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Any true value in flocking an 8" SCT?

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#1 miniqtone

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Posted 17 April 2019 - 06:56 PM

I know that some folks have done this and I'd like to hear about what if any real improvements were experienced by doing so.

Thank you!



#2 yellobeard

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Posted 17 April 2019 - 08:02 PM

It depends on how the 8" is build..
But in general the tube diameter is big enough to not need flocking inside.
In case of a SCT, the mount of the schmidt corrector plate acts as a 'natural' stop (diaphragm), that, along with the fact that the tube is quite short, makes flocking not nessesary in most cases.

However....

In some cases, the inside of the baffle tube that extents from the central hole in the primary mirror, does need flocking attention.
You can test it by pointing the scope at the sky during daylight, use a high quality, low magnification eye piece, and look at the exit pupil at a distance of some 15 inch. You should clearly see the small illuminated disk, with the black obstruction in the middle. When you look at that disk, absolutely no light should appear around that disk! The disk should be very bright, exactly round with total darkness around its edge!
Any fuzzy light around it is caused by internal reflections, in most cases from the inside wall of that baffle tube in the primary mirror.
That fuzzy light definitely pulls down your contrast, especially during daylight!
But... thats during the day, which is the most drastic way of making even the slightest reflections visible!
Some of us want perfect, simply because when there are no internal reflections during the day, they certainly will not be there at night, which is a much more friendly situation for a scope as it comes to internal reflections.

But! There is one exeption to that 'more friendly situation'.. The Moon! The Moon also is much less 'forgiving' as it comes to internal reflections!

Big examples of reflecting baffle tubes, are most of the affordable 9-12cm maksutov scopes, like for example the Celestron C90.. There, the baffle tube reflects like a mirror, showing nice arcs of light when bright stars are just outside the field of view, those scopes definitely show bad contrast when used during daylight. And if there is one type of scope size that is very suitable and practical for use during the day, than its the C90!
Flock that baffle tube, and you will be amazed of the increase of image contrast!
With 8" scopes, like the C8 and Meade 8", which are more expensive, more time is spent in the factory, to minimize internal reflections.

So, to make a long story way longe.... sorry, shorter:

Flocking helps, when applied on the right spots. But the effect will be much less at night.
Test your scope the way I mentioned earlier, a big haze of light around the exit pupil shows that flocking will improve image quality