4
\$\begingroup\$

This is on my 600D. I'm a noob so forgive if it's obvious. There's a clear moire-like interference pattern on the viewfinder on the 50mm which is not as obvious at all on the kit lens. It's especially obvious when looking at out-of-focus bokeh but doesn' show up in the photos.

Improve this question
\$\endgroup\$

1 Answer 1

Reset to default
10
\$\begingroup\$

It sounds like you're observing the laser etched glass focussing screen. A focusing screen requires a rough surface so an image can be formed for you to view through the viewfinder.

Ground glass used to be used for this purpose but now glass etched in a circular pattern with a laser is used, to improve the brightness of the viewfinder when used with slower lenses. This pattern is probably what you're interpreting as moire.

Here's what a standard DSLR focussing screen looks like close up:

Improve this answer
\$\endgroup\$
6
  • 1
    \$\begingroup\$ I'll add that the reason Mel is seeing it with this lens is that being a 1.8 its letting in a LOT more light than a kit lens, making the viewfinder much brighter and making the effect much more pronounced and noticeable. (I have seen a similar effect with the 50mm 1.4 on my D800) \$\endgroup\$
    – Digital Lightcraft
    Commented Oct 23, 2013 at 16:15
  • \$\begingroup\$ Thanks. I thought it was something like this. I just don't get why it becomes so much more apparent when the lens is out of focus. \$\endgroup\$
    – mel
    Commented Oct 23, 2013 at 16:22
  • 1
    \$\begingroup\$ its probably because of the DETAIL that is in-focus makes it less apparent. \$\endgroup\$
    – Digital Lightcraft
    Commented Oct 23, 2013 at 16:23
  • \$\begingroup\$ The glass most likely isn't laser-etched, as laser polishing is an extremely new technology being researched at the Fraunhofer instutite in Germany. Rapid local heating a la a laser tends to cause glass to explode. \$\endgroup\$
    – Brandon Dube
    Commented Mar 7, 2016 at 0:16
  • \$\begingroup\$ @BrandonDube, it may be something of a hybrid etching, similar to what's done for some steps of IC manufacture: a photosensitive mask is applied, the laser + some chemical wash removes part of the mask, and then chemical etching is done on the parts where the mask was removed. \$\endgroup\$
    – Nate S.
    Commented Jan 15, 2020 at 17:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.