Question about aps-c sensors

[Touché! Good Sir]

If I use an aps-c specific lens on an aps-c specific camera, do I still multiply the focal length and aperture by the crop factor as it is done with full frame lenses?

[Sunshine1868]

yes.

[ALwin]

If I use an aps-c specific lens on an aps-c specific camera, do I still multiply the focal length and aperture by the crop factor as it is done with full frame lenses?

 

Focal lengths of a lens never change, it is the field of view and equivalent focal length that you have to take into consideration.

 

A 50mm lens is always a 50mm lens whether you put it on a tiny sensor camera, full frame or large format camera.  But the angle of view (field of view) changes depending on the sensor size.

 

As for the Aperture you need to consider a few things, if you use a 75mm lens on a full frame camera, to get the same field of view on a Nikon APS-C body, you need to use a 50mm lens.  The diameter of the iris opening at f/2.8 for a 75mm lens is not the same as the diameter of the iris opening for a 50mm lens at f/2.8.

 

75/2.8 = 26.8mm

50/2.8 = 17.9mm

 

There is also a difference in the thickness of the Depth of Field.

 

Using this tool: http://www.dofmaster.com/dofjs.html

A 75mm lens on a full frame camera at f/2.8 gives you a DOF of about 0.12m for a subject standing 2m away from the camera.

 

To get the same DOF or as close to it as possible, a 50mm lens on a Nikon APS-C camera with a 50mm lens has to be using about f/1.8.  Which is about 1.3 stops faster.

 

Keep in mind I did the calculations using "virtual lenses" of two different focal lengths.  A longer focal length on a larger sensor to keep the same field of view.

 

A similar result would also occur if I used the same lens on both sensor sizes.  However in this case the camera with the smaller sensor would be a bit further away from the subject than the camera with the longer sensor, in order to make sure both cameras see the exact same field of view.

 

If I kept both cameras the same distance away from the subject, which makes the smaller sensor camera see an apparent narrower field of view, the DOF should be the same or close to the same on both cameras.

[Sunshine1868]

^what he said. but yes. 

[ShadowCaptain]

If I use an aps-c specific lens on an aps-c specific camera, do I still multiply the focal length and aperture by the crop factor as it is done with full frame lenses?

 

the focal length on lenses "ie 50mm" is always written in full frame terms

 

So a 50mm lens designed for an APSC camera, will give a 75mm (or 80mm if canon) field of view

 

If you want a 50 to be a 50 - you need a full frame ;D

[Touché! Good Sir]

@Sunshine1868 and @ALwin .... Uh?

Wait...even if the lenses are aps-c specific the equivalent focal length is different from what is mentioned?

I know that we have to find the equivalent focal length and aperture by multiplying with the crop factor and I still am confused so could you please explain a bit better.. Please?

[Touché! Good Sir]

@ShadowCaptain maybe you can help?!

Lol ninja'd by you

[Touché! Good Sir]

the focal length on lenses "ie 50mm" is always written in full frame terms

So a 50mm lens designed for an APSC camera, will give a 75mm (or 80mm if canon) field of view

If you want a 50 to be a 50 - you need a full frame ;D

OK makes sense... Then will using full frame lenses on aps-c sensors make any difference from using aps-c specific lenses with similar specs?

[ALwin]

OK makes sense... Then will using full frame lenses on aps-c sensors make any difference from using aps-c specific lenses with similar specs?

 

It makes no difference, I already explained it in my post.

 

Now what will make a difference is if you're using a cheap 18-55 kit lens or an expensive 24-70 f/2.8 lens.  The quality of the glass elements, the speed of the lens and the nano coatings will be very different.

[ALwin]

the focal length on lenses "ie 50mm" is always written in full frame terms

 

Not really, the focal length of a lens is always a mathematical calculation based on the designs of the lens' elements.  It's not based upon any sensor or film size.  Nikon DX lenses, for example, which are designed for APS-C bodies and would cause serious vignetting on Full Frame bodies simply produce a smaller image circle.  It's done this way so to try and make it cost less than if it was designed to be compatible with both Full Frame and APS-C bodies.

 

Some of the minerals used in the manufacture of these glass elements can be expensive.  If it takes for example a total of 100kg of minerals mixed and melted together to make 10 normal glass elements, that same amount could probably be used to make 15 glass elements for a cropped sensor lens.

