24-85mm 3.5-4.5 vs off-brand 24-70mm 2.8

[fjrabon]

The maximum f-stop for a lens is defined as the focal length of the lens divided by the entrance pupil diameter. The entrance pupil diameter depends upon the design of the lens; for any particular focal length the larger the entrance pupil the faster the lens will be and , generally, the larger the lens elements required which is one of the reasons that fast lenses are usually larger, heavier and more expensive than slower versions.

For a given lens the maximum f-stop remains constant regardless of the format of the camera on which it is mounted - a f2.8 FX lens will still be a f2.8 lens on a DX body and will have the same depth of field characteristics as a f2.8 DX lens of the same focal length. What does change is the angle of view between th DX and FX formats when using lenses of the same focal length.

As far as I can see the one useful part of the Equivalence article is near the middle where there is the comment 'The point of photography is making photos'. The time spent wading through the article would be much better spent putting this into practice - I don't see anything else in the article that would improve your photography.

Well, you're right in some ways, but I think you're missing the point. A given focal length at f/2.8 will have a dramatically smaller DOF on a FX body (and thus full frame sensor) than it will on a DX body (and thus crop frame sensor). Sure, 'equivalence' doesn't change the literal definition of what aperture and f-stop means, but it is a way of figuring out what apertures you need on a crop frame to replicate the DOF of a full frame (and vice versa).

Which bit have i misunderstood? The thread has wandered all over the place since starting as '24-85mm 3.5-4.5 vs off-brand 24-70mm 2.8 - What's your thoughts?' to considering that '17-50mm/2.8 on DX is equivalent 26.5-77.5mm/4.3 on FX. So, the 28-300mm would have larger aperture at all range that the 17-50mm cover. Distortion can be corrected, but sharpness couldn't.'. The Nikon 28-300mm is f3.5-f5.6 and it is this whether or not it is used on a DX or a FX body. The fact that a lens has to be closed down further on a larger format to achieve a given depth of field has no effect on its performance on the smaller format. When either of the lenses are used the f2.8 will still be faster than f3.5-f5.6.

If you would read what people wrote instead of getting defensive, you would see that I never said you misunderstood anything. I said you missed the whole point of it.

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[EchoingWhisper]

It depends on what you mean by 'really f/2.8'

If you mean that the maximum ratio of the element to the pupil is 1/2.8, no matter what, then sure.

If you mean that the DOF is the same, then no.

Well, i dont really care what it is on a full frame camera since i dont own or plan on owning one. As long as its f2.8 on my D90 im happy. i dont even use 2.8 very often, but i like having the option if i need it. Thanks for clarifying things for me though. I was worried for a minute.

If you put equivalence on the DX format, a f/2.8 on FX is similar to f/1.8 on DX. It's DX 2.8, but equivalent to FX 4.3.

[EchoingWhisper]

An f/stop is the same on the same format no matter it is DX or FX. But once you use the DX lens on DX sensor and FX lens on FX sensor, then you'll need equivalence. You might not agree with this statement, but let's get back to my original question that involved ONLY FX, because I think FX has better performance-price ratio.

Nikkor 24-85mm 3.5-4.5 (ruled out this choice because the 28-300mm seems to be a better bang for the buck) vs off brand 24-70mm 2.8 vs Nikkor 28-300mm 3.5-4.5

So here's the final question - third party 24-70mm 2.8 vs Nikkor 28-300mm 3.5-5.6 VR

It's a hard decision. The 24-70mm 2.8 I will be choosing definitely will not have VR (the one with VR costs $400-500 more).

So, here it is -
24-70mm 2.8 PROS -
Freezes motion (both camera shake and subject movement)
Less depth of field creates more 3D looking image and better portraits
Sharp
24-70mm 2.8 CONS -
High risk of not being compatible with the body and bad quality control
Lacks zoom range, but I could live with it
Bad resale value
Would have to resort to select larger aperture instead of slower shutter speeds which greatly lacks depth of field
28-300mm 3.5-5.6 VR PROS -
Great zoom range
Could choose to use slower shutter speeds without camera shake (without a tripod), to get more depth of field
Better support and quality control
Good resale value
28-300mm 3.5-5.6 VR CONS -
Depth of field not as dramatic as the 2.8, but still better than all DX 2.8 lenses
May be soft, but should be outside my 'too soft' zone
Couldn't freeze motion blur as well

I kinda like this site, although the response may not go with my opinions, but there are always people responding.

[prakhardeep]

It's a hard decision. The 24-70mm 2.8 I will be choosing definitely will not have VR (the one with VR costs $400-500 more).

AFAIK, only Tamron has a VC 24-70 and rest all are non-VC/VR and Tamron one is cheaper than those (Read Nikon/Canon).

Also, if you want to compare all the 24-70's then hit YouTube - Broadcast Yourself. and watch 24-70 comparison series by thatnikonguy.

[EchoingWhisper]

I mean, the Tammy VC is $400/$500 more expensive than other third part 2.8s.

