So everybody knows about the 1.6 and 1.3 crop for smaller censors.

What I'm proposing is that the focal length doesn't actually change so you quite clearly are not brought closer to your subject. And your image is not actually cropped as per say but this is the best way to explain it really.

This is really what I think, your angle of view thru the lens is actually less. So if 35mm is supposed to give you a view of 90 deg on a full frame, on an APS is is reduced to 60 deg. Hence the feeling of wanting to say its a 58mm.

I just feel it's wrong to call it a different focal length when your subject is not actually in all realist brought closer to the frame but it is simply 'viewed less'...

What do you think?

PeeWee, I have a 30mm lens I use to get about a 50mm crop through my viewfinder, actually a 45mm crop with the 1.5 Nikon sensor.  I have a 50mm that gives me a 75mm crop view.

But, you are correct.   The 50mm is not giving me the magnification of a 75mm..the view is still the same size, that is, a person in the 50mm will be the same size as  person in a 50mm on a 35mm camera..but the width and height of the frame will be smaller for the digital, larger for the 35mm.  I have not gained a thing in focal length, only gotten a smaller image overall to the eye.

The 30mm looks  close to the same frame size to the eye as a 50mm on 35mm but the objects in the view are smaller, as this is really a 30mm lens and I get the 30mm size of things in the view, not more.

I agree.  And, I agree this subject gets quite confusing and the more we directly compare 35 and less than full frame digital the more confusing it can become..it is sort of an apples or oranges sort of comparison.

Just for fun and knowledge I will throw in another bit of info.  We see compact digitals advertised as having perhaps a "10X" zoom.    In binocular speak, 10x is 10 power or a magnification of 10.  What about this 10X zoom?   It might very well mean the camera lens will zoom from lets say 18mm to 180mm..wow, a 10x zoom!  

50mm is considered 1:1 magnification wise.  A 100mm is 2x in magnification or binocular terms.   A 10X magnification will take 50mm x 10 or a 500mm lens.  The 180mm on the compact with the 10x zoom is getting 180mm/50mm = 3.6 magnification.  That is 3.6X in binocular terms, far from a real 10X magnification.

Yikes, I have not been out of bed long enough to do this sort of post...Tom.

If what I have said is incorrect and it is me who is confused, someone please correct me..thanks.

Yeah people get fooled into buying compacts on the zoom and MP size, were as they would get a far better buy by doing a bit of research before hand.

You're basically right, but does it really matter?  How much difference is there between taking a picture with a 30mm and 1.5 cropfactor  or a 45mm at full frame from the same spot?

So your focal length doesn't actually change., that's correct. But you do get the same picture. Aside from maybe a small difference in DOF perhaps?

Haha...
Let's look at it another way...

let's say you can write 200 words on a stamp with a 1mm pen. But suddenly they decide to reduce the size of the stamp with 50%, so if you continue using the 1mm pen, you can only write 100 words on the new stamps...
Wouldn't it be fair to say that, assuming that the new smaller stamps have become the new standard, if you start using a 0.5mm pen, you can double the amount of words on the new stamps..?
It all depends how you look at it. Of course the 200 words written with the 0.5mm pen will be smaller than with the 1mm pen, but the amount of information will be the same.

Or is this just more confusing..? ;o)
Maybe I have been too long out of bed already to do this sort of post...

Hehe - ok, i managed not to get confused... do i get a cookie? (i did have to re-read some parts tho...)

Interesting to think of it - rather than just accepting the "crop factor" thingey.  I think the only problem is when you are using wide angles as the size of the subject / perspective difference between focal lengths is a lot greater than when you use telephoto's.  I would assume that the difference is sooo small that you can safely use say a 200mm lens on a 1.6x crop to get what you might expect to see using the FF version of that lens (320mm?), but not in the ranges where changes in wide angle focal lengths make a huge difference in terms of size of subject relative to background / perspective.

Did that make sense? Do you even agree?... i am just making an educated guess at things here...

Actually your perspective doesn't change. You can't magically see something with a wide angle lens that you don't see with a telephoto, not counting the stuff that just falls out of frame.

Consider this setup (setup in 3D Studio with a camera and focal lengths):

The box at the bottom is the camera

Now this picture is taken using a 85mm lens
This one is made using a 24mm lens:

Now if I upscale that to match the size of the 85mm shot:

You see they're are exactly the same. Light doesn't not bend around corners just because you change your lens. Using a wideangle lens just lets you put more into the frame.

I used to be concerned a bit about all of this but no more.  I simply use what I have and take my shots with that..composing the image in the frame I have to work with.   

What does concern me a bit is the way some advertisers do play into the game and sometimes mislead possible buyers.   

As far as crop factor is concerned, I see it this way too, an impossible trick to pull off but easy to think about:  Lets say you could make a contact print from a digital sensor, a contact print the exact size of the frame.  Now, make one with the film from a 35mm using the same lens.   The size of objects in the frames should be the same but the digital frame will be smaller, leaving out some info on the edges.

I agree Tom - that's what I don't like about it is the advertisers and the sales people.

