Beginner Lens confusion - DX or not DX

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Stephen
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#1
Just listened to Ken Rockwell discussing changing lenses on crop frame and full frame cameras. I understand the bit about using a DX lens on a full frame and the consequences. But I'm unclear about using a non-DX lens on a crop sensor. I'm a bit thick on the technical side of things. I've used an 85mm on my Nikon D500 for ages. Should I have bought a DX 85mm instead. What am I losing/wasting in terms of image/quality, if anything at all. Be gentle with me.
 
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#2
Just listened to Ken Rockwell discussing changing lenses on crop frame and full frame cameras. I understand the bit about using a DX lens on a full frame and the consequences. But I'm unclear about using a non-DX lens on a crop sensor. I'm a bit thick on the technical side of things. I've used an 85mm on my Nikon D500 for ages. Should I have bought a DX 85mm instead. What am I losing/wasting in terms of image/quality, if anything at all. Be gentle with me.
Using an FX lens on DX is no bad thing generally, you will just be 'seeing' through the centre area of the glass (usually good anyway) and will have the advantage of being able to use the lens on full frame as well.
The other way around does not really have the same level of advantage, I have both DX & FX and given the choice would choose an FX lens every time (though ultra wide angle lenses can be more specific).
 
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#4
The only real advantage of a DX lens is that it can be made smaller and lighter, because it doesn't need to cover the FX frame. DX makes sense for all those 18-x standard zooms, less so for most primes (Nikon do a nice 35mm DX, though).
 
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#5
FYI Ken Rockwell is a bit of a marmite reviewer.
Some like, but many don’t.

As gramps and retune have said, FX lens on DX camera works fine. Penalty is they are usually a bit heavier and a bit more expensive.
I use only FX lenses on my D500.

If you ever decide to move to an FX camera you will already have some lenses.
 
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#6
I've got the 35mm DX, 50mm and 85mm FX lens. Bought a D700 last year and use a couple of the D series lenses with it.
 
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#7
Using full frame lens (FX) on crop frame camera (DX) is safe and fine.

Using crop frame lens (DX) on full frame camera (FX) can work but leaves vignetting around the photos.


Using full frame lens on crop frame camera is kind of like using a big family size suitcase for one person having an overnight stay. You have just clean underwear, spare shirt, pyjamas, and that's all, in a big suitcase with lot of empty spaces around it. So crop frame lens were made to be smaller, just enough to cover the crop frame sensor, in a similar way as having a smaller overnight bag for your few clothes. The idea of having crop frame lenses is to shave off weight, bulk, and costs.

But once you upgrade your crop frame camera (like the D500) for a full frame camera (like the D700), the crop frame lenses will leave your photos with vignetting around the images. So your option is to change your crop frame lenses for full frame lenses.

Normally for a photographer who is happy to stay with a crop frame camera for life, having crop frame lenses does save money, specially if DX lenses are cheaper than FX lenses.

But for a photographer who wants to upgrade from crop camera to full frame camera, it does not justify the costs, as the photographer will have to spend on changing the lenses too.

Thus if a photographer were to already have full frame lenses while using a crop frame camera, and should the photographer decided to upgrade the camera from crop to full, then the photographer will save money because he/she already got full frame lenses for a full frame camera.

You said "I've got the 35mm DX, 50mm and 85mm FX lens. Bought a D700 last year and use a couple of the D series lenses with it."

The D700 is a full frame, therefore the 50mm and 85mm FX lenses are fine with it. But when it comes to the 35mm DX lens, you can use it, but watch out for vignetting around the photos. Your options are, keep the 35mm, but if there are vignetting so use a photo editing software to do what you can with the photo, or change the 35mm DX for a 35mm FX.

If you had a 35mm FX in the first place when you had your D500, and later upgraded to a full frame like the D700, no problem there.
 

Stephen L

I asked a Stupid Question Once...
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#8
Using an FX lens on DX is no bad thing generally, you will just be 'seeing' through the centre area of the glass (usually good anyway) and will have the advantage of being able to use the lens on full frame as well.
The other way around does not really have the same level of advantage, I have both DX & FX and given the choice would choose an FX lens every time (though ultra wide angle lenses can be more specific).
That’s my thought also. Buying FX lenses, even if you have a DX camera at the moment, gives a degree of future proofing.
 
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#9
The FX 35mm will give good image quality across the whole FX frame, and will be great on DX, as a 50mm-ish equivalent. The DX 35mm, I've had 2, and they aren't in the same class as any full frame 35mm Nikkor. Admittedly my first one was a particularly bad copy; Nikon felt it was bad enough to refund me. But it's a 'cheap' lens. Not to say you can't take great pictures with it; my second copy was fine. But tbh I'd rather have a FX version, even for shooting on DX. It's just better quality all round.
 
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#10
From my understanding of it, and Gramps seems to imply the same' lens quality drops off towards to outer edges of the lens so using only the central area of a FX lens on a DX camera should reduce or eliminate any quality issues. Not that quality drop off is much of an issue with today's lenses especially with top brands like Nikon etc.
 
