Crop sensor confusing!

[nic bike]

well i think i understand crop sensors and after looking at the comparisons thread can see a big difference but i've got a question about teleconverters and crop sensor so if i had a 300mm lens and then times that by the crop sensor (1.6) i get 480mm so if i had a 2x teleconverter would i be adding on 300mm to this to make 780mm or would i be doubling it to make 960mm?

thanks in advance for any answers! (if any sums are wrong tell me)

 

[natjag]

your adding the 2x convertor to the lens focal length, making the lens 600mm, so with the crop you'll have a 35mm equivalent of 960mm

 

[BRASH]

My understanding is you'll double the whole focal length so 960



Edit

Ah beaten to it:bang::bonk:

 

[nic bike]

Thanks both of you !

 

[CT]

well i think i understand crop sensors and after looking at the comparisons thread can see a big difference but i've got a question about teleconverters and crop sensor so if i had a 300mm lens and then times that by the crop sensor (1.6) i get 480mm so if i had a 2x teleconverter would i be adding on 300mm to this to make 780mm or would i be doubling it to make 960mm?

thanks in advance for any answers! (if any sums are wrong tell me)

LOL. Your sums aren't wrong, but you really need to leave the 1.6X crop factor out of the equation - it's very misleading.

When digital SLR cameras first appeared we were bombarded with info about the 1.6X crop for no other reason than that people felt the need to tell us how the new sensor format compared to the 24X36mm 35mmm film format which everyone was familiar with. In the process they've left behind a legacy of confusion which I don't think will ever go away.

The focal length of a prime lens is fixed and doesn't change regardless of what size senor you put behind it or what compatible film body.Your 300mm lens with a 2X TC becomes a 600mm lens - that's it - forget the 1.6X crop factor.

If you and I stood side by side, both using the 300mm lens with 2X TC with you shooting on a 1.6X crop sensor and me shooting on 35mm film, we'd both put exactly the same size image of the (let's say) Robin, on the sensor and on the film.

Your Robin would fill the frame so much better on your smaller sensor though, whereas my Robin would look somewhat lost in the frame and need a lot more cropping at the editing stage.

The 1.6X crop factor means that I would need to be shooting with a 960mm lens to fill my larger film frame to the same proportions as you, but for you to think you realistically have a 960mm lens would be a bit daft.

 

[HuntingMartians]

Here.

On the left is the image projected by a "traditional" lens (like a Canon EF or a Sigma DG): the image circle is large enough to cover a full-frame sensor or a frame of 35mm film. On the right is the same view through a designed-for-digital lens (such as a Canon EF-S or a Sigma DC) with the same focal length. It's simply a smaller piece of glass, which is why it's cheaper, and you can see why they only work on crop-factor cameras.

Now can we please cut out all the "20mm is really 32mm" nonsense?

This is from this
So a 300 mm lens is 300 mm no matter what.

 

[nic bike]

Thanks thisphotoguy and CT so know all i need to know if a lens says 300mm i take it as that and forget all this crop sensor stuff. (i think I'm starting to take it in)

 

[mrgubby]

a "crop sensor" cannot obviously affect the focal length of the glass placed in front of it but it does change the effective field of view that you end up with.

It doesn't give you 1.6 x focal length but it does give you the same results (ignoring DOF / hyperfocal etc )

 

[30psi]

Its worth noting that the only real time the cropped sensor becomes an issue is when selecting a wide angle lens.

Traditionally something like the 16-35mm is sold as a wide angle lens which indeed it would be for full frame.

If you wanted a true wide angle lens for say a 400d then you wouldn't find the 16-35 to work as a wide angle.

As a result you would have to use the 10-22 lens (equivalent to a 16-35 on full frame) but it only works on the cropped sensor cameras.

Its only at the wide end of the scale does the cropped sensor become an issue, but at least there is the 10-22 lens to solve this.

 

[RogDen31]

Its worth noting that the only real time the cropped sensor becomes an issue is when selecting a wide angle lens.

Traditionally something like the 16-35mm is sold as a wide angle lens which indeed it would be for full frame.

If you wanted a true wide angle lens for say a 400d then you wouldn't find the 16-35 to work as a wide angle.

As a result you would have to use the 10-22 lens (equivalent to a 16-35 on full frame) but it only works on the cropped sensor cameras.

Its only at the wide end of the scale does the cropped sensor become an issue, but at least there is the 10-22 lens to solve this.

So to go one step further would a FF fisheye lens [say a Nikon 16mmf2.8 for example] still give a fisheye view of 180deg when fitted to a cropped sensor body [Nikon D80] or do you have to have a DX fisheye [Nikon 10.5f2.8DXAF]

 

[30psi]

I think it would be correct to say the wide angle view of a full frame fisheye lens would be reduced on a crop sensor'd DLSR.

 

[CT]

So to go one step further would a FF fisheye lens [say a Nikon 16mmf2.8 for example] still give a fisheye view of 180deg when fitted to a cropped sensor body [Nikon D80] or do you have to have a DX fisheye [Nikon 10.5f2.8DXAF]

Yep - you answered your own question there. You'd need a DX version for Nkon or an EF-S for the Canon equivalent.