Go Back   Steve's Digicams Forums > Digicam Help > What Camera Should I Buy?

Reply
 
Thread Tools Search this Thread
Old Mar 12, 2007, 3:44 PM   #1
Junior Member
 
Join Date: Mar 2007
Posts: 4
Default

I'm new to the DSLR area and am getting conflicting answers on the difference betweenthe identicallens on a DSLR and a film SLR (by the way, I am considering a Nikon D40 kit, the 70-300 VR Tele, and the SB600 flash).

I understand that the angle of view will be less on a DSLR than a film cameragiven a specific lens length. I have also been told that the Tele will have an effective focal length of 105 - 450. Does this mean that if I put the lens on a film camera and than a DSLR the image will appear closer (larger), or will the field of view just decrease?

I have had a Canon A1 for some 28 years now and it's still cranking out great photos.

This DSLR stuff is all new to me!

:?




nuzzy90532 is offline   Reply With Quote
Sponsored Links
Old Mar 12, 2007, 5:49 PM   #2
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

A 35mm camera makes exposures on a strip of film that is 35mm wide. That exposure is 24mm x 36mm.

On a Nikon D40, the image sensor is 15.6mm x 23.7mm, so the same lens on a 35mmSLR will have a narrower field of view on the D40. Since the 35mm film exposure is about 1.5 times the size of the image sensor in the D40 (24/15.6 = 1.54, 36/23.7 = 1.52), a lens with a focal length of 70mm (like the 70-300 VR you mentioned) would have about the same field of view as a 105mm lens on a 35mm SLR (70 x 1.5 = 105). That's why you were told that the 70-300 would have a 35mm equivalent focal length of 105-450.

The terminology in your message was incorrect. The lens doesn't have an "effective focal length". The lens doesn't actually change its focal length when it's mounted on one camera or the other; the cameras create different size images, so the field of view is different. The focal length of 105-450 reflects the smaller image size, and is just a number to help users of 35mm cameras understand what field of view they will get from their digital cameras.
Attached Images
 
TCav is offline   Reply With Quote
Old Mar 12, 2007, 6:02 PM   #3
Junior Member
 
Join Date: Mar 2007
Posts: 4
Default

Thanks, I think I understand the field of view issue.

Let me rephrase the other part ofmy question: Will using the 70-300 on my DSLR have the same 'reach' as using a 300 plus a 1.5 extender on a 35mm? Will both now have the same magnification? Let's leave out the field of view issue completely.
nuzzy90532 is offline   Reply With Quote
Old Mar 12, 2007, 6:46 PM   #4
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

nuzzy90532 wrote:
Quote:
Let me rephrase the other part ofmy question: Will using the 70-300 on my DSLR have the same 'reach' as using a 300 plus a 1.5 extender on a 35mm? Will both now have the same magnification? Let's leave out the field of view issue completely.
The magnification issue and the field of view issue are the same issue. Yes, the 70-300 on a dSLR will have the same 'reach' as the 70-300 plus a 1.5x teleconverter on a 35mm SLR. The dSLR does it physically by using a smaller image size; the 35mm SLR does it optically by using the teleconverter.
TCav is offline   Reply With Quote
Old Mar 12, 2007, 7:04 PM   #5
Junior Member
 
Join Date: Mar 2007
Posts: 4
Default

Perfect.....thanks!!!
nuzzy90532 is offline   Reply With Quote
Old Mar 13, 2007, 3:29 AM   #6
Super Moderator
 
peripatetic's Avatar
 
Join Date: Nov 2004
Posts: 3,599
Default

Quote:
The terminology in your message was incorrect. The lens doesn't have an "effective focal length".
What nonsense!

"Effective focal length" means that focal length which would give an equivalent field of view on a 35mm film camera.

You may deplore the use of the term, you may think it misleading and inaccurate, but that is how it is used. And used by all the manufacturers, so taking an individual to task for using it is churlish in the extreme. It is a term now in common usage and the meaning is clear. Furthermore the OP used it perfectly correctly.

For most users the single most important factor in lens selection is its field of view and having a standard frame of reference is a good thing. Of course it would be better still if that frame of reference was expressed in degrees of angle of view, but that is not the case.

