October 20, 2014, 06:17:23 PM

Author Topic: Crop sensors need cropped lenes  (Read 20874 times)

neuroanatomist

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Re: Crop sensors need cropped lenes
« Reply #30 on: August 10, 2013, 11:31:53 AM »
So you're saying the sensor size changes the numerator (focal length), and that's wrong, too. Focal length and max aperture are intrinsic properties of a lens, the sensor doesn't change them.
No, the sensor size does not change the FL. You are changing it, to get the same picture.

Maybe I'm not changing focal length, just moving forward or back...  Or maybe I'm taking a different picture. 

How often do you shoot with your smartphone at 200mm?

Just once, when I mounted my 70-200 II on my iPhone with an iPhone-to-EF Mount Adaptor that I borrowed from a friend.
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Re: Crop sensors need cropped lenes
« Reply #30 on: August 10, 2013, 11:31:53 AM »

Mt Spokane Photography

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Re: Crop sensors need cropped lenes
« Reply #31 on: August 10, 2013, 11:38:05 AM »
I used to have a 7D. A camera I took many pictures with and really enjoyed. But I was using it mainly behind L series lenses because I wanted the quality that those lenses provide. This has proved to be a good investment as I now have a 5D3 and a 1Dx and the lenses work with them.

I don't want more megapixels, I've got more than I uses almost always. And before anyone suggests it I certainly don't want more just so I can crop them away.  :P

One of my main problems with all this kit is the weight, carrying 40Kg on a trek to a wild life photo opertunity can be a pain.

When the 7D2 comes out the thing that would get me to buy one would be if light weight lens were available with similar quality to the L series but making use of the reduced diameter needed for the smaller sensor. (While they are at it they can reduce the price as the elements aren't as big.  ;) )

I know its not going to happen but it would be nice if it did. ------- Just think a nice quality 200-400 with built in 1.4x at about 1/2 the weight and cost in front of a crop sensor giving equivalent view to a 300 to 900 on a FF.  8)

( BTW There can be little doubt that someone who thinks they know better will ridicule this idea. If they convince me that they are right I will claim I was being sarcastic  ;D )




Also forgot to say, yes I'm carrying a couple of ff bodies and several big whites plus tripods flashes a hide a chair, it all adds up.

But ...Those tripods and flashes  and  hide a chair are still needed, its only the lenses that will change.  Flashes don't get smaller due to sensor size, in fact, they might get bigger to keep ISO's lower.
 
We are certainly not going to see the big white equivalent of a EF-s, there would be no market.  the price is determined in part by the number produced and sold, so a item that does not have a lot of sales must pay for R&D, and tooling over fewer units, the price then takes a jump.
 
I think we all wish for lighter and less expensive lenses while retaining or improving lens quality. 

Pi

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Re: Crop sensors need cropped lenes
« Reply #32 on: August 10, 2013, 11:41:56 AM »
So you're saying the sensor size changes the numerator (focal length), and that's wrong, too. Focal length and max aperture are intrinsic properties of a lens, the sensor doesn't change them.
No, the sensor size does not change the FL. You are changing it, to get the same picture.

Maybe I'm not changing focal length, just moving forward or back...  Or maybe I'm taking a different picture. 

Are we still talking about the Pentax 35-70 on crop vs. the 70-200 on FF? If you are taking a different picture, then this would be a different conversation. You can take different pictures with the same combo, as well.


Quote
How often do you shoot with your smartphone at 200mm?


Just once, when I mounted my 70-200 II on my iPhone with an iPhone-to-EF Mount Adaptor that I borrowed from a friend.


Would you post the result? That wold be interesting to see!

moreorless

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Re: Crop sensors need cropped lenes
« Reply #33 on: August 10, 2013, 11:55:39 AM »
The discussion really seems to be focused on two different things...

1.Making a smaller/cheaper lens for ASPC with the same focal length.

2.Making a smaller/cheaper lens for ASPC with the same field of view.

The second clearly being possible while the first probably isn't.

