ASP-C vs Full frame compression

marki6ce · May 28, 2013

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame? Or will i only get the flattering compression with an actual 85 or 100 lens?

thanks

ARShutterbug · May 29, 2013

The focal length is not a primary factor when determining depth-of-field. The focal length influences how close you can be to the object being photographed, as does the size of the recording format, but it is the physical size of the lens aperture and the distances between the objects and the camera that determine the depth-of-field. If you want to smooth the background blur, you need to move the person being photographed further from the background objects and closer to the camera, and then begin increasing the size of the lens aperture.

http://www.dpreview.com/glossary/optical/depth-of-field

Deleted1929 · May 29, 2013

Compression is simply a result of perspective and the angle of view you choose defines that.

So the field of view covered by the shot is all that matters, not the sensor itself. We describe field of view using focal length equivalent on full frame for shorthand, so you can say that the crop and full frame sensor require different physical focal lengths as you described. So if the full frame focal length is 150mm and the crop is 1.5x then you need a 100mm focal length lens to get approximately the same field of view.

Tamron make a 60mm f2 macro lens that might suit you. Sigma make or made a 70mm f2.8 macro. Canon make a 60mm f2.8 macro. Photozone.de have detailed reviews of all of them.

--

StephenG

marki6ce · May 29, 2013

Deleted1929 said:
sjgcit wrote:

Compression is simply a result of perspective and the angle of view you choose defines that.

So the field of view covered by the shot is all that matters, not the sensor itself. We describe field of view using focal length equivalent on full frame for shorthand, so you can say that the crop and full frame sensor require different physical focal lengths as you described. So if the full frame focal length is 150mm and the crop is 1.5x then you need a 100mm focal length lens to get approximately the same field of view.

Tamron make a 60mm f2 macro lens that might suit you. Sigma make or made a 70mm f2.8 macro. Canon make a 60mm f2.8 macro. Photozone.de have detailed reviews of all of them.

--

StephenG

So do I really need a prime lens in the 60-70mm range as the ones you are describing above since i have a 17-70 zoom "macro"?

Deleted1929 · May 29, 2013

Well only you know if you "need" a prime macro lens, but the main difference between a true prime macro and your zoom is that the prime can do a 1:1 reproduction and your zoom can only manage 1:2.7.

Put another way, the true prime macro lens can fill the frame with a smaller physical object than your zoom can. It can do this because it can focus closer than your zoom.

Whether you need to do that is something only you know.

--

StephenG

Richard the picture man · May 29, 2013

marki6ce said:
marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame?

As I understand it, no.

marki6ce said:
Or will i only get the flattering compression with an actual 85 or 100 lens?

Correct, as I understand it.

marki6ce said:
thanks

I have been taught that say, a 50mm is always a 50mm with 50mm characteristics, regardless of which type of body it is mounted on (APS or Full frame). The difference is that the APS will crop the picture more, but, the 50mm characteristics will not change.

Deleted1929 · May 29, 2013

I think people are muddling up compression and depth of field.

Compression is just perspective and field of view.

Depth of field equivalence is a completely different thing.

Draek · May 29, 2013

marki6ce said:
marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame? Or will i only get the flattering compression with an actual 85 or 100 lens?

thanks

What you call "compression effect" is actually named "perspective compression", it depends solely on perspective, and perspective depends solely on position---or in the case of portraits, distance to the subject, since you can't rearrange someone's ears or such.

Tom Axford · May 29, 2013

marki6ce said:
marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame? Or will i only get the flattering compression with an actual 85 or 100 lens?

thanks

To answer your question directly: on an APS-C camera a 70mm lens will give you exactly the same image as you get with a 1.6 x 70 = 112mm lens on a FF camera (because 1.6 is the crop factor for Canon APS-C). This means any compression effect will be the same.

To be even more precise, if you want the depth of field to be the same too, you need to also multiply the f-number by the crop factor.

