new to digital SLRs

[BrianM 1]

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You can compare a 15mm EF mount on a full frame and it is about the same as a 10mm on an EF-S on a cropped sensor.

Well, sort of, but not really. A 10mm lens behaves like a 10mm lens, regardless of the sensor. The sensor changes only the field of view by cropping off the edges. A photo from a 10mm lens on a 1.6 crop sensor will not be the same as a photo from a 16mm lens on a fullframe sensor, with the exception of having the same field of view. Use the same lens on both sensors, then crop the photo from the fullframe sensor in photoshop, and then you will have the same photo.

In fact, the crop sensor does not even give you more magnification, as is commonly believed (though it does allow you to better fill the frame with the same lens). Take the same photo with the same lens, crop one in photoshop to get the same field of view, and the advantage will go to the sensor with the higher photosite density, regardless of sensor size.

"It's amazing what you can learn while you're not talking." - Skydivesg

[BMFin 0]

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. Use the same lens on both sensors, then crop the photo from the fullframe sensor in photoshop, and then you will have the same photo.

Are you sure ? I always thought lager sensor will create narrower DOF.

[pilotdave 0]

The change in DOF is only perceived because to get the subject to fill the frame with the same lens on a full frame camera as on a cropped camera, you need to be closer. That's what creates the narrower DOF, not the fact that the sensor is bigger.

So if you use the same lens at the same distance with a full frame and with a cropped camera, the pictures will look the same... except that the full frame camera will capture more area around the subject. The cropped camera doesn't magnify the image, but it may "focus" more pixels on the subject than the full frame, everything else being equal. So it kind of has an advantage in that digital zoom kinda way.

Dave

[BrianM 1]

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. Use the same lens on both sensors, then crop the photo from the fullframe sensor in photoshop, and then you will have the same photo.

Are you sure ? I always thought lager sensor will create narrower DOF.

Yep, I'm sure. The sensor has absolutely nothing to do with DOF. The lens does. The lens projects an image on the sensor which is converted to an electrical signal. The larger the sensor, the more of the projected image it captures, but it does not (can not!) change the projected image. All the smaller sensor is doing is, effectively, cropping the photo; you can achieve exactly the same effect by using a larger sensor and cropping in photoshop.

Edit to add: We generally get more DOF with smaller sensors because we use a different focal length to achieve the same FOV.

"It's amazing what you can learn while you're not talking." - Skydivesg

[BrianM 1]

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The cropped camera doesn't magnify the image, but it may "focus" more pixels on the subject than the full frame, everything else being equal.

If "everything else being equal" includes the resolution, yes. Otherwise - it might, or it might not. It depends on how much bigger the sensor is, and how much higher resolution - hence my comment about photosite density, which is what really matters. There's a reason that dpreview.com lists pixel density in their camera database.

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So it kind of has an advantage in that digital zoom kinda way.

Can have, yes - but I would not call it digital zoom! Digital zoom refers to interpolating pixels (just like upsizing in photoshop), and will have worse image quality than a higher density sensor which will give you higher resolution on your desired subject.

"It's amazing what you can learn while you're not talking." - Skydivesg

[BMFin 0]

Ok.. Thanks for the info.. (both of you)

[cratermaker 0]

No, the DoF scale on the lens is NOT converted. There are three main types of camera bodies 1.5/1.6/full frame(Nikon/Canon/Full Frame) The DoF is different for each. This is due to the Circle of Confusion(CoC) in calculating the DoF for each conversion figure. Go to the link below and try it out. Note the CoC at the bottom of the chart. It will change each time you change camera body(1.5/1.6/full frame) and the lens length remains the same.
http://www.dofmaster.com/doftable.html