18 replies to this topic

[Talv]

Hi Guys,

 

I've been struggling to understand something with FX and DX lenses on crop sensors. I have a Nikon d5200 which is a 1.5x crop sensor. I'm aware of what it means relative to a full frame sensor but I'm slightly confused as to working out actual focal lengths.

 

I have a 50mm FX f1.4 prime and a 35mm f1.8 DX prime too.

 

To my understanding to work out the actual full frame equivalent focal length I need to multiply the lens focal length by the crop factor.

 

So (35mm x 1.5 = 52.5mm equivalent) and (50mm x 1.5 = 75mm equivalent).

 

But since the 50mm is an FX lens and only part of the lens is being used by my crop sensor camera,  do I need to then multiply by the crop factor again? - this doesn't seem right to me.

 

Or have I got this confused and the 35mm DX lens is set to the 35mm equivalent already so I don't need to multiply this by the crop factor? And only need to do the maths when using an FX lens on a crop sensor.

 

I hope that makes some sort of vague sense to some one. I asked a couple of other people I know and they understood the question but didn't know the answer!

 

Thanks in advance!

 

[Stas]

If you have croped sensor than you always have to multiply by crop factor. On both FX and DX lens is written focal length for full frame cameras.

[Merco_61]

A 35 mm lens is a 35 mm lens no matter what size the sensor is. Focal length is a physical property of the optics. The difference is that the DX lens can be made smaller and lighter since it doesn't have to cover the full FX image circle because the sensor is smaller.

If you only use DX format the whole FX confusion is unnecessary, just think of 35 mm as close to what you see sharply with one eye (normal lens). Focal lengths under 35 mm are wider in view angle and above 35 are narrower.

 

For FX the normal is 50 mm or a bit less.

 

The whole crop factor nonsense can be a help if you use both formats, but what counts is what you see in your viewfinder when composing the picture.

[Tony892]

I am a bit confused, does this mean I can use an FX lens on my D7100? All the lenses I currently have are DX.

[Talv]

I am a bit confused, does this mean I can use an FX lens on my D7100? All the lenses I currently have are DX.

 Yes you can use an FX lens on a DX camera, my brother just bought a 70-200 f2.8 FX lens today which works fine on my d5200 and as I said in the original post I use my FX 50 on my d5200 too!

[Merco_61]

Of course you can, the D7100 is compatible with most lenses made after 1977. Your manual probably has a compatibility matrix hidden on the first page of the technical information, I have never seen a Nikon manual that doesn't.

[Talv]

If you have croped sensor than you always have to multiply by crop factor. On both FX and DX lens is written focal length for full frame cameras.

 

 

A 35 mm lens is a 35 mm lens no matter what size the sensor is. Focal length is a physical property of the optics. The difference is that the DX lens can be made smaller and lighter since it doesn't have to cover the full FX image circle because the sensor is smaller.

If you only use DX format the whole FX confusion is unnecessary, just think of 35 mm as close to what you see sharply with one eye (normal lens). Focal lengths under 35 mm are wider in view angle and above 35 are narrower.

 

For FX the normal is 50 mm or a bit less.

 

The whole crop factor nonsense can be a help if you use both formats, but what counts is what you see in your viewfinder when composing the picture.

 

 

Brilliant thank you guys that's really cleared it up for me. So whenever I'm using a cropped body irrespective of lens to get the DX focal length I need to multiply by the crop factor.

[Merco_61]

Brilliant thank you guys that's really cleared it up for me. So whenever I'm using a cropped body irrespective of lens to get the DX focal length I need to multiply by the crop factor.

Or rather: To get the FX equivalent you multiply the focal length with the crop factor.

[greenwing]

A 35 mm lens is a 35 mm lens no matter what size the sensor is. Focal length is a physical property of the optics. The difference is that the DX lens can be made smaller and lighter since it doesn't have to cover the full FX image circle because the sensor is smaller.

If you only use DX format the whole FX confusion is unnecessary, just think of 35 mm as close to what you see sharply with one eye (normal lens). Focal lengths under 35 mm are wider in view angle and above 35 are narrower.

 

For FX the normal is 50 mm or a bit less.

 

The whole crop factor nonsense can be a help if you use both formats, but what counts is what you see in your viewfinder when composing the picture.

 

Couldn't have put it better!

[Tony892]

Thanks for the info, learnt something else new today, however, would I be true in saying that generally the more appropriate lens with a D7100 would be a DX?

[Merco_61]

Thanks for the info, learnt something else new today, however, would I be true in saying that generally the more appropriate lens with a D7100 would be a DX?