I was in  jessops and hears the guys trying to sell a Nikon D40 and a 24mm lens (the more expensive one). While he was at the back I told the guy looking to buy that he should get the 17/18mm lens coz it'll give him more of a view due to the crop factor. He claims the camera was a gift for his daughter (nice bloody gift) and he knew what he was looking for but I could see in his eyes that I had put some doubt into his mind as to whether his lens choice was now right...

Rich - I get what you're saying but I still gotta go on my rebelious path and say that I'm into this new way of things about viewing angles and no longer crop factor. To me it's like a 18mm lens with a smaller front element so you see less... Make sense?
P.S. HERE'S YOUR COOKIE :D It's a Double choc chip one...

Gir - I like your explaination with the pen thing, pretty illistrative way of explaining it, now can I see that stamp with 200 legable words on it please? HEE HEE

Rinze - i wasnt refering to that effect. i was refering to the size of the subject / perspective relative to the framing, not the crop - to get the false 85mm crop there you are probably cropping more than the 1.6x of the sensor.

Get that same setup and take a shot with an 85mm lens, then move the camera closer and take the same shot with a wider angle lens so that on frame the subject is exactly the same size... the background thus changes.   It is that change in perspective i was referring to

Let me think about this out loud. To test my theory in 3DS Max you will have to take 2 shots.  So set up on your screen a measuring marker - side of a window to pull over the "viewfinder" so you can match the object size in the viewfinder when it comes to changing focal distances. Also a simple setup would be a sphere with a chequered background in the distance:

Shot 1 - 10mm so the sphere is a good size - say 50% of the frame.  Then take the result into photoshop and crop it by the 1.6x factor.

Shot 2 - 16mm so the sphere is the same size on screen as the previous shot *make sure you are measuring agains tthe CROPPEd version of that shot - this is where the measuring marker is useful (just resize a notepad window or something). You will obviously have to move the camera to get the same size of sphere in the frame.

Now shot 1 represents the 10mm on a 1.6 crop sensor, the 16mm the "equivalent on a full frame".  The subjects should be the same size on frame, but i am guessing that the chequered background will show a difference of perspective.

You could then try a similar thing with 200mm and 320mm to see what the difference is...

Hope that helps to explain what i was talking about - as it is a very difficult thing to explain i think :)

Thanks for the cookie... hope it is a bendable/soft one - hate the ones that just snap - they suck

Yeah - viewing angle is a good way of seeing it i suppose... I am just used to what 18mm means on a 1.6 crop anyway so i'll get to the problem when i get a FF ;)

You're changing too many variables. The point was if a picture taken with a 45mm on a full frame camera would be different from a 30mm on a 1.5 crop camera. Taken from the same position I would say no.  12mm vs 8mm would be the same too.

The subject size on the sensor itself will differ, but when viewing the images, the subject will be the same because the sensor itself differ in size, thus eliminating the difference.

Did you try what i proposed? as i have a feeling it is exactly what you are saying, but i am talking about the differences in the background, not the subject size. 

Thinking about it, i might be wrong... so could you test it in 3ds max, i'd love to know.  Because if you dont need to move the camera then i am wrong - i just assumed you would need to move the camera to get the same size of subject.  So well done Vera - you confused me after all - making me think about other related things and get confused :)

Allright, here's what I've done:
Same sort of setup, 45mm and a 30mm lens, but now I've rendered both lens views to 720x480 (35mm = 36x24mm so I took 20 pixels per mm) to represent the image the fullsize sensor/film would receive. Then I cropped the 30 to 474x314 (nikon sensor = 23.7 x 15.7). Then I scaled that image up to 720x477 (yes, there's a 3px difference I know it's because of the sensor size) to represent a print or what you'd see through the viewfinder of a nikon dslr.

I think that's basically what you meant. As you can see the fullsize 45mm version and the 30mm with the cropfactor will give you the same object size in your print... and your viewfinder. Here's the images:

I think I get what Rich is getting at with the perspective thing, but just to add to the confusion.... When using my old compact I would often find, especially with landscapes, that the perspective seemed to be stretched and when reviewing the shots objects in the distance would appear smaller in comparision than they would to my eye. The lens is a 10x zoom equivalent to 38-380mm. However on the SLR using the kit 18-55mm  the final shot is very close indeed to what my eye sees.

• Andy

Comparing compacts to SLR's is very tricky because you not only change the sensor size, you also change the lenses and actual focallenghts, lens size. How are you judging the images.. On the camera or on the computer?

To really compare you should take the same picture with both camera's and see the result. I wouldn't be surprised it the 35mm equivalent focallength reported by the compact doesn't match up. That doesn't mean the the basics of scaling stuff doesn't apply, it just means the manufacturer is just misinforming you.

That's all very nice, but when you take a portrait of someone with a wide wide angle depth seems to be exaggerated. When you take the same pic with a teletele, it appears to be flattened.

When, theoretically, you can move enough backwards (beware when you're on the edge of a cliff!) you can cover the same view with that tele as with that wide angle. But it won't be the same shot.
You'll cover that same width and height, but the shot will be completely different.

