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D7200 & Sigma Lens help/Question


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10 replies to this topic

#1
Ajones

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Hi all
Just a beginner question...
I have a nikon d7200 which is a crop sensor camera(DX x1.5 crop) if im correct, apparently d7200 is an F mount.

I mainly shoot avaition photos, so i have a sigma 150-500mm F mount lens, would this focal length of be timsed by x1.5 so equivalent to 225-750 or will it stay at 150-500 if its the F mount?

Many thanks for any help

(I also have the nikon 18-300, which is equivalent to 28-480 when used on crop cameras)

#2
Adam

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The focal length never changes, so your 150-500mm lens's focal length is 150-500mm, and your 18-300mm is 18-300mm.  The "crop factor" conversion only comes into play if you're trying to compare what DX/FX lens you would need for your DX camera to get the same field of view as an FX lens on an FX camera, and vice-versa.

 

This article explains things in more detail and may therefore be helpful:

The Crop Factor Unmasked - Articles and Tips | PentaxForums.com



#3
Ajones

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Ok thank you,
So even with 1.5x crop it will still be 500mm max for my sigma lens?

#4
Merco_61

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It is 500 mm, but the field of view is the same as a 750 on 24x36 mm.

The equivalence is nonsense. Just see it as a different format. The focal length is a physical property of the lens, a crop because of a smaller sensor does not give the same result as using a longer lens on the bigger format as the depth of field won't change because of the crop.

Unless you use both formats, just accept DX as another format, just like µ4/3, FX, 44x33 digital medium format, 6x4.5, 6x6, 6x7 and 6x9 cm analog medium formats or the large formats.

 

Every format has its own strengths and weaknesses. The DX is a good compromise between reasonable noise levels and a bigger depth of field compared to FX without having to stop the lens down into diffraction levels. µ4/3 takes this even further. Medium format has  shallower depth of field.



#5
fallout666

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when i use my 150-500mm i was at 900mm at long end900mm and 225mm on short end. give tip when using 150-600 on D7200 do not do double crop. what i mean do not crop in your photo since you all ready made to 900mm on long end if try crop in more will not look so good. 



#6
Ajones

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Thank you, so my sigma lens will still be the equivalent to 750mm at full frame even if my camera is an F mount and the lens is also?

#7
Jerry_

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Thank you, so my sigma lens will still be the equivalent to 750mm at full frame even if my camera is an F mount and the lens is also?


No - as others explained a focal length is a physical measure. A 500mm lens will always be a 500mm and never become a 750mm.

However, as also mentioned, what changes with the size of the sensor is the field of view, ie a kind of zoom that will be shown on the picture. However you will only realize - and matter about - this difference if you use cameras with different sensor sizes with the same FX lens.

What this means, is that the smaller sensor will only show a center part of the picture that a larger sensor would show. Or, from a processing point, the picture that you get from a smaller sensor is the same that you would get if you take the picture from a larger sensor and then remove a border part (ie *crop* the picture in postprocessing).

As the computer screen (or printed picture), uses the (cropped) picture to fill in the same area size as the full picture, this makes that resulting picture look as if it was zoomed in, ie having a smaller field of view (or as if it was taken with a longer focal length, therefore the mentioned crop-factor).

Why is it usefull to have the smaller sensors with such larger zooms if you can get the same result by cropping a picture taken with a larger sensor? The reason are the **available Megapixels** . If the picture is taken on a D7200 with 24MP then you have the detail of the 24MP to work with. If the same picture was taken with the same lens and focal length on a D750 with 24MP and then cropped to show the same zoom factor, the available number of Megapixels in the cropped area would only be +-44% (ie +-10,5MP). This is valid if the two sensors (DX-FX) have the same number pixels, it would not apply if the camerabody with the FX sized sensor had much more pixels (this applies between the D850 with 45MP and the D500 with 20MP)


To « complicate » things, the above applies if you have a lens designed for FX sensors, as these are designed to project a larger picture to the sensor.
If you had a lens designed for a DX-sized sensor, the picture on a camerabody with a DX sensor would be the same as if it was taken with a lens designed for a FX-sized sensor.
However if you used that lens (designed for a DX-sized sensor) on a camera body with an FX-sized sensor, the resulting picture would be the same, though only using less than half the available numlber of pixels on the sensor (in the center area)

#8
Ajones

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Thank you, hopefully 1 last one

My new lens i have coming is the NIKON DX 18-300MM will that image still be cropped by 1.5x or will it not happan as the camera and lens is DX?

#9
g4aaw pete

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Here's my 10p worth - as an example.

 

Two lenses both 300mm max focal length.

AF-s 18-300 DX

AF-s 28-300 Full frame

 

7Quj6Y6.jpg

 

Camera D3300 (DX)

 

Two images using the DX lens at 300mm & FF lens at 300mm ( in a dimly lit area of two door knobs).

 

1v5zqdB.jpg

gNLjJVF.jpg

 

Your new lens will perform as stated on its label,18mm - 300mm

 



#10
Merco_61

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Yes, it will be cropped. The only difference between FX and DX lenses is the projected image circle. An FX lens needs to cover 24x36 mm without vignetting, so they are usually made to cover an image circle of about 55-65 mm. A DX lens only needs to cover 16x24 mm, so an image circle of 37-45 mm is sufficient. This smaller image circle lets the engineers make physically smaller lenses with less mass without losing picture quality.

 

Edited, I had misremembered the dimensions of the DX sensor.



#11
Ajones

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Perfect, as i didnt want it to work out that one of my lenses will be cropped by 1.5x and not the other..
So both will be cropped is what im after, as i do avaition photography so big big lens starting at 150mm can be too zoomed in for some places(such as when they come over my head)