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Old January 11th, 2008, 09:35 AM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
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Join Date: Jun 2006
Location: Netherlands
Posts: 4,053

Originally Posted by Herbert Dorfan View Post
Hi Bart,
Thank you for the benefit of your elegant thinking. Two qustions that come from my inexperience: Is it important that plane of the digital sensor of my 1dMk3 be parallel and centered with my lcd monitor, as I am able to make things work with my <200mm lenses, but not with my 300mm f2,8 where I don't see colors? (I have lens opened to 2.8). Do you have any suggestions how to accomplish this, if it is necessary?
Hi Herb,

It is not absolutely necessary to have the target and the sensor plane parallel. If they aren't then you will probably see a zone of moiré parallel to the in-focus plane. However, it is beneficial for repeatable focus to do have things approximately parallel.

Reasons for not achieving the moiré can be;
- too far out of focus, but that's also what the crosshairs are for, a visual clue and as well as an AF sensor aid
- distance too close, or magnification to large (which is the same), which prevents small enough detail to cause moiré
- distance much too far, which will cause the moiré to have too low an amplitude to see
- the lens has too low resolution
- or the manual focus is too reactive to nail the exact spot, try slower manual focus adjustments

You may have to vary the shooting distance a bit with your 300 mm. It should be plenty sharp enough to achieve moiré (color or monochrome), but requires shooting from a bit further away. It can also help to not use the maximum Life View zoom. Sometimes x5 is good enough or even better to see moiré clearly, try toggling the different magnifictions at some different distances.

I am actually working on an improved target version right now, one that's less distance critical. So your feedback on the final condition that you needed to see the moiré can help me a lot (I don't have the 300mm to test myself).

You might want to try this target which has a little resemblance to the direction I'm thinking of for the new target. The moiré from that target will manifest itself as concentric smaller rings.

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