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DPChallenge Forums >> Web Site Suggestions >> Focal Length ?
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 12/19/2006 11:02:29 AM · #1
A check box similar to the ones for aperture, ISO, and shutter speed might be helpful, esp for the P&S owners, in helping to decide which lenses that they may want to purchase later, as they improve their equipment. I always try to post the lens focal length from the exif file with each capture, in the comments box for that reason.
12/19/2006 11:18:31 AM · #2
It would be easier if cameras reported that info more straightforwardly; mine gives a reading like this:

Focal length - 600 - 7200 mm (100 mm)

If anyone wants to translate Canonspeak into English, be my guest : )

Also, do you want people to list the actual focal length or the 35mm equivalent?
 12/21/2006 12:16:04 AM · #3
Thank you for the observation, GeneralE.
I shoot with a Fuji S3 Pro most of the time with the med sized 12meg sensor, and the exif file reports the actual focal length of the lens at the time of capture, so it's handy for me to post in the photogs comments box. I understand that with different size sensors, that the cameras will have different angle of view with the same focal length lens.
This would likely confuse the heck out of most folks who aren't too deeply involved in the mechanics of photography, so maybe it's not such a good idea after all.
Even referenced to 35mm it would still be somewhat confusing for those who don't use a DSLR.
Confusion Abounds.


12/21/2006 01:27:53 AM · #4
Also, depending on your camera, some hardware can report what it receives as the focal length, but doesn't take into account the sensor's multiplication factor.

My camera has a multiplication factor of 1.5, so it reports 300mm on my longest lens, but in actuality, it is 450mm (when expressed in a 35mm film context).

I use the free Opanda's IEXIF viewer to see the detailed information on my photos and it show both the "Focal Length" and the "Focal Length in 35mm Film", with the difference being the multiplication factor of your sensor.
 12/21/2006 01:34:18 AM · #5
my camera reports the actual focal length, not the numbers in 35mm equivalent. Actually I'd rather it shows the 35mm equivalent coz I'm lazy to do the maths, lol

actually, I think this suggestion may be useful.
 12/21/2006 01:34:45 AM · #6
A value for focal length isn't really useful unless you know that the image you are looking at hasn't been cropped.
 12/21/2006 01:41:47 AM · #7
Originally posted by jmsetzler:
A value for focal length isn't really useful unless you know that the image you are looking at hasn't been cropped.


Nor is it really useful unless you know things like distance to subject , distance to background, etc. It's really not a useful stat without some sort of context to place it in.
 12/21/2006 01:47:18 AM · #8
I think it would be useful for people trying shots for the time. It would give them a starting place. Say for instance someone wanting to take some lightning shots.
 12/21/2006 01:56:03 AM · #9
Originally posted by NstiG8tr:
I think it would be useful for people trying shots for the time. It would give them a starting place. Say for instance someone wanting to take some lightning shots.


or a shot of the moon - I'm always curious to the focal length used, regardless of the cropping done.
 12/21/2006 02:16:13 AM · #10
Originally posted by crayon:
or a shot of the moon - I'm always curious to the focal length used, regardless of the cropping done.


For the following moon shot, I used a 300mm lens (or on my camera, 450mm). However, I did crop it just a bit--just for composition and "rule of thirds" :-)



Message edited by author 2006-12-21 02:20:18.
 12/21/2006 02:19:28 AM · #11
use opanda iexif viewer. its great and tellsyou both focal lengths
 12/21/2006 09:48:04 AM · #12
Maybe someday, focal length will be assigned a number, similar to an ISO or EV number, in order to compare apples to apples when discussing it.
Now we have several ways of expressing it, so now even a new standard would be confusing for a while.
12/21/2006 09:54:53 AM · #13
Originally posted by MelonMusketeer:
Maybe someday, focal length will be assigned a number, similar to an ISO or EV number, in order to compare apples to apples when discussing it.
Now we have several ways of expressing it, so now even a new standard would be confusing for a while.


How would one express such a measurement? I'm not sure a "standard" could work.

For example, 3x zoom on a digital P&S isn't going to give the same DoF as a 150mm lens on a full-frame sensor, although it would fill the frame the same.

Message edited by author 2006-12-21 09:56:32.
 12/21/2006 10:06:32 AM · #14
Posting the focal length is a good idea, but it's really of somewhat limited use. Even within the DSLR world, a focal length of 100mm might mean an angle of view of 20° (35mm sensor) or 13° (APS-C) or even 10° (2.0x crop cams). Add to that the fact that we don't know what was cropped, and we see that knowing only the focal length tells us little about the final work. If we knew the camera focal length and aperture, that's far more useful, especially if the photographer includes information on cropping.
 12/21/2006 10:22:55 AM · #15
i agree that the info has limitations ... but i still wish is were present.
 12/22/2006 11:35:16 PM · #16
Too bad the exif files don't convert focal length to "angle of view". That would seem to be a more universal numbering system with the several different size sensors now in use.

Lesg, 300mm is good for the moon, 300 and a 2X extender works just about right if the lenses work well when paired up. Shoot both ways, then compare if you have a Tconverter. Maybe there is a tutorial about it. Do a search in "tips".
12/23/2006 07:59:47 PM · #17
Personally, I think focal length should be reported as is, not converted to 35mm equivalent.

Medium and large format shooters have never felt the need to convert their focal lengths to 35mm equivalent, why should we need to do that for digital capture? I thought the important thing about focal length is not how it affects the crop, but how it affects the relationship between items within the frame at different distances from the camera.
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