[chris]

EchoingWhisper: 'Depth of field not as dramatic as the 2.8, but still better than all DX 2.8 lenses' - no it isn't - over the 28-70mm range the 28-300mm FX lens is slower than the DX lens which is f2.8. You will be using either lens on your DX body so there is no need for 'equivalence' just look at the lens specs. If you put either lens on a FX body the 24-70mm f2.8 is still faster though it would give either vignetting or edge distortion on the larger format.

fjrabon - I wasn't being defensive, if I missed the whole point of it then I misunderstood. You are correct that 'equivalence' lets you calculate the f-stops needed to reproduce a particular DoF with differing formats but the OP is going to be using their selected lens on a DX body so what would be required on a FX body is completely irrelevant.

[Nikon_Josh]

EchoingWhisper: 'Depth of field not as dramatic as the 2.8, but still better than all DX 2.8 lenses' - no it isn't - over the 28-70mm range the 28-300mm FX lens is slower than the DX lens which is f2.8. You will be using either lens on your DX body so there is no need for 'equivalence' just look at the lens specs. If you put either lens on a FX body the 24-70mm f2.8 is still faster though it would give either vignetting or edge distortion on the larger format.

I wasn't going to explain this to him, but then I realised I couldn't be bothered to waste my breath!

[EchoingWhisper]

EchoingWhisper: 'Depth of field not as dramatic as the 2.8, but still better than all DX 2.8 lenses' - no it isn't - over the 28-70mm range the 28-300mm FX lens is slower than the DX lens which is f2.8. You will be using either lens on your DX body so there is no need for 'equivalence' just look at the lens specs. If you put either lens on a FX body the 24-70mm f2.8 is still faster though it would give either vignetting or edge distortion on the larger format.

I wasn't going to explain this to him, but then I realised I couldn't be bothered to waste my breath!

I mean, I am likely to buy a D600 if it comes, that's why I needed to talk about equivalence. I just want some time to decide. If I were to buy my current setup immediately after I made up my mind before, I would have gotten a totally different setup. More time to decide means less wrong choices. Sorry for not stating that if I'm not clear.

[chris]

EchoingWhisper: 'Depth of field not as dramatic as the 2.8, but still better than all DX 2.8 lenses' - no it isn't - over the 28-70mm range the 28-300mm FX lens is slower than the DX lens which is f2.8. You will be using either lens on your DX body so there is no need for 'equivalence' just look at the lens specs. If you put either lens on a FX body the 24-70mm f2.8 is still faster though it would give either vignetting or edge distortion on the larger format.

I wasn't going to explain this to him, but then I realised I couldn't be bothered to waste my breath!

I mean, I am likely to buy a D600 if it comes, that's why I needed to talk about equivalence. I just want some time to decide. If I were to buy my current setup immediately after I made up my mind before, I would have gotten a totally different setup. More time to decide means less wrong choices. Sorry for not stating that if I'm not clear.

I will try one last time.

'Equivalence' is telling you what f-stop you need to set on a FX lens on a FX body to get the same DoF as a DX lens of the same focal length on a DX body. It does not change the fundamental properties of a lens - the maximum f-stops of the lenses are what they are because of the lens design and do not change with different formats. The differences are that FX lenses have a larger image circle than DX lenses so that they can adequately cover the larger format. As format size increases so a lens has to be stopped down further to give a particular DoF compared with a smaller format.

You do not need to use equivalence just because you might buy a FX body - you just need to understand that a DX lens will not cover the full FX format satisfactorily
but even if it did it would still have the same maximum f-stop as when used on a DX body.

'Equilivance' as you are using it is a means of determining what lens setting to reproduce DoF when using different formats - it is not some magic formula that can change the characteristics of a lens between formats and cannot be used to compare two lens in the way that you are doing.

Over and out.

[EchoingWhisper]

I wasn't going to explain this to him, but then I realised I couldn't be bothered to waste my breath!

I mean, I am likely to buy a D600 if it comes, that's why I needed to talk about equivalence. I just want some time to decide. If I were to buy my current setup immediately after I made up my mind before, I would have gotten a totally different setup. More time to decide means less wrong choices. Sorry for not stating that if I'm not clear.

I will try one last time.

'Equivalence' is telling you what f-stop you need to set on a FX lens on a FX body to get the same DoF as a DX lens of the same focal length on a DX body. It does not change the fundamental properties of a lens - the maximum f-stops of the lenses are what they are because of the lens design and do not change with different formats. The differences are that FX lenses have a larger image circle than DX lenses so that they can adequately cover the larger format. As format size increases so a lens has to be stopped down further to give a particular DoF compared with a smaller format.

You do not need to use equivalence just because you might buy a FX body - you just need to understand that a DX lens will not cover the full FX format satisfactorily
but even if it did it would still have the same maximum f-stop as when used on a DX body.

'Equilivance' as you are using it is a means of determining what lens setting to reproduce DoF when using different formats - it is not some magic formula that can change the characteristics of a lens between formats and cannot be used to compare two lens in the way that you are doing.

Over and out.

You need to crop the DX lens anyway if you put it on a FX lens, that's why you need equivalence.