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Reducing flare on Fujian 35mm f/1.7 C-mount lens
Posted By: BigMackCam, 11-25-2015, 09:15 AM

Like many Pentax Q enthusiasts, I acquired the well-known Fujian 35mm f/1.7 C-mount lens to use on my Pentax Q7 (with appropriate C-to-Q adapter). It's not a bad little lens - quite well made, with a character all its own... but as anyone who owns one will know, it's extremely susceptible to internal reflections and flare, making it all but unusable in many situations.

The main cause of the internal reflections is the chrome-plated lens mount, the inner surface of which is exposed to the path of light from optics to sensor. By painting the inner exposed areas of the lens mount with matt black paint, these reflections can be minimized. What follows is my own approach to this well-known modification. It takes just 10 - 15 minutes and is very easy to do. I hope it's of use to others.

Instructions:

1. You will need a clear work surface, small cross-head screwdriver, small paint-brush, alcohol wipes and some matt black paint. I used Tamiya XF-1 Flat Black water-based acrylic. It's worth noting that some matt modelling paints dry with a satin finish (particularly when applied to metal), but Tamiya XF-1 has a very flat finish indeed, which is optimal for the task at hand.



2. Looking at the rear of the lens, you can see that the chrome-plated mount is held in place by three cross-head screws. Remove these screws and set them aside where they can't be mislaid or knocked onto the floor.

3. Lift the mount away from the lens. Mine had some thin, oily residue on the face that mated to the lens. Whether yours does or not, thoroughly clean the mount with an alcohol wipe. This will help the paint to adhere.



4. Give the paint pot a good shake before opening to ensure the contents are mixed properly.

5. Using the brush, apply the matt black paint to the tubular inner surface of the mount, and the back edge of the threaded section (being careful to avoid painting the threads themselves). Use only a little paint - the coating should be thin. Allow a few minutes for the paint to dry, then give it a second coat.



... When finished, it should look like this:



6. Re-fit the mount to the lens (the threaded section facing outwards - obviously!). Replace the three screws and gently tighten them.



7. Attach the lens to the camera and check that the aperture markings are visible in normal use. If they're not, you'll need to remove the lens, take the screws out of the mount and rotate it one or two thirds of a turn in the appropriate direction before refitting the screws.

And that's it. You'll find that the lens no longer suffers from crippling reflections. It won't be entirely flare resistant, of course - there are clearly other surfaces and components in its construction that contribute to this. However, it's a major improvement and makes this fun little lens genuinely useful.

Good luck!
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11-25-2015, 10:15 AM   #2
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Hi, this is a great tutorial. Congratulations!
I wonder if you could post some before and after shots to see the actual impact of the improvement.
11-25-2015, 10:34 AM   #3
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QuoteOriginally posted by carrrlangas Quote
Hi, this is a great tutorial. Congratulations!
I wonder if you could post some before and after shots to see the actual impact of the improvement.
Thanks for the feedback. Much appreciated

I took some before shots when it was sunny outside, but unfortunately the weather had completely changed by the time I'd completed the work

What I can say is, this doesn't remove "normal" flare, which may be down to the inadequacy of the lens coatings (if, indeed, there are any - looks like there may be, but if so, they will be minimal). So, there is still a lack of contrast in many images even after the modification, but mostly this can be addressed in post processing or by cupping your hand over the end of the lens when shooting. However, it gets rid of the reflections that cause complete washing out of the image in anything approaching decent light.

It's definitely worth the effort, but not a cure-all
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