Lens for CANON EOS D5 close range photogrammetry bridges

[alexanderjimh]

Hi!
I am going to use a Canon EOS D5 for scanning bridges some meters away. This is going to be used later to do research and analysis. I understand I need a fixed zoom wide-angle lens but which one? The bridges are considered large items and I need a good lens to get the best result I can get with that camera. Do anyone have previous experience using this camera or do anybody know which lens would make the best work? Note that too wide angle lenses would create too much distortion in the outer area of the images.

Thank you all!

[SAV]

Hi alexanderjimh,

I guess you mean Canon EOS 5D, not D5. 
Are you getting a Canon 5D Mark III or Mark IV?

They are both full frame DSLRs, but Mark IV has a resolution of 30.1 MP vs 22.3 MP for the Mark III. This will make a difference for your ground sampling distance (GSD), which depends on these four factors:

  1) Distance to object
  2) Physical sensor size
  3) Sensor resolution
  4) Focal length

I suggest to get a lens with a fixed focal length somewhere between 24 - 50 mm. I think 28 mm or 35 mm are probably the best choice for your purpose. You might want to hire a few lenses first for testing purposes before buying one.

In the end it your lens choice will depend on your distance from the bridge when taking pictures and on the GSD/resolution you are aiming for.

Regards,
SAV

[alexanderjimh]

Hi!

Thanks for the answer.
I already have the camera so I am not getting another one. The distance to take photos, as I have read for bridges, is somewhere between 7-15 m from the object. However we are going to try out the equipment before hand so that we can get good images when we are at the sites.
I will try out lenses with that focal length.

Anybody else have some input?

Regards,
Alex

[cadm8]

The distance to take photos, as I have read for bridges, is somewhere between 7-15 m from the object.

In case you're not aware about it, you can use this tool for calculating GSD, as SAV is suggesting
https://support.pix4d.com/hc/en-us/articles/202560249-TOOLS-GSD-Calculator#gsc.tab=0

[SAV]

Hi again Alex,

There is not really a 'distance for bridges' when taking pictures. It will depend on the level of detail you want to resolve in your 3D model and on the chosen hardware (digital camera + lens), as mentioned in my earlier post. The 'level of detail' is represented in the GSD, which can be easily calculated in advance (see link in cadm8's post).

For example, you could increase the distance to your object but still get the same GSD by using a lens with a different focal length.

You should also consider the computational power that is required to process your images. If you want to get a mm resolution model of the whole bridge, you will not just need to pick the right camera, lens and distance to the object, but also the right hardware that is able to process all of it at the required resolution.

Regards,
SAV

Hi!

Thanks for the answer.
I already have the camera so I am not getting another one. The distance to take photos, as I have read for bridges, is somewhere between 7-15 m from the object. However we are going to try out the equipment before hand so that we can get good images when we are at the sites.
I will try out lenses with that focal length.

Anybody else have some input?

Regards,
Alex

[Pingacha]

Thanks to what you publish.