lens rating(size) in 35mm terms

[coolpix]

A digital 70-300mm lens is said to equal 115-450mm lens in 35mm speak. How is this possible and is what i see through the view finder 300mm or 450mm.

[gooseberry]

Hi coolpix,

Since most DSLRs have an imaging sensor which is smaller than the size of traditional 35mm frames (except for a few very expensive full frame models), the image taken with a particular lens on a DSLR will be cropped as compared to a full 35mm frame.

For example, take a 70mm lens. It is a still 70mm lens no matter whether you are using a film or digital SLR (ie focal length does not change). However, on the digital SLR the image is cropped (the size of the crop is dependant on the size of the sensor). This cropping of the image creates an image with an equivalent field of view (or FOV) of a longer focal length lense. All current Nikon DSLRs have a FOV crop factor of around 1.5x. So a 70mm lens on a Nikon DSLR will have an aparent FOV of a 105mm lens.

[stubbsy]

Coolpic

It's not a good idea to ask the same question in different places. An hour before this, you posted the same Q in Absolute Beginners Questions (http://forum.d70users.com/viewtopic.php?t=1803).

Given, like me, you're a newbie there are a multitude of reasons for this (one possibility is you thought the Q was better in Genreal discussion so posted again)

Problem is this fragments answers for yourself & others since different people give different answers in the 2 threads.

If you want a posting moved to another area, I'm sure Gary or Leigh would be happy to oblige.

Cheers

[coolpix]

I placed it here an hour later as i relised that i had placed it in the wrong section.

Sorry if this has upset anyone but as a new member having to learn where things go and all the rules, one sometimes makes mistakes.

[Greg B]

Nobody will be upset coolpix, we don't do that here. Stubbsy was just giving you the good oil for future reference

[stubbsy]

coolpix

Sorry if this has upset anyone but as a new member having to learn where things go and all the rules, one sometimes makes mistakes.

I doubt you upset anyone. As Greg B suggested I figured the reason might have been something like what you describe. On point about getting Gary or Leigh to move a post is I'm not sure how you do this Figure someone else can shed light.

[gstark]

On point about getting Gary or Leigh to move a post is I'm not sure how you do this Figure someone else can shed light.

It's as easy as sending Leigh or myself a PM, and asking whether we feel you've placed the question in the correct thread.

In this case, either place, but not both, would be acceptable, but as has been pointed out, we're certainly not going to bash your knees in with a baseball bat for this sort of transgression.

At least not on your first offence.

Seriously, we also had some discussion on this about 6 weeks or so ago, and I suspect that if you did a forum search on crop factor you would not only find that thread, but IIRC, the discussion was very enlightening in terms of providing just about any answer you'd need for this type of question.