# Thread: Help With Image Circle For Chamonix 045N-2

1. ## Help With Image Circle For Chamonix 045N-2

I am in the market for a 90mm lens for my Chamonix 045N-2

The one I have my eye on is a 90mm f/8 Copal 0 with an image circle of 216mm @ f/22 at infinity

Does anyone know if this will give me full movements with the Chamonix 045N-2?

2. ## Re: Help With Image Circle For Chamonix 045N-2

Hi Ian,

The diagonal of 4x5 is 163mm, so its radius is 81.5mm.

Take the maximum rise and shift of your camera as the two sides of a right triangle.
Find its diagonal and add that to the 81.5mm radius. Double the sum to get the diagonal.
If that diagonal is less than or equal to 216mm, your lens will cover, otherwise no.

Example:
10mm rise, 7mm shift.
The diagonal of that movement = sqrt( (10 * 10) + (7 * 7) ) = sqrt( 149 ) = 12.2
12.2 + 81.5 = 93.7. Double that gives a total diagonal of 187.4.
That's less than your 216mm image circle, so the lens will cover.

Use the actual rise and shift for your camera to make that determination.

- Leigh

3. ## Re: Help With Image Circle For Chamonix 045N-2

Brilliant Leigh, thanks for that

4. ## Re: Help With Image Circle For Chamonix 045N-2

Does the Image circle get smaller or bigger as you focus closer ?

5. ## Re: Help With Image Circle For Chamonix 045N-2

Larger. The image circle is the base of the cone of light thrown out behind the lens. The farther you are from the tip of the cone, the lens, as you focus closer and the lens moves away from the film the larger the cone grows.

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