comparing the field of view of the 17-85 on a cropped DSLR to the field of view of the 28-135 on a full-frame camera, then the field of view given by the two different cameras is very similar.

 

[996GT2]

Using a 17-85 on a XS is about the same as using a 28-135 on the 5D or 1Ds Mark III (which are full-frame cameras).

The 18-55mm IS lens that the XS comes with is actually quite good for the price...it does almost everything the 17-85 does, but has a slightly shorter range and no USM focusing. Image-quality wise, though, it is comparable to the 17-85.

Several good "upgrade" zoom lenses to get a for an APS-C camera in the $300-400 range are listed below. These 3 lenses are do-it all "walkaround" lenses that can suit a variety of shooting conditions, from landscapes to portraits to psuedo-macro.

Tamron 17-50mm f/2.8 XR Di II
Sigma 18-50mm f/2.8 EX DC Macro
Sigma 17-70mm f/2.8-4.5 DC Macro

I would skip the 17-85 IS, since it distorts quite a bit at 17mm. The Sigma and Tamron lenses show about 2.5% barrel distortion, which is already quite noticeable, but the Canon shows a whopping 4% barrel distortion at 17mm. This means you have to go back and correct a lot of wide-angle shots in software, which is a pain.

Also, despite having IS, the 17-85 has a slow aperture range and does not focus very close (1:5 max magnification). Build quality is also worse than the Sigma EX series. The only thing the Canon really has going for it is the fast USM focusing, but the other lenses I listed are also quite fast in the AF department (but louder than the Canon).

 

[GTaudiophile]

http://en.wikipedia.org/wiki/Crop_factor

 

[extra]

Get the 18-55mm IS that just comes with the kits, for starters--optically it's awesome, it's just a little slow.

Then get the 55-250mm IS that often also comes in a kit (avoid the 75-300).. the 70-300mm IS is also good but more expensive.. optically they are about the same. The 55-250 is optically *awesome* it's just a little slower lens, but hey that's okay because it's also small and light!

Then get the 50mm 1.8 off of craigslist or something (got mine for $50)... its not the best lens, but it's cheap and fast... upgrade to the 50mm 1.4 later.

So you've got 17-55=included in kit
55-250mm IS=$250
50mm 1.8 = $50-80

 

[ElFenix]

Originally posted by: corkyg
The printed ratings of EFS lenses do not take into account the crop factor.

Why is somewhat of a puzzlement since the EFS lenses cannot be used on a full frame EOS camera.

But - that's the way it is.

that would be even more confusing. the only number that makes sense is to put the actual focal length on the lens. a 60 mm lens is a 60 mm lens is a 60 mm lens and will throw the same image regardless of what piece of film or imager is behind it. the angle of view will be dependent upon the film/imager, of course, but only up to the limit of the image circle thrown by the lens.

Originally posted by: lesch2k
new question added: Does the 1.6 x magnification factor also apply when using an EF lens?

Is the 17-85mm EF-S lens very similar to the 28-135mm EF lens?

yes. and sorta maybe.

if you put a 17-85 on a 40D and a 28-135 on a 5D and take pictures from the same position, you'll get the same perspective and roughly the same angle of view at either end of the zoom range. if you then also open up the 17-85 on the 40D by 1.33 stops compared to the 5D, you'll have roughly the same depth of field as well.

however, if you have two 40Ds, one with the 17-85 and one with the 28-135, then you'll have a different angle of view at either end of the zoom range.

 

[lesch2k]

thanks for the help all got it finally ! now if only i can decide how much my budget is...

 

[finbarqs]

the EASIEST way to look at the "crop" factor is to take an image... let's say, 8.5x11 picture. Now let's add our 1.6x crop factor (approx 40%) to that exact image .. so that would be... 3.4x4.4. remember, we are not SHRINKING the image, we're CROPPING. What does that mean? We take some scissors, and we cut the image into the 3.4x4.4 size. That means you'll loose some things in the picture such as an arm, a leg, maybe some trees, etc. No we take that EXACT 3.4x4.4 picture with missing limbs, trees, etc. and blow it back up to 8.5x11. Doesn't it look "zoomed-in?" well that's exactly what a crop factor does!

 

[lesch2k]

Originally posted by: finbarqs
the EASIEST way to look at the "crop" factor is to take an image... let's say, 8.5x11 picture. Now let's add our 1.6x crop factor (approx 40%) to that exact image .. so that would be... 3.4x4.4. remember, we are not SHRINKING the image, we're CROPPING. What does that mean? We take some scissors, and we cut the image into the 3.4x4.4 size. That means you'll loose some things in the picture such as an arm, a leg, maybe some trees, etc. No we take that EXACT 3.4x4.4 picture with missing limbs, trees, etc. and blow it back up to 8.5x11. Doesn't it look "zoomed-in?" well that's exactly what a crop factor does!

