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Red Filter on Monochrom


IkarusJohn

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I promised wattsy I'd run a bit of a test in another thread.

 

I forgot my tripod, and was a bit underwhelmed with subjects, so I chose the Sea Scouts clubhouse at Devonport - middle distance, handheld, ISO 320, Noctilux, focused using a 1.4x magnifier.  I maintained the aperture at between f4 & f5.6 to try to control the depth of field, shutter speed between 1/3,000 and about 1/1,000.  What we're looking for here is a shift in the depth of focus - that is the clarity of the image at the sensor resulting from the shift to an all red wavelength.

 

The first is our control shot, taken without any filter.  In all shots I've focused on the corner of the building - sorry again it's a bit of a boring shot.  I've done pretty much no post processing, other than cropping to give the same image.  Happy to provide the DNGs to anyone who wants them.

 

 

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Edited by IkarusJohn
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Next, same shot, but with a Heliopan Yellow 15 filter

 

 

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Finally with a Heliopan Red 25

 

 

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Here's a crop from the centre of the last one.

 

 

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So what is your conclusion?

 

I can't see too much wrong with the crop shot, but there's nothing to compare it with. As has been said the red wavelength is problematic in all aspects of photography, it's just that B&W shows it up more often if it is going to be a problem.

 

Steve

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http://www.l-camera-forum.com/topic/247310-color-filters-chromatic-aberration-and-focus-shift/

 

I believe that any focus shift is due to chromatic aberration of the lens. I did a test with a Pentax 85/4.5 Ultra-achromatic lens on the M Monochrom, same filters used on a Pentax 50/1.4 on the M Monochrom. Shift in the point of focus was evident on the 50/1.4 Achromat (corrected for two zero-crossings) but not on the 85/4.5 (corrected for four zero-crossings). The 85/4.5 is a fluorite and quartz lens, for use from UV through to Infrared.

Edited by fiftyonepointsix
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Okay, so here is the Summicron 28/2 ASPH, no filter

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And here it is with a B+W red 46 091

 

 

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The red focus shift should be apparent with the lens wide open, otherwise depending on the lens DOF will often cover it, so if it is going to be apparent it's wide open lenses or tele lenses that have narrow DOF. But my guess would be it's a rarefied set of events that makes people put a strong red filter on the lens and not want to stop it down for more DOF at the same time, such as in typical landscape photography.

 

Steve

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I'm not saying the issue doesn't exist, and I would be very interested to know when it becomes an issue.  I would have to say that if what Steve says is true, it would most likely be an issue wide open with a subject at middle distance.  Not sure I'd use a red filter for an image like that ...

 

i will ill give it a go, and I will get my tripod out. Any other ideas welcome. 

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