So an image taken on APS-C at 70mm f/5.6 will be exactly the same (except for minor variations due to lens quality and sensor quality) as one taken on FF at 112mm f/9.

Richard the picture man · May 29, 2013

Tom Axford said:
Tom Axford wrote:

Tom Axford said:

marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame? Or will i only get the flattering compression with an actual 85 or 100 lens?

thanks

Click to expand...

To answer your question directly: on an APS-C camera a 70mm lens will give you exactly the same image as you get with a 1.6 x 70 = 112mm lens on a FF camera (because 1.6 is the crop factor for Canon APS-C). This means any compression effect will be the same.

To be even more precise, if you want the depth of field to be the same too, you need to also multiply the f-number by the crop factor.

So an image taken on APS-C at 70mm f/5.6 will be exactly the same (except for minor variations due to lens quality and sensor quality) as one taken on FF at 112mm f/9.

That seems like saying, take a picture with say a 50mm lens and crop it in pp to give the same "view" as 100mm, and you will have the same perspective compression as a picture taken with a 100mm lens.

Try it and see the difference.

Or am I misunderstanding your post ?

dsjtecserv · May 29, 2013

Richard the picture man said:
Richard the picture man wrote:

Richard the picture man said:

Tom Axford wrote:

Richard the picture man said:

marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame? Or will i only get the flattering compression with an actual 85 or 100 lens?

thanks

Click to expand...

To answer your question directly: on an APS-C camera a 70mm lens will give you exactly the same image as you get with a 1.6 x 70 = 112mm lens on a FF camera (because 1.6 is the crop factor for Canon APS-C). This means any compression effect will be the same.

To be even more precise, if you want the depth of field to be the same too, you need to also multiply the f-number by the crop factor.

So an image taken on APS-C at 70mm f/5.6 will be exactly the same (except for minor variations due to lens quality and sensor quality) as one taken on FF at 112mm f/9.

Click to expand...

That seems like saying, take a picture with say a 50mm lens and crop it in pp to give the same "view" as 100mm, and you will have the same perspective compression as a picture taken with a 100mm lens.

Yes, that's exactly what it means.

Richard the picture man said:
Try it and see the difference.

Good idea. Have you? You'll find that the cropped picture has exactly the same size and position relationship among objects as the shot with the longer focal length. Those relationships are determined only by the viewing position relative to the objects. A camera can only record the light the reaches it, and the light rays reflected from objects in the field come from fixed locations relative to each other; a lens can't rearrange objects or change the locations from which the rays emanated. This isn't limited to photography: if you just sit and look at a scene, the perspective relationships among the objects just are what they are from where you are sitting. You can't do anything with your eyes to alter that. Neither can a lens.

Richard the picture man said:
Or am I misunderstanding your post ?

No, you did read it correctly. Hope the above explanation helps.

Dave

Richard the picture man · May 29, 2013

dsjtecserv said:
dsjtecserv wrote:

dsjtecserv said:

Richard the picture man wrote:

dsjtecserv said:

Tom Axford wrote:

dsjtecserv said:

marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame? Or will i only get the flattering compression with an actual 85 or 100 lens?

thanks

Click to expand...

To answer your question directly: on an APS-C camera a 70mm lens will give you exactly the same image as you get with a 1.6 x 70 = 112mm lens on a FF camera (because 1.6 is the crop factor for Canon APS-C). This means any compression effect will be the same.

To be even more precise, if you want the depth of field to be the same too, you need to also multiply the f-number by the crop factor.

So an image taken on APS-C at 70mm f/5.6 will be exactly the same (except for minor variations due to lens quality and sensor quality) as one taken on FF at 112mm f/9.

Click to expand...

That seems like saying, take a picture with say a 50mm lens and crop it in pp to give the same "view" as 100mm, and you will have the same perspective compression as a picture taken with a 100mm lens.

Click to expand...

Yes, that's exactly what it means.

dsjtecserv said:

Try it and see the difference.

Click to expand...

