Fisheye and macro lens recommendatiions for 5100

Related question .... have I got this right?

100mm lens on conventional SLR = 100 mm in 35mm format

100mm FX lens on FX camera = 100 mm in 35 mm format
100mm FX lens on DX camera = 167 mm in 35 mm format

100mm DX lens on FX camera = not compatible
100mm DX lens on DX camera = 167 mm in 35 mm format

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Originally Posted by Mediaman09

Hmmm, so as the 5100 is a DX formatted camera, should I be concerend that is 105 mm lens is NOT optimized for a DX-format ??

A lens optimized for DX formatted camearas, sounds like there is some disadvantage in buying an FX lens vs DX lens - What is it?

Interestingly, FX lenses perform best on DX sensor cameras. Why? Because the DX sensor is only recording light coming from the "sweet spot" section of the lens and thus your images contain little to no vignetting as well as little to no barreling or pinchushing.

Thank you for the corrections re equivalent focal length.

I updated the list accordingly...but have some new questions re (4) and (6) ...

1) 100mm lens on conventional SLR = 100 mm in 35mm format
2) 100mm FX lens on FX camera = 100 mm in 35 mm format
3) 100mm FX lens on DX camera = 150 mm in 35 mm format ( Nikon has a 1.5x crop factor)
4) 100mm DX lens on FX camera = 66 mm ?? ( FX camera will step down to DX sensor size so you will get a cropped picture, and at a lower resolution)
5) 100mm DX lens on DX camera = 150 mm in 35 mm format ( Nikon has a 1.5x crop factor
6) 100mm Legacy F-mount lens on a DX camera = ?? mm. For example I have an old 28 mm wide angle
Nikkor f2.8 No. 486439. What is the equivalent focal length on the 5100?

4 - a 100mm DX lens on an FX will be 100mm
5 - I do not believe a DX lens will work very well on a 35mm camera. If it does I suspect you will actually see the areas not covered in the DX lens.
6 - It will also have the same effect as an FX lens on a DX camera with a crop value of 1.5. So your 28mm lens will have the same field of view as a 42mm lens.

Keep in mind that a DX camera does not increase the focal length of a lens. We typically referring to a 100mm becoming a 150mm but in fact it just crops out the sides of the image to give the equivalent view that a 150mm lens on an FX camera body would give.

So, if I understand this correctly (what are the chances !! ... ANY lens that I put on my 5100, be it legacy, DX or FX, will have a focal length/field of view as stated on the lens ! And if I interchange them all I will see no difference... ie 100mm DX lens, 100mm FX lens or 100 mm legacy lens will all look the same on my 5100....and all three will look the same as what a 150mm lens would like on an FX camera. Correct? Almost?

With all these 1.5 multipliers, I had initially (incorrectly) assumed that my new 18mm-200 lens would have the same 'wide angle' view my old legacy 28mm lens ( eg 18 x 1.5 = 27 m which close to 28mm). But in fact, the old 28 mm lens also gets the 1.5 factor as its equivalent to 42mm !. Indeed when I interchange both lenses, the new 18mm is a much wider angle than the old 28mm (ie I am essentially comparing 27 mm to 42mm).

The point being that, if I got this right (and at the risk of oversimplifying) , I need not be concerned about calculating equivalent focal lengths if I have a mix of DX, FX and legacy lenses ; they will all behave as expected, ie my new 18mm zoom is that much wider than my old legacy 28mm, which is that much wider than my old 43-86 zoom, which is that wider than my new 105 FX macro.

By gummy...I think you've got it!! Nothing you wrote can I disagree with - A DX camera treats all lenses the same. It's only FX cameras that makes any changes to a lens, the DX just powers on.

One thing I would like to add is that an FX lens will perform better on a DX camera than on an FX camera due to the fact the DX imaging cuts out the corners and edges where lenses suffer the most distortion and vignetting. So from my point of view, buying only FX lenses for your DX camera is both good for your IQ and as well as paves the way to move to FX if you ever choose to.

Originally Posted by Dave_W

Interestingly, FX lenses perform best on DX sensor cameras. Why? Because the DX sensor is only recording light coming from the "sweet spot" section of the lens and thus your images contain little to no vignetting as well as little to no barreling or pinchushing.

Old thread I started a while back, but still relevant.

A nagging question I have is this - How does one reconcile the statement "DX lenses are optimized for DX cameras", with "FX lenses perform best with the DX sensor"

That is, when choosing a lens for a DX camera, is there a rule of thumb as to whether FX or DX is the wiser lens choice ?

My next lens purchase, will be an ultra wide angle. Should I be looking for DX or FX or does it not matter at all??

(Another purchase after that might be a fisheye for special/distorted effects ; less concerned there as I would likely go with a cheaper nin-Nikon choice. )