Digital cameras 101

[rhinorick]

I have searched digicamhelp and did not find any info on focal lengths.  If I missed a post or page of info, please let me know.  

My question is this ....  What is focal length?  When I look at the EXIF data on my photos, it says what the focal length was when the photo was taken.  I don't understand what that is telling me.  

How does focal length play into zoom, macro, etc.?  Can I change the focal length?  Or is it changed by the amount of "zoom"?

Thanks in advance!  

[Mike54]

Rick,
"The focal length of a lens is defined as the distance in mm from the optical center of the lens to the focal point, which is located on the sensor or film if the subject (at infinity) is "in focus"."

Perhaps this link will help? (Scroll down a bit)

[ShutterbugGail]

I have searched digicamhelp and did not find any info on focal lengths.  If I missed a post or page of info, please let me know.  

Hmmmmm, this information should have returned when you searched, though perhaps the 35mm equivalent term wasn't obvious enough to relate it to focal length.

http://www.digicamhelp.com/learn/glossary/35mm-equivalent.php

[rhinorick]

Thank you both for the links.  

Gail, the chart on your link's page shows 116mm for focal length, etc.  Is that then what the 35mm - 420mm on my FZ50 means?  Is that focal length?

That is why I don't understand why my photos show small numbers for focal length when I am using 420mm for zoomed in shots.

Your page also makes a very good point about "zoom".  Advertising of digital cameras can be VERY misleading.  One camera has a 35-420mm lens, which is 12x, and another has 25-300mm and is also touted as being 12x zoom.  300mm is not 12x magnification, but only about 8.5x (on the 35mm standard).  I emailed one photo magazine that compared digital cameras and told them they should have explained that.

Which leads to another point in all of this .... is 35mm "as the eye sees it"?  Therefore 12x magnification would in fact be 420mm?  That is the way I have read it when it made the most sense to me - on Canon's and Panasonic's web sites.    Others sources were just plain confusing.    

Therefore, a number less than 35mm is wide angle, and a number greater than 35mm is zoom.  Is that correct?

(or course, that is using 35mm numbers, not digital sensor numbers)

Perhaps this discussion will help in not only understanding focal lengths, but also for those who are looking to buy a digital camera and want to understand zoom power.

[Mike54]

"and another has 25-300mm and is also touted as being 12x zoom.  300mm is not 12x magnification"
Actually it is 12X.      The magnification is based on the lowest focal length (25MM).

The 35MM - 420MM on your FZ50 is the range of focal length available. In other words you can use the lens at any focal length between 35MM and 420MM. If you're shooting landscapes for example you would generally shoot to the lower end (35MM). For wildlife you would use the long end (420MM).

[rhinorick]

You hit the nail on the head there when you said "range".  That is where the ads are misleading.  They say "12x zoom", when they should say "12x zoom range", or "12x focal length range".

It is not actually "12x zoom" power or magnification in all cases.  Again, from my  understanding, 420mm is in fact 12x magnification from "normal".  But 300mm would not be.

Ok, I think you have answered my other question.  For my FZ50's 35mm - 420mm lens, that does mean focal length.  Ok, got it.    Thanks Mike.

Now, back to the other part of my question ... why then does the EXIF data on my photos show much smaller numbers than what I am actually using for focal length?  Like you said, I use 420mm for most of my wildlife photos, yet the EXIF data says a smaller, 2-digit number. (I don't remember the numbers exactly at the moment)

Ohhhhhhhhh  ....   I think I might know.  The numbers in the EXIF data are the digital focal lengths aren't they?

[Mike54]

Again, from my  understanding, 420mm is in fact 12x magnification from "normal".  But 300mm would not be.

The "X" of a lens is based on the smallest focal length of the lens. In the examples you gave the 300MM would be 12x25 or 300MM. In the case of your 420MM, were the smaller number 25MM rather than 35MM the "X" factor would be 16.8X. The "range" of the lens or "X" factor is determined from the lens capabilities not from the so called "norm" (assumed to be 35MM).

[rhinorick]

Ahhhh ... yes!!!!

I checked.  One of my photos said 89mm for focal length.  That is 595mm (which is about the focal length I was using) divided by 6.6...

So, that must be what it is. The focal length shown in the EXIF data is the digital equivalent.  

Cool.

Now I understand it.  At least I think.  

Now, back to the other part of my question ... is 35mm "normal"?

[rhinorick]

Sorry, I was typing my reply before I saw your reply Mike.    So 35mm is "normal".  Thanks.

Yes, I understand the "range" thing for "X".  I think it is very misleading to consumers.

A 25mm - 300mm lens does indeed have a range of 12.  But it does not have a zoom power/magnification factor of 12.  And when the average consumer sees "12x", they expect 12x magnification.  

I hope they come to digicamhelp first and find out the difference.  

Thanks again Mike and Gail.

[ShutterbugGail]

 I emailed one photo magazine that compared digital cameras and told them they should have explained that.

I'd be interested in hearing their response!

[ShutterbugGail]

Sorry, I was typing my reply before I saw your reply Mike.    So 35mm is "normal".  

No. A "NORMAL" lens is considered 50mm in 35mm terms:

http://www.digicamhelp.com/learn/glossary/normal-lens.php

I realize it's somewhat difficult for all of us to get our heads wrapped around, but the difficulty in getting consistent numbers with digital cameras is because of varying sensor size and resolution.

Personally, I don't pay that much attention to focal length; I just see which zoom range best frames a shot.

[ShutterbugGail]

This dpreview thread will show you how complicated this subject is:

http://forums.dpreview.com/forums/readflat.asp?forum=1002&message=23340655&changemode=1

Personally, I don't really think about it.

[rhinorick]

Thanks for the links Gail.

I agree it is complicated.  I usually don't consider it either.  And I certainly don't think about it when taking a shot.  

It was just now that I am paying more attention to the EXIF data, in posting photos, learning which settings are working best for me, etc., I noticed the focal length there was not jiving with the settings I was using.

I had forgotten about the digital conversion.  

(that 50mm "norm" does not coincide with what Canon and Panasonic say, maybe because of sensor size ... but there again, it doesn't matter - the ads are still misleading and misrepresenting the products   )  So maybe this thread can help advise some consumers to be aware.

[Mike54]

 

No. A "NORMAL" lens is considered 50mm in 35mm terms

Quite right. My bad, I knew that.:-/ It's just been so long since I've thought in "35MM terms".

[rhinorick]

Ok, I did some further checking because I knew Gail would know and that the info I got was either wrong or I misunderstood.

And now Mike has also confirmed my suspicion.

I found several sources that claim 50mm (actually 43mm) as normal.

Here is a great explanation HERE. (still tmi there   )

Thanks again Gail and Mike.

Makes me sad to now know that the FZ50 was also misrepresented.

But I am pleased as I can be with its zoom range, which is more than most other "compact" digitals, so I can't complain.