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Flocking the inside of SCT?

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#1 TheRCMan

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Posted 19 November 2005 - 05:40 PM

I have heard of people removing the corrector plate and installing flocking paper to the inside of the tube for improved contrast.

This was what a guy from the local club said.

"Now before doing this I could look into the tube through corrector plate and very easily see the tube wall. After installing the flocking paper I was shocked at the difference when looking into the tube. Even using a flashlight trained directly on the tube wall I cannot see the tube wall! It's like looking into a completely dark cave. All you can see is the primary mirror and the central baffle tube. I'm told that the addition of flocking paper to an SCT makes a huge improvement in contrast at the eyepiece".

Has anyone else done this with similar results? If so will the scope need to be re-collimated after the procedure?

Thanks!

#2 NeoDinian

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Posted 19 November 2005 - 06:18 PM

There are a few links on the net where people have done this.

You need to check the mark on the corrector before removing it (Or make a mark if there is none). This is so you re-align the corrector in the right place when assembling... You should check the Columnation (Spelling?) when finished.

But all in all, everyone who has done this have all boasted the increased contrast and a major reduction in off-access light.

#3 Psa19one

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Posted 19 November 2005 - 07:53 PM

I've done this to my 12" LX200. It is a project that requires some patience and care, but I found it to be well worth it. The contrast increase is notable (especially since Meades in particular have rather satin-based paint on the inside of the OTA!). Here's some pointers...

(1) As mentioned above, make sure your corrector is marked for its position before you take it off. A little dab of white-out on the edge of the corrector and the housing where it sits will suffice. Also, be careful to set it in a nice, safe place (away from kids, traffic, etc.) while you work.

(2) I bought my flocking paper from Scopestuff. It's good stuff...but quite sticky on the back and not too forgiving if you misplace it in the OTA and have to pull it up to reset it. Still, mine has stuck quite well in the OTA and not peeled up through all temps.

(3) Once you take the corrector off, I would also highly recommend you take the mirror out as well. Trying to flock the OTA with the mirror still in there is a recipe for disaster if the flocking paper happens to touch the mirror and sticks (and it will stick!) -- plus you will be less able to get the paper to the bottom of the OTA. It's better to remove the mirror assembly and be nervous for a few minutes doing it than being nervous for hours hoping you don't hit the mirror with the flocking paper. I am a novice and was able to do this without problem. Just be careful and place the mirror in a very safe place. I also gently covered mine with a towel (not touching the glass, but like a tent to keep dust off). You'll have to take off the focus knob to get the mirror out, but just be patient and careful. You will be able to do it. Note what washers, etc., go where as you disassemble the focus knob. Store them in a safe spot as well. Once you have completely gutted the OTA, you're ready to start flocking.

(4) Once your OTA is gutted, clean the inside walls with a damp cloth and let it dry completely. Measure the length of your OTA so you know how *long* your strips must be. I then cut my flocking paper into about 4 inch wide strips and flocked it in columns from the bottom of the OTA to the top, all the way around. Take your time. If it isn't perfect, don't sweat it! :)

(5) When you're done flocking, get one of those cheap lint-removers from Wal-Mart (the kind that uses sticky roll of paper you can use, tear off the used section and have new sticky paper). Roll it around all over your flocking to remove fuzzies that would otherwise end up on your mirror. Do this several times until you aren't picking up much black fuzz anymore.

(6) Put your mirror back in, re-attach your focus knob to you mirror housing, put your corrector back on (with the white-out marks matched up) and your set set go (though you'll likely want to collimate).

I also used ultra-flat black Krylon paint on the inside of my baffle tube. You might or might not want to do that. I think the Meade baffle tube is WAY too shiny and causes unnecessary reflections (despite its baffles). Here is an EXCELLENT link for further descriptions of all these things...

http://www.mapug-ast...UG/Contrast.htm

Hope this helps!

#4 Rusty

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Posted 19 November 2005 - 08:29 PM

I flocked my N11, and it made a slight - but noticeable - difference, most evident on bright objects.

You'll probably have to touch up collimation a very slight amount.

#5 trainsktg

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Posted 19 November 2005 - 09:12 PM

The Quantum Maksutovs came factory-flocked...so it should help to do so as a mod to your Schmidt.

Keith

#6 TheRCMan

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Posted 20 November 2005 - 12:04 AM

Neo,

col·li·mate ( P ) Pronunciation Key (kl-mt)
tr.v. col·li·mat·ed, col·li·mat·ing, col·li·mates
To make parallel; line up.
collimation

n : the accurate adjustment of the line of sight of a telescope


To adjust the line of sight of (an optical device).

#7 TheRCMan

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Posted 20 November 2005 - 12:36 AM

Kevin,

Thanks for the excellent description! :)

#8 matt

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Posted 20 November 2005 - 09:12 AM

Greg, there is an article by Jay Emirzian on astromart on how he collimated his C9.25. I can attest the result is very good - I'm the present owner of the scope! ;)

#9 NeoDinian

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Posted 20 November 2005 - 10:51 AM

Neo,

col·li·mate


Hey, it was late, and I was half asleep. :)

#10 TheRCMan

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Posted 20 November 2005 - 12:11 PM

Matt,

I will check it out thanks!

Neo,

No problem. :-)

#11 Psa19one

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Posted 20 November 2005 - 01:15 PM

Greg,

Another thing -- in addition to flocking and good collimation (and, by the way, if you don't have Bob's Knobs for easier collimation, they are a VERY worthwhile purchase...and cheap at under $20), cooling your OTA is essential for good seeing.

