The Focal Length Multiplier Confusion

[denizenx]

LOL jialat man

PLANE - totally not related, it's just a slice from the image circle.
i.e. if u use small CCD in medium format the FLM will be damn big, BUT the image looks like a crop from a MF film. if u use the same CCD in DSLR, it will look like a croap from a 35mm film.

1. the 35mm lens makes a PICTURE from the SCENERY,
2. the complete PICTURE is stored as IMAGE CIRCLE.
3. the FRAME/PLANE takes a CROP. 35mm takes a BIG CROP, DSLR takes a SMALL CROP.

repeat for medium format...

 

[denizenx]

the important point must be that the LENS used for two diff sensors (film or ccd) MUST BE THE SAME.

sigh. repeat:

1. the 645 lens makes a PICTURE from the SCENERY,
2. the complete PICTURE is stored as IMAGE CIRCLE.
3. the FRAME/PLANE takes a CROP. 645 film takes a BIG CROP, DSLR CCD takes a DAMN SMALL CROP.

how, can?
try drawing all the light beams like doing physics lab.
think the canon glossary's DoF diagram is very good...

 

[Kho King]

Originally posted by denizenx

3. the FRAME/PLANE takes a CROP. 35mm takes a BIG CROP, DSLR takes a SMALL CROP.

Yup, this one I know...so if I take another crop of 35mm in photoshop after digitizing the image, it should be the same as the crop done in DSLR, right?! :rbounce:

Forget about medium format...let's not make it more confusing...

 

[Larry]

i'm developing a headache trying to follow this thread and the various explanations and definitions...

 

[StreetShooter]

OK Can't be bothered to read the whole thread, but just jump right in. Otherwise how to start an argument? :devil:

Compare a medium format 80mm f2.8 picture with one taken by a 35mm camera using say 85mm f2.8 lens. Then compare this again to one taken by a P&S digicam at 80mm (in 35mm equivalent).

You can see immediately that the medium format one has almost zero DOF (making for very nice effect), while the P&S digicam one will have almost everything in focus (making it look cheap).

Not sure how that helps, but hey, always happy to add to the confusion.

 

[ckiang]

Originally posted by Kho King


CK, I understand 35mm is not a crop of medium format...as they both using different lenses (lens behave differently) and the distance between lens to film ratio are different...and many other differences that I am not sure of. I don't know much about medium format...so let's discuss more on 35mm.

CK...sincerely...tell me how can DOF change when the CCD size is 1.5x of 35mm as compare to full frame 35mm CCD...I really can't see how...:dunno: (assume every other things remain the same...lens, camera...etc.)

That is the part which confuses most people (myself included). Replace "1.5x FLM DSLR" with "APS", see if it make more sense? That 1.5x is not quite a crop, tho it might appear to be. It's like using a totally different system (e.g. APS), and the lens thus appears to be different as well.

Regards
CK

 

[Kho King]

StreetShooter, u r not helping to clear up the cloud...

I understand the differences in your example...but that's TOTALLY different than using a SAME camera, SAME lens, SAME subject...but just different CCD SIZE! :rbounce:

I need break...continue later... :what:

 

[ckiang]

Originally posted by StreetShooter
OK Can't be bothered to read the whole thread, but just jump right in. Otherwise how to start an argument? :devil:

Compare a medium format 80mm f2.8 picture with one taken by a 35mm camera using say 85mm f2.8 lens. Then compare this again to one taken by a P&S digicam at 80mm (in 35mm equivalent).

You can see immediately that the medium format one has almost zero DOF (making for very nice effect), while the P&S digicam one will have almost everything in focus (making it look cheap).

Not sure how that helps, but hey, always happy to add to the confusion.

Let's not bring in consumer DCs as well, it's already confusing enough!

Back to your analogy.
80mm on a Medium Format is roughly equivalent to 40-50mm on a 35mm system.

80mm on a 35mm system is well, 80mm.

80mm on a DSLR with that 1.5x FLM has the effect of being a 120mm.

80mm (REAL) on a consumer DC probably has something like the equivalent of 400mm.

All are different systems. I believe the confusion comes because we are trying to compare the DSLR and 35mm full frame as the same, and trying to relate to each other.

Regards
CK

 

[ckiang]

Split the FLM discussions onto a new thread.

Regards
CK

 

[Larry]

Originally posted by ckiang
Split the FLM discussions onto a new thread.

Regards
CK

i was just about to suggest that...

 

[denizenx]

Originally posted by Kho King


Yup, this one I know...so if I take another crop of 35mm in photoshop after digitizing the image, it should be the same as the crop done in DSLR, right?! :rbounce:

Forget about medium format...let's not make it more confusing...

yes.

no, it applies for MF as well. ONLY if the CCD was mounted in the MF camera!

 

[denizenx]

Originally posted by Larry
i was just about to suggest that...

lol no wonder I felt like marty mac fly when i hit POST...

 

[denizenx]

Originally posted by ckiang


Let's not bring in consumer DCs as well, it's already confusing enough!

