Photo-a-day

[brammers]

Actually, let's put it a different way and go to extremes. Which sounds better to you - that I want to buy a Panasonic Lumix DMC-TZ6 because it's got a 4.1-49.2mm zoom? Or because it's got a 25-300mm equivalent zoom?

That's all we do when we quote equivalent focal lengths - we take into account the sensor crop. We're not pretending anything is magnifying anything - it's just waaaaaaaaaaaaaaaaaaaaaaaaaaaay simpler for everyone.

[mmh]

We know this mmh - it's just that the only 'correct' way to represent the view of a lens across formats is FoV measured in degrees.

I know that a 100mm lens, compared to how it would look on the established 35mm film standard, will look the same on my a900, but will look like a 160mm lens on 35mm on Bobster's 30D, a 150mm lens on my old 7D and a 200mm lens on an Olympus.

Could you give me the angle of view in degrees for all of those combinations without looking them up? I haven't got a clue. Hence the use of the 35mm standard for field of view. We use the word 'equivalent' because other things are not the same.

I think thats the point... its still 600mm.... its an equivalent to a full frame, but ur still shooting at 600mm... so why post with the "equivalent" as the focal length.... people that know that you have a cropped sensor and you tell them you did 960mm... they might think... oh, i wonder what he used and multpily it by 1.6 to find out what he used... that'd be nuts...

post what you used not the equivalent :/ post equivalent if you want, but dont make it the primary unit, because its not what was used :/

I couldnt work out any of the angles at all if im honest, i dont even have any idea what they mean...

[brammers]

I think thats the point... its still 600mm.... its an equivalent to a full frame, but ur still shooting at 600mm... so why post with the "equivalent" as the focal length.... people that know that you have a cropped sensor and you tell them you did 960mm... they might think... oh, i wonder what he used and multpily it by 1.6 to find out what he used... that'd be nuts...

I've just answered that in the point above. So you know that Bobster's camera has a 1.6x crop factor. But did you know the crop factor of the Panasonic above? So should people using one of those say that they took their shots at 7.2mm? What would you think if I told you that I just LOVED using 15mm on my old Minolta A2, by far my favourite focal length. My grandma's best friend just bought a new camera with 15mm of zoom - isn't that amazing! Personally, I can't understand why people aren't just satisfied with a 35mm f2 and a roll of Ilford XP2 - in my Mamiya 645...

That's why we use equivalents - waaaaaaaaay too many formats out there to cover them all and posting 'I took this with a 15mm zoom (8x crop factor)' is just tiresome. 35mm equivalent rocks.

Don't worry about the FoVs - I haven't got a clue either. I used an online calculator to look them up in the example above.

[brammers]

Oh - and when I said 'other things are not the same' I was primarily referring to the DoF changing between formats at the same focal length, as well as the nature of the infocus/OoF transition.

[mmh]

I've just answered that in the point above. So you know that Bobster's camera has a 1.6x crop factor. But did you know the crop factor of the Panasonic above? So should people using one of those say that they took their shots at 7.2mm? What would you think if I told you that I just LOVED using 15mm on my old Minolta A2, by far my favourite focal length. My grandma's best friend just bought a new camera with 15mm of zoom - isn't that amazing! Personally, I can't understand why people aren't just satisfied with a 35mm f2 and a roll of Ilford XP2 - in my Mamiya 645...

That's why we use equivalents - waaaaaaaaay too many formats out there to cover them all and posting 'I took this with a 15mm zoom (8x crop factor)' is just tiresome. 35mm equivalent rocks.

Don't worry about the FoVs - I haven't got a clue either. I used an online calculator to look them up in the example above.

haha, yeah i hadnt thought about that above, and i was typing whilst you posted it...

dunno, maybe its just in my mind, but compacts are totally different... its not like you will take a pictrue of the moon quoting the focal length on a compact anyways... you might take a good picture of the moon on one, but anyone who knows enough about cameras to show the focal length probably isnt going to be too fond on the picture quality that comes with them...

I think on DSLRs its something more useful...

I guess ur right tho... i dunno... just a gripe of mine, I'd rather see what focal length was used rather than the equivalent focal length.... but not so much on compacts... haha... im just weird i guess

[Bobster]

its not magnifying anything... its just not capturing as much as a full frame :/

this isnt beef with you, its beef with the way photographers in general look at cropped sensors...

its not magnifying anything more... if you put the same lens on a full frame camera, you will see the same, just more around the image aswell...

in order to capture the same amount of image as a 1.6 crop camera with a 600mm lens, you need to have a 960mm on a full frame.. (of equivalent megapixels), do you not? so thats not seeing the same is it?

[Blastuk]

nice shot bob, was that your only shot or were there blurred attempts?

[mmh]

in order to capture the same amount of image as a 1.6 crop camera with a 600mm lens, you need to have a 960mm on a full frame.. (of equivalent megapixels), do you not? so thats not seeing the same is it?

but you'll get a different DoF if you use a 960mm on full frame...

its still hypothetical... why do we need to know what it "could" be on a full frame, when its not shot on a full frame?

[Bobster]

nice shot bob, was that your only shot or were there blurred attempts?

i shoot a burst of 3 shots, the other 2 werent quite as sharp..