 

Now on tiny sensor cameras manufacturers mention 35mm equivalent focal lengths because Full Frame seems to be the de facto standard by which they measure things.

[Touché! Good Sir]

It makes no difference, I already explained it in my post.

Now what will make a difference is if you're using a cheap 18-55 kit lens or an expensive 24-70 f/2.8 lens. The quality of the glass elements, the speed of the lens and the nano coatings will be very different.

After reading your original post the second time I understood it!

[ALwin]

After reading your original post the second time I understood it!

 

It was the best I could do without going all technical and rocket science.  The main thing is the focal length value written on a lens never changes.  What changes is how much you see when looking through the lens.

[ShadowCaptain]

Not really, the focal length of a lens is always a mathematical calculation based on the designs of the lens' elements.  It's not based upon any sensor or film size.  Nikon DX lenses, for example, which are designed for APS-C bodies and would cause serious vignetting on Full Frame bodies simply produce a smaller image circle.  It's done this way so to try and make it cost less than if it was designed to be compatible with both Full Frame and APS-C bodies.

 

Some of the minerals used in the manufacture of these glass elements can be expensive.  If it takes for example a total of 100kg of minerals mixed and melted together to make 10 normal glass elements, that same amount could probably be used to make 15 glass elements for a cropped sensor lens.

 

Now on tiny sensor cameras manufacturers mention 35mm equivalent focal lengths because Full Frame seems to be the de facto standard by which they measure things.

 

 

I was just trying to relate it into laymen terms

 

Basically

 

Full frame, 10mm = 10mm

APSC 10mm = 15/16 mm depending on crop factor

MFT 10mm = 20mm

 

 

the 10mm part is always written as if applied to a full frame camera

 

So if you buy a 10mm MFT lens, it would only be 10mm if fitted to a full frame camera, when its on the MFT camera it becomes 20mm

 

 

That is about as simple as I can explain it, without using ANY technical language - even if its not 100% accurate

[Captain_Slow]

If I use an aps-c specific lens on an aps-c specific camera, do I still multiply the focal length and aperture by the crop factor as it is done with full frame lenses?

 

you also will want to multiply your aperture by the crop factor to get equivalent light gathering expectations as well as similar depth of field. 

 

so a 50mm F1.4 on a Nikon APSC would be similar to a Full Frame shooting at 75mm F2.1 (1.5 Crop factor)

[ALwin]

so a 50mm F1.4 on a Nikon APSC would be similar to a Full Frame shooting at 75mm F2.1 (1.5 Crop factor)

 

Whether mounted on a Full Frame or APS-C camera, a 50mm f/2.8 will have the same diameter iris opening.

 

If the cropped sensor camera and larger sensor camera are both kept the same distance from the subject which means the focusing distance is the same then the DOF will be the same.

 

But if you change it so that the cropped sensor sees the same composition, meaning moving the cropped sensor camera further back, as the larger sensor then you have to take into account the change in DOF as there is now a change in the focusing distance.  So to keep the same DOF, you'd need to change the aperture which changes the exposure value a bit.

 

 

To keep things simple, just focus mainly on the focal length's field of view crop factor.  The Aperture and DOF changes are not as important.  All that's needed for a photographer to understand is that larger Aperture = shallower DOF.

[ShadowCaptain]

SNIP

 

 

SNIP

 

 

Just because its easier this Tony Northup video explains this stuff if the OP is interested - but honestly at this point its just numbers

 

http://petapixel.com/2014/03/28/concise-explanation-crop-factor-affects-focal-length-aperture/

[ALwin]

Just because its easier this Tony Northup video explains this stuff if the OP is interested - but honestly at this point its just numbers

 

http://petapixel.com/2014/03/28/concise-explanation-crop-factor-affects-focal-length-aperture/

 

Yeah, I know.  At this point it's just a matter of numbers.  However FYI, Tony Northrup is oversimplifying and his explanation is a bit misleading.

 

Anyway as I said, the main thing to worry about is the crop factor applying to the field of view.  How it applies to Aperture and DOF is not as important.  

 

How many photographers go out there and take a photo saying "OK I'm going to use f/2.8 or f/5.6 because the DOF is X centimeters thick."  They just dial in the Aperture they want which will give them the DOF that will provide sharpness to the parts of the scene they want to focus on and blur out the rest.