My guess is that with crop cameras the market for a lens with 70-200mm FOV isn't that great, that range seems to be well suited for things like event photography and I'm guessing most pro's are going to be using  FF. On ASPC I think the demand is much more long longer fast lenses for wildlife/sports use.

neuroanatomist

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Re: Crop sensors need cropped lenes
« Reply #34 on: August 10, 2013, 12:16:22 PM »
Are we still talking about the Pentax 35-70 on crop vs. the 70-200 on FF? If you are taking a different picture, then this would be a different conversation. You can take different pictures with the same combo, as well.

I wasn't, ever.  Sprogon stated that f/2.8 is f/2.8, and you apparently disagreed. 

How often do you shoot with your smartphone at 200mm?
Quote
Just once, when I mounted my 70-200 II on my iPhone with an iPhone-to-EF Mount Adaptor that I borrowed from a friend.
Would you post the result? That wold be interesting to see!

It really wouldn't - I just used it out the window of my 8th floor office.

However, what was I actually using?

1) 70-200mm f/2.8,
2) 535-1528mm f/2.8, or
3) 535-1528mm f/21? 

Sounds like I'd say #1, you'd say #3, and Panasonic would print #2 on the side of their lens barrel, like they do on the Lumix FZ200.  ::)
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Etienne

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Re: Crop sensors need cropped lenes
« Reply #35 on: August 10, 2013, 12:33:01 PM »
I have a Tokina 50-135 f/2.8 equiv to 80-112 mm.
It's a great lens. Much smaller than my 70-200L 2.8 IS II. BONUS: It is par-focal and that makes a big difference in video.
Pair that with a Tokina 11-16 f/2.8 and it is a great light-weight package for crop.
You could also add Sigma 30 1.4 and/or Canon 50 1.4.

Daniel Flather

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Re: Crop sensors need cropped lenes
« Reply #36 on: August 10, 2013, 12:54:43 PM »
If I won a big lottery I'd put out a bounty for someone to build a lens like that if Canon didn't take it up.

Or just buy what's current and hire a assistant to haul your sh*t around.
« Last Edit: August 10, 2013, 01:19:31 PM by Daniel Flather »
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Re: Crop sensors need cropped lenes
« Reply #36 on: August 10, 2013, 12:54:43 PM »

Pi

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Re: Crop sensors need cropped lenes
« Reply #37 on: August 10, 2013, 01:23:33 PM »
However, what was I actually using?

1) 70-200mm f/2.8,
2) 535-1528mm f/2.8, or
3) 535-1528mm f/21? 

Sounds like I'd say #1, you'd say #3, and Panasonic would print #2 on the side of their lens barrel, like they do on the Lumix FZ200.  ::)

You were shooting (1), which was equivalent to (3); and (2) is wrong any way you look at it.

neuroanatomist

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Re: Crop sensors need cropped lenes
« Reply #38 on: August 10, 2013, 01:27:14 PM »
However, what was I actually using?

1) 70-200mm f/2.8,
2) 535-1528mm f/2.8, or
3) 535-1528mm f/21? 

Sounds like I'd say #1, you'd say #3, and Panasonic would print #2 on the side of their lens barrel, like they do on the Lumix FZ200.  ::)
You were shooting (1), which was equivalent to (3); and (2) is wrong any way you look at it.

Someone should tell Panasonic...   ;)
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Pi

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Re: Crop sensors need cropped lenes
« Reply #39 on: August 10, 2013, 01:29:28 PM »
However, what was I actually using?

1) 70-200mm f/2.8,
2) 535-1528mm f/2.8, or
3) 535-1528mm f/21? 

Sounds like I'd say #1, you'd say #3, and Panasonic would print #2 on the side of their lens barrel, like they do on the Lumix FZ200.  ::)
You were shooting (1), which was equivalent to (3); and (2) is wrong any way you look at it.

