Newbie question on conversion factor of lenses


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myhome50

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Sep 21, 2005
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#1
question on conversion factor of DSLR lenses.

The last para of this article
http://www.cameras.co.uk/blog/2007/07/buying-lenses-for-slr-camera.html
reads …” a conversion factor needs to be applied to the focal length of the lens in most cases”

Question 1
Different DSLR got different conversion factor ?

Question 2:
If the above is true, what are the conversion factor of Canon, Nikon and Olympus DSLR camera?

I’ve been using different types of camera, mostly compact, ultra-zoom, and some so-called bridge camera like Fuji 9600, but never DSLR. One reason for considering DSLR is to see the “bigger picture” ie wide angle lense. Many times, I’m restricted by the 35 mm or 28 mm fixed lense that I thought maybe if I buy a DSLR, I can squeeze more things, without having to move backward to get the wide angle shot.

After reading the above article, I am having doubt about considering DSLR.
Am I missing some important info here? There is no way that a kit lense of say, 18-55 mm really start from 18 mm ?

Thanks
 

Michael

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Apr 5, 2005
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#2
First of all let me state this:
A 50mm lens is and remains a lens with 50mm focal length regardless of what sensor the camera body has.

The usage of a conversion factor for the focal length for different sensors is simply wrong. A 200m lens does not become a 300mm lens when attached to a D70. What changes is how much of the picture circle ends up in the picture or in other words the crop factor. A D70 crops a smaller picture out of the picture circle produced by the 200mm lens than a full frame body (D3), but the optic reproduction remains the same.

The crop factors between different DSLRs and brands is indeed different, 1.5 for Nikon DX and 1.6 for Canon.
 

LittleWolf

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Jan 23, 2005
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#3
question on conversion factor of DSLR lenses.

The last para of this article
http://www.cameras.co.uk/blog/2007/07/buying-lenses-for-slr-camera.html
reads …” a conversion factor needs to be applied to the focal length of the lens in most cases”

Question 1
Different DSLR got different conversion factor ?

Question 2:
If the above is true, what are the conversion factor of Canon, Nikon and Olympus DSLR camera?
Answer 2: No, it is not true. There is no conversion factor for focal lengths.

Answer 1: Because of Answer 2, this one is redundant

Answer 3 (to a question not asked): This blog entry contains a lot of nonsense. Statements like "when you attach a 35mm lens to a digital SLR it increases the zoom capacity" clearly show that the author doesn't know what (s)he's talking about. (Same goes for the agencies that advertise certain cameras in Singapore with deliberate lies, like "28mm lens" when it's focal length is only a few mm ...)

There is no way that a kit lense of say, 18-55 mm really start from 18 mm ?
There "is way", although the useable image circle might be compromised to make it affordable.
 

ykia

Senior Member
Apr 23, 2005
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#4
FOV Crop Factor (or converstion factor) only changes the angle of view of the lens. So with a 1.6x FOVCF, a 10mm angle of view is like a 16mm angle of view, all else remains the same, except for depth-of-field, which will be different when compared to a 16mm lens mounted on a full-frame camera.

Canon has FOVCF of...
1x or Full-frame: 1Ds series & 5D
1.3x: 1D series
1.6x: 3xxD, 400D, 10D, 20D, 30D, 40D

Nikon has FOVCF of...
1.5x: D40, D50, D70, D80, etc
1x: D3
Not sure about the rest.

Olympus has FOVCF of 2x (or the 4-thirds system)

question on conversion factor of DSLR lenses.

The last para of this article
http://www.cameras.co.uk/blog/2007/07/buying-lenses-for-slr-camera.html
reads …” a conversion factor needs to be applied to the focal length of the lens in most cases”

Question 1
Different DSLR got different conversion factor ?

Question 2:
If the above is true, what are the conversion factor of Canon, Nikon and Olympus DSLR camera?

I’ve been using different types of camera, mostly compact, ultra-zoom, and some so-called bridge camera like Fuji 9600, but never DSLR. One reason for considering DSLR is to see the “bigger picture” ie wide angle lense. Many times, I’m restricted by the 35 mm or 28 mm fixed lense that I thought maybe if I buy a DSLR, I can squeeze more things, without having to move backward to get the wide angle shot.

After reading the above article, I am having doubt about considering DSLR.
Am I missing some important info here? There is no way that a kit lense of say, 18-55 mm really start from 18 mm ?

Thanks
 

myhome50

New Member
Sep 21, 2005
10
0
0
#5
Answer 2: No, it is not true. There is no conversion factor for focal lengths.

Answer 1: Because of Answer 2, this one is redundant

Answer 3 (to a question not asked): This blog entry contains a lot of nonsense. Statements like "when you attach a 35mm lens to a digital SLR it increases the zoom capacity" clearly show that the author doesn't know what (s)he's talking about. (Same goes for the agencies that advertise certain cameras in Singapore with deliberate lies, like "28mm lens" when it's focal length is only a few mm ...)



There "is way", although the useable image circle might be compromised to make it affordable.
Could it be that the article is only referring to compatibility issue of slightly older type of lense that can be used for both DSLR and film SLR, then the conversion factor must be taken into consideration

where else

when referring to new generation of DLSR lenses, we don’t need to take conversion factor into consideration
i.e an 18-55 mm kit lense of D40 REALLY starts at 18mm and end at 55 mm

thanks
 

Michael

New Member
Apr 5, 2005
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#6
Could it be that the article is only referring to compatibility issue of slightly older type of lense that can be used for both DSLR and film SLR, then the conversion factor must be taken into consideration

where else

when referring to new generation of DLSR lenses, we don’t need to take conversion factor into consideration
i.e an 18-55 mm kit lense of D40 REALLY starts at 18mm and end at 55 mm

thanks
lets talk first compatibility and to keep it simple lets stick to Nikon and the D40. Only AFS lenses support all the function of the D40, however you can attach also older AF and even AIS lenses to the D40. However, you loose AF function on the former and light metering on the later but you are still able to take a picture with a bit more effort though.
DX lenses are engineered such that the light circle projected by the lens onto the sensor is just as big as the DX sensor and does not cover the traditional 35mm format. The are also engineered to project the light rays more parallel on the sensor so that they hit the sensor perpendicular (this did not matter so much for film...). So, what the article says is a bit rubbish.

now regarding focal length. the 18-55mm kit lens has a focal length of 18-55, it really starts at 18mm and ends at 55mm but you cannot expect the same angle of field at 18mm with the D40 as at 18mm on the 35mm format. So if you would attach the 18-55 to an film camera you will capture a wider angle than when it is mounted on the D40 BUT this did not change the focal length, the sensor of the D40 just cuts a smaller picture (besides that the 18-55 is probably a DX and will not fill the 35mm format completely).
 

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