confusion over focal length of lenses

I personally have no problems with the traditional means of relating the field-of-view (FOV) or angle-of-view of a lens back to an equivalent focal length lens on a 35mm film frame. It has effectively become a base unit relative to the most widely used photographic format of the last century. Just as base units of mass, force, etc relate back to a measurement which may no longer mean anything to us, the same will most likely happen with lens classification as 35mm film becomes a distant memory.

 

Barrie

Thanks for the posting - there are always quite a few postings all over the internet on this subject

I wouldn't get too concerned the debate will go on forever


Cheers

 

I'll have to agree with Ray here, Barrie. Your classification just seems too complicated to me (I know it's not, that's why I typed "seems"). Since I am so used to the 35mm system, it must by now be a part of my DNA, so a 35mm-equivalent FOV makes perfect sense to me without even having to think about it. Considering how many people use that convention, I'd hazard a guess that I am not alone! :smile:

 

I understand the 35mm film frame and therefore what to expect from particular focal lengths on that system. It's only natural that I will double the focal length in my head on a 4/3 mount to understand how much I'm going to get in the shot.

 

I think we should stop comparing everything to 35mm and accept that this is a micro four thirds forum.

Personally, I'm unfamiliar with 35mm fields of view for given focal lengths. What really gets on my wick is when people start throwing in 35mm focal lengths (occasionally with the unqualified adjective "equivalent") without explaining why.

My previous camera has a zoom lens that goes from 6.1 to 61mm, and that's recorded in its EXIF data. If I were to start converting all my focal lengths to whatever gave the same field on that, others would feel much as I do when they start doing so with 35mm.

Grebeman: Rather than going with the diagonal, I'd rather just go with the horizontal. Then I can estimate the calculated field angle against the floor plane.

 

35mm has been around since the 1930's... You can't just expect that to change overnight. Besides... in the last 10-15 years, how many different sizes of sensors have been produced/sold. Measuring different formats against a well known "yardstick" makes it easier for all sorts of people to have discussions while staying on the same page. I have no doubt similar type of discussions were held when 135 started to overtake Medium Format in popularity.

Somewhat related...

The U.S. has been using the english system and has yet to move to the metric system for the same reason. Heck, even England has moved on.

 

For folks who have used other formats besides m4/3, the simple 2x FOV relationship to 35mm/FF works fine. To those who haven't used anything besides 4/3 or m4/3, it's irrelevant - they're used to getting whatever they see from their lenses, and no reference point is needed. Having to memorize some giant table of fractional numbers would be overly complicated and unecessary IMO.

Besides, where's all the fuss made over m4/3 and 35mm? The fuss is normally about aperture/DOF comparisons/equivalency), and less about FOV (which is easy to understand).

 

Actually I did the opposite of what Barrie (grebeman) did. I divided the focal length by the diagonal - the reason I did that was so that the larger numbers corresponded to the long lenses. I also prefer it because the number also corresponds to the magnification factor of the lens based on "normal". I did this back in the early '70s before I saw others that were more like Barrie's example. So don't hit me.

Code:

			Lens Equiv	
FOV	FL/Diag	Diag/FL	4/3	35mm
116.2	0.311	3.214	7	14
109.2	0.356	2.813	8	16
102.7	0.400	2.500	9	18
96.7	0.444	2.250	10	20
86.3	0.533	1.875	12	24
77.6	0.622	1.607	14	28
67	0.756	1.324	17	34
58.7	0.889	1.125	20	40
53.1	1.000	1.000	22.5	45
48.5	1.111	0.900	25	50
25.4	2.222	0.450	50	100
12.8	4.444	0.225	100	200
6.4	8.889	0.113	200	400
4.3	13.333	0.075	300	600
3.2	17.778	0.056	400	800

I always started from "normal" for whatever format I was using and then went from there.

As for those who complain we are not using the metric system - we are using millimeters to refer to lenses, not inches. What more do you want?

Edit: Here is the link to my spreadsheet I created this morning if anybody is interested. Haven't done arctangent functions in years!

http://www.narnian.net/photos/FOV-Table.xlsx

 

All I'm saying is that (micro) four thirds should be that yardstick, on this forum.

 

and some people may just prefer to use 35mm as their yardstick (or their 0.9144metrestick perhaps) ... I'm not quite sure where the "should" comes into it on an open forum ?

 

Like it or not, 35mm became the dominant film standard in the mid-late 20th century and that status was confirmed in the digital age when "full-frame" was used to describe DSLRs with an equivalent size sensor. As others have pointed out, there are far more sensor sizes now than there were film sizes (in common usage, anyway), so it is handy to have a single, normalizing standard. The obvious choice is 35mm/full-frame.

It doesn't mean that everyone needs to think that way, especially on a forum dedicated to one particular format. However, realize that not everyone here is experienced in or wholly dedicated to :43:, so using that 35mm standard can help ensure that we're all on the same page. If you have a gut feel for what a 17mm or 140mm lens gives you in :43:, then just ignore the "(34mm or 280mm equivalent)" that is invariably placed after it.

I do like the idea Narnian presented about using focal length divided by sensor diagonal so that longer lenses have a higher measure (loosely giving a magnification feel to it), but others might prefer the inverse, so that wider AOV lenses have a larger number. Either way, though, many people don't want to have to think about diving by the actual sensor diagonal or lens FL in the course of a conversation to figure out if a lens is wide or not. Like many here, if you tell me that you have a 24mm lens, I have a very instinctive feel for how that will work on a 35mm/FF camera; I have to tell myself it's a 48mm equivalent when on a :43: camera. Those coming into photography and :43: at the same time won't have such problems. As such, the "24mm (48mm equiv.)" description works because it helps both groups. I look at the equivalent focal length, while the other group looks at the actual focal length.

 

This is why I really don't understand all the fuss. We should just accept each others views