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Forget flocking your Cat.
There is a misconception that "flocking" the inside of an OTA does something to improve contrast. It does bugger all. Another misconception is that it is the fault of there being a secondary mirror/obstruction that is to blame for the reduction of contrast. The for the effects of the secondary mirror to be apparent, it is necessary to eliminate ALL the other sources of unwanted/scattered/reflected light from within the OTA. Only once these have been eliminated will the true extent of the effect of the secondary be apparent. And this is far less than you think.
To get to the nuts and bolts of what is seen as reduced contrast that is often seen in SCT's and other Cats you need to drop the idea that just because some piece of aluminium is anodized to a black colour that it is doing the job you expect - to eliminate reflections. Black anodised aluminium is a terrible material when examined in the way light actually enters the OTA and travels past these components - at shallow angles of incidence. When you look down into the OTA of an SCT with a light source, you will find that there are an extraordinary number of black anodised surfaces that are glowing with reflected & scattered light coming off these. See the first pic below.
It is important to also compare Cats that do have a known level of better contrast in order to see why this is the case. The second pic below shows the inside of an Intes Mak with light being shone at a very similar angle to that in the SCT. You will notice there is a striking difference in the finish of the baffle tube all along its length and that of the secondary obstruction. This Intes is not perfect either, but the different ways that the guts of the scope have been dealt with are now obvious.
Intes Maks are known for having a series of baffle rings down the length of the OTA. Yet there are other Cats and Cassegrains also known for superior contrast and these scopes do not have this series of baffle rings. Yet what they all have in common is the way the baffle tube of the primary and secondary mirrors have been dealt with on the outside AND inside. And what all these scopes and SCT's do have in common is the inside of the tube of the OTA, they are all painted with a flat black - yet it is SCT's that have the contrast issue.
Adding flocking to the inside of the OTA is tinkering along the edges that will gain you bugger all, because the REAL culprit of the reduced contrast has been left totally unaltered.
When I received the 7" Intes Mak, a previous owner had installed a roll of flocking inside the OTA, right over the series of baffle rings! All this was doing was shedding masses of wee black fibres all over the optics and did nothing to improve contrast - this previous owner had no idea about what flocking was actually doing an only created more problems and solved none. I removed this ridiculous addition to the inside of the OTA and contrast was none the worse, but I had a crap-load of black fibres to try to remove.
My current Cat is a 9" Santel Mak. Unlike Intes Maks, this Russian made Made does not have any baffle tubes inside it. The inside of the OTA is just like an SCT. However, the way the baffle tube coming off the primary mirror is made and finished is totally different to that of an SCT, and this is the source of its better contrast. Not too long ago I did a side by side comparison of this 9" Santel Mak with a 10" APM-Wirth Mak. The target object was the Moon. We used the exact same eyepiece and diagonal in both scopes so this was not a factor in what was seen in both scopes. Through the Santel the black of space with the Moon in the FOV looked like a very dark shade of grey, far darker than that provided by an SCT. Through the APM-Wirth, the same black of space WAS BLACK, not some dark shade of grey! When we looked down into each scope with the Moon shining into each scope, we could see the small areas inside the Santel that were the sources of scatter that reduced the contrast, but the APM-Wirth Mak had none of these anywhere along the baffle tube. And neither scope makes use of that series of rings like Intes uses. This APM-Wirth really has that "refractor-like" level of contrast.
Like I said, adding flocking is not doing anything that you think it is achieving. Not by a longshot. You want to actually improve contrast in your scope? Then deal with the true source of internal reflections and light scatter.
Alex.
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