[ShadowCaptain]

Yeah, I know.  At this point it's just a matter of numbers.  However FYI, Tony Northrup is oversimplifying and his explanation is a bit misleading.

 

Anyway as I said, the main thing to worry about is the crop factor applying to the field of view.  How it applies to Aperture and DOF is not as important.  

 

How many photographers go out there and take a photo saying "OK I'm going to use f/2.8 or f/5.6 because the DOF is X centimeters thick."  They just dial in the Aperture they want which will give them the DOF that will provide sharpness to the parts of the scene they want to focus on and blur out the rest.

 

 

I agree, too many people focus on the numbers etc, it doesnt matter, as long as you know how your photos look when you change the settings on your camera,  thats all that matters

[Captain_Slow]

Whether mounted on a Full Frame or APS-C camera, a 50mm f/2.8 will have the same diameter iris opening.

 

If the cropped sensor camera and larger sensor camera are both kept the same distance from the subject which means the focusing distance is the same then the DOF will be the same.

 

But if you change it so that the cropped sensor sees the same composition, meaning moving the cropped sensor camera further back, as the larger sensor then you have to take into account the change in DOF as there is now a change in the focusing distance.  So to keep the same DOF, you'd need to change the aperture which changes the exposure value a bit.

 

 

To keep things simple, just focus mainly on the focal length's field of view crop factor.  The Aperture and DOF changes are not as important.  All that's needed for a photographer to understand is that larger Aperture = shallower DOF.

not true!

get a 50mm f1.8 put it on a crop sensor and shoot at f1.8

and get a 70-200 f2.8 put it on a full frame and shoot it at 75mm and f2.8

 

you will see extremely similar results. 

 

obviously the Iris opening is the same, it doesnt change just cuz you change bodies, but the light gathered and depth of field changes.

[ALwin]

not true!

get a 50mm f1.8 put it on a crop sensor and shoot at f1.8

and get a 70-200 f2.8 put it on a full frame and shoot it at 75mm and f2.8

 

you will see extremely similar results. 

 

obviously the Iris opening is the same, it doesnt change just cuz you change bodies, but the light gathered and depth of field changes.

 

Yes that is for two different lenses.  I am talking about putting the same lens on two different cameras.  What I am talking about contains conditions that cause the change.  While using the same 50mm f/1.4 lens on both cameras (e.g. I am using a Nikon D7000 and a D700).

​

A. Keeping the APS-C and FF camera the same distance from the subject, which shows different compositions.

If both the D7000 and the D700 have the same 50mm prime lens with the same Circle of Confusion and set to f/2.8 and both are placed 2 meters away from the subject, while the D7000 will have a tighter composition, the thickness of the DOF will be the same.  This is basically the same as taking the photo captured with the D700 and cropping out the area that the D7000 sees.

 

 

B. Moving the APS-C camera a bit further away from the subject to get the same composition of the scene, which changes the focusing distance of the lens on the APS-C camera.

However if now I move the D7000 further back so that while the D700 remains 2 meters away from the subject but the D7000 now stands 3 meters away, to get the same composition, the DOF on the D7000 has changed because the focusing distance of the 50mm lens has changed.

 

 

I'm not disagreeing with you about using a 50mm lens on a D7000 and 75mm lens on a D700.  I am clarifying that the crop factor applies to the Aperture and DOF only when using lenses of different focal lengths or when keeping the keeping the compensation the same with the same lens on two different cameras.

[ALwin]

Going back to Point A I made in my previous comment, there is something else to consider.  Again I will use the D7000 (APS-C) and D700 (Full Frame) as an example, both cameras using the same 50mm lens.

 

If the subject that I am photographing is a large empty white canvas for painting, and both cameras are placed 2 meters away from the canvas.  Both cameras will give the same shutter speed as the correct exposure for a given ISO and Aperture.

 

However now if I paint a large portion of the center of the canvas black (I am not painting it entirely black, there will still be white borders), the internal exposure meters of the cameras will tell me to use two different shutter speeds.  The camera will tell me to use a slightly slower shutter speed on the D7000.  Because the composition of the D7000 will contain a larger proportion of black areas than the D700.

 

If I use my light meter to measure the light falling on the empty canvas and the painted canvas, it will give me the same exposure settings that can be used with both cameras.  But if I use the internal exposure meter of the camera, which does the calculation based on light reflecting off the subject, the exposure settings for the painted canvas will be different.