Someone should tell Panasonic...   ;)

A good lawyer?

carlh

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Re: Crop sensors need cropped lenes
« Reply #40 on: August 10, 2013, 03:57:59 PM »
The issue of a cropped 2.8 and equivalence to 4.2 FF is sure to get some folks wound up and may well produce some long posts.  ;D

Certainly  :)

A FF lens being used with an APS-C sensor results in a slower system, lens+sensor. Since the APS-C sensor only captures 40% of the light projected by the lens on the image plane, the combination is slower than if the same lens had been used with a FF sensor. The lens is of course the same and doesn't know what sensor you place behind. But a lens on its own will not produce any pictures. You need a sensor as well. Really, I cannot see the controversy.

Quote
My view would be that with any lens designed to be used on a crop sensor, most of the photons entering the lens will hit the sensor, subject of course to the rectangular sensor reading a round lens. In contrast only 40% of the photons that would have hit the sensor on a full frame body will be used in a crop body (assuming a 1.6 crop) with a FF lens.

I'm getting more convinced that long lenses specifically designed for crop bodies would have a weight benefit. I still can't see Canon or Nikon making them. But maybe someone like Sigma might just do it to give themselves a USP.

What you are describing is called a speed booster, and it is available today for mirror less cameras.

http://www.metabones.com/buy-speed-booster

If, as you suggest above, you take, say, a 300 mm f/4 lens and project the otherwise wasted FF-photons onto the smaller APS-C sensor, the smaller sensor would still record the same FOV and the same amount of light as the FF sensor. This is because the aperture still has the same absolute size 300/4=75 mm.

However, by doing this you also decrease the focal length of the lens by a factor 1.6. So, while the absolute size of the aperture stays constant, its relative size increases to about f/2.5.

So, there you have it. The same FOV and the same amount of light captured by APS-C and FF. But, you have to decrease the FL with the crop sensor and keep the absolute aperture the same. This of course increases the relative size of the aperture. Hence the f/4 on FF is equivalent to f/2.5 on APS-C.

Unfortunately, if you want to capture a certain amount of light from a distant object the optics need to be of a certain size. You cannot fool the laws of physics just by cropping the sensor. Otherwise, why would e.g. the astronomers keep building larger and larger telescopes if they could just achieve the same thing by cropping their imaging sensors.

This is why its rather pointless to design APS-C only tele lenses. For WA lenses on the other hand its a different story as you can position the lens elements closer to the sensor due to the smaller mirror. Or lack of a mirror.

 

Skulker

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Re: Crop sensors need cropped lenes
« Reply #41 on: August 10, 2013, 05:02:51 PM »
Well Carl that was a long post  ;D

however you seem to have misunderstood my meaning.

I was not describing or promoting a speed booster, although that would, be one way of making use of the photons that are wasted when you put a bigger than needed lens (such as FF) on a smaller sensor (such as APS)

I would redesign the lens so it did not collect light that was not used. So it would be either lighter or brighter. Or maybe a bit of both.

Please don't try to imply that I'm thinking to break, fool, or in any way mess with the laws of physics.  8) cos I ain't. If you think that is what I'm trying to do then you are misunderstanding me.

The main reason that I'm not talking about this or that f stop or focal length is that as an engineer is that to me it is irrelevant what sensor is behind a lens, when it comes to describing its physical properties.
If you debate with a fool onlookers can find it VERY difficult to tell the difference.

Pi

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Re: Crop sensors need cropped lenes
« Reply #42 on: August 10, 2013, 05:34:57 PM »
I would redesign the lens so it did not collect light that was not used. So it would be either lighter or brighter. Or maybe a bit of both.

The way to do this is to make the front glass element less curved, with all the implications of this on the rest or them.  An EF, say, 70-200/2.8 lens has actually a wider FOV than a hypothetical EF-S 70-200/2.8. By doing so, you will get better performance - a good enough reason to design such a lens, IMO. But ... it would not be smaller, really. The front element will be more or less of the same  diameter, approximately equal to 200/2.8 The back one would not be smaller but the size of the back is fixed by the mount anyway.