Good idea. Have you? You'll find that the cropped picture has exactly the same size and position relationship among objects as the shot with the longer focal length. Those relationships are determined only by the viewing position relative to the objects. A camera can only record the light the reaches it, and the light rays reflected from objects in the field come from fixed locations relative to each other; a lens can't rearrange objects or change the locations from which the rays emanated. This isn't limited to photography: if you just sit and look at a scene, the perspective relationships among the objects just are what they are from where you are sitting. You can't do anything with your eyes to alter that. Neither can a lens.

dsjtecserv said:

Or am I misunderstanding your post ?

Click to expand...

No, you did read it correctly. Hope the above explanation helps.

Dave

Tom Axford · May 29, 2013

Dave has explained it very clearly so I will not repeat what he said.

As he mentioned in an earlier post, "perspective compression" or "perspective distortion" is a rather different phenomenon. There is a tutorial demonstrating it at:

http://photo.tutsplus.com/tutorials...ls/exploring-how-focal-length-affects-images/

In the example images in that tutorial, notice that the camera position does not remain the same (it is adjusted to keep the model at about the same size in the frame), whereas in the discussion in this thread, we have assumed that the camera position does remain the same.

Richard the picture man · May 29, 2013

Tom Axford said:
Tom Axford wrote:

Dave has explained it very clearly so I will not repeat what he said.

As he mentioned in an earlier post, "perspective compression" or "perspective distortion" is a rather different phenomenon. There is a tutorial demonstrating it at:

http://photo.tutsplus.com/tutorials...ls/exploring-how-focal-length-affects-images/

In the example images in that tutorial, notice that the camera position does not remain the same (it is adjusted to keep the model at about the same size in the frame), whereas in the discussion in this thread, we have assumed that the camera position does remain the same.

Thanks Tom, I am going to relearn or at least get it straight in my mind, this FF v APS focal length thing . As mentioned in an earlier reply I have decided to do some tests myself.

Talk about making life hard for myself, I have just discovered that the guy with a FF Canon 5dIII has moved away. So, I will get out my film Minolta (the only FF I posses and take it from there. Looks like it will be a long haul.

dsjtecserv · May 29, 2013

Richard the picture man said:
Richard the picture man wrote:

Richard the picture man said:

Tom Axford wrote:

Dave has explained it very clearly so I will not repeat what he said.

As he mentioned in an earlier post, "perspective compression" or "perspective distortion" is a rather different phenomenon. There is a tutorial demonstrating it at:

http://photo.tutsplus.com/tutorials...ls/exploring-how-focal-length-affects-images/

In the example images in that tutorial, notice that the camera position does not remain the same (it is adjusted to keep the model at about the same size in the frame), whereas in the discussion in this thread, we have assumed that the camera position does remain the same.

Click to expand...

Thanks Tom, I am going to relearn or at least get it straight in my mind, this FF v APS focal length thing . As mentioned in an earlier reply I have decided to do some tests myself.

Talk about making life hard for myself, I have just discovered that the guy with a FF Canon 5dIII has moved away. So, I will get out my film Minolta (the only FF I posses and take it from there. Looks like it will be a long haul.

Actually you don't need to make it that hard on yourself! You can observe the principle with any camera. Take a wide angle picture of a scene, preferably one with objects at a range of different distances from the camera, but close enough together than they will still be in the frame with a longer focal length. Then (without changing position) shoot the scene with a longer focal length, framing around the objects that are at different distances. Process the two shots from different focal lengths, and then crop down the wide angle so it matches the framing of the longer focal length. You'll see that the object relationships are the same between the cropped wide angle and the uncropped long focal length. If you resize the cropped one, you should be able to lay it over the other, and (except for differences in distortion characteristics of the two lenses) they should match up perfectly.

This would be the same thing as using a longer focal length on a full frame to match the framing of a crop sensor. Except in this case you are cropping the (wide angle) image after it is shot, instead of in camera, but the effect is the same.

