effect of DSLR cropping factor on F-number ?


Status
Not open for further replies.

ekoswara

New Member
Feb 21, 2004
7
0
0
#1
Hello all,

I have a Nikon D-SLR which have a cropping factor of 1.5x. If Iam using a 50mm f/1.8 lens at wide open, does this mean my lense will turn into a 75mm f/1.8 or will it become 75mm f/2.7 ?

Please enlighten me. Thank you
 

blurblock

Senior Member
May 30, 2003
3,827
0
0
ytphoto.clubsnap.org
#2
ekoswara said:
Hello all,

I have a Nikon D-SLR which have a cropping factor of 1.5x. If Iam using a 50mm f/1.8 lens at wide open, does this mean my lense will turn into a 75mm f/1.8 or will it become 75mm f/2.7 ?

Please enlighten me. Thank you
It will still be 50mm f/1.8, just with the cropping factor, you get a 75mm effect only. Your lens will not become 75mm f/1.8 or 75mm f/2.7 (whatever that is ;P ).

Just picture this, instead of seeing the whole pictures full frame, you only see portions of it.
 

ST1100

Senior Member
Jun 18, 2003
1,785
0
0
Singapore, Bedok
#3
It is an effective 75/1.8. The 'f1.8' brightness applies to every single spot in the image, so no matter how small your sensor is, it is still f1.8.
 

#4
To clearify further the issue, a 75/1.8 and a 50/1.8 has very different depth of view. Both blurblok and ST1100 gave a good explanation of the 1.8 issue.

Assuming you have a subject 2m away from the focal point in the lens, using a fix aperture of 1.8, the results with 50 and 78mm lens are as follows:

focal length,depth of view
50mm,0.169m
78mm,0.068m

As you can see, if the lens does become a 78/1.8, the subject will have sharp nose and super blur ears at f1.8. That is not the case when you shoot such an object. So you will only see 78mm equivalent of image and lens performance is still a 50/1.8. It maybe a bit confusing to state that a 50/1.8 lens become a 78/1.8 lens when put on a DSLR.

Regards.
 

Status
Not open for further replies.