Who knows the answer to this? (crop 1.6 + 1.4tc)

levihaynes

levihaynes

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Levi
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I have a canon 50D which has a crop factor of 1.6

I wish to add a 1.4tc to my sigma 120-300 lens.

The question is: In which order do I calculate the figures??

For instance:-

(1.6 + 1.4) * 300 = 900mm
(1.6 * 300) * 1.4 = 672mm


:cuckoo:
 
funny, I was wondering the exact same thing. I await answers!
 
I believe it is
1.6 * 300 + 120 = 600mm

Because it's the 1.6 crop times by the 300mm lens. Then you add the 1.4 convteror which is (1.4* 300) = 420-300 = 120 so the amount it adds on top of the 300

But I could be wrong :)
 
I multiply all the figures but wouldnt
the exif give the correct focal length?
 
Thanks for the quick replies.

Currently the Exif data doesn't show up the crop factor of my 50D so I doubt it will add the 1.4tc either.

If I multiply them all together it doesn't matter which order I calculate them it comes to the same answer of 672mm. :thumbs:

Still not sure that makes it 'right' though LoL
 
all we know is it makes the object bigger in the picture :lol:
 
and if I were to selotape a magnifying glass to the end of the lens...



































macro?? :lol:
 
This is a joke right. They are all multiplication factors, no adding involved!

300mm lens x 1.4x converter is 420mm

420mm lens on a 1.6x crop body would give an approx AOV of a 672mm lens on FF (420 x 1.6)
 
J4MIE_P said:
I believe it is
1.6 * 300 + 120 = 600mm

Because it's the 1.6 crop times by the 300mm lens. Then you add the 1.4 convteror which is (1.4* 300) = 420-300 = 120 so the amount it adds on top of the 300

But I could be wrong :)
Click to expand...

And you are :p
 
Nothing different there then :p
 
I bring in the crop factor last.
300X1.4=420X1.6crop=672.
I believe this to be the correct formula.
 
If you're talking about real image size, then it's just 300x1.4. The 1.6x crop HAS NO EFFECT ON IMAGE SIZE.

Sorry about the shout, but I find it hard to believe that photographers have so little grasp of optical principles that they cannot understand that a lens system will produce the same magnification no matter what size sensor/film is used.

This pic shows it:

mountain_hare.jpg


The original was on a medium format 6x6 camera with an 80mm lens. With a 35mm camera with the same lens and from the same place, the image would have been that within the red rectangle, while with a small sensor it would have been in the yellow rectangle.

QED
 
I never worry about the crop factor,just use what you need.
 
Somelier said:
I find it hard to believe that photographers have so little grasp of optical principles that they cannot understand that a lens system will produce the same magnification no matter what size sensor/film is used.QED
Click to expand...

I dont see why you find the concept hard, that a bunch of amateur togs havnt grasped every nuace of photography ?? and would like to ask a bunch of like minded friendly soles to assist.

ps. not having a go, I like your explanation
 
Somelier said:
If you're talking about real image size, then it's just 300x1.4. The 1.6x crop HAS NO EFFECT ON IMAGE SIZE.

Sorry about the shout, but I find it hard to believe that photographers have so little grasp of optical principles that they cannot understand that a lens system will produce the same magnification no matter what size sensor/film is used.

This pic shows it:

mountain_hare.jpg


The original was on a medium format 6x6 camera with an 80mm lens. With a 35mm camera with the same lens and from the same place, the image would have been that within the red rectangle, while with a small sensor it would have been in the yellow rectangle.

QED
Click to expand...

While what you say about film is true, this is not so with a sensor.
With a sensor you also have to take into account the number of pixels.

Regards

Mike
 
The answer is 1.4* the focal length - i.e 1.4 * 300mm = 420mm.

That is the effective focal length of the TWO lenses.

That is true whether the lenses are attached to a FF or a crop camera.

The crop factor only allows a comparison to be made between the different crops by referring them all to a 35mm film camera which is 36x24mm.

When lenses are used on different crop camera the focal lenth doesn't change but the FIELD OF VIEW does.

Therefore for simplicity we can say that, referrenced to the 35mm format, putting any focal length on a cropped camera will be the same as using a longer lens on the 35mm format.