Dave

beagle1 · May 29, 2013

marki6ce said:
marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame? Or will i only get the flattering compression with an actual 85 or 100 lens?

thanks

actually that "compression" factor is dependent on the distance from the subject and not the focal length or size of the sensor. But yes, the longer telephotos help you achieve that when you stand away from the subject and zoom in so the perspective or angle is better at longer distances. Which is good for people portraits.

Klipsen · May 29, 2013

Richard the picture man said:
Richard the picture man wrote:

That seems like saying, take a picture with say a 50mm lens and crop it in pp to give the same "view" as 100mm, and you will have the same perspective compression as a picture taken with a 100mm lens.

Actually, that's exactly what happens:

Picture 1 close up at 28 mm.

Picture 2 as far away as I could go and zoomed to make the mouse and alarm clock the same size as in the first picture. Note the shift in perspective. Now, some would say it's because of the change in focal length, but it's not.

Picture 3 same distance as picture 2, but zoomed out to 28 mm.

Picture 4 cropped from picture 3. Remember: this picture was taken from the same distance as picture 2 and at the same focal lenght as picture 1.

It appears then, that distance, not focal length determines perspective. Focal length on the other hand determines how much you get into the picture from the outset.

--
Ceterum censeo soleam calidam ISO esse delendam.

Klaus dk · May 29, 2013

Richard the picture man said:
Richard the picture man wrote:

Richard the picture man said:

marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame?

Click to expand...

As I understand it, no.

As I understand it, yes. You will get more DoF /less background blur, but the perspective (and compression) will be the same.

Richard the picture man said:
Richard the picture man said:

Or will i only get the flattering compression with an actual 85 or 100 lens?

Click to expand...

Correct, as I understand it.

No, on APS-C, 85 mm will give a perspective compression like 135 mm on FF.

Richard the picture man said:
Richard the picture man said:

thanks

Click to expand...

I have been taught that say, a 50mm is always a 50mm with 50mm characteristics, regardless of which type of body it is mounted on (APS or Full frame). The difference is that the APS will crop the picture more, but, the 50mm characteristics will not change.

That is true, but the cropping will affect the field of view thus giving you the same perspective as an 80 mm lens on FF.

From the same standpoint, take a picture of the same scene with a WA and a telephoto lens. If you crop the WA picture, so that the resulting image shows exactly the same field of view as the telephoto lens, the two pictures will have identical perspective.

DoF will be the same for same F-stop and same focal length regardless of sensor size, but that is not what the OP asked.

Richard the picture man said:
--
Regards - Richard
Happy guy with a K5
N.B. All my Images, even the bad ones, are Protected by Copyright

John Deerfield · May 29, 2013

marki6ce said:
marki6ce wrote:

Hi everyone,

I'm considering a prime lens, primarily for portraits and perhaps some macro in the 85-100mm range for my EOS 500d.

I want to take advantage of the compression effect of the short-medium telephoto range. I have a 17-70mm zoom, essentially a "fake" 110mm max focal length on my crop dSLR.

Quit using the term compression as it might apply to photography, it does nothing but confuse people. If you buy Ansel Adam's book "The Camera" (which throughly discusses lenses), I don't think you will find the word compression.

marki6ce said:
My question is, does this "fake" 110mm give the same compression effect that a "true" 110mm would give on a full frame? Or will i only get the flattering compression with an actual 85 or 100 lens?

Oops, there's that word: compression. Lose it. As others have pointed out, there is perspective. And perspective is based on distance. That's it. So, using your terminology, the "fake" 110mm would be exactly the same as the 110mm on a full frame camera. Why? The distance never changed. Now perspective is the size relationship of objects in the image. On the other hand, shooting at the same distance, using a full frame camera (insert similar FoV focal length, in this case 110mm), you will have a more shallow DoF and you background will go more OoF with the full frame camera. So there is going to be an aesthetic difference in the two images.

marki6ce said:
thanks

NetMage · May 29, 2013

Just had to congratulations on a really clear and easy to see example!

ASP-C vs Full frame compression

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