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.

[bwhinnen]

Because the sensor has an area 1.5 times smaller than that of a 35mm. So we get all the focal lengths increased by a factor of 1.5. What you see thought the viewfinder is what you get on the sensor as far as I can tell, others may be able to be more exact.

Cheers
Brett

[Deano]

The idea of a focal length multiplier is a misnomer. It is actually a crop factor in that the smaller sensor (smaller than the area of 35mm film) only sees part of the image circle available from the lens. There is no increase in the magnification. Therefore, what you see through the D70 viewfinder (and on the image) with a 100mm lens is an area equivalent to that produced by a 150mm lens on a 35mm film camera.

At least that is how I understand it.

Cheers
Dean

[bwhinnen]

That makes more sense than a multiplier, which is why I suppose everyone says an effective 35mm focal length of XX.

It's always good to learn something new

Thanks
Brett

[Greg B]

There is an excellent thread somewhere that covered this in detail Brett, but for some reason I can't find it.

The terminology raised there was Field of View. The DX sized sensor results in a narrower FoV on a given focal length than a "full" sized sensor (ie same size as a 35mm neg). So the Fov on a 300 mm lens with a DX sensor is the same field of view on a 450 mm lens for a full sized (35mm) sensor.

I notice that the number of degrees in the field of view for lenses is mentioned for DX and for 35mm on the Maxwells site

[phillipb]

One point that has always intrigued me about this, the size of the sensor being smaller than a 35mm film camera has the same effect as enlarging a print. When you do this with the actual print, the resolution decreases the more you enlarge it, would this be true of the lens?
In other words is the quality of the final result the same if you use a particular lens with both a 35mm and a DSLR? (Not witstanding any differenses between film and digital).

[gstark]

Greg,

Was this the thread you're thinking of?

http://forum.d70users.com/viewtopic.php ... rop+factor

As good as the discussion was in that one, I seem to think that there may still be one other thread that we're not yet seeing.

[Greg B]

Gary, That wasn't the thread I was thinking of, but you are right, it is a beauty. I just enjoyed reading the whole thing again.

Recommended for any newcomers.

The thread on FoV and 35mm v DX had some very interesting points, but I just can't find it. I have looked with several different search terms too.

[bwhinnen]

Is this the one you are thinking of? Interesting read none-the-less...

Cheers
Brett

[Greg B]

I think that's it Brett, thanks.

Hey coolpix - read the thread in Brett's link....

[gstark]

Greg,

Both of them in fact. The second of these refers to another thread somewhere within its body, and I suspect that this "other" thread is the other one we're refering to from here.

[Mj]

One point that has always intrigued me about this, the size of the sensor being smaller than a 35mm film camera has the same effect as enlarging a print. When you do this with the actual print, the resolution decreases the more you enlarge it, would this be true of the lens?
In other words is the quality of the final result the same if you use a particular lens with both a 35mm and a DSLR? (Not witstanding any differenses between film and digital).

The simply answer to your first question is 'yes' and the second 'no'.

It always amuses me that the crop factor or FOV, if you like, is sold as a positive when all it really means is that the camera captures a smaller frame of the image provided by the lens.

Michael.

[tsanglabs]

Is this the one you are thinking of? Interesting read none-the-less...

Cheers
Brett

This post has cleared up a lot for me thanks for finding it. Maybe some of this information could summarised and placed in the FAQ.

[coolpix]

I followed Brett's thread and it answered all the questions that i had.

Thanks heaps.

[Greg B]

One point that has always intrigued me about this, the size of the sensor being smaller than a 35mm film camera has the same effect as enlarging a print. When you do this with the actual print, the resolution decreases the more you enlarge it, would this be true of the lens?
In other words is the quality of the final result the same if you use a particular lens with both a 35mm and a DSLR? (Not witstanding any differenses between film and digital).

The simply answer to your first question is 'yes' and the second 'no'.

It always amuses me that the crop factor or FOV, if you like, is sold as a positive when all it really means is that the camera captures a smaller frame of the image provided by the lens.

Michael.

I guess we need to consider the amount of information being captured/stored on the area available. If you consider one side of a vinyl record, and compare that to a cd, or compare a cd to a dvd, we don't think in terms of the size being the determinant of information.

I don't know how much information is stored on a 35mm film negative compared to a DX CCD. Probably more, but that may change.

[stubbsy]

I'm exhausted!

Just read both threads (the one pointed to by Gary & the one by Brett). What great info

Thanks guys and thanks coolpix for asking the question. I finally understand this stuff (scary)

Cheers

[gstark]

Michael

It always amuses me that the crop factor or FOV, if you like, is sold as a positive when all it really means is that the camera captures a smaller frame of the image provided by the lens.

Have you ever wondered what happens to all of those lost pieces of images that we've photographed? All of thos chopped off bits that get ignored because of the smaller sensor?

There must be a heap of them lying around inside the camera somewhere.

[gstark]

Greg,

I guess we need to consider the amount of information being captured/stored on the area available. If you consider one side of a vinyl record, and compare that to a cd, or compare a cd to a dvd, we don't think in terms of the size being the determinant of information.

I don't know how much information is stored on a 35mm film negative compared to a DX CCD. Probably more, but that may change.

It's not just the amount of information that's stored, it's also the manner of storage that's important too.

Let's work with your analogy of the vinyl record vs CD for a moment: who amongst us thinks that while CDs provide a cleaner source of music, vinyl sounds "warmer" ? I do, for one.

The difference is because the vinyl is using analog methods of storage; in the conversion from analog (which is how the music is originally created) to digitial, there will be a loss of data. A very small loss, but it's a loss, nonetheless.

The process of digitial imaging involves a similar A-D conversion process, and there's a similar small loss of data as a result.

So, to my mind, there are two points here:

1: good high quality colour film does store more data than, say, the 6.2MP sensors in our D70s. This is simply due to the variable nature of silver halide/grain as compared with the fixed structure within a digicam's sensor, but it will eventually change as sensor sites become smaller and more plentiful in any given sensor size.

2: Notwithstanding point 1: above, the AD conversion processes are inherently lossy (to a very small degree) and there will always be a (tiny) loss of data due to this conversion process.

[Killakoala]

Have you ever wondered what happens to all of those lost pieces of images that we've photographed? All of thos chopped off bits that get ignored because of the smaller sensor?

In the electronics industry we say that any lost data has gone into a 'bit bucket'.