Why is there an ISO difference between Crop and Full Frame images I've taken?

Swanseajack said:
Some interesting reading on this thread, for someone like me who doesn't get involved to much in the tech side of cameras.

Anyway...........

I had a thought a few months ago when I was purchasing my 70-300 lens for my Nikon. I was looking at the Nikon 70-300vr which has a front element filter size of 67mm and the Tamron 70-300vc lens which has a front element filter size of 62mm, so in theory the Nikon lens should let in about 7.5% more light than the Tamron due to it being more surface area, but the apertures for the lenses are roughly the the same...Tamron f4-5.6 and Nikon f4.5 -f5.6.

The above is based on the filter thread size for the lenses, so the glass will be a little smaller and with this thought, would this affect the above sampling or similar tests?

I just checked the current versions of the Nikon lenses Rob is using and the 70-200 has a filter size of 77mm and the 300mm has a filter size of 52mm?? or are the speccing a drop in filter for the prime as 52mm seems very small

70-200 spec > https://www.nikonusa.com/en/nikon-products/product/camera-lenses/af-s-nikkor-70-200mm-f%2f2.8g-ed-vr-ii.html#tab-ProductDetail-ProductTabs-TechSpecs

300 spec > http://www.nikonusa.com/en/nikon-products/product/camera-lenses/af-s-nikkor-300mm-f%2f2.8g-ed-vr-ii.html#tab-ProductDetail-ProductTabs-TechSpecs
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The 300mm f2.8 is a drop filter, if it had a front fitting filter like the 70-200 it would be roughly 120mm.
 
From the help in the thread above my current thinking the 1-1.3 stop difference has been made up of several variables. Changes in ambient light, better metering, larger amount of dark background, lens breathing, sensor dynamic range difference. if all of these added 1/3 stops each it would soon add up to 1-1.3 stop difference. The only way would be to test it again to see if it could be replicated.
 
No two camera models are likely to measure light in exactly the same way. Especially in the pattern of the measuring area.
Even the same camera and lens, when moved over the same scene gives different results. As different parts gain prominence.
However if an incident meter reading were taken, such considerations are neutralised and consistent exposures are obtained , provided the light falling on the subject does not change.

Secondly the Iso calibration between camera models and sensors is rarely identical.

Taking those two shots with exposures set using an incident meter, and setting the same fixed Iso on both the cameras and the meter.would show any differences especially if the lenses were then swapped and the shots repeated.

However you would still not know if it were a shutter speed or aperture variation or a combination of all three variables.

This is a phenomenon that photographers have always lived with and is easily compensated for, for any lens and camera combination, if it is both consistent and troublesome enough.
 
They are different scenes, so what is hitting the sensor is different.

Of course, both of a squirrel, but the wider one has much more 'scene'

Or a cloud went overhead
 
Swanseajack said:
Some interesting reading on this thread, for someone like me who doesn't get involved to much in the tech side of cameras.

Anyway...........

I had a thought a few months ago when I was purchasing my 70-300 lens for my Nikon. I was looking at the Nikon 70-300vr which has a front element filter size of 67mm and the Tamron 70-300vc lens which has a front element filter size of 62mm, so in theory the Nikon lens should let in about 7.5% more light than the Tamron due to it being more surface area, but the apertures for the lenses are roughly the the same...Tamron f4-5.6 and Nikon f4.5 -f5.6.

The above is based on the filter thread size for the lenses, so the glass will be a little smaller and with this thought, would this affect the above sampling or similar tests?

I just checked the current versions of the Nikon lenses Rob is using and the 70-200 has a filter size of 77mm and the 300mm has a filter size of 52mm?? or are the speccing a drop in filter for the prime as 52mm seems very small

70-200 spec > https://www.nikonusa.com/en/nikon-products/product/camera-lenses/af-s-nikkor-70-200mm-f%2f2.8g-ed-vr-ii.html#tab-ProductDetail-ProductTabs-TechSpecs

300 spec > http://www.nikonusa.com/en/nikon-products/product/camera-lenses/af-s-nikkor-300mm-f%2f2.8g-ed-vr-ii.html#tab-ProductDetail-ProductTabs-TechSpecs
Click to expand...

