Nikon "DX" format questions

embenderembender Registered Users Posts: 26 Big grins
edited May 14, 2012 in Cameras
I am trying to wrap my head around the terminology and meaning of "DX" format so that I can more intelligently purchase lenses for my Nikon D300 and get what I am expecting. My understanding is that DX means the sensor is 1.5 times smaller than a full frame sensor (FX?), and therefore, when the light from a lens is focused on the sensor, the light blankets the sensor and some of it falls off the edge and the sensor misses some of the image. The net effect is that of zooming, making the image appear closer and cropped vs what it would look like on a full frame sensor. Is that correct?

Then my next question, if I want a 35mm lens, for example, and I want the field of view to be that of the traditional 35mm film camera, then for a DX-format camera, I would need to actually use a 35/1.5 mm lens or ~24mm lens. And if I want a traditional 24mm lens, then I would need to purchase a 24/1.5 = 16mm lens. Is that correct?

If that is correct, then what about for "DX" labeled lenses? Are they "true" focal length for DX-format cameras, or does the above formula still apply? I.e., does a 35mm DX lens appear as a traditional 35mm lens, or does it appear as a 35*1.5mm = ~52mm lens?

What I mean by "DX" labeled lens is something like this: "AF-S Nikkor 35mm f/1.8G DX"

Would that lens appear to my DX format D300 camera as a 52mm lens, or as a traditional 35mm lens?

Finally, let's say, hypothetically (:D), that I recently intended to purchase a 50mm lens, specifically something like this "Nikon AF-S Nikkor 50mm f/1.4G Autofocus Lens", thinking I was getting a traditional 50mm lens, but in reality, because of my "DX-format", is it really equivalent to a 50*1.5 = 75mm lens?

I *think* I know the answer, but it would be great to get some confirmation from the experts. I am relatively new to all this and don't want to make too many (more) expensive mistakes as I am trying to understand what this stuff means.

Thanks!

Comments

  • FearNothing321FearNothing321 Registered Users Posts: 123 Major grins
    edited April 27, 2012
    embender wrote: »
    I am trying to wrap my head around the terminology and meaning of "DX" format so that I can more intelligently purchase lenses for my Nikon D300 and get what I am expecting. My understanding is that DX means the sensor is 1.5 times smaller than a full frame sensor (FX?), and therefore, when the light from a lens is focused on the sensor, the light blankets the sensor and some of it falls off the edge and the sensor misses some of the image. The net effect is that of zooming, making the image appear closer and cropped vs what it would look like on a full frame sensor. Is that correct?

    Then my next question, if I want a 35mm lens, for example, and I want the field of view to be that of the traditional 35mm film camera, then for a DX-format camera, I would need to actually use a 35/1.5 mm lens or ~24mm lens. And if I want a traditional 24mm lens, then I would need to purchase a 24/1.5 = 16mm lens. Is that correct?

    If that is correct, then what about for "DX" labeled lenses? Are they "true" focal length for DX-format cameras, or does the above formula still apply? I.e., does a 35mm DX lens appear as a traditional 35mm lens, or does it appear as a 35*1.5mm = ~52mm lens?

    What I mean by "DX" labeled lens is something like this: "AF-S Nikkor 35mm f/1.8G DX"

    Would that lens appear to my DX format D300 camera as a 52mm lens, or as a traditional 35mm lens?

    Finally, let's say, hypothetically (:D), that I recently intended to purchase a 50mm lens, specifically something like this "Nikon AF-S Nikkor 50mm f/1.4G Autofocus Lens", thinking I was getting a traditional 50mm lens, but in reality, because of my "DX-format", is it really equivalent to a 50*1.5 = 75mm lens?

    I *think* I know the answer, but it would be great to get some confirmation from the experts. I am relatively new to all this and don't want to make too many (more) expensive mistakes as I am trying to understand what this stuff means.

    Thanks!

    You are correct
    Nikon D800, Pentax K1000

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  • PupatorPupator Registered Users Posts: 2,322 Major grins
    edited April 27, 2012
    You are correct on all fronts. The DX label doesn't change the way you do the calculation, it's just telling you that the lens won't function as expected on an FX sensor.

    So the 35mm DX lens has the same focal length as any other 35mm lens would: which is a 52.5mm FF equivalent field of view.

    This is why it's so surprising that Nikon has yet to make a set of wide primes for DX.
  • FearNothing321FearNothing321 Registered Users Posts: 123 Major grins
    edited April 27, 2012
    Pupator wrote: »
    You are correct on all fronts. The DX label doesn't change the way you do the calculation, it's just telling you that the lens won't function as expected on an FX sensor.

    So the 35mm DX lens has the same focal length as any other 35mm lens would: which is a 52.5mm FF equivalent field of view.