Back to your analogy.
80mm on a Medium Format is roughly equivalent to 40-50mm on a 35mm system.

80mm on a 35mm system is well, 80mm.

80mm on a DSLR with that 1.5x FLM has the effect of being a 120mm.

80mm (REAL) on a consumer DC probably has something like the equivalent of 400mm.

All are different systems. I believe the confusion comes because we are trying to compare the DSLR and 35mm full frame as the same, and trying to relate to each other.

Regards
CK

woohoo... I am only confused cos I dunno how is focal length related to the real world... i.e. 50mm equiv on ALL types shoot the same FOV at the same spot? ignoring DOF/perspective/FLMs
just frame sizes made for the camera...

 

[denizenx]

Originally posted by Darren
Darren drops a 10-Kiloton H-Bomb on Red Dawn's fully-protected, visored head .... *kaboom* .... thereby pulverising and obliterating Red Dawn from the face of the Earth. Inexplicably, even with the huge blast and in the midst of the 2km deep crater and ravaged countryside, and in contrary to all known laws of physics and logic, a dented and scarred Leica lens cap sit forlornly in the centre of the blast site which signifies the last known location of Red Dawn ... ... ...

:rbounce: :rbounce:

:devil:

haha another marty mac fly...
so the red dot symbolises the rising sun?

 

[denizenx]

all give up liao?

 

[Darren]

ok ok got to jump in here to clear up some confusion on the FOV, FLM ....

Take this scenario:-

If you compare a picture taken from the same spot, using a 50mm lens set at f/5.6 busing a normal film SLR and a DSLR, and on the same subject, you will find that the image taken with the DSLR to have the SAME DOF as the image taken with the film SLR.

The image from the DSLR will appear bigger as it will have been "magnified" to print at 4R, but if you then enlarge the film SLR image to an equivalent "magnified" dimension (6R) then cut it down to 4R size, the resulting image will be EXACTLY the same as the DSLR.

I can see that this will take some convincing - my weekend project will be to burn some film and nuke some electrons and come up with the "Definitive Guide to DSLR Myths and Misconceptions about FOV/DOF and Why Having a Bigger CCD isn't better than a Smaller CCD because its not the Size that Matters, its how u use it, dummy!"

 

[denizenx]

Originally posted by Darren
ok ok got to jump in here to clear up some confusion on the FOV, FLM ....

Take this scenario:-

If you compare a picture taken from the same spot, using a 50mm lens set at f/5.6 busing a normal film SLR and a DSLR, and on the same subject, you will find that the image taken with the DSLR to have the SAME DOF as the image taken with the film SLR.

The image from the DSLR will appear bigger as it will have been "magnified" to print at 4R, but if you then enlarge the film SLR image to an equivalent "magnified" dimension (6R) then cut it down to 4R size, the resulting image will be EXACTLY the same as the DSLR.

I can see that this will take some convincing - my weekend project will be to burn some film and nuke some electrons and come up with the "Definitive Guide to DSLR Myths and Misconceptions about FOV/DOF and Why Having a Bigger CCD isn't better than a Smaller CCD because its not the Size that Matters, its how u use it, dummy!"

amen! hallelujah! sorry KK...

I think it got worse when we brought DOF and the other cameras in... but each case is the same per camera system...

 

[ckiang]

Originally posted by Darren
ok ok got to jump in here to clear up some confusion on the FOV, FLM ....

Take this scenario:-

If you compare a picture taken from the same spot, using a 50mm lens set at f/5.6 busing a normal film SLR and a DSLR, and on the same subject, you will find that the image taken with the DSLR to have the SAME DOF as the image taken with the film SLR.

The image from the DSLR will appear bigger as it will have been "magnified" to print at 4R, but if you then enlarge the film SLR image to an equivalent "magnified" dimension (6R) then cut it down to 4R size, the resulting image will be EXACTLY the same as the DSLR.

I can see that this will take some convincing - my weekend project will be to burn some film and nuke some electrons and come up with the "Definitive Guide to DSLR Myths and Misconceptions about FOV/DOF and Why Having a Bigger CCD isn't better than a Smaller CCD because its not the Size that Matters, its how u use it, dummy!"

That was what I thought initially.

But it appears that assuming the same subject distance, the 50mm lens on a DSLR with 1.5x FLM will have the DoF of a 75mm lens, not a 50mm lens.

Regards
CK

 

[denizenx]

Originally posted by ckiang


That was what I thought initially.

But it appears that assuming the same subject distance, the 50mm lens on a DSLR with 1.5x FLM will have the DoF of a 75mm lens, not a 50mm lens.

Regards
CK

it shouldn't be... only the FOV changes...
where is ur source of this info?

 

[Darren]

Originally posted by ckiang
But it appears that assuming the same subject distance, the 50mm lens on a DSLR with 1.5x FLM will have the DoF of a 75mm lens, not a 50mm lens.

denizenx is right, the DOF does not change, only the FOV.