DX lens on a APS-C DSLR: IS there a crop factor?

DX is Nikon's term for a 1.5x crop frame.

The 35mm f1.8 is a DX lens, so it only creates an image large enough top cover a DX sensor not an FX one. It's a DX lens. As such it works as it's intended to on a DX system.

However from another point of view, like any lens, the field of view of the 35mm lens on DX is like a 52.2mm lens on a full frame system.

kimpenonal said:

kimpenonal wrote:

I have a confusion about the crop factor of DX lenses on a APS-C DSLR's.

I own a nikon D7000 and I purchase 18-200mm f/3.5-5.6 VR II separately.

and now I am planning to buy a prime lens which is AF-S DX 35mm f/1.8G

My question is Is there a crop factor for this DX lens on a APS-C camera? Do I have to consider the 1.5x crop factor to have a 52.5mm equivalent? or 35mm DX is 35 in APS-C camera.?

Click to expand...

Yes there is still exactly the same crop factor on DX lenses as with FX lenses, the difference is that the image circle(the circular image projected into the camera by the lens) from a DX lens is only large enough for a DX sensor.

This smaller image circle allows ffor smaller and less complex(and so cheaper) lens designs of which the 35mm 1.8 is a perfect example.

kimpenonal said:

kimpenonal wrote:

I have a confusion about the crop factor of DX lenses on a APS-C DSLR's.

I own a nikon D7000 and I purchase 18-200mm f/3.5-5.6 VR II separately.

and now I am planning to buy a prime lens which is AF-S DX 35mm f/1.8G

My question is Is there a crop factor for this DX lens on a APS-C camera? Do I have to consider the 1.5x crop factor to have a 52.5mm equivalent? or 35mm DX is 35 in APS-C camera.?

Click to expand...

...although some lenses may have stickers on them, or the box, that has the FX equivalent focal lengths.

So, an DX lens that is marked as a 35 / 1.8 will have the AOV (angle of view) and aperture as an FX lens that is marked as a 35 / 1.8 when mounted on a DX body.

Focal length is a physical property of the lens. It never changes. A 35mm lens is a 35mm lens whether used on a APS-C body, 135 format body, medium format body, or a home-made body.

"Crop factor" (if you insist on thinking in those terms) is a function of sensor size, not lens focal length or image circle size.

Cameras with different sensor sizes affect the angle of view of a given lens, regardless of the size of the image circle or the focal length of the lens.

kimpenonal said:

kimpenonal wrote:

I have a confusion about the crop factor of DX lenses on a APS-C DSLR's.

I own a nikon D7000 and I purchase 18-200mm f/3.5-5.6 VR II separately.

and now I am planning to buy a prime lens which is AF-S DX 35mm f/1.8G

My question is Is there a crop factor for this DX lens on a APS-C camera? Do I have to consider the 1.5x crop factor to have a 52.5mm equivalent? or 35mm DX is 35 in APS-C camera.?

Click to expand...

The so-called "crop factor" is exactly what it implies; it's like taking a full 36x24mm frame of film, and cutting it down to about 22x17mm, trimming away the edges. The lens does not change its focal length for the crop; you simply get less of an angle of coverage.

It is rather unfortunate that people have started to talk about "35mm full frame equivalent" focal lengths, because they are not focal lengths at all. This metric should have been degrees of angle, so it is never confused with a focal length. Now you have people saying things like "I am shooting 560mm with an APS-C" when they really are shooting a 400mm lens, leaving someone else to think that they are actually using a 560mm lens. The people who started this nomenclature clearly did not do a lot of thinking.

Short answers:




Yes there is a crop factor

And 35mm on the 35mm f1.8 will provide the same field of view as 35mm on your 18-200.

Rather than think of this in terms of focal length, you should think of it in terms of field of view.

A 35 mm lens whether DX or FX will have nearly the same field of view on a DX camera body, as a 50 mm lens does on an FX camera body. Thus the 1.5 x factor. The focal length is a property of the lens itself. If you look up the lens specifications on a website like B & H Photo, they will provide the field of views. If it is an FX lens, they should list the field of views for both DX and FX bodies. A DX lens as someone posted previously is designed to provide an image that fills a DX sensor. Using a DX lens on an FX camera will result a vignetting effect since the image will not totally cover the larger sensor. Conversely, using an FX lens on a DX body will provide a cropped image since the lens is designed to fill an FX sensor, so some of the image will fall outside the edges of the smaller DX sensor. Hope this helps.

thank you that the best reply...

thank guys for all your helpful replies...

While you are 100% correct , by introducing a new semantic point of view to the discussion you are to a great extend confusing the issue. OP means does this lens on a APS-C camera produce an image with less coverage of the scene (hence enlarged or cropped, etc.) than the same focal length lens would produce on a FF sensor. If it were the same exact FF lens in each case, you would have no trouble allowing use of “crop” to describe the situation. But since the APS-C –specific lens can’t cover the whole FF sensor with an image, you make the point that cropping is not happening. Like I said, correct but confusing to those who use “crop” to mean the relationship of the image on APS-C to the image on FF, both produced by lenses appropriate to their respective sensors whether any image area has been lost in the case of the smaller sensor or not. We may not like certain terminology as it is popularly used, but fighting it (like resisting the Borg) is futile.

Of course it doesn't end there. Just consider the nearly universal use of the term “crop” as an adjective in these discussions, which it is not. The correct word to use as an adjective is “cropped”, the past participle. Mostly due to the diversification of English speaking societies by folks who do not use a past participle in their native tongues, such as East Asians, the adjectival past participle is rapidly disappearing. Crop instead of cropped is just one example. Others are fry instead of fried (as in rice), reserve instead of reserved (as in parking) ice instead of iced (as in tea), dome instead of domed (as in stadiums), etc. The list is endless. And endlessly frustrating.

Unfortunately there is nothing to be done about it, just as there is nothing to be done regarding your point. I think that using the term “crop factor” for the relationship between the images on FF frame and APS-C frame sensors with the same focal length lens whether any image area has been lost or not is here to stay. Tilting at this windmill just confuses the discussion. I ought to know; I have tried to do it often enough!

Robert