[Nicolas06]

That's not what I said or was even implying. I was talking strictly of focal length - two pictures taken from the same location with different focal lengths (regardless of sensor size).

Don't get this point... A 15mm is a tele for most point of shoot, a wide angle for micro 4/3 and pretty extreme on FF. And you will get compressed perspective on the P&S with a 15mm, while you'll get wide angle distorsion on FF with the same focal lens of 15mm.

Typically and that part of the wide angle problem on APSC, is that take a wide angle on FF, it can have pretty extreme perspective on FF... Put it on FF and most of this effect is gone.

A focal lens mean nothing for me in term of rendering, perspectives and field of view without the associated sensor.

[stevebrot]

You must be using new math or something. Are you talking about sensor size or light transmission?

Its a new trend, Dave. Everything from sensor noise to resolution to focal length is now expressed in stops. Why? I am not quite sure except that it may have something to do with determining absolute equivalence between apples and oranges.*


Steve


* or cumquats to cucumbers or some such...

[Nicolas06]

So true. Even on a 36mp d800, the DX crop mode is a paltry 15mp. That's good enough for posting to Facebook, and even then you're pushing it.

Yeah that wonderfull! I mean, you can pay 2000$ more for a D800 to get the same result an outdated APSC provide.

That's perfectly ok, I mean you can have on FF body for some other reason, don't have the money for a 600mm prime and don't feel the need for an APSC as you can crop exactly how you want this way on a 400mm.

And for this shoot you just use the center of your sensor... if it is APSC size you keep... Then you also get the iso capabilities of APSC, the rendering of APSC and the deph of field of APSC (that last one might not be problematic).

But if you want the field of view of 600mm with you FF, ideally you get a 600mm... And then you get 36MP 600mm (if it is a 600mm high quality prime of course), with the high iso capabilities and rendering. And that's nice... but REALLY expensive, heavy and bulky.

That's a choice, a compromise of ultimate quality, price, weight, size... For tele lenses, APSC simply give more duck for the bucks !

And that's until a point... if you already brought a 600mm and a 24MP APSC... there not really something practical available on FF to compete.

[RonHendriks1966]

Yeah that wonderfull! I mean, you can pay 2000$ more for a D800 to get the same result an outdated APSC provide.

Well people buy the K-3 so they can crop it into a micro 4/3th

[OregonJim]

Don't get this point... A 15mm is a tele for most point of shoot, a wide angle for micro 4/3 and pretty extreme on FF. And you will get compressed perspective on the P&S with a 15mm, while you'll get wide angle distorsion on FF with the same focal lens of 15mm.

Ok, you're the second person who took my comment in a totally different direction, so I'll restate it in a different way:

Take a sensor of any size you wish. Put a 400mm lens in front of it and take a picture of a single scene with several subjects at different distances. Now, put a 600mm lens in place of the 400. Change nothing else. In the 600mm shot, the subjects will appear to be closer together than in the 400mm shot. Thus, the compression is greater with the longer lens.

Now, change the sensor size. There is still the exact same difference in compression - all you have is a bigger (or smaller) field of view.

My original point was to refute the claim that a 400mm lens on APS-C is equivalent to a 600mm lens on FF. It is not. It is simply equivalent to another 400mm on FF in which the image has been cropped.

[normhead]

Ok, you're the second person who took my comment in a totally different direction, so I'll restate it in a different way:

Take a sensor of any size you wish. Put a 400mm lens in front of it and take a picture of a single scene with several subjects at different distances. Now, put a 600mm lens in place of the 400. Change nothing else. In the 600mm shot, the subjects will appear to be closer together than in the 400mm shot. Thus, the compression is greater with the longer lens.

Now, change the sensor size. There is still the exact same difference in compression - all you have is a bigger (or smaller) field of view.

My original point was to refute the claim that a 400mm lens on APS-C is equivalent to a 600mm lens on FF. It is not. It is simply equivalent to another 400mm on FF in which the image has been cropped.

The first rule of equivalence is "there is no such thing as equivalence", so hard to argue with you there. However 400mm on APS-c gives you the same FoV as 600 on an FF, and from the the same distance, the same compression. There may be minor differences on some aspects of the image... but it would be nit picking to discuss it.

If your question is, "What APS-c lens do I use to give me the approximate same reach as 600mm on FF" the answer is 400mm. What you're going on about I have no idea. Maybe you need to post a few images, taken from the same spot, 600mm on FF, and 400mm on APS_c. As far as I know, what's usually referred to as compression is dictated not by the length of the lens, but by the distance from the subject... so, you really need to show us what you're talking about for this one. Either you define compression differently than everyone else or you're wrong.

[OregonJim]

The first rule of equivalence is "there is no such thing as equivalence", so hard to argue with you there. However 400mm on APS-c gives you the same FoV as 600 on an FF, and from the the same distance, the same compression

Agreed, there is no such thing as equivalence.

I disagree, however, that "400mm on APS-c gives you the same FoV as 600 on an FF, and from the the same distance, the same compression".

Same fov, yes. Same compression, no. Think about it: Changing the sensor size does nothing to alter the image projected by the lens. The lens doesn't care if the sensor is 1mm square or the size of a house. It continues to project the same image. Compression is a function of both focal length and distance to subject. Sensor size plays no role at all in the equation!