I see where you're coming from, but the size of the front element is pretty much unrelated to f/number. It's the diameter of the aperture diaphragm that counts though even that too can be an unreliable guide with many modern and complex lens designs when it becomes the 'effective relative' diameter that matters.

chris malcolm said:
Just as a very general observation, I've often tried to compare the same shot on two different lenses. Sometimes I do it when I'm outside and all set up for a shot, and have some time to kill. So many of those tests have been degraded by a stop or so of lighting difference I didn't notice at the time that I've decided wherever possible to do such tests indoors at night with my own controlled artificial light.
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I know what you mean! I find this all the time with my work that often requires perfectly constant light for a period of maybe 20 minutes or so (for comparison testing). With anything other than a perfectly blue sky (rare) or completely overcast (not good for pictures) it's very unusual. Drives me mad LOL

cosmicma said:
the way i understand it is it's something to do with overall light at a given aperture
in other words a full frame sensor with an aperture of F2.8 will gather more light than a crop sensor at the same aperture because of the bigger area of the full frame sensor or am i barking up the wrong tree with these thoughts ?

it would go some way to explaining the differences in ISO
Click to expand...

Yes, full frame gathers more than twice the light/photons of APS-C but that's factored into the ISO rating. Where is does show up is at higher ISO, where the FF camera would have the same noise level at, say, ISO6400 as the APS-C camera at ISO3200. Assuming sensors of similar generation.

Terry, two problems with an incident meter reading. Firstly, the meter knows nothing about what happens after the light enters the lens (T.stop, aperture accuracy, true ISO etc). The second difficultly is that you'd have to ask the squirrel to hold the meter :D
 
HoppyUK said:
Yes, full frame gathers more than twice the light/photons of APS-C but that's factored into the ISO rating.
Click to expand...

It gathers more light but it is spread over a bigger area (assuming the lenses are cxhosen to give the same field of view) so the net result is the same.

Just as a 35mm frame of FP4 has the same ISO rating as a 5" x 4" piece.


Steve.
 
Steve Smith said:
It gathers more light but it is spread over a bigger area (assuming the lenses are cxhosen to give the same field of view) so the net result is the same.

Just as a 35mm frame of FP4 has the same ISO rating as a 5" x 4" piece.


Steve.
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I'm pretty sure we've had this exact same discussion with HoppyUk not 2 months ago.
 
I personally rather dislike the "equivalence" discussion... there is no such thing. Different gear/choices will give different results, it's always a tradeoff. It's just like the idea of "zooming with your feet" using a prime...it's nonsense.

As far as exposure goes (light per area), sensor size makes no difference. If I put my D810 into DX mode the exposure doesn't change. Nor does it change if I choose to use my 1" sensor Nikon1V2 instead. The "settings" do change if I use my Fuji which is ISO rated using the SOS method, but the exposure doesn't (assuming consistent/proper metering).

Unless I'm mistaken, the ISO difference should have made the D800 image 1 stop brighter. It *did* make the image ~ .3 stop brighter. So the unaccounted for difference is .7 stop. And it begs the question as to *how* the ISO was set/determined. If done manually you will be limited to a max accuracy of 1/3 stop (or less depending on the setting). SO, guessing manual settings with .3 stop accuracy, and a metering display accuracy also of .3 stop...that would explain the .3 stop difference. If set by auto ISO the camera can choose "in between settings" not available to you directly for more accuracy (i.e. ISO 560 as in this image).


Immature Bald Eagle by Steven Kersting, on Flickr
 
HoppyUK said:
I see where you're coming from, but the size of the front element is pretty much unrelated to f/number. It's the diameter of the aperture diaphragm that counts though even that too can be an unreliable guide with many modern and complex lens designs when it becomes the 'effective relative' diameter that matters.