    This is why it's so surprising that Nikon has yet to make a set of wide primes for DX.

    $$$

    Probably isn't much of a market for them
    Nikon D800, Pentax K1000

    You don't take a photograph, you make it. ~Ansel Adams

    Blue Moon Originals
  • mstensmstens Registered Users Posts: 78 Big grins
    edited April 28, 2012
    $$$

    Probably isn't much of a market for them

    Further more, why would they? It'd cost more to completely retool for dx lenses. As it is, they're shared with fx and film bodies.
  • angevin1angevin1 Registered Users Posts: 3,403 Major grins
    edited April 28, 2012
    mstens wrote: »
    Further more, why would they? It'd cost more to completely retool for dx lenses. As it is, they're shared with fx and film bodies.

    $$$

    Probably isn't much of a market for them

    No. I suspect there is plenty market for DX only lenses.

    I've often thought if I were a Manufacturer/Seller of lenses I'd clearly state on the lens box; 50mm f/1.8 fov FX, 75mm f/1.8 fov DX. Yet. What does that all mean to the average consumer? I'd venture little. Oh sure some folks just love the technical aspects of lenses. But really unless you've shot 35mm (film) and know what that FOV looks & feels like, You'll never really get the FX/DX thing anyway.

    Personally I think it is a mistake to label a lens DX and have it's FOV different from what it is advertised as: 35mm f/1.8 with FOV of 52mm? Weird~to me.
    tom wise
  • PupatorPupator Registered Users Posts: 2,322 Major grins
    edited April 28, 2012
    $$$

    Probably isn't much of a market for them
    mstens wrote: »
    Further more, why would they? It'd cost more to completely retool for dx lenses. As it is, they're shared with fx and film bodies.

    Couldn't disagree more with both of you. The market for them is as large as for any other DX lens at this point.

    Here's an interesting read from Thom Hogan:
    New 28mm Lens
    April 23 (news and commentary)--In addition to the Nikon D3200, Nikon announced a new lens, the 28mm f/1.8G AF-S. Suggested retail price is US$700, a lower price than many expected.

    Okay, so WTF? We've now got a complete modern set of historical fast lenses (24, 28, 35, 50, 85). That's for FX bodies that already excel in low light. What's the DX user to think? Right, they've got basically two of the five, none wide (35mm f/1.8DX, 50mm f/1.4 or f/1.8 as a somewhat short substitute for an 85mm equivalent).

    Nikon's lens announcements of late have been bordering on absurd. The 28-300mm has no body on which it performs great (well, okay, it makes a decent 42-450mm equivalent for DX bodies, but that's not how Nikon marketed it). The lens doesn't make Nikon's own D800 recommended lens list, and it seems a bit bizarre as a possible D4 lens. Meanwhile, the unexpected 40mm DX macro works okay on a Nikon 1 body (with FT1 adapter), but wasn't really necessary for DX once the 60mm macro appeared. Lately it really feels like the wrong folk are designing the wrong lenses for the wrong cameras.

    Meanwhile:

    CX needs something wider than 28mm equivalent, and it needs it yesterday. It also needs a couple of small, fast primes (particularly portrait).
    DX needs a whole range of things: true wide angle primes at 24mm and 35mm equivalent at a minimum, a PC-E wide, a true portrait lens for DX, a 70-200mm f/2.8 equivalent (preferably 50-135mm f/2), a far better 18-200mm, a faster and fixed aperture 24-120mm equivalent, and more.
    FX is still missing a few primes, most notably 18/20mm and 105/135/180mm, plus the PC-E lenses really need redesign so that they work fully on a D800 body and have switchable tilt/shift.
    Let me put things a different way. When I go out to shoot events, sports, or wildlife (with FX bodies), I don't have any lens compromises I make. None. I'd like to see a really fast moderate telephoto (e.g. 105mm or 135mm f/2 AF-S), but I don't feel like I'm short lenses: what I need pretty much exists.

    But when I go out to shoot FX landscapes, I miss the 20mm f/2.8 and have to make a choice between the 14-24mm (no filters) or less capable 16-35mm, and I've got a 24mm PC-E that has a fixed tilt/shift orientation while all my Canon buddies not only have changeable orientation, but they also have a wider tilt/shift option. Bzzzt. Someone asleep at the wheel, especially for a company with a state-of-the-art 36mp body that screams landscapes.

    Heaven help me when I go out to shoot DX. I make lens compromises all over the place. Basically, I have to pick a zoom to go wide at all. I have no PC-E option that's reasonable. I end up with bigger FX lenses than I need, and bastardized focal lengths from what I want (e.g. using a 50mm f/1.4G when I want a 58mm f/1.4). Bzzzt. Not only someone asleep at the wheel, but the vehicle's veering off the road and about to crash.

    Things don't get better when I go CX. Compared to my m4/3 kit, I have compromises all over the place except for one (the 30-110mm, which is a sterling performer). Bzzzt. Still asleep at the wheel, and the competition's got the pedal to the metal and pulling away.