So putting a 420mm equivalent focal length on a 1.6 crop camera will be the same as putting a (420mm*1.6 = 672mm) lens on a FF camera (where the sensor size is 36X24mm - the same as the 35mm format).
 
Somelier, whilst you are strictly correct, quoting effective focal lengths relative to a 35mm frame does give some indication of the magnification, and the answer is 672, though I thought it was always 42 :lol:
 
i think somelier was saying that sensor size determines the physical size of the image you capture, which is what we talk about when referring to film equivalent and crop factors and stuff. the number of pixels in an image gives the.. er.. "digital" size, so to speak.

and strictly, magnification (expressed as 1:1, 1:1.5 or 0.3789576x, etc.) is the ratio between the actual size of the subject and the projected image. the lens+teleconverter combo and shooting distance will determine this. what complicates this for some is different sensor sizes.

say you have a 10MP full frame sensor and a 10MP (1.6x) APS-C sensor. using the same optics for both, the smaller sensor records a cropped/"more-zoomed-in" image, but the lens would have projected the same image anyway, and the projected image is what gives the magnification, not the dimensions of the digital file.

as for the original question, (300 x 1.6 x 1.4 = 672) or (300 x 1.4 x 1.6 = 672) is how you calculate the 35mm equivalent for your combination. and yeah, what fracster said. might help in planning what gear to get, but just shoot with whatever is necessary.
 
Between a fullframe and crop sensor: Focal length doesn't change; Zoom also doesn't change; It's a matter of magnification.
Because that magnification, relative to a full frame, has 12 pixels, it's like you just walked closer to the subject, so you're not losing quality. A cropped sensor when shown pixel for pixel with a full frame sensor will seem as it 'zoomed' in on the image when it really magnified it (by 1.6 in the case of your camera).

So therefore, if you want to compare zoom power (not focal length) then you can use basic mathematics (remember BEDMAS [brackets exponents division multiplication addition subtraction]) and you're equation would be

1.4*1.6*lens focal length

(Doesn't matter in what order you multiply)

And this number would be relative to a full frame or 35mm (ff would be 1.4*lens focal length)

Cropped sensors play tricks on people. Especially with f stops. To achieve the equivalent of a 1.8 on fullframe you'd have to have a 1.4 on a crop sensor. But that would be a theme for another thread ;)
 
slicemydrive said:
I dont see why you find the concept hard, that a bunch of amateur togs havnt grasped every nuace of photography ?? and would like to ask a bunch of like minded friendly soles to assist.

ps. not having a go, I like your explanation
Click to expand...

I agree, it's arrogance of this calibre that makes me want to punch walls. So what every photographer doesn't have an in depth understanding of how it all works. I'm pretty sure everyone driving a car doesn't know exactly how the engine works either.
 
trencheel303 said:
I agree, it's arrogance of this calibre that makes me want to punch walls. So what every photographer doesn't have an in depth understanding of how it all works. I'm pretty sure everyone driving a car doesn't know exactly how the engine works either.
Click to expand...

Cars have engines?!?!

joking ;)
 
Thanks for all your replies. I can now make sense of the multiplication involved and is really easy to understand.

I'm currently not a professional photographer and are still learning. I agree that the fundamentals of photography should be known, just as a driver for instance needs to know how a car will handle under different circumstances. Only by experience and asking questions can someone learn and progress. I do intend taking my 'hobby' to the next level, and yet I still won't know everything... just as a person who passes their driving test isn't a 'better' driver because they have passed.

I've learn't much from reading on this forum and am very gratefull to the helpfull folk who contribute. At some point I can hopefully return the favor. Thanks again for your help everyone. :thumbs:
 
Markk said:
<snip>

Cropped sensors play tricks on people. Especially with f stops. To achieve the equivalent of a 1.8 on fullframe you'd have to have a 1.4 on a crop sensor. But that would be a theme for another thread ;)
Click to expand...

To convert f/numbers between formats for depth of field purposes, you also use the crop factor.

In terms of DoF, f/1.8 on full frame is the equivalent of f/1.125 on a Canon 1.6x crop - roughly one and a quarter stops.
 
HoppyUK said:
To convert f/numbers between formats for depth of field purposes, you also use the crop factor.

In terms of DoF, f/1.8 on full frame is the equivalent of f/1.125 on a Canon 1.6x crop - roughly one and a quarter stops.
Click to expand...

Oh that quarter ;)
 
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