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Re: Crop sensors need cropped lenes
« Reply #42 on: August 10, 2013, 05:34:57 PM »

dougkerr

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Re: Crop sensors need cropped lenes
« Reply #43 on: August 10, 2013, 06:05:52 PM »

Quote
A FF lens being used with an APS-C sensor results in a slower system, lens+sensor. Since the APS-C sensor only captures 40% of the light projected by the lens on the image plane, the combination is slower than if the same lens had been used with a FF sensor. The lens is of course the same and doesn't know what sensor you place behind. But a lens on its own will not produce any pictures. You need a sensor as well. Really, I cannot see the controversy.

Not so.

The effect of a lens on exposure depends on its f-number. For, say, an f/4.0 lens, the luminance on the sensor for some part of the scene of course does not depend on the sensor overall size.

If we have two cameras, one with a larger sensor that the other, both with sensor systems that we operate at an ISO SOS of ISO 400, then for a given scene, the same exposure result will be obtained with the same shutter speed and f-number.

Indeed, the total amount of light captured across the entire sensor is less for a smaller sensor than for a larger one. But the light per unit area (the property to which the sensor responds, for any given ISO sensitivity) will remain the same.

Best regards,

Doug

 

Quote
My view would be that with any lens designed to be used on a crop sensor, most of the photons entering the lens will hit the sensor, subject of course to the rectangular sensor reading a round lens. In contrast only 40% of the photons that would have hit the sensor on a full frame body will be used in a crop body (assuming a 1.6 crop) with a FF lens.

I'm getting more convinced that long lenses specifically designed for crop bodies would have a weight benefit. I still can't see Canon or Nikon making them. But maybe someone like Sigma might just do it to give themselves a USP.

What you are describing is called a speed booster, and it is available today for mirror less cameras.

http://www.metabones.com/buy-speed-booster

If, as you suggest above, you take, say, a 300 mm f/4 lens and project the otherwise wasted FF-photons onto the smaller APS-C sensor, the smaller sensor would still record the same FOV and the same amount of light as the FF sensor. This is because the aperture still has the same absolute size 300/4=75 mm.

However, by doing this you also decrease the focal length of the lens by a factor 1.6. So, while the absolute size of the aperture stays constant, its relative size increases to about f/2.5.

So, there you have it. The same FOV and the same amount of light captured by APS-C and FF. But, you have to decrease the FL with the crop sensor and keep the absolute aperture the same. This of course increases the relative size of the aperture. Hence the f/4 on FF is equivalent to f/2.5 on APS-C.

Unfortunately, if you want to capture a certain amount of light from a distant object the optics need to be of a certain size. You cannot fool the laws of physics just by cropping the sensor. Otherwise, why would e.g. the astronomers keep building larger and larger telescopes if they could just achieve the same thing by cropping their imaging sensors.

This is why its rather pointless to design APS-C only tele lenses. For WA lenses on the other hand its a different story as you can position the lens elements closer to the sensor due to the smaller mirror. Or lack of a mirror.
[/quote]

jrista

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Re: Crop sensors need cropped lenes
« Reply #44 on: August 10, 2013, 06:27:39 PM »
However, what was I actually using?

1) 70-200mm f/2.8,
2) 535-1528mm f/2.8, or
3) 535-1528mm f/21? 

Sounds like I'd say #1, you'd say #3, and Panasonic would print #2 on the side of their lens barrel, like they do on the Lumix FZ200.  ::)

You were shooting (1), which was equivalent to (3); and (2) is wrong any way you look at it.

It would be equivalent to #2. Lenses focus light. Aperture affects the amount of light focused at any given point resolved at the sensor plane. Cropping out the center doesn't change the fact that an f/2.8 lens focuses the same amount of light on the center point of an APS-C sensor as on an FF sensor. Yes, total quantity of light imaged is less, but the amount of light focused anywhere on the sensor is the same. Therefor, an f/2.8 lens is an f/2.8 lens, regardless of the size of the sensor (even the microscopic iPhone sensor will still receive the same amount of light at the center as an APS-C or FF.)
« Last Edit: August 10, 2013, 06:38:38 PM by jrista »

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Re: Crop sensors need cropped lenes
« Reply #44 on: August 10, 2013, 06:27:39 PM »