    So, welcome the 28mm f/1.8G if you will. But it doesn't exactly fill a large hole (the previous 28mm f/1.4 sold about 7000 units in 13 years, though it was considerably more expensive). It's as if the road crew came and laid some oil over a small crack, but ignored the nearby potholes.
  • MusetekMusetek Registered Users Posts: 42 Big grins
    edited May 3, 2012
    I agree with Thom Hogan, but I'd go one better: DX needs a replacement for the D300s. Great, we've got the D4 and the D800, and there are all sorts of rumors about an entry-level FX body. But what about the "pro" DX body? As good as the D7000 is, it's not a replacement for the D300s, I frankly wouldn't want the D800 for a variety of reasons, and the D4 is out of my price range. I'll be a little uneasy until they announce the D400.
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  • T. BombadilT. Bombadil Registered Users Posts: 286 Major grins
    edited May 3, 2012
    Your understanding is essentially, though not _completely_ correct.

    "The net effect is that of zooming" isn't quite right. It is more accurate to say the net effect is that of cropping. The reason this distinction matters (to some, perhaps not to you) is that a 50mm lens used at a particular distance from the subject will provide the same depth of field on DX and FX cameras (if distance to subject is the same). In other words, the depth of field when it is used on a DX will not mimic a 75mm on FX.

    embender wrote: »
    I am trying to wrap my head around the terminology and meaning of "DX" format so that I can more intelligently purchase lenses for my Nikon D300 and get what I am expecting. My understanding is that DX means the sensor is 1.5 times smaller than a full frame sensor (FX?), and therefore, when the light from a lens is focused on the sensor, the light blankets the sensor and some of it falls off the edge and the sensor misses some of the image. The net effect is that of zooming, making the image appear closer and cropped vs what it would look like on a full frame sensor. Is that correct?
    . . .
    Bruce

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  • Matthew SavilleMatthew Saville Registered Users, Retired Mod Posts: 3,352 Major grins
    edited May 4, 2012
    I've never understood the obsession with FX for consumers / beginners. I think this obsession is mostly fueled by higher end amateurs and prosumers, who THINK that the market is ripe for a $1500 "beginner full frame camera".

    Historically speaking, with digital technology, progress has always been in the "direction of smaller". Pretty much every electronic device out there used to be a huge brick, and now it fits in the palm of our hand.

    ...So why is it so hard to fathom the notion that smaller sensors will eventually improve the point of being totally acceptable by the masses? Sure, full-frame sensors will always have an advantage. But as lens sharpness technology advanced, even in the days of film, "everybody" switched to 35mm for casual shooting. Smaller is always more convenient.

    I'm looking forward to seeing what can happen with Nikon's DX format, in a professional or advanced amateur capacity. The D7000 has been an amazing camera with great DR and overall IQ, shutting up those who brag about how their full-frame body is so vastly superior. Maybe it's still superior in many ways, but that's not the point. The point is that each year, DX makes roughly the same amount of progress that FX makes, and it is providing a great new option to even the most demanding photographers.

    Just my opinion...

    =Matt=
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  • jthomasjthomas Registered Users Posts: 454 Major grins
    edited May 5, 2012
    embender wrote: »
    If that is correct, then what about for "DX" labeled lenses? Are they "true" focal length for DX-format cameras, or does the above formula still apply? I.e., does a 35mm DX lens appear as a traditional 35mm lens, or does it appear as a 35*1.5mm = ~52mm lens?

    I don't believe anyone has addressed this question specifically, though you have probably figured this out by now. All Nikon lenses reflect their true focal length, so a 35mm DX lens has the same focal length as a 35mm FX lens. The only difference is that DX lenses cast a smaller image circle which is large enough for a DX sensor but not for an FX sensor. This allows Nikon to make the DX lenses smaller and lighter.

    If you mount a DX lens on a full-frame (FX) camera, you will most likely see dark corners, or "vignetting" because of the smaller image circle.
  • embenderembender Registered Users Posts: 26 Big grins
    edited May 14, 2012
    jthomas wrote: »
    I don't believe anyone has addressed this question specifically, though you have probably figured this out by now. All Nikon lenses reflect their true focal length, so a 35mm DX lens has the same focal length as a 35mm FX lens. The only difference is that DX lenses cast a smaller image circle which is large enough for a DX sensor but not for an FX sensor. This allows Nikon to make the DX lenses smaller and lighter.

    If you mount a DX lens on a full-frame (FX) camera, you will most likely see dark corners, or "vignetting" because of the smaller image circle.

    Thank you, jthomas, for addressing that part in particular, and thanks to all who helped to explain the format and focal length effects so clearly.
  • embenderembender Registered Users Posts: 26 Big grins
    edited May 14, 2012
    Your understanding is essentially, though not _completely_ correct.

    "The net effect is that of zooming" isn't quite right. It is more accurate to say the net effect is that of cropping. The reason this distinction matters (to some, perhaps not to you) is that a 50mm lens used at a particular distance from the subject will provide the same depth of field on DX and FX cameras (if distance to subject is the same). In other words, the depth of field when it is used on a DX will not mimic a 75mm on FX.

    Great distinction, I did not even think of that.
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