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Is an IR/UV filter needed?


Alberti

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I recently bought an Orion-18 28mm F5.6 lens and coded it as Summaron. The lens has the same structure. [I like it for its compactness and low 'profile'.] I use it on my M240 but bought it for Monochrom.

However, I notice some small tinge of purple on the top of this image in the sky.  Should I use an IR/UV filter on this lens like on the M8? The Orion accepts 40.5 mm filters. 

This reminds me of the M8. I remember JaapV once said the M240 has some IR issues. And would [sometimes] need a light IR filter. I tried the M8 filters by Leica on the M240 but did not like the result. Probably way too strong.

The following filters in 40.5 mm are available: 

  • 370-670nm 
  • 400-700nm 

Which of the above is do you think appropriate?

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Thanks. My idea is that the 370-670nm  is the less strong option; the band being wider, so interfering less.  But indeed, it is slight in this picture.

Just to show how it can be; For reference, using an Elmar 24: to me that is perfectly balanced. 

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Edited by Alberti
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4 hours ago, Alberti said:

Thanks. My idea is that the 370-670nm  is the less strong option; the band being wider, so interfering less.  But indeed, it is slight in this picture.

Just to show how it can be; For reference, using an Elmar 24: to me that is perfectly balanced. 

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Yes, there are different spectral transmissions but the intensity is not really relevant As long as the IR is cut off, the only difference might be in very deep reds.

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