I know what you mean! I find this all the time with my work that often requires perfectly constant light for a period of maybe 20 minutes or so (for comparison testing). With anything other than a perfectly blue sky (rare) or completely overcast (not good for pictures) it's very unusual. Drives me mad LOL



Yes, full frame gathers more than twice the light/photons of APS-C but that's factored into the ISO rating. Where is does show up is at higher ISO, where the FF camera would have the same noise level at, say, ISO6400 as the APS-C camera at ISO3200. Assuming sensors of similar generation.

Terry, two problems with an incident meter reading. Firstly, the meter knows nothing about what happens after the light enters the lens (T.stop, aperture accuracy, true ISO etc). The second difficultly is that you'd have to ask the squirrel to hold the meter :D
Click to expand...

The same answer to both, is that it doesn't need to.......
An incedent reading removes all variation due to subject matter, and pegs the exposure exactly.
I always hold my own meter, provided it is in the same light as the subject you get an identical reading.

The meter used on a full frame or aps or indeed a compact camera are calibrated to measure the same light input. The size or number of pixels or their pixel size is a total red herring.

The reflective exposure reading component Will make a difference, with special regard to spot, average or multi pattern mode chosen.
As will the focal length chosen as the proportion of subject matter to background content will change, with either a change of focal length or of viewpoint.
The above have no influence on an incident reading at all.
 
sk66 said:
I personally rather dislike the "equivalence" discussion... there is no such thing. Different gear/choices will give different results, it's always a tradeoff. It's just like the idea of "zooming with your feet" using a prime...it's nonsense.

As far as exposure goes (light per area), sensor size makes no difference. If I put my D810 into DX mode the exposure doesn't change. Nor does it change if I choose to use my 1" sensor Nikon1V2 instead. The "settings" do change if I use my Fuji which is ISO rated using the SOS method, but the exposure doesn't (assuming consistent/proper metering).

Unless I'm mistaken, the ISO difference should have made the D800 image 1 stop brighter. It *did* make the image ~ .3 stop brighter. So the unaccounted for difference is .7 stop. And it begs the question as to *how* the ISO was set/determined. If done manually you will be limited to a max accuracy of 1/3 stop (or less depending on the setting). SO, guessing manual settings with .3 stop accuracy, and a metering display accuracy also of .3 stop...that would explain the .3 stop difference. If set by auto ISO the camera can choose "in between settings" not available to you directly for more accuracy (i.e. ISO 560 as in this image).


Immature Bald Eagle by Steven Kersting, on Flickr
Click to expand...

Your third paragraph contradicts the second.

It's very possible to not know or care about equivalence, provided you never change camera format. But if you do, and want to know about the differences you're seeing, then check the DPReview link posted above. You'll want to know about how the crop factor affects field of view for a start, and also how depth of field changes, also by the crop factor. There's a lot more to it than that though and the crop factor, or crop factor squared, comes up time and again.

That DPReview link doesn't go into how equivalence affects lens performance, but it most certainly does. Better sharpness is probably the number one reason folks switch from APS-C to full-frame. The crop factor is part of the calculation there too.
 
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HoppyUK said:
Your third paragraph contradicts the second.
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I don't think I contradicted myself... the question is the accuracy of the method used to determine/set the exposure (i.e. manual w/ .3 stop accuracy). And the variability to "the settings" SOS vs REI ISO ratings may introduce.

I understand how a smaller sensor affects things... and that's my point. You can't get to the exact same point with different formats; something has to give... there is no "equivalence."
Larger sensors are not "sharper," but a larger sensor of equivalent MPs is* (less demanding of lens resolution and aperture selection). And smaller formats aren't more noisy per se... smaller pixels are. It's how you use those pixels that determines if the final output will be noisier (i.e. output size/cropping). You always have an advantage with larger size/more MP's if you are downsampling/same output size (and the lens can resolve to that level at the chosen aperture). But that all goes out the window if you crop the larger/higher MP sensor image.

I use a D810, a D4, and a V2... they all have different purposes and there are times where each one is "the best choice" for overall IQ (at 1:1 or smaller output).

(* "may be" in the center at least... but this also discounts lenses optimized for the smaller sensor and system specific lenses)
 
HoppyUK said:
Your third paragraph contradicts the second.

