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f stop and crop sensors

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No, then try "convoluted"!

Still having trouble (I know "convoluted" is a big word and hard to pronounce)? Then my last offering is "seriously confused"... ;-)

--
Charlie Davis
Nikon 5700, Sony R1, Nikon D50, Nikon D300
HomePage: http://www.1derful.info

"If ever a time should come, when vain and aspiring men shall possess the highest seats in Government, our country will stand in need of its experienced patriots to prevent its ruin."
-Samuel Adams, 1776
 
She? made it much too "complicated" .... and is inherently WRONG anyway.

IGNORE EVERYTHING she? said, (including where she suggest that higher ISO setting results in "lower" noise) ...

Most of the other people got it right ....

f/stop remains the same, thus exposure (ISO, shutter speed & f/stop setting) remains the same.

Only the effective focal-length changes, (as in cropping) ...

and effective DOF increases. (albeit, as you saw, you can get into a complicated discussion of DOF).

--
Thanks for reading .... JoePhoto

( Do You Ever STOP to THINK --- and FORGET to START Again ??? )
 
VipinM said:
This is in response to the original question.

The depth of field should remain exactly same if you are using same settings on both camera. Only difference will be that, in case of cropped sensor you will get a digitally stretched image of center part of full sensor camera image.

Consider following case.

I take a snap (snap 'F') of a object which is 10 meters away from camera with a 50mm lens on a full sensor camera at f/1.4. I take another snap (snap 'C') of same object at same distance on a 1.5x cropped sensor at same f stop (f/1.4).

Now the two snaps will be different in terms of dimensions. That means, the snap C will be a center crop of snap F. If I print an image using snap C without cropping, and I print another image from snap F with a cropped size that matches visual size of snap C (here when I say visual size that means, the snap F is cropped in such a way that it includes the center part of the image which is exactly visible in snap C and this image is stretched to fit exact paper dimensions of printed image of snap C), are these two printed images are going to have different dof or they will be exactly same?

As I understand, these two images should be exactly same.

Also you can see in the dof calculator which is mentioned above changes the circle of confusion value from .02 to .03 when changing from a cropped to a full size censor. This is because they are trying to match relative pixel resolution of two sensors. So I am not sure whether changing circle of confusion value in these calculation is absolutely correct or not but, I believe that this is the factor which is giving the different dof values for different camera sensors.

Please correct me if I am wrong.
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What you’re trying to say is technically correct, but your description is convoluted (and sometimes wrong) and the concept is irrelevant to begin with.

What you call “digitally stretched”, everyone else calls magnification, and it applies to very image printed from any sensor. The smaller the sensor, the more it will be magnified when printed at a certain size. Image quality across cameras can only be fairly compared at the same print size. Comparing a larger full-frame print to a smaller crop-sensor print is unfair to the larger sensor and has no justification in science.

Nobody prints the images from their compact cameras the size of postage stamps...what purpose would be served by comparing such images to larger images?
Absolutely none.

.
 
Graystar said:
What you call “digitally stretched”, everyone else calls magnification, and it applies to very image printed from any sensor. The smaller the sensor, the more it will be magnified when printed at a certain size. Image quality across cameras can only be fairly compared at the same print size. Comparing a larger full-frame print to a smaller crop-sensor print is unfair to the larger sensor and has no justification in science.
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To avoid confusion, magnification should always refer to the relative size of the image of a subject projected on the film plane by a lens in comparison to the size of the actual subject. Taking a film negative or a digital negative and making it bigger for the purpose of printing is called enlargement. Ever heard of a machine called an enlarger back in the film days?
 
Here's what you will discover:
  • From the same distance, your lenses will get you an image that fills the frame more on the 7D than the 5D - giving you the impression that you are shooting with a higher focal length lens.
  • Your F4 and F1.4 lenses will give you the same shutter speed at the same ISO, F-setting, and light level. No exposure changes there.
  • At the same F-setting, and SAME FRAMING of your subject (move up with your 5D, or back up with the 7D), your lenses will give you noticeably LESS Depth of Field with the 5D when compared to the 7D.
  • One minor point... you can shoot at a couple higher F-settings with the 5D before you see "diffraction" set in. Diffraction is a breakdown of the image that you get at about F11 and higher.
  • One other minor point - if you saw any darkness or blurring in the corners of your 5D images, especially at the largest Aperture (F1.4 or F4), those will likely go away with those lenses on the 7D.
Hope that helps. I can explain why these things occur, but others seem to do better with the technical side of this issue.

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Bossier City, Louisiana
http://www.pbase.com/ericsorensen
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Eric, why respond to a post made a year and a half ago? If you had new information, just start a new, more modern thread. Many of these people aren't here anymore.

Always check the date on a thread and see is it is old like this. :)

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Cheers, Craig

Follow me on Twitter @craighardingsr : Equipment in Profile
 
This is a pretty old forum posting from August 2010. Many of the people will not be here anymore. When you find one via a search, always check the date to make sure it's a good idea to revive. Been there myself. :)

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Cheers, Craig

Follow me on Twitter @craighardingsr : Equipment in Profile
 
you've actually described what t-stop is, which is the actual amount of light hitting the sensor. Each lens has a different t-stop even having the same, f-stop. fstop is a relational value to the diameter of the diaphragm relative to lens diameter.
 