[normhead]

Agreed, there is no such thing as equivalence.

I disagree, however, that "400mm on APS-c gives you the same FoV as 600 on an FF, and from the the same distance, the same compression".

Same fov, yes. Same compression, no. Think about it: Changing the sensor size does nothing to alter the image projected by the lens. The lens doesn't care if the sensor is 1mm square or the size of a house. It continues to project the same image. Compression is a function of both focal length and distance to subject. Sensor size plays no role at all in the equation!

Jim, the issue was thoroughly discussed on the forum a while ago, you might look for the thread. If you shoot from the same distance with a 15 mm and a 600 mm lens, and crop to the same size, you get the same compression.

Look at the examples here.
Myths About Lens Compression | Scott Bideau Photography

I remember when the discussion was held on the forum, quite a few members, including myself were surprised, because we were brought up to believe compression was a product of using telephoto lens. But it turns out, it was the fact that you had to stand back further to get the same image with a telephoto lens that made the difference. Take the same image for the same point with any focal length lens you want, make small part of the image the same size with every lens, and you'll get the same compression. Only distance from subject plays a role.

[JimmyDranox]

Mostly, we don't have clear data about real pixel sizes, about the size of microlenses in front of it, about quantum efficiency, and signal to noise ratio at pixel level for different sensors to make a clear comparison.

More, every lens can be measured by something called Airy disc. The smaller this disc is, more energy is transmitted by the lens to the sensor on a certain surface. And the faster the lens, the smaller the Airy disc is. And not only the speed of the lens makes the size of this disc.

We have data about all of this? No.

So, all we can do is to make some coarse and subjective comparison between apples and oranges.

[stevebrot]

the issue was thoroughly discussed on the forum a while ago

...and also several years ago. Compression with long lenses is sort of a photographic legend and can be had from a wide angle shot at the same camera position using a simple crop.* I have comparison photos somewhere that I posted to this site about five years ago. The bottom line is that using a smaller sensor is a simple crop.

One of these days I will have to write an article for this site titled "Top Ten Myths Of Perspective and DOF" or something like that.


Steve

* FWIW, I too was dumb-founded when I was able to easily use my K10D to test some of the maxims of photography and found that "tele perspective", "flattening" and "foreshortening" did not exist.

[ElJamoquio]

My original point was to refute the claim that a 400mm lens on APS-C is equivalent to a 600mm lens on FF. It is not. It is simply equivalent to another 400mm on FF in which the image has been cropped.

That's wrong, FWIW.

[jsherman999]

Agreed, there is no such thing as equivalence.

Of course there is! Last I checked the laws of physics have not been breached. Here's a quick overview with image examples.

I disagree, however, that "400mm on APS-c gives you the same FoV as 600 on an FF...".

Same fov, yes. Same compression, no.

Exact same compression, yes. (Norm was R. Norm was Ri. I'll try again - Norm was R. Right!)

Think about it: Changing the sensor size does nothing to alter the image projected by the lens. The lens doesn't care if the sensor is 1mm square or the size of a house. It continues to project the same image. Compression is a function of both focal length and distance to subject. Sensor size plays no role at all in the equation!

Only distance to subject affects compression, because what we call 'compression' (relative perceived distance of objects from one another in the frame) is an effect of perspective - and perspective is only a function of distance to subject.

Here's a quiz (for anyone,) which of the following are true and which are false:

1) If you were take a 20mm shot and a 200mm shot on the same format from the same place and then cropped the 20mm shot to the same FOV as the 200m shot, both images would show the same 'compression'.
2) If you were to take the shot above but not crop the 20mm image, they would still show the same compression in that part of the image, but it would be harder for the viewer to notice because the area would be much less magnified.
3) If you were to take a 400mm shot on aps-c and a 600mm shot on FF, both images would have the same FOV *and* compression - if you took them from the same position.
4) If you were to take a 400mm shot on FF and aps-c from the same position, then cropped the FF shot to match the FOV of the aps-c shot, they would have the same compression and FOV.
5) If you were to take a 400mm shot on aps-c and a 400mm shot on FF, moving forward with the FF shot so the FOVs match, the FF shot would have less compression.


.

[stevebrot]

How about a different set of hornets?

A long lens will produce the same amount of "wide-angle distortion" as an ultra-wide at the same lens-to-subject distance.


Steve

[Nicolas06]

The first rule of equivalence is "there is no such thing as equivalence", so hard to argue with you there. However 400mm on APS-c gives you the same FoV as 600 on an FF, and from the the same distance, the same compression. There may be minor differences on some aspects of the image... but it would be nit picking to discuss it.

It depend what is law of equivalence for you. Mathematically you can find the focal lens and apperture to get the same field of view, the same amount of light and same deph of field as another format.

[normhead]

It depend what is law of equivalence for you. Mathematically you can find the focal lens and apperture to get the same field of view, the same amount of light and same deph of field as another format.

If you have the same lens design, the same sized pixels etc. etc, etc.. The variables that go into camera design, and lens design will always mean that equivalence is a rough guideline and hardly a law. But, its a convenient on the fly conversion for rough comparisons. It's mostly used for ridiculous arguments that have no meaning in the real world, and are better ignored than followed.