 

Depends on what you want to do, there are no DX equivalents to the 85/1,4 or the MicroNikkor 105.

If you want to make shallow DOF portraits and be close enough to establish a rapport with your subject the 50/1.8 or 1.4 are hard to beat.

My set of lenses for the D300 were a 24/2.8AI, a 50/1.8AF-D, a 105/2.5AI, a 70-300 AF-S VR and a 17-55/2,8DX.

[BeerBelly]

Thanks for the info, learnt something else new today, however, would I be true in saying that generally the more appropriate lens with a D7100 would be a DX?

I wouldn't say so. If you use an FX lens on a DX sensor you only use a center portion of the lens optics, which is usually sharper thus giving you a better overall image. Although in the case of the D7100 you have to take into account that 24 mpix aps-c sensor puts a lot of stress on the lens to resolve that kind of detail..
.which means that with poorer optics you see flaws where in a 12 mpix sensor for instance, you wouldn't.

[Russ]

Thanks for the info, learnt something else new today, however, would I be true in saying that generally the more appropriate lens with a D7100 would be a DX?

No. I use a 70-200/f2.8 on my D7100 heaps, and a few other FX lenses. Just use the appropriate FLs for what you want to achieve and don't worry if it's an FX or DX lens. All your crop sensor is doing, is cropping the photo for you without asking you!

[Tony892]

Interesting, what are the characteristics of the lower fixed lenses, particularly FX. What sort of shots are you looking at when using them?

[Russ]

the lower fixed lenses

Qué (in my best Manuel impression)

[Merco_61]

Interesting, what are the characteristics of the lower fixed lenses, particularly FX. What sort of shots are you looking at when using them?

If you mean lower priced primes the 50/1.8 is a very nice, if a bit short portrait lens.

The 24/2.8 stands up well even with the demanding D7100 sensor and is quite nice for street shooting where you might need the speed and a 2.8 zoom is too noticeable.

An 85/1.8 is IMO a bit long for portraits, but if you have the room to take a step or two back it is a nice medium telephoto. The old AF-D was smaller than the AF-S and therefore easier to use unnoticed.

 

I like to be a fly on the wall rather than *the photographer* because candids seem *to me* to be more relaxed. Even in portraiture I have found it easier to get people to relax when i don't disappear behind the hood of a hulking big 2.8 zoom. That's why I put emphasis on the small, unobtrusive nature of the primes.

[Tony892]

If you mean lower priced primes the 50/1.8 is a very nice, if a bit short portrait lens.

The 24/2.8 stands up well even with the demanding D7100 sensor and is quite nice for street shooting where you might need the speed and a 2.8 zoom is too noticeable.

An 85/1.8 is IMO a bit long for portraits, but if you have the room to take a step or two back it is a nice medium telephoto. The old AF-D was smaller than the AF-S and therefore easier to use unnoticed.

 

I like to be a fly on the wall rather than *the photographer* because candids seem *to me* to be more relaxed. Even in portraiture I have found it easier to get people to relax when i don't disappear behind the hood of a hulking big 2.8 zoom. That's why I put emphasis on the small, unobtrusive nature of the primes.

Is there a particular make of 24/2.8 that you would recomend? My wish for lenses is growing by the day.

[Merco_61]

Is there a particular make of 24/2.8 that you would recomend? My wish for lenses is growing by the day.

Any Nikkor, but the AIS would not be my first choice because it is a bit harder to focus precisely than the AI. The AI has a bit more contrast than the AF and AF-D, the AF has the convenience of autofocus and the AF-D gives the best results when using flash.

The really old 7-group 24-s (Nikkor-N, Nikkor-N.C. and Nikkor-K) are, even if converted for AI coupling, a bit prone to flare.

For use on a DX body the HN-3 hood is a better choice than the HN-2 they were supplied with. The HN-3 is still current as it is the hood for the 35/2AF-D

[K-9]

Is there a particular make of 24/2.8 that you would recomend? My wish for lenses is growing by the day.

 

If you don't need to go that extra tad wider, I highly recommend the 28mm f2.8 AI-S manual focus lens.  It's the only wide angle, non tilt/shift Nikkor that does not have barrel distortion.   Focuses ridiculously close for a non macro lens (some slight distortion does appear with objects close to the lens), and one of the sharpest lenses Nikon has made.  There's a reason it's still in production since 1981.  Here's a new one from BandH:

 

http://www.bhphotovi...?Ntt=NI2828&N=0