That's because the telelens isn't the wideangle lens corrected for cropsize ;) The point is that a 30mm on a 1.5 cropsize nikon wil yield the same image as a 45mm on a fullsize sensor taken from the same position. What you're talking about is comparing wideangle vs telephoto lenses which is a whole different subject matter. Taken from the same position, the wideangle and tele will give you the same perspective, but the subject in question will differ very much in size.

The only difference between the 45 and the 30 will arguably be the DOF because that is related to the focal length.

Been dazed and confused for so long it's not true...
that's what the thread is all about, no?
she wants to confuse us, and you all take it seriously.

lol.
you're right

Since I mentioned the fact that I use a 30mm and expect the image to be about the frame of a 45mm ff, considering the 1.5 factor of the Nikon..you are correct.  The frame is what I consider the same here. Sure, the size of the subject within the frame is different than a 45mm would show..the shot is with a 30mm lens.    Anyway, well, err...

Well all I can say is I say that Danny should take his 5D and 20D and use the same lens on it at the same aperture, with no cropping resize each image to 400px wide and then we will see what it's really all about!!! Then on the fullframe take a shot at the supposed 1.6x rate that the APS is supposedly seeing and see if the 'flatness' appears better or worse - which is what Tan is talking about which is what I'm talking about. Honestly I don't think computer graffics will cut it. Plus the camera and object MUST stay at the same positions through out the whole exercise...

Anyone else got a FF and APS censor handy - and can try this?

SO here is the criteria:

Ingrediants:
One FF camera,
One APS camera (1.3, 1.5 or 1.6 is fine)
One lens that fits on both cameras - has to be made for the FF cam
One tape measure
One tripod

Method:
Set up tripod.
Take FF camera, attach lens, fit on tripod. Shoot subject at 24mm while subject is 1m away.
Take APS camera, attach lens, fit on tripod. Shoot subject at 24mm while subject is 1m away.
Take FF camera, attach lens, fit on tripod. Shoot subject at 31mm (for 1.3 APS censor) or 36mm (for 1.5 APS censor) or 38mm (for 1.6 APS censor).

Baking time:
Import photos, resize to 400px width while height is auto adusted.
Upload photos onto this thread.

Result:
One soft bendy cookie for Rich.

Still not conviced by my images :P

Draw an image of a lens facing a sensor or film frame.  Make the sensor larger or smaller, the film larger or smaller.  Make the sensor or film several sizes within the largest.   The lens gives what it does. The frame size accomodates more or less and that is it..essentially.  What comes from the lens is the same.   

When I shoot a 30mm and get a 45mm frame, I get all the problems of the wider angle lens..though with this lens, the problems have not been apparent compared to some other brands.   Enough from me..I repeat myself.        Tom.

Tom, you say exactly what I've shown with my renderings :)

3DGuy, Yeppie, that is correct as far as I can tell.      Tom

PeeWee, here is a little experiment anyone can try if their lens is 50mm or if they have a zoom with focal lenght markings...meaning mostly a DSLR.     

Set the focal length to 50mm.  This is the 1:1 or life size image view in 35mm.  Look through the viewfinder and with the other eye open look at the actual scene.  I will bet the views are the same size.   No magnifiaction and no reduction in image size.   So, my Nikon set at 50mm shows a viewfinder image the same size as my other eye sees...it does not see a magnified view of the 75mm lens.    Sure, the crop will be like from a 75mm but the image size...well, just try this simple experiment.    

I thought my last post was my last on this thread. Alas...had to type a bit more.   I believe lots of the confusion is in how this subject is presented and described.  That can often lead to more confusion.  Simple experiments will show what is really happening, as do the graphics shown here.

Maybe this is all from me on this one...Tom.

Ok, this starting to get quite confusing, lol.  :biggrin:

Maybe this will help?...

en.wikipedia.org/wiki/Crop_factor

Yip that's all it is, is  a crop factor...

What I propose is that it might not be just a crop issue but an angle of view issue too.

Sorry 3D - I'm not convinced at all... Simply because it's generated. Like a scientific exteriment can be thought out, planned and written down when it comes to the physicals of actually doing it, it doesn't always work...

Sounds to me like I can calculate the force I will transfer to your head with a stick moving at 20mph, but you won't believe it until I actually boink you over the head with said stick and you gain a headache

It''s not all that complicated IMHO. The 1st 2 renders show what a fullsize sensor would receive from the scene. Just placing a smaller sensor in that place (i.e. the cropped version) shows what the sensor would receive on the 1.5 cropsize sensor.  I didn't make up the measurements, I looked them up. So yes, the physical size on your sensor will be different. But the end result when viewing/printing the picture will be the same. Sure there is a slight discrepancy because the actual cropfactor isn't 1.5.. it's something like 1.51 or 1.52. depending on what side of the sensor you measure.

Yeah I get what you're saying and it does makes sense. I just like to agree to disagree.

I still wanna see someone do it physically. And I'm sticking by my theory of cropping and angle of view...

:D

I think at 20MPH I would actually be dead not just get a headache :(