When I say "cool", I mean not only letting it sit out for 3 or 4 hours at sunset, I also mean using a CAT Cooler. Now, you can buy a Lymax for over $120, or you can make your own for under $10. Check out this link:

http://www.starcrwzr.com/cooler.htm

I noticed a HUGE difference when I had my cooler in my OTA for a good 30-45 minutes before viewing. SCTs can be very funny about tube currents -- and the more aperature you have, the more picky they are! :)

#12 TheRCMan

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Posted 20 November 2005 - 02:22 PM

Thanks Kevin!

Cool link! I may just have to make one... :D

#13 TheRCMan

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Posted 02 December 2005 - 10:06 AM

Hey Everyone!

Well I finally received my C5 in the mail the other day. It is a very nice scope. I haven't had a chance to use it due to all the snow we have been getting but I have noticed that the inside of the tube could use some flocking. Although it was painted with a flat black paint, it does seem to reflect a lot of light. As soon as the opportunity arises I will post a review of its construction and initial tests for factory collimation etc.

#14 Clive Gibbons

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Posted 02 December 2005 - 12:41 PM

Here's a test to try.
Take off the visual back of the SCT and look up the back of the scope (peering up the primary baffle tube).
You'll see the inside of the primary baffle tube and the secondary mirror and baffle tube.
Can you see the inner surface of the OTA? Bet ya can't.
Since you can't see the inside of the main tube, there's no way that light grazing off that surface will make it to the focal plane. Light grazing off that surface and hitting the primary mirror also won't make it to the focal plane.
You can do ray traces to show this, too.
So, is there a point to flocking the inside of the OTA?

One way to test this:
Get two identical SCTs, one flocked and the other not. Use the same eyepieces in both. Ask folks to look thru both, without knowing which is flocked and which isn't. Can they tell the difference? Otherwise, you're relying on how you think you remember the unflocked scope performed vs. the flocked one... which isn't a reliable way to judge.

#15 TheRCMan

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Posted 02 December 2005 - 02:53 PM

Very good information! :)

What about the light reflecting off the tube and hitting the primary mirror? Then you will have stray light in the focal plane correct? Won't that lighten up the image some(washout)? I am sure this would be more profound when observing in an area where it isn't completely dark like my front yard.

#16 TheRCMan

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Posted 02 December 2005 - 02:55 PM

Oh, I was just thinking. Wouldn't a good test be to stand at a distance from the scope and shine a flashlite at the scope from an angle? (say to mimic a street light) If you notice a difference then flocking would be good right?

#17 Clive Gibbons

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Posted 02 December 2005 - 04:11 PM

Very good information! :)

What about the light reflecting off the tube and hitting the primary mirror? Then you will have stray light in the focal plane correct? Won't that lighten up the image some(washout)?


Hi Greg.
Thanks!

WRT stray light reflecting off the side of the tube and hitting the primary mirror, no those rays won't reach the focal plane. At worst, they'll illuminate whatever dust or other imperfections there are on that mirror surface and cause an infinitesimal increase in scattered light.
Orders of magnitude less than what you'd be able to notice.

#18 TheRCMan

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Posted 03 December 2005 - 01:21 AM

Thanks again!

So it is not worth the time and effort. Got it! :D

#19 Psa19one

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Posted 03 December 2005 - 09:48 AM

Hi Clive! :)

Interesting. I found that flocking my OTA and blackening my baffle tube increased contrast on my 12" LX200. I "tested" this by making notes on several DSOs before and after this proceedure. In varying sky conditions, I have still noted an increase in contrast from before. I wouldn't have even bothered to go through the trouble, but many people on MAPUG argue convincingly that it helps. Anyhow... just my experience. ;)

#20 Clive Gibbons

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Posted 06 December 2005 - 11:10 AM

Hi Clive! :)

Interesting. I found that flocking my OTA and blackening my baffle tube increased contrast on my 12" LX200. I "tested" this by making notes on several DSOs before and after this proceedure. In varying sky conditions, I have still noted an increase in contrast from before. I wouldn't have even bothered to go through the trouble, but many people on MAPUG argue convincingly that it helps. Anyhow... just my experience. ;)


Hi Kevin.
Flocking/blackening the primary baffle tube *is* often a good thing to do. Many of the ones I've seen aren't "dead blackened" and will generate grazing reflections. This is most noticeable when looking at a big, bright object such as the Moon.

Clear skies,

Clive.

#21 Starman1

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Posted 06 December 2005 - 06:15 PM

Yes, it was on the Moon (with a lot of off-axis light) that I noticed the difference. The contrast was definitely visually enhanced.
Here's what I did:
1) pull the mirror all the way back into its cell, so it'd be out of the way.
2) laid in strips 6" wide, bumping the end up to the beginning of the mirror cell, where there is usally a small lip. I went all the way around, laying the strips in with the edges just touching, and the lengths cut to go from the mirror cell to the corrector cell. Result: no after-the-fact peeling.
3) I flocked the inside of the secondary baffle (visible directly through the back of the primary), and the outside of the primary baffle (with narrow strips).
This took more than one afternoon because I worked slowly and carefully.
The first night out, the background sky, when bright stars or the Moon were in the field of view, the sky was noticeably blacker.
But the effects were quantified when the faintest star seen in the scope went down a couple tenths of magnitude. Apparently, the scattered light reduced the limiting magnitude of the scope very slightly. A couple tenths is not much, but it did change the views of a lot of faint nebulae.
In essence, is flocking worth it? Yes.
What ticks me off about it, though, is that if the SCT manufacturers would use a blacker paint (such as the Japanese ultra-black model paint discussed on these forums), flocking would be unnecessary and there would be no noticeable difference if it were done. This might cost them $0.50 more per scope.
Of course, collimation should be checked upon reassembly. I had to turn one screw 1/64th turn.


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