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#11
From my understanding of it, and Gramps seems to imply the same' lens quality drops off towards to outer edges of the lens so using only the central area of a FX lens on a DX camera should reduce or eliminate any quality issues. Not that quality drop off is much of an issue with today's lenses especially with top brands like Nikon etc.
You do not use only the central area of a FX lens on a DX camera. The light forming the central area, and every other part of the image on the sensor, comes from every part of the lens - except where the aperture blinds have blocked it. You do use only the centre part of the image circle so that can have advantages.
 
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#12
You do not use only the central area of a FX lens on a DX camera. The light forming the central area, and every other part of the image on the sensor, comes from every part of the lens - except where the aperture blinds have blocked it. You do use only the centre part of the image circle so that can have advantages.
Seems like I've mis-understood it then.
 
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#13
Seems like I've mis-understood it then.
When using FF lenses on a smaller format sensor you will not see some of the weaknesses you'll see on a FF camera such as mushy corners or bad vignetting as they're effectively cropped out and you'll only see the relatively good central area but there may be disadvantages too as the image will need to be magnified more and this could lead to other issues such as a less sharp picture.

I've seen this when using FF film era lenses on MFT where the results can be average to poor but when using the same lenses on FF the results can improve to good.
 
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#14
A lens designed for a smaller sensor will have a mixture of benefits, depending the designer's priorities:
- more zoom range
- wider max aperture (lower f/number)
- smaller/lighter
- better optical performance
- cheaper

If you use lenses designed for full-frame on a crop-sensor camera, you get none of these upsides and are paying for something (the full-frame coverage) that cannot be used. In addition, if you later move to full-frame, the change in effective focal length is considerable so you'll most likely need to replace lenses anyway.

Edit - eg two Canon lenses, similar cost:
- EF 17-40mm f/4L (super-wide on FF, standard-range zoom on a cropper)
- EF-S 17-55mm f/2.8 IS (standard-range zoom on a cropper)

The benefits of lenses specifically designed for smaller formats apply mostly to shorter focal lengths and the advantages are reduced with say, telezooms.
 
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#15
A lens designed for a smaller sensor will have a mixture of benefits, depending the designer's priorities:
- more zoom range
- wider max aperture (lower f/number)
- smaller/lighter
- better optical performance
- cheaper

If you use lenses designed for full-frame on a crop-sensor camera, you get none of these upsides and are paying for something (the full-frame coverage) that cannot be used. In addition, if you later move to full-frame, the change in effective focal length is considerable so you'll most likely need to replace lenses anyway.

Edit - eg two Canon lenses, similar cost:
- EF 17-40mm f/4L (super-wide on FF, standard-range zoom on a cropper)
- EF-S 17-55mm f/2.8 IS (standard-range zoom on a cropper)

The benefits of lenses specifically designed for smaller formats apply mostly to shorter focal lengths and the advantages are reduced with say, telezooms.
With Nikon and Pentax you can use lenses designed for APS-C on full-frame models; I think on Nikon the lens is detected and the camera defauls to DX mode automatically, whereas on the K-1 there is a switch to change formats (regardless of the lens fitted, meaning you could shoot in square format too).. IIRC EF-S lenses cannot be used on ff EOS bodies..

Back to topic - I didn't realise Nikon did a DX 85mm, especially when the FX AF-D is less than £300. If the DX 85 works on the D500 then great!
 
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#16
With Nikon and Pentax you can use lenses designed for APS-C on full-frame models; I think on Nikon the lens is detected and the camera defauls to DX mode automatically, whereas on the K-1 there is a switch to change formats (regardless of the lens fitted, meaning you could shoot in square format too).. IIRC EF-S lenses cannot be used on ff EOS bodies..

Back to topic - I didn't realise Nikon did a DX 85mm, especially when the FX AF-D is less than £300. If the DX 85 works on the D500 then great!
With Nikon, you can override the DX crop with DX lenses, to use the whole of the frame with a DX lens on an FX F-mount body. I used a Tokina 11-20mm zoom on FX, and whilst the image circle diameter was insufficient to cover the whole frame at the wider end, by 16mm, it covered the whole frame. However, on my Z6, there is no option to change to FX format; the camera only seems to shoot on DX crop mode.

The DX 85mm is an f3.5 macro lens, so very different from the 85mm f1.8D. Equivalent to a 127.5mm lens on FX. The D lens won't AF on some DX bodies (I think it's the D50, D70, D80, D90, D1/2/300 and D7xxx series have the AF drive motor, others don't). You're losing the faster aperture on the DX lens, but then you do have the 1:1 macro capability, and they go for around £220ish s/h, so a real bargain. For a short tele lens on DX, then the 50mm FX lenses offer a 75mm equivalent. You can't beat the AF-S 50mm f1.8G for value here.
 
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Allen
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#17
Just listened to Ken Rockwell discussing changing lenses on crop frame and full frame cameras. I understand the bit about using a DX lens on a full frame and the consequences. But I'm unclear about using a non-DX lens on a crop sensor. I'm a bit thick on the technical side of things. I've used an 85mm on my Nikon D500 for ages. Should I have bought a DX 85mm instead. What am I losing/wasting in terms of image/quality, if anything at all. Be gentle with me.
I am as well ;)
 
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