---
the 1.6 crop shot


this is the same shot, using the same setup (600mm) as seen with a full frame 8.2 mega pixel camera..


oh look its smaller

you'll have to enlarge it by 1.6x more to get the same size..

without getting into the mathematics of everything about FoV etc, its so much easier to multiply by 1.6, and it happens in camera as well

[mmh]

i shoot a burst of 3 shots, the other 2 werent quite as sharp..

---
the 1.6 crop shot


this is the same shot, using the same setup (600mm) as seen with a full frame 8.2 mega pixel camera..


oh look its smaller

So did you crop the original picture?

as its "bigger"...

why didnt you take into account your post processing cropping when you post the focal length?

coz for it to be taken on a full frame camera then you'd need a bit more than 960mm focal length

[Whiternoise]

FoV makes more sense than focal length!

And surely manual focus isn't much of an issue if you're shooting at those kinds of distances (i.e. the moon) - it's going to be on infinity anyway

[Bobster]

So did you crop the original picture?

as its "bigger"...

why didnt you take into account your post processing cropping when you post the focal length?

coz for it to be taken on a full frame camera then you'd need a bit more than 960mm focal length

i don't have a full frame camera, so i shrunk the image to scale from my 1.6 crop to FF..

FoV makes more sense than focal length!

And surely manual focus isn't much of an issue if you're shooting at those kinds of distances (i.e. the moon) - it's going to be on infinity anyway

ok, go set your longest lens on infinity without looking through the view finder, point it at something distant and see how in focus it actually is

and without looking up anything can you tell me the FoV of 122mm from the top of your head?

[mmh]

i don't have a full frame camera, so i shrunk the image to scale from my 1.6 crop to FF..

Therein is my point...

the original picture you showed was a crop of a shot taken on a 1.6x cropped sensor with 600mm on the front of it... you took the hardware crop into consideraton, but not the post processing crop... why not? why the difference?

if the original is the one u used for FF image example, and you cropped that to 1.6x crop for your original photo in this thread... then it would be 600mm x 1.6(hardware crop) x 1.6(post processing crop) = 1536mm equivalent if you want your initial shot on a full frame camera with no cropping...

but wait, youve lost sensor size if you want to direct compare...

what was a 8.2mp camera has become 5.125mp camera... because you cropped in post....

so you would need a 1536mm focal length on a 5.125mp full frame camera to get the same picture...

see my point? why bother using equivalents? why not just say, i took this on 600mm lense on an APS-c camera... let the person at the other end worry about equivalents if they want to...

it just sounds like you were trying to impress people saying i shot this at "960mm hand held (with no IS )"... doesnt do it for me im afraid...

[Whiternoise]

Tsch, it's not my fault lens manufacturers can't design lenses so that when you swing the focus to infinity - i've never understood that. Why not just make the focus wheel screw a little less so that it's actually on infinity, not a fraction past.

I was saying that over one or the other, field of view is more relevant than focal length. Focal length makes sense when you have lenses on an optical rail and you're working out lens parameters, but in the real world it's just a property of a lens (or a series of optical elements that we call a single lens). Could you tell me what focal length i should use so that some object that occupies 5" of my FoV will fill the frame? In astronomy, field of view is much more useful than focal length. You'd say you want to observe 0.1 square degrees (or minutes, seconds etc of arc as necessary). Saying "we'll need a lens with a focal length of 4m isn't that handy!

I.E that if ALL lenses were sold with FoV instead of focal length it would be easier. We're all used to focal length, so we're comfortable - and i bet if i asked you to pick the focal length that would give me 10 square degrees of view you wouldn't be able to tell me either - it's simply a matter of convention. If we used FoV, it could be commonplace to say "i'd like to buy a lens that will zoom in to 20 degrees " or a wide angle say 240degs - though it would be more proper to use radians.

edit:

Oh, and due to various small angle approximations, alpha = distance/focal length where alpha is the angle of view and d is the sensor size so - say 36mm. Thus, 36/122 is about 1/3 in rads which is 18 degrees ish. Granted i had to look it up, but easily done in my head remembering a=d/f

[Blastuk]

though not used in practice, the angle of view is usually listed in the product specifications..

and the infinity focus thing is a leeway for temperature variations afaik

[brammers]

I.E that if ALL lenses were sold with FoV instead of focal length it would be easier. We're all used to focal length, so we're comfortable - and i bet if i asked you to pick the focal length that would give me 10 square degrees of view you wouldn't be able to tell me either - it's simply a matter of convention. If we used FoV, it could be commonplace to say "i'd like to buy a lens that will zoom in to 20 degrees " or a wide angle say 240degs - though it would be more proper to use radians.

That wouldn't work at all. FoV is a property of focal length and sensor size - NOT a property of the lens - it changes if you change the lens or the sensor. Put a 35mm lens on an APS-C sensor and you get one FoV, put it on a FF sensor and you get a wider one, put it on 645 and you get one that's wider still. You'd have to go in and say 'excuse me sir, I'd like a lens that results in a FoV of 30degrees when combined with an imager with a diagonal of 5.6mm' or whatever.

FoV only works as a result - the resulting angle of view is the same no matter what combination of lenses and crop factors you put behind it. Guess what else works like this? Equivalent focal length...