Brivers said:
you've actually described what t-stop is, which is the actual amount of light hitting the sensor. Each lens has a different t-stop even having the same, f-stop. fstop is a relational value to the diameter of the diaphragm relative to lens diameter.
Click to expand...
The post to which you replied (made in 2010) did not describe T-stop. It discussed, among other things, the effect of keeping the f/stop the same when the sensor size is changed. This is related to the larger topic of equivalence.

T-stops, which are common in video usage, are just f/stops corrected for lens transmission. The poster made no reference to this topic at all.
 
mick92627 said:
Newbie question here. I have 2 Canon lenses, EF 24-105mm f/4L IS USM, and EF 35mm f/1.4L USM. Usually they are attached to my 5D Mk1.

I am getting a 7D today. I know it's a crop sensor with a 1.6x mag factor, so my lenses are really 38-168mm and 56mm.

My question is: does that effect the f/ number as well? I think it doesn't, but I want to be sure. So for the 2 lenses mentioned above, the f/ will remain f/4 and f/1.4 and widest aperture, correct?

Also, are there any other considerations I should be aware of in taking EF lenses and putting them on crop sensor (EF-S) bodies?

Thanks in advance for any and all who care to take a run at this.
Click to expand...
As far as exposure is concerned (that is to say the brightness of the light falling on the sensor) your lenses will indeed still have a maximum aperture of f/4 and f/1.4 respectively. But the depth of field will be increased by a factor of 1.6 stops at any given focal length and aperture setting.

Some people may also mention what they call noise equivalence but you can safely ignore that controversial theory, which has no scientific basis.
 
I just noticed this thread is many years old. What is all that about then?
 
Porky89 said:
I just noticed this thread is many years old. What is all that about then?
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The poster "Brivers" decided to respond (incorrectly, as it happens) to a comment made in 2010. Because of my general churlishness, I responded to his post to correct it while also noting that he had brought it back from the dead. This is how people like me get their kicks.

The recent activity brought it to the top of the post pile, which is where you came in.

Are you using flat view? It's easier to see the dates in threaded view which gives you the ability to make an informed decision about making a comment.
 
mick92627 said:
Newbie question here. I have 2 Canon lenses, EF 24-105mm f/4L IS USM, and EF 35mm f/1.4L USM. Usually they are attached to my 5D Mk1.

I am getting a 7D today. I know it's a crop sensor with a 1.6x mag factor, so my lenses are really 38-168mm and 56mm.
Click to expand...
Just to be clear, your lenses remain 24-105mm and 35mm. Changing sensor size or film size doesn't change the focal length of the lens. The crop sensor simply CROPS away the outer edges of your image. Thus, your resulting image appears more "zoomed in", but in reality it isn't. Cropping is not the same as zooming. It's a 1.6x CROP factor not "mag" factor.

So, if you are standing 15' from your subject and you take a photo with a 56mm lens on a 5D, then you would need to use a 35mm lens on a 7D from the same distance in order to end up with the same composition.
mick92627 said:
My question is: does that effect the f/ number as well? I think it doesn't, but I want to be sure. So for the 2 lenses mentioned above, the f/ will remain f/4 and f/1.4 and widest aperture, correct?
Click to expand...
Correct. The f-number is a measurement of the focal length divided by the diameter of the aperture. The size of the lens does not change simply because you put it on a different camera.

Likewise, cropping a photo in Photoshop won't have any effect on the physical lens.
mick92627 said:
Also, are there any other considerations I should be aware of in taking EF lenses and putting them on crop sensor (EF-S) bodies?
Click to expand...
Yes. Depth of Field. Say you like your 56mm lens on the 5D. You take a nice portrait shot which a nice blurry background using f/2.8. Now put the 56mm on the 7D, The first thing you'll realize is that you're too close to the subject. You'll need to back further away to compose the same shot because the shot is cropped. However, you've just increased the subject to camera distance. This in turn increases the depth of field. So, your background is less blurry now. You'll need to compensate by opening the lens more.
mick92627 said:
Thanks in advance for any and all who care to take a run at this.
Click to expand...
 
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mick92627 said:
So if I have a fast lens that takes good exposures in low light on a FF sensor, that same lens is going to take essentially the same good exposure in low light, AT THE SAME SETTINGS, on a crop sensor.

But I will have a narrower angle of view, and a wider depth of field.

Is that correct?
Click to expand...
If you do not change the distance from the camera to the subject, then the depth of field remains the same. So, you will ALWAYS have a narrower angle of view.
 
Bob said:
mick92627 said:
So if I have a fast lens that takes good exposures in low light on a FF sensor, that same lens is going to take essentially the same good exposure in low light, AT THE SAME SETTINGS, on a crop sensor.

But I will have a narrower angle of view, and a wider depth of field.

Is that correct?
Click to expand...
If you do not change the distance from the camera to the subject, then the depth of field remains the same. So, you will ALWAYS have a narrower angle of view.
Click to expand...
You surely mean a narrower angle of view and same depth of field or same angle of view and greater depth of field? Or anywhere in between depending on camera to subject distance of course.
 
See you all again in 2019!
 
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