Using full frame lens on crop body cameras ?

[Joey]

It is true that what is 'acceptably in focus' will change with enlargement of the final image and the viewing distance but that is a subjective matter.

DOF is entirely subjective. That is why in the definition of DOF the word "acceptably" precedes sharp; acceptable to what?

There are figures for 'acceptable' circle of confusion for various formats

Yes but what does that refer to? As a file on a HDD an image has no DoF, am image does not have an intrinsic DoF value until it is given an output size and viewing distance, these have become normalised but they are the defining factors. The aperture size creates the DoF, the output magnification defines it. The CoC figure is generally an 8"x10" print viewed at 12", which corresponds to any other print viewed at the distance of its diagonal. People with better acuity will always find 'standard' DoF wanting.

Interestingly, and touched on by the Wikipedia article, the difference in the amount of enlargement involved in producing a given image from a crop sensor rather than a full frame and the effect on the acceptable circle of confusion size should mean you get LESS depth of field from a crop camera.

That is exactly what I wrote in my scenario number 2, "The DOF for the crop camera is less than the ff camera." if a comparison is made of that shooting scenario.

As Wikipedia puts it:"The comparative DOFs of two different format sizes depend on the conditions of the comparison. The DOF for the smaller format can be either more than or less than that for the larger format. "

I know, that is why I gave examples of how that can be illustrated, along with the third option, scenario 1, where the DoF can be the same from both formats. As I said, "There are three situations for comparison and you have to decide which method you use because the outcome is different."

So the question can be boiled down to a core element, why does a shorter focal length result in deeper dof? The answer is a shorter focal length results in smaller subject magnification, subject magnification is a core element of DoF, and, for the same exposure value a shorter lens has a smaller physical aperture for the same numerical aperture value, and aperture size is the other core element of DoF.

I reckon we're in agreement then. We owe a debt of gratitude to Tony Northrup for giving us the motivation to engage in debate about these matters. I admit to a little nostalgia for the days when lenses had depth-of-field markings...

 

[BozillaNZ]

The only elements that would be smaller are the small elements nearest the camera. The largest grouping would be the same. on lenses longer than 50 or 60 mm it makes a hardly recognizable difference.

Telephoto yes, wide angle no. Just look at EF 24 2.8 and EF-s 24 2.8. The EF-s one is actually a 38 equivalent FoV one so it's narrower and a lot smaller.

Using a 70-200 on crop would be less wasteful than using a 16-35

 

[Don Haines]

The only elements that would be smaller are the small elements nearest the camera. The largest grouping would be the same. on lenses longer than 50 or 60 mm it makes a hardly recognizable difference.

Telephoto yes, wide angle no. Just look at EF 24 2.8 and EF-s 24 2.8. The EF-s one is actually a 38 equivalent FoV one so it's narrower and a lot smaller.

Using a 70-200 on crop would be less wasteful than using a 16-35

or you could compare it against the EF40 F2.8.....

You can't really compare pancakes against normal lenses... Although Canon's pancakes are very high quality designs, and the performance for the price is stellar, there are sacrifices in IQ compared to regular lens of similar design and materials.... the sharper you bend light, the greater these problems get, particularly the prism effect where you start focusing different colours in different places.

but more to the point, you are correct in saying that for the wider angles, there are size and weight savings with EFS mounts...... but the large elements still remain the same size.

 

[erjlphoto]

From the video I've posted below, it looks as though it's a (big) waste of money to purchase high rent full frame glass

...I wanted the 7D mark II with a Canon EF 70-200mm f/2.8L IS II USM Lens. If what I'm seeing in the video below is correct and I sure would assume so, that this combination is a total waste of money....

Actually, that sounds like a great combination for action/sports or even general use. You will likely have the 70-200 mmii is long after you have replaced the 7D mk ii. The lens will still be awesome if you eventually go FF.

 

[tron]

It's no waste, particularly if you might get a FF body down the road. Glass lasts a long time, bodies change faster. I never used the kit lens on my T2i or purchased any EF-S lenses for it. I purchased L glass to go with it and and kept adding to the collection. The 24-105L was my first L and it got a lot of use. Three years later I purchased a 6D. Some lenses that are soft around the edge might even benefit from a crop sensor ;-)

I later decided to go the M route for my crop sensor and added some EF-M lenses for it. I occasionally mount some L glass on it.

+1 Exactly! I think FF L lenses is the obvious way to go if someone intends to upgrade to FF.

The only thing someone with APS-C camera may have to get in EF-S is 10-22 or 10-18.

 

[tron]

I haven't watched any of his videos and now that I read this thread I do not think I will in the future!