It's very possible to not know or care about equivalence, provided you never change camera format. But if you do, and want to know about the differences you're seeing, then check the DPReview link posted above. You'll want to know about how the crop factor affects field of view for a start, and also how depth of field changes, also by the crop factor. There's a lot more to it than that though and the crop factor, or crop factor squared, comes up time and again.

That DPReview link doesn't go into how equivalence affects lens performance, but it most certainly does. Better sharpness is probably the number one reason folks switch from APS-C to full-frame. The crop factor is part of the calculation there too.

Why are smaller formats more noisy
Click to expand...

Bigger has undoubtedly always been better... but there is no need to dress it up with some magical "equivalence "
Bigger can mean less enlargement is necessary. Or that you need to open up the aperture less to reduce the depth of field. Or can refer to many other factors with a mathematical relationship. Unfortunately Bigger has also always meant chunkier and heavier and perhaps less convenient.

In real life we chose a camera of a particular format because it is "convenient, cost effective, does what you want it to do, and is good enough".

My little Fuji X20 is good enough at the sizes I need and for what I need it for. Were it not, I would use or buy something different.
I never used 35mm professionally, except for the very few occasions that a client wanted 35mm slides. Howevr I rarely used anything else for my happy snaps after the Dslr became "good enough".

Format sizes never have an equivalence of usefulness, one always stand out as the better option.

I under stand all the mathmatics and theory behind crop factors, focal length, apertures, magnification, exposure, fields of view, etc. to the extent that I now rarely have to think about them to make my choices.

"Equivalence " does not effect lens performance. because red herrings rarely do much at all, but magnification to the final image certaily does.
Hence... if you want big and good ...Start big.

Equivalence is an confused observation not science. It is a very poor way of thinking about relationships, it seems to confuse and blind with science, in equal measure, rather than give accurate explanations that people can actually understand.

When Photographers used many and varied formats, neither crop factors nor equivalence were ever used to explain anything. They seem to be a totally unnecessary product of the digital age.
 
Faldrax said:
The caveat to that is that you also have a 'T' value for lenses, which is the light transmission value - but for the majority of SLR type lenses, the Aperture and T values are the same I believe (though happy to be corrected by anyone with more detailed understanding :))
Click to expand...

chris malcolm said:
The more glass in a lens the less light gets through it, and so the greater the difference between the lenses' T-stops (how much light actually gets through) and their f-stops (how much light would get through if there were no loss). Lens coatings also play a part in light loss. Other things being equal (which they're usually not) there will be more glass in a zoom lens than a prime.
Click to expand...

HoppyUK said:
Apertures should be the same in theory, but in practise the T.stop may be different (though not much, and nowhere near one stop)
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According to DXO the 300mm is 0.4 stops brighter than the 70 - 200:

http://www.dxomark.com/Lenses/Compa...-f-2.8G-IF-ED-on-Nikon-D7100__478_792_223_865
 
Terrywoodenpic said:
Bigger has undoubtedly always been better... but there is no need to dress it up with some magical "equivalence "
Bigger can mean less enlargement is necessary. Or that you need to open up the aperture less to reduce the depth of field. Or can refer to many other factors with a mathematical relationship. Unfortunately Bigger has also always meant chunkier and heavier and perhaps less convenient.

In real life we chose a camera of a particular format because it is "convenient, cost effective, does what you want it to do, and is good enough".

My little Fuji X20 is good enough at the sizes I need and for what I need it for. Were it not, I would use or buy something different.
I never used 35mm professionally, except for the very few occasions that a client wanted 35mm slides. Howevr I rarely used anything else for my happy snaps after the Dslr became "good enough".

Format sizes never have an equivalence of usefulness, one always stand out as the better option.

I under stand all the mathmatics and theory behind crop factors, focal length, apertures, magnification, exposure, fields of view, etc. to the extent that I now rarely have to think about them to make my choices.

"Equivalence " does not effect lens performance. because red herrings rarely do much at all, but magnification to the final image certaily does.
Hence... if you want big and good ...Start big.