So if you don't like the term then fine, but for the rest of us it is usefully used to convey information and there is no confusion over the meaning.


peripatetic is offline   Reply With Quote
Old Mar 13, 2007, 1:35 PM   #7
Senior Member
 
mtngal's Avatar
 
Join Date: Nov 2005
Location: Frazier Park, CA
Posts: 16,056
Default

As a technical matter, there is a difference between magification and field of view. I finally came to grips with the difference between these two things one day recently, when I was stitching together a 3 frame panorama (3 different pictures that are put side-by-side to make a continuous picture). The magnification of one frame of the picture is the same as the magnification of the whole panorama, however, the field of view is significantly smaller with one frame, when compared with the whole panorama.

The diagram posted shows how much smaller a dSLR sensor is compared to a 35mm film frame, so a picture taken with the same lens on a dSLR won't be actually magnifying the subject any, it will be essentially cropping out some of the sides and top that a film camera would capture.

As a practical matter, they come out to be the same thing - the image you see on a dSLR picture appears closer/more magnifiedbecause it fills the frame more fully than with a film camera. Have I now fully confused everyone?
mtngal is offline   Reply With Quote
Old Mar 13, 2007, 1:48 PM   #8
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

peripatetic wrote:
Quote:
Quote:
The terminology in your message was incorrect. The lens doesn't have an "effective focal length".
What nonsense!

"Effective focal length" means that focal length which would give an equivalent field of view on a 35mm film camera.

You may deplore the use of the term, you may think it misleading and inaccurate, but that is how it is used. And used by all the manufacturers, so taking an individual to task for using it is churlish in the extreme. It is a term now in common usage and the meaning is clear. Furthermore the OP used it perfectly correctly.

For most users the single most important factor in lens selection is its field of view and having a standard frame of reference is a good thing. Of course it would be better still if that frame of reference was expressed in degrees of angle of view, but that is not the case.

So if you don't like the term then fine, but for the rest of us it is usefully used to convey information and there is no confusion over the meaning.

The focal length of a lens doesn't change, so the "effective focal length" is the "focal length". What does change is the field of view.

Neither Canon nor Pentax quote a 35mm equivalent focal length or field of view. Nikon refers to a "Picture Angle" for both 35mm and Nikon DX format cameras. Sony refers to angles of view for 35mm and APS. Fuji and Olympusrefer to "equivalent to ... on a 35mm camera." The EXIF Spec (V2.2) refers to "Focal length in 35 mm film". So a more correct term to describe what happens to the field of view would be "35mm equivalent focal length".

While you and others might be comfortable with the use of the term "effective focal length", it is not technically correct, andthe use of the term created the confusion that caused nuzzy90532to start this topic. And I suspect that nuzzy90532is not alone.

So the term you use that is intended to eliminate confusion, actually creates more confusion. You and others are free to use whatever language you please, but if you want people to understand you, you should use the same language as everyone else. And everyone else is using "equivalent".
TCav is offline   Reply With Quote
Old Mar 13, 2007, 3:33 PM   #9
Junior Member
 
Join Date: Mar 2007
Posts: 4
Default

Now, let's really have some fun! :P

The SB600 has the ability to match it's flash to the lens setting. Since the markings on the lens are 35mm equivalents, will the flash illuminateaviewing angleindicated on the lens, say 18mm, or does it illuminate a 27mm area?

Or is this too much of nothing to worry about?
nuzzy90532 is offline   Reply With Quote
Old Mar 13, 2007, 4:25 PM   #10
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

nuzzy90532 wrote:
Quote:
The SB600 has the ability to match it's flash to the lens setting. Since the markings on the lens are 35mm equivalents, will the flash illuminateaviewing angleindicated on the lens, say 18mm, or does it illuminate a 27mm area?
Actually, according to Nikon, the D40is compatible with their Creative Lighting System, so it can use the Power Zoom feature of the SB600, so the speedlight should always illuminate the field of view of the lens.

BTW, the specs on the SB600 are for flash from 24mm to 85mm (on a 35mm SLR). This would be a field of view of from 84 to 28.5 degrees, or 16mm (24/1.5) to 56.7mm (85/1.5) on the D40, which will cover the entire range of the 18-55mm kit lens.
TCav is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 12:14 AM.