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Flocking an SCT to improve contrast

using Self Adhesive Flocking paper from Edmunds Scientific

*This involves the removal of the Corrector. It is up to you to know how to do that correctly. It is not discussed here.*

It is best to cover your Primary mirror *BEFORE* you wish you had done so..

I use my Meade 12" LX200 Classic often to observe occultations. Asteroidal Occultations usually involve a completely dark scene, but Lunar Occultations always involve some amount of light from the bright lunar limb entering the OTA at a shallow incident angle. As shown in the image below, the inside of the OTA is very shiny. This off axis light eventually will enter the on axis optical path, greatly reducing the contrast of the image. In my case, usually video.

Adding flocking to the inside of the OTA greatly improves the situation.. You'll note the flocked images below are so dark to the camera, they came out grainy..

Unflocked w/ Corrector in place

Flocked, Corrector removed


Unflocked w/ Corrector in place

Flocked, Corrector removed

Flocked, Corrector removed


Unflocked outside of Secondary

Flocked outside of Secondary - Optional


How to Apply - Read all before you begin.

There is a different method you might prefer.

This is how I did it. I am Right Handed.

WARNING - The adhesive is quite aggressive and bonds instantly and permanently.

I used a straight edge to cut 6 to 8 inch strips that would reach from the back of the OTA (mirror end) to the front (Corrector End). I also placed the scope on a table on a quilt so the scope can be rolled, allowing the area to receive the strip of flocking to be down. Pull back a couple inches of backing. With the left hand handling the exposed adhesive flocking to be applied, reach down the OTA until your knuckles brush the edge of the Primary and start applying the flocking, smoothing with the left hand while slowly pulling the protective backing out the front of the OTA with the right.. Where the flocking starts near the primary, does not have to be perfect. The only thing you don't want is any trapped air / bubbles. Not the end of the world, as a needle will solve any such problems, and once you do the first strip, you'll see it's actually rather simple.

Applying the additional strips of flocking takes a touch of effort, as it is preferable to butt the edges together. Overlapping a small amount works too, but leaving gaps between the strips is less than ideal, as is too much overlap.  Also, as it's next to impossible to do it perfectly, do not worry what it looks like. In the dark it is completely invisible.

One important note - as you get close to applying the last strip to complete the project, you may have to trim a couple of the strips so that you don't end up with a very small strip to apply. For example, if you are installing 8" strips, and you still need to cover 10 inches, it is far better to install 6 and 4 inches, than an 8 and a 2".. By the time you have applied enough strips to get close to done, you'll know the size pieces you can handle, but think about the ending as you progress..


How to Apply - Alternate Method

You can buy a large - 24 x 36 inch for example - laminated desk calendar. Measure the depth of the OTA from the Primary to the corrector and cut this dimension from the calendar, making it 20 x 36 for instance.. (This is not an actual number! Measure your OTA!) This measurement does not need to be tight. An inch short is good, as the OTA near the mirror doesn't need perfect flocking.

Roll the calendar and insert it into the OTA and release. Mark where it overlaps, and pull it out and cut it, but don't cut it short. A small overlap is ideal. Test fit the calendar until it's correct.

Once the calendar is the proper size, remove it. Two people can flock it in one large flock, or strips can be applied.

When finished, slide the calendar in tight to the corrector end of the OTA and it'll "snap" into place and you're done..


Vacuuming the Flocking

This is only needed if you do any trimming of the flocking inside the OTA, as opposed to doing all cutting and trimming outside the OTA and just brushing it off. Wouldn't hurt, but the flocking is quite dust and lint free.


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This site was last updated 08/10/16

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