Equivalence is an confused observation not science. It is a very poor way of thinking about relationships, it seems to confuse and blind with science, in equal measure, rather than give accurate explanations that people can actually understand.

When Photographers used many and varied formats, neither crop factors nor equivalence were ever used to explain anything. They seem to be a totally unnecessary product of the digital age.
Click to expand...

Equivalence is just a term, it's actually about differences and their effects. It is certainly not 'confused observation' and very much rooted in science, but with results that are clearly visible and easy to prove if you want to.

The reason why at least a basic understanding is useful today is because we use the same lenses on different format cameras - quite unlike the film era. That's what this thread is about. And most people's first introduction to digital will have a been a crop-format DSLR that they used with lenses from their old film camera. So you need a conversion value to know what the difference is, ie the crop factor. That is equivalence at its most basic and everyone uses it, but there is much more to equivalence for those that want to know more about how changing format also impacts pretty much everything, things like depth of field, and camera-shake, ISO, noise and dynamic range, lens sharpness etc etc.
 
HoppyUK said:
The reason why at least a basic understanding is useful today is because we use the same lenses on different format cameras - quite unlike the film era.
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I have a 65mm lens on my 6x12 camera. I can also put it on my 5x4 camera. I can also use my 5x4 camera with a 120 roll film back with 6x9 or even 6x6 formats.

Same lenses, different formats, film.

Film users don't tend to think of crop factors, we just kniow what we consider to be standard for each format and work it out from there.


Steve.
 
Steve Smith said:
I have a 65mm lens on my 6x12 camera. I can also put it on my 5x4 camera. I can also use my 5x4 camera with a 120 roll film back with 6x9 or even 6x6 formats.

Same lenses, different formats, film.

Film users don't tend to think of crop factors, we just kniow what we consider to be standard for each format and work it out from there.


Steve.
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Its mostly futile to even consider "equivalence" when you consider than different formats can have a different aspect ratio and normal is relative.
 
Steve Smith said:
I have a 65mm lens on my 6x12 camera. I can also put it on my 5x4 camera. I can also use my 5x4 camera with a 120 roll film back with 6x9 or even 6x6 formats.

Same lenses, different formats, film.

Film users don't tend to think of crop factors, we just kniow what we consider to be standard for each format and work it out from there.


Steve.
Click to expand...

Absolutely.
That is the way it has always been.
Digital has added nothing new.
you only need to understand the basics and the rest follows...

A lens you bought for a 10x8 field camera would also work on a 6x9
however you did need to know the coverage, as a short focus lens for a 6x9 would not likely cover on 5x4. But many but not all 65mm ones
would. This is the same reason that aps lenses rarely work on full frame...(an Angulon would not, but later super Angulons would)
 
Terrywoodenpic said:
an Angulon would not, but later super Angulons would
Click to expand...

My Super Angulon 65mm just about covers 5x4. I use it on 6x12 usually. Schneider's data sheet says it was designed for 6x9 so there is a certain amount of getting away with it involved!


Steve.
 
Terrywoodenpic said:
Absolutely.
That is the way it has always been.
Digital has added nothing new.
you only need to understand the basics and the rest follows...

A lens you bought for a 10x8 field camera would also work on a 6x9
however you did need to know the coverage, as a short focus lens for a 6x9 would not likely cover on 5x4. But many but not all 65mm ones
would. This is the same reason that aps lenses rarely work on full frame...(an Angulon would not, but later super Angulons would)
Click to expand...

LOL @ you guys :) What do you mean digital has added nothing new?!

You can make as many contrary references as you like but they represent a tiny minority. In the film era, 99.999% of all photos were all taken on 35mm film, and the same lenses behaved in exactly the same way on different cameras. That is what's changed - APS-C and full-frame digital formats are both in very wide use and with the same lenses on both. Often by the same photographers on the same day, as with Rob in this thread. And they behave differently.

I know you know and understand equivalence, but not everyone has the benefit of decades of professional practise ;)
 
Ì
HoppyUK said:
LOL @ you guys :) What do you mean digital has added nothing new?!