Somewhat false - what you have described is a digital zoom resulting in a loss of 60% of the detail. crop factor is an optical zoom affect whereby the middle part of the picture is in more detail.

What you have described would be true if you compared a 20 MP full frame camera that was cropped to a 11 MP ASP-C camera.

Alternatively crop factor can be explained as putting all sensor pixels into the middle part of the image. the pixels are now smaller (by ~40%, so you get more digital noise) but capture the same level of detail, just as using a 1.6 X optical lens.

In ASPC cameras the lens will still provide a focused image on both the sensor and the area around the sensor in which no image is captured.

 

[Madwand1]

Originally posted by: lesch2k
crop factor is an optical zoom affect whereby the middle part of the picture is in more detail.

No, that's just wrong.

 

[shocksyde]

I swear some of you people are going out of your way to confuse others.

Let's make this easy:

You put an 18-55mm lens on a Canon XSi (1.6 crop factor), you get what APPEARS to be a ~29-88mm lens (18-55 multiplied by 1.6). No, it is not actually a 29-88mm lens, but the field of view looks like it is, so just pretend it is. There is absolutely no reason to claim "Oh, it's still an 18-55mm! It's not a 29-88mm!!"

EF-S lenses, even though they (mostly) only fit on crop Canon cameras, are still labeled with their ACTUAL focal range. So a Canon 10-22 EF-S is labeled as 10-22mm, but APPEARS to be a 16-35.

Hope that keeps it simple for you.

 

[shocksyde]

Originally posted by: Madwand1

Originally posted by: lesch2k
crop factor is an optical zoom affect whereby the middle part of the picture is in more detail.

No, that's just wrong.

Some people who have both crop and full-frame cameras will use their crop camera for birding, air shows, etc. because the crop camera gives them what is essentially a 1.6x teleconverter. He was right on the "optical zoom effect" part.

 

[Madwand1]

Originally posted by: shocksyde
Some people who have both crop and full-frame cameras will use their crop camera for birding, air shows, etc. because the crop camera gives them what is essentially a 1.6x teleconverter. He was right on the "optical zoom effect" part.

So more people misunderstand the effect and think that they get a free "optical zoom" with a crop and that makes it OK? Tell you what -- I'll sell you a mask which will give you a 100x crop factor, which you can use at airshows for a 100x "optical zoom effect"! Woo hoo! How much would you pay for that?

 

[shocksyde]

Originally posted by: Madwand1

Originally posted by: shocksyde
Some people who have both crop and full-frame cameras will use their crop camera for birding, air shows, etc. because the crop camera gives them what is essentially a 1.6x teleconverter. He was right on the "optical zoom effect" part.

So more people misunderstand the effect and think that they get a free "optical zoom" with a crop and that makes it OK? Tell you what -- I'll sell you a mask which will give you a 100x crop factor, which you can use at airshows for a 100x "optical zoom effect"! Woo hoo! How much would you pay for that?

I'm sorry you're so broken up about it, but many people at POTN recommend a crop body for such uses. I guess they don't know what the hell they're talking about.

 

[Madwand1]

Originally posted by: shocksyde
I'm sorry you're so broken up about it, but many people at POTN recommend a crop body for such uses. I guess they don't know what the hell they're talking about.

I'm not "broken up" -- I'm getting pretty excited about my 100x zoom sales. Now if you're arguing that a crop factor works as a teleconverter, then pony up and buy my 100x crop factor "teleconverter". I'll get you a deal.

 

[shocksyde]

Originally posted by: Madwand1

Originally posted by: shocksyde
I'm sorry you're so broken up about it, but many people at POTN recommend a crop body for such uses. I guess they don't know what the hell they're talking about.

I'm not "broken up" -- I'm getting pretty excited about my 100x zoom sales. Now if you're arguing that a crop factor works as a teleconverter, then pony up and buy my 100x crop factor "teleconverter". I'll get you a deal.

Go on Google and look up "crop camera birding" and take a look at the discussions.

Instead of coming up with imaginary products, why don't you concentrate your energy on proving me wrong?

 

[Madwand1]

Originally posted by: shocksyde
Instead of coming up with imaginary products, why don't you concentrate your energy on proving me wrong?

It's called reductio ad absurdum, and is a valid proof technique. Why don't you make the effort to actually understand it yourself instead of relying on claims others are making and getting it wrong?

 

[shocksyde]

Originally posted by: Madwand1

Originally posted by: shocksyde
Instead of coming up with imaginary products, why don't you concentrate your energy on proving me wrong?

