Mirror cropped?

Innocence · Oct 8, 2006

Hi all!

Wondering if the mirror on aps dslrs are cropped ! Because I went to play with a friend's lenses because he has a large range of focal lengths - wanted to help me figure out what I would need.

He had something near 18mm (a nikon zoom haha I havent researched any nikon - but know that their field of views are cropped by 1.5x) and it didn't seem all that wide?

On my point and shoot (which I will be soon upgrading out of - but will still keep for rainy days, literally haha) I always wish that I am able to zoom further out! So I wanted to get a wide angle.

After this long story, I'm wondering if what I saw through the viewfinder was cropped or not.

Thanks!

He also had a ~10-20 (which was much more to my liking! But then I pointed it at people, and even when I got fairly close, they seemed far away! he he)

fmw · Oct 8, 2006

I sold my 18mm f2.8 Nikkor just yesterday. It was an outstanding lens. But it was designed for a 35mm format camera. On a digital Nikon it is the equivalent of about a 28mm lens because the CCD in a Nikon digital is housed in a smaller frame. So a lens designed for a 35mm Nikon camera will work effectively like a longer lens by a factor of 1.5X when used on a digital Nikon.

Innocence · Oct 9, 2006

thanks for the reply fmw, i was thinking about this today at university, and I realised that my question doesnt really make sense, since the light converges towards the sensor and the mirror is before the sensor, so images naturally will appear "cropped" regardless if the sensor is cropped or not.

Rob · Oct 10, 2006

Innocence said:
thanks for the reply fmw, i was thinking about this today at university, and I realised that my question doesnt really make sense, since the light converges towards the sensor and the mirror is before the sensor, so images naturally will appear "cropped" regardless if the sensor is cropped or not.

This is true, but perhaps not to the extent you may think... some "pro" level SLR cameras have a mirror very close to real. My F3HP is awesome, especially for someone with glasses and a beer habit - it's allegedly 100% WYSIWYG.

On most DSLR cameras I think you're working with about 90-95% of the sensor's size with the mirror. The issues which occur are generally to do with cropping as you get slightly more than you can see. The angle of correction probably isn't handy to calculate whilst in the field, so I'd say, just go with it and learn parrot fashion what's included.

Rob

W.Smith · Oct 11, 2006

Innocence said:
[...] He had something near 18mm (a nikon zoom haha I havent researched any nikon - but know that their field of views are cropped by 1.5x) and it didn't seem all that wide?

18mm x 1.5 = 27mm. That lens was a 27/28mm (35mm equivalent), so a medium wide angle.
It's not the FoV that is cropped, but rather the focal length that is multiplied. That '1.5' is a 'focal length multiplier', not a 'crop factor'.

[...] He also had a ~10-20 (which was much more to my liking! But then I pointed it at people, and even when I got fairly close, they seemed far away! he he)

Which, with that focal length multiplier of 1.5 works out to 15 - 30 mm in 35mm equivalent.

Big Mike · Oct 11, 2006

W.Smith said:
18mm x 1.5 = 27mm. That lens was a 27/28mm (35mm equivalent), so a medium wide angle.
It's not the FoV that is cropped, but rather the focal length that is multiplied. That '1.5' is a 'focal length multiplier', not a 'crop factor'.

Which, with that focal length multiplier of 1.5 works out to 15 - 30 mm in 35mm equivalent.

Welcome to the forum.

I have to disagree with you. The focal length of lens does not change one bit...whether it's mounted on a 35mm camera, a digital camera or being used as a paper weight. To that extent, the light that passes through the lens does not change either. The only thing that changes when you use one of the DSLR cameras in question...is the size of the area recording the image. These DSLRs have a sensor that is smaller than 35mm film...so they only record the centre portion of the image being projected by the lens. This is effectively a 'crop' of the projected image.

Also, since the focal length is not actually multiplied, you do not get any more 'magnification' with the lens, on these DSLR cameras ...you are just seeing a smaller portion of the scene (which may be more magnified in to fill the viewfinder).