You can make as many contrary references as you like but they represent a tiny minority. In the film era, 99.999% of all photos were all taken on 35mm film, and the same lenses behaved in exactly the same way on different cameras. That is what's changed - APS-C and full-frame digital formats are both in very wide use and with the same lenses on both. Often by the same photographers on the same day, as with Rob in this thread. And they behave differently.

I know you know and understand equivalence, but not everyone has the benefit of decades of professional practise ;)
Click to expand...

what is new, is that the understanding of photography and optics is far more likely to be limited.
Lenses perform identically on all formats, however the capture of that image will differ.
there is even a similarity between film speeds and grain size compared to sensor sensitivity and pixel density/size.

It might help some people if the included angle of field was marked on all lenses ... where a lens could be fitted to both an aps and a full frame both included angles could be given. However the so called crop sizes is a function of the camera sensor not the lens. The image circle produced and the focal length, remain the same what ever the lens might be fitted to.
 
Steve Smith said:
My Super Angulon 65mm just about covers 5x4. I use it on 6x12 usually. Schneider's data sheet says it was designed for 6x9 so there is a certain amount of getting away with it involved!


Steve.
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There are two series of Super Angulons the later ones had a wider image circle.
I have used the older ones on 5x4 but they allowed no movements at all, and required the lens to be perfectly centered. They were never intended for 5x4 use, and not recommended. The vignetting was poor to say the least, though they did produce a circular compensating nd filter for one aperture setting.
 
HoppyUK said:
but there is much more to equivalence for those that want to know more about how changing format also impacts pretty much everything, things like depth of field, and camera-shake, ISO, noise and dynamic range, lens sharpness etc etc.
Click to expand...
But in order for you to make any of those direct comparisons you must *also* make some other assumption; same output size, same MP count, etc... IMO there's too many variables these days for any simplified statement.
 
Terrywoodenpic said:
It might help some people if the included angle of field was marked on all lenses ... where a lens could be fitted to both an aps and a full frame both included angles could be given.
Click to expand...
You're expecting people to learn FOV and correlate that to desired framing? Without looking??? Sheesh!
 
Terrywoodenpic said:
Bigger has undoubtedly always been better...
Click to expand...
I wouldn't quite say "always"... I will choose a smaller sensor for IQ (DOF) when I can't/don't want to stack (i.e. handheld high magnification macros).

IMO, the shallow DOF advantage of a larger sensor is way overplayed... For me, I use a larger sensor for higher ISO performance (D4) *or* for larger output size (D810). Technically, I can "kind of" get both from the D810, but not at the same time. (I'm ignoring the many times I use the D810 for "cropability" because it might as well be an APS)
 
sk66 said:
I wouldn't quite say "always"... I will choose a smaller sensor for IQ (DOF) when I can't/don't want to stack (i.e. handheld high magnification macros).

IMO, the shallow DOF advantage of a larger sensor is way overplayed... For me, I use a larger sensor for higher ISO performance (D4) *or* for larger output size (D810). Technically, I can "kind of" get both from the D810, but not at the same time. (I'm ignoring the many times I use the D810 for "cropability" because it might as well be an APS)
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You can take macro images on a 10x8 camera. The depth of fied has always been an issue. The bigger the format the more shots needed in the stack. Small sensors are used for convenience not absolute necessity. 35mm was the format of choice using microscope adapters, though some people used half frame.
Specialised areas of photography can certainly break the bigger is better "rule"
 
"Bigger is better" for image quality - always has been, always will be. It's hard to argue with that, and the science backs up practical experience. But as Terry also said, smaller formats are more "convenient" and that's more subjective - smaller, lighter, cheaper and more manageable, and increasingly, image quality is more than good enough.
 
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I experienced something similar to this recently.
Parameters were fixed. Portable studio, with background and studio lights. D810 on full manual mode. Iso 200, f8, 1/250th
I swapped lenses from Nikon 24-120 f4 g ed vr to tamron 24-70 f2.8 vr.
The tamron was significantly brighter over a few test shots. Scratched my head, ran out of time & went back to the 24-120.
Not had the chance to repeat the experiment to try to figure out what was going on.
 
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