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Why a 300mm Dome

After reading recent mailings as to the size of the pie shapes appearing short and the space between the pies and the radar eye looking large on club spec domes, I have researched and theorized the following cause.

It seems that the official profile on the club site was made by tracing the photo labeled #1. After trying many methods, I have determined that taking a photo to be used to create and accurate profile of a spherical object is very difficult.

I have conducted experiments by photographing an 18" ball from different angles to see the effects of angle and distance as it pertains to capturing a profile by tracing the photo. Here is a rule of photography that helped me...

Depth of field decreases as you increase your focal Length.

So...

The farther away the camera is, the more accurate the profile.

As depth of field increases (camera gets closer) the more the profile of an object distorts, In photo #1 the center of the camera lens is on plane with the bottom of the dome. The focal length is relatively short, we can't see the detail on top of the dome. In the #3 and #4 photo, even with, the center of the camera lens below the plane of the bottom of the dome, because the focal length is longer we can see some dome top detail. In order to get the most accurate profile of an item with a camera, we want the longest possible focal length and/or 0 depth of field. A single view drawing has no depth of field as seen in #2.

Note to members: if you want the most accurate profile, get as far away as possible, then zoom in to fill your frame. This will reduce the depth of field and you will be able to see 49%+ of the object.


The Photos on this page are being shown for reference only and are the property of their respective owners. Please do not duplicate.

 

 

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