A bit confused re: FX lense on DX body. Need clarification.

[Rob5589]

I have a D5200 and a Sigma 17-50 2.8. I was looking at the Nikon 70-300 f 4.5-5.6 af-s vr, used at KEH.

So, is this lense on my 5200 actually going to be 105-450 mm? Leaving a huge gap from 50mm to 105mm?

Am I looking at this correctly?

Thanks

 

[jaomul]

Yes and no. It remains 70-300 but it's field of view is 105-480. In practical terms your framing ability will have a gap, but not as much as you think because your 17-50 as well has crop factor and acts like a 26-75.

 

[Aloicious]

nope. 50mm is 50mm is 50mm, same with 70-300, its still a 70-300...regardless of what body it is used on

the whole mm conversion stuff is not accurate, nor useful, for much except in comparing the field of view (only the field of view, it does not change the actual focal length whatsoever) between a full frame FX sensor, and a APS-C DX sensor, in fact the whole "1.5x conversion factor" becomes simply wrong when you start getting into varied and equivalent pixel densities. So unless you're in a situation where you've got both an FX and DX body with the correct pixel densities, you're trying to figure out what lens to use on each to have equivalent field of views, its not helping you in any way. ALL lenses are sold, marked, and marketed as their real true focal lengths*, which is a physical property of the lens and completely independent of whatever sensor it is used on. a "DX" lens simply has a smaller image circle that it projects, so it will not cover an FX frame, its not actually a different zoom length as a non-DX lens with the same focal length.

so do not get bogged down in the whole conversion factor stuff, in fact just forget it altogether...focal length is focal length, you have a 17-50, if you get the 70-300, you'll also have a 70-300...its really as simple as that...if you happen to be shooting next to a FX body user and you want to compare images, or you happen to get a second body which is an FX body, then yeah, some sort of conversion factor would be useful depending on the situation, but in the meantime, just ignore it all. if X focal length works to get the picture you want, who cares what a similar field of view would be on a different body. go out and shoot and be happy.

*manufacturing tolerances and other miniscule anomalies aside...I know someone is going to come along and shout "but 300mm might actually be 298mm!!!!! and what about focus breathing!! OMG!"...I'm not worrying about that stuff to keep things simple.

 

[RichieT]

I used this combination with my D300 and you'll be fine. That 1.5 "crop factor" applies to a dx lens like the sigma as well as the full frame 70-300. The difference between 50mm and 70mm (or 75 and 105 cropped) is a step or 2 closer or further from your subject.

 

[astroNikon]

First of all an FX lens will work on a DX body (though if AF may be an issue if the DX body does not have a focus motor and the lens is not an AFS lens with a built in motor).

Read this ... I hope it helps
FX - DX Lens Crop Factor

and
http://www.thephotoforum.com/forum/...rence-between-full-frame-cropped-sensors.html

 

[astroNikon]

FYI .. there are lenses now that specific the FX and DX Field of View on them
So they could have 24-70 and 36-105 marked on them. I've seen them ... i'm trying to find one as an example.

 

[Braineack]

I have a D5200 and a Sigma 17-50 2.8. I was looking at the Nikon 70-300 f 4.5-5.6 af-s vr, used at KEH.

if you buy it, youll have two lens that cover a range between 17-300mm. With only a small gap of coverage between 50-70mm that you can make up with your feet.

 

[astroNikon]

... Found it .. lenses that specific TWO "focal lengths"
but it wasn't DX lenses .. it was those other Nikon 1 lenses
on the lens

Nikon 1 Nikkor 70 - 300 VR
Equiv 135 189 - 810

1 NIKKOR VR 70-300 f/4.5-5.6 lens | Compact Super-Telephoto Zoom Lens for Nikon 1 Cameras

But I thought I saw it on some DX lens too .. but I'm not going to search all the lenses out there lol


But anyways it doesn't change what the lens is once it's on a body. The sensor is smaller or larger and the image projected by the lens does not change it's size. Thus the sensor may capture a larger or smaller percentage of the projected image. If you think that a Full Frame camera captures the "entire image" then a Crop sensor capture only a "small window" of that full image. Other sensors, being smaller, can capture a smaller size yet.
A DX specific lens is designed with less glass and small diameter because it is then designed to create a smaller overall image more similar to the smaller sensor, thus reducing the overall cost of the lens. If you use a DX lens on a FF frame the FF image would have black around the edges because the lens does not create a large enough image.


But I really wouldn't worry about it unless you start looking at getting into Ultra Wide Angle lenses.

 

[Rob5589]

Much clearer, thanks for all the info guys. Thanks for the links Astro, and no need to search all the other lenses. :mrgreen:

ETA: KEH had a EX+ for a good price so I picked it up