It's called reductio ad absurdum, and is a valid proof technique. Why don't you make the effort to actually understand it yourself instead of relying on claims others are making and getting it wrong?

Explain to me why using a full frame camera with a 400mm lens is better for birding than using a crop camera with a 400mm lens. If you can't, then I'll just dismiss you as argumentative with no actual substance.

Take a look at this discussion. Pay attention to mentions of having to crop the full frame image to obtain the same field of view as the crop camera. A 5DII cropped 60% will result in a 9MP image. A shot with the 50D needs no cropping and is 15MP.

 

[996GT2]

Originally posted by: Madwand1

Originally posted by: shocksyde
I'm sorry you're so broken up about it, but many people at POTN recommend a crop body for such uses. I guess they don't know what the hell they're talking about.

I'm not "broken up" -- I'm getting pretty excited about my 100x zoom sales. Now if you're arguing that a crop factor works as a teleconverter, then pony up and buy my 100x crop factor "teleconverter". I'll get you a deal.

For some applications, a crop-sensor camera is superior to a full-frame. For example: shooting relatively stationary birds from a long distance.

Let's use the example of a popular long lens for birding and sports: the Canon 400mm f/5.6L. If you put this lens an EOS 50D, then the effective focal length is 640mm. You also get less vignetting in the corners at wide-open aperture due to the smaller sensor. Now, from ISO 100-400, the most commonly used daylight ISOs (for birding, airshows, etc) there is not much (if any) difference between the image quality of an EOS 50D and an EOS 1Ds Mark III. It is only when you start getting into the higher ISOs of 1600 and above that full frame really starts to shine. The EOS 50D is actually also a little bit faster than an EOS 1 Ds Mark III: 6.3 FPS vs. 5 FPS.

So, let's say you wanted a 640mm lens on a 1Ds Mark III. Either you pony up the cash for a 600mm f/4L (which costs about 8 times more), or you slap a teleconverter onto the 1Ds Mark III.

Let's consider option 2, the TC.

Canon only makes a 1.4x and 2x TC, but other companies do make a 1.7x TCs that comes close to the 1.6x crop factor on Canon APS-C cameras. So, let's say you slap that 1.7x TC onto the 400mm f/5.6L and put the combination on a 1Ds Mark III.

The first issue is that you've no longer got an f/5.6 lens. Since a 1.7x TC takes away 1.5 stops of light, you've now got a 680mm f/9.5 Lens. This combination WILL NOT autofocus even on the 1Ds Mark III, which requires a minimum of f/8 to AF.

The second issue is image quality. Let's say you are just super awesome at manually focusing with a very dark f/9.5 viewfinder and somehow manage to get good focusing accuracy. You've still got to deal with the degradation of image quality imposed by the TC.

Or, you could have just stuck to using the 400 f/5.6L on an EOS 50D with no image quality loss and fully working AF. Take your pick...

 

[ElFenix]

for birding it's really about getting the maximum number of pixels on a target. even with a 600 mm lens it may be hard to fill the frame. the crop cameras make it easier to get more pixels on the bird. considering that the 1ds3/5d2 have about the same density as a 20D, the 50D allows you to get 2x the number of pixels on the bird for the same actual focal length as the 1ds3 and 5d2. also, the 50D has a higher continuous rate than the 1ds3/5d2. so you get more pixels on the bird and more images.

 

[finbarqs]

the only part where i'm wrong, was i didn't mention the mega-pixel count for that small space. Then of course, you're going to get into pixel density too. But I'm just trying to keep things in perspective. So does that mean, the Canon G10 is the BEST bird camera, if you slap on the 20x zoom lens? i mean, you have 14.7mp in a smaller than APS-C sized sensor!

Truth be told, cropped sensor is exactly that. Cropped. Just a high MP crop. does high MP equate to more detail? not necessarily. you slap on a 200 lens on a crop, and slap it on a full frame, you'll get the SAME EXACT picture, except the crop will just be smaller. punch your mp count into that frame, and that's what you're going to get. Sharper? arguably yes. More detailed? perhaps. But what can I say, why don't they just make a super small aps-c sized sensor that's 10mm (aps-c is ~22mm) and call that "the super bird zoom camera". the thing is, what you see is what you get. APS-C, you just get it cropped. Personally I like my frame to be as big as I want, and then crop down when I don't want it.

When i used my aps-c camera (D300) i'm always wishing I had more frame when I'm close to a subject with a given DOF i'm viewing. With a FF, I have my problem solved.

 

[996GT2]

Originally posted by: finbarqs
When i used my aps-c camera (D300) i'm always wishing I had more frame when I'm close to a subject with a given DOF i'm viewing. With a FF, I have my problem solved.

Time for a Tokina 11-16?