Dx vs non-Dx lens Aperture

[Stoogley]

I did a cursory look and couldn't find the answer to my question, maybe some one can shed some light (so to speak).

I understand the difference in the circle of coverage between DX and non-DX lenses, the former having a smaller circle.

But, is there any difference in the relative influence of the aperture at a given focal length?

In other words, does a 100mm focal length setting on a DX lens at f/8 would provide the same DOF and amount of light as does a FF 100mm lens at f/8?

Stoog

 

[Big Mike]

You will get more DOF with the smaller sensor, other factors being equal.

This is one reason why photographers love full frame cameras, they give a shallower DOF, which (in a general sense) tends to separate the images from typical DSLR photos and especially point & shoot photos. So further to this, point & shoot cameras have tiny sensors....and typically give a rather deep DOF.

Now on the flip side, there is sometimes an advantage to getting a deeper DOF. For example, I know a wedding photographer who has all the best cameras and lenses that he could want. Canon 1D, 1Ds, and even a Nikon D700. But he still carries a crop body, 40D, with him. He likes that he can get more DOF at F2.8 with the 40D, than he can with the 1Ds at F2.8. Of course, you could stop down the lens on the 1Ds to get more DOF, but then you sacrifice on shutter speed.
Of course, if we are being practical, you can typically use a higher ISO on the full frame bodies, so you can afford to stop down without sacrificing the shutter speed. But the fact remains that you get more DOF with a smaller sensor.

 

[KmH]

More = deeper.

 

[Patrice]

The OP asked about fx vs dx lenses, not sensor size. I believe if you take two similar focal length lenses, one 'dx' and one 'fx', (ie: 35mm dx and 35mm fx) set at the same aperture and focused on an object 5 feet away, then the dof will be the same.

The idea that dx gives you deeper dof comes from the fact that to get the same image framing on a dx sensor as you do on an fx sensor you have to back up some from the subject. The distance to subject thus increases therefore so does the dof.

 

[SunnyHours]

FF lenses are just slightly bigger in diameter...so it should not do such a big difference in Aperture between FF and DX. The Aperture is calculated in Lux (I guess) so the same amount of Lux coming in the FF will be equal to the DX...that's just my guess from my understanding of how a camera works though... The DOF is a different story though...

 

[kundalini]

EDIT:
Removed link since it concerns cropped vs full frame cameras and not specifically lenses. Cheers.

 

[boomer]

The OP asked about fx vs dx lenses, not sensor size. I believe if you take two similar focal length lenses, one 'dx' and one 'fx', (ie: 35mm dx and 35mm fx) set at the same aperture and focused on an object 5 feet away, then the dof will be the same.

The idea that dx gives you deeper dof comes from the fact that to get the same image framing on a dx sensor as you do on an fx sensor you have to back up some from the subject. The distance to subject thus increases therefore so does the dof.

This.

Plus as your distance increases from your subject, your focus point moves closer to infinity. Its harder (compared to FX with FF sensor and keeping the same framing) to blow the background out of focus with DX as you have to be farther away as Patrice just mentioned. The closer you get to infinity focus, the less out of focus your background will be.

 

[Stoogley]

Thanks guys.
That is pretty much what I thought it might be but good to get some insights on it....

 

[djacobox372]

You will get more DOF with the smaller sensor, other factors being equal.

This is one reason why photographers love full frame cameras, they give a shallower DOF, which (in a general sense) tends to separate the images from typical DSLR photos and especially point & shoot photos. So further to this, point & shoot cameras have tiny sensors....and typically give a rather deep DOF.

Now on the flip side, there is sometimes an advantage to getting a deeper DOF. For example, I know a wedding photographer who has all the best cameras and lenses that he could want. Canon 1D, 1Ds, and even a Nikon D700. But he still carries a crop body, 40D, with him. He likes that he can get more DOF at F2.8 with the 40D, than he can with the 1Ds at F2.8. Of course, you could stop down the lens on the 1Ds to get more DOF, but then you sacrifice on shutter speed.
Of course, if we are being practical, you can typically use a higher ISO on the full frame bodies, so you can afford to stop down without sacrificing the shutter speed. But the fact remains that you get more DOF with a smaller sensor.

An often overlooked advantage of larger sensors.

However, technically speaking, it isn't the sensor size that is giving you the shallower DOF, it's the longer focal lengths. For example: a 35mm f1.8 DX lens may achieve the same composition as a 50mm f1.8 full-frame, but the DOF will be shallower on on the full-frame camera because the focal length is longer.

 

[Helen B]

There are conditions when you will get less depth of field with a cropped sensor. With the same final 'print' size, same focal length, subject distance and aperture a cropped sensor will have less DoF (and field of view) than a full-frame sensor. With the same field of view, subject distance and aperture a cropped sensor will have more DoF (and the image will have been taken with a shorter focal length lens) than a full-frame sensor. There was a recent discussion of this here.

Best,
Helen

 

[enzodm]

FF lenses are just slightly bigger in diameter...so it should not do such a big difference in Aperture between FF and DX. The Aperture is calculated in Lux (I guess) so the same amount of Lux coming in the FF will be equal to the DX...that's just my guess from my understanding of how a camera works though... The DOF is a different story though...

No, aperture is the ratio between focal length and aperture diameter, so it should be the same in both. It is related to amount of light reaching the sensor, but how much light reaches it, depends also on glass features. I would be interested in seeing a test with same lens same scene same aperture with APS and FF bodies, to see shutter speed; unfortunately is impossible to have exactly identical conditions (e.g., you have to move closer with FF).