Confuse with DX...


Liang10

New Member
Aug 27, 2010
2
0
0
#1
I'm a newbie in dslr, very confuse with the DX format of nikon. Let say i gt a D40 and i mount a 35mm on it. what is focus length im getting? isit a eye view just like a 50mm on a D3X?:confused:
 

kei1309

Senior Member
Apr 12, 2010
7,312
23
0
Earth
www.facebook.com
#2
I'm a newbie in dslr, very confuse with the DX format of nikon. Let say i gt a D40 and i mount a 35mm on it. what is focus length im getting? isit a eye view just like a 50mm on a D3X?:confused:
yup..

because the DX format is an APS-C sized sensor.

you need to multiply the focal length of the lens by 1.5 times...

FX is full frame so a 50mm lens on it, will still be 50mm...but not just any lens, but lenses made specially for FF
 

Liang10

New Member
Aug 27, 2010
2
0
0
#3
Thanks! But what about a fx 50mm on d40? What will the focal length be?
 

spree86

Senior Member
Feb 3, 2009
4,774
0
0
Bishan
www.flickr.com
#5
I'm a newbie in dslr, very confuse with the DX format of nikon. Let say i gt a D40 and i mount a 35mm on it. what is focus length im getting? isit a eye view just like a 50mm on a D3X?:confused:
Yup that's correct, at the same focal length, a 35mm has a field of view of 52.5mm on a DX camera as compared to the 35mm on an FX camera.
 

spree86

Senior Member
Feb 3, 2009
4,774
0
0
Bishan
www.flickr.com
#6
Thanks! But what about a fx 50mm on d40? What will the focal length be?
Just for your info, the same 1.5 crop applies to DX lenses as well. Also, if a DX lens is used on an FX camera, the image will be cropped as well.
 

Rashkae

Senior Member
Nov 28, 2005
19,105
12
0
#7
Just for your info, the same 1.5 crop applies to DX lenses as well. Also, if a DX lens is used on an FX camera, the image will be cropped as well.
Not quite. But you'll get vignetting.
 

Sep 24, 2009
794
0
0
SG_ID
www.flickr.com
#8
FX lenses:
- on FF cameras : effective focal length will be the actual focal length
- on DX/crop cameras : effective focal length = actual x 1.5
(FX lenses can be used on both FF and DX cameras)

DX lenses:
- on FF cameras : effective focal length will be the actual focal length (but there will be severe VIGNETTING)
- on DX/crop cameras : effective focal length = actual x 1.5
(DX lenses are suitable for DX cameras only, not meant for FF cameras)

hope this helps.. :)
 

Sep 24, 2009
794
0
0
SG_ID
www.flickr.com
#9
Not quite. But you'll get vignetting.
yes, the image will not be cropped.. the effective focal length will still be the same, but severe vignetting will cause the edges look like as if it is cropped into rounded shape..

bet TS will be confused now.. hehe.. :confused: :lovegrin:
 

ZerocoolAstra

Senior Member
Mar 13, 2008
9,522
0
0
rainy Singapore
#10
FX lenses:
- on FF cameras : effective focal length will be the actual focal length
- on DX/crop cameras : effective focal length = actual x 1.5
(FX lenses can be used on both FF and DX cameras)

DX lenses:
- on FF cameras : effective focal length will be the actual focal length (but there will be severe VIGNETTING)
- on DX/crop cameras : effective focal length = actual x 1.5
(DX lenses are suitable for DX cameras only, not meant for FF cameras)

hope this helps.. :)
Not for all DX lenses :)
 

Michael

New Member
Apr 5, 2005
829
0
0
47
Thailand
www.pbase.com
#11
please get it right and stop that none sense!!! a lens with 50mm focal length will ALWAYS have 50mm focal length regardless if you mount it on a DX or FX camera! what happens when you mount a lens on a camera body with different sensor sizes is a varying part of the image circle is cropped out. A FX camera will crop a bigger picture than a DX sensor. so the angle of the view of field changes which gives the appearance that the focal length changes. However, the perspective of the lens does not change! so a 35mm on a DX sensor still does not provide the same perspective as a 52mm on a FX sensor.
the difference between a DX and FX lens is the size of the image circle. A FX lens produces a bigger image circle, a DX lens a smaller.
 

ZerocoolAstra

Senior Member
Mar 13, 2008
9,522
0
0
rainy Singapore
#12
please get it right and stop that none sense!!! a lens with 50mm focal length will ALWAYS have 50mm focal length regardless if you mount it on a DX or FX camera! what happens when you mount a lens on a camera body with different sensor sizes is a varying part of the image circle is cropped out. A FX camera will crop a bigger picture than a DX sensor. so the angle of the view of field changes which gives the appearance that the focal length changes. However, the perspective of the lens does not change! so a 35mm on a DX sensor still does not provide the same perspective as a 52mm on a FX sensor.
the difference between a DX and FX lens is the size of the image circle. A FX lens produces a bigger image circle, a DX lens a smaller.
to be precise, a lens does not provide a perspective. The perspective is what you get based on your position relative to the objects in your frame.

but yes, I will certainly agree with your point that the focal length of a lens does not change, regardless of what camera body (FX or DX) it is mounted to.
To be fair, some ppl did use terms like 'effective focal length', which though technically still not accurate, sorta gets the point across :)
 

spree86

Senior Member
Feb 3, 2009
4,774
0
0
Bishan
www.flickr.com
#14
FX lenses:
- on FF cameras : effective focal length will be the actual focal length
- on DX/crop cameras : effective focal length = actual x 1.5
(FX lenses can be used on both FF and DX cameras)

DX lenses:
- on FF cameras : effective focal length will be the actual focal length (but there will be severe VIGNETTING)
- on DX/crop cameras : effective focal length = actual x 1.5
(DX lenses are suitable for DX cameras only, not meant for FF cameras)

hope this helps.. :)
The 35mm f1.8 DX actually works pretty well on a full frame, with very little vignetting.
 

Michael

New Member
Apr 5, 2005
829
0
0
47
Thailand
www.pbase.com
#15
to be precise, a lens does not provide a perspective. The perspective is what you get based on your position relative to the objects in your frame.
but yes, I will certainly agree with your point that the focal length of a lens does not change, regardless of what camera body (FX or DX) it is mounted to.
To be fair, some ppl did use terms like 'effective focal length', which though technically still not accurate, sorta gets the point across :)
yes sorry about that, the perspective is indeed dependent on the distance between camera and object. Essentially you gotta step backwards if you increase the focal length and you want to maintain the size of the subject in the frame. so the focal length influences the distance to the subject. it further influence how much of the background is included, the longer the focal length the less background is included which creates the compression effect in a telelens. if you use a wide angle lens then more background is included and the scene is stretched. in other words with a 35mm on a DX body you still need to be closer to your object than with a 50mm on a FX body. Therefore the frame shot on the FX body has a feel that is more compressed than the frame from the DX body.
 

ZerocoolAstra

Senior Member
Mar 13, 2008
9,522
0
0
rainy Singapore
#16
Hi Michael, I agree with your post except for the last part about the diff between DX and FX.
If the distance remains unchanged, the 2 formats give essentially the same perspective to the image. So neither is more "compressed" than the other.
For example I am seated across the dining table from my 2 friends. I first shoot with DX + 35mm lens, then FX + 50mm lens. Since I haven't moved between shots, they would look very similar in terms of perspective. DOF difference, but not perspective difference.
 

Rashkae

Senior Member
Nov 28, 2005
19,105
12
0
#17
Hi Michael, I agree with your post except for the last part about the diff between DX and FX.
If the distance remains unchanged, the 2 formats give essentially the same perspective to the image. So neither is more "compressed" than the other.
For example I am seated across the dining table from my 2 friends. I first shoot with DX + 35mm lens, then FX + 50mm lens. Since I haven't moved between shots, they would look very similar in terms of perspective. DOF difference, but not perspective difference.
Except for background... The 50mm and the 35mm will create a subtly different background perspective and this won't change because APS-C doesn't actually change the focal length, it just crops.
 

ZerocoolAstra

Senior Member
Mar 13, 2008
9,522
0
0
rainy Singapore
#18
Except for background... The 50mm and the 35mm will create a subtly different background perspective and this won't change because APS-C doesn't actually change the focal length, it just crops.
so far have not done an actual side-by-side comparison, but I think you have a point there.

anyway this sort of digresses from TS' original question, so better to leave it at that :)
cheers!
 

daredevil123

Moderator
Staff member
Oct 25, 2005
21,645
63
48
lil red dot
#20
Oops sorry, I was talking about the DX crop mode, should have been more specific.
DX crop mode is a setting. It is defaulted to "Auto DX crop" on most FX cameras out of the box. But you can turn it off so the camera will not do the DX crop when a DX lens is detected.

This will force the camera to shoot in FX mode all the time, irregardless of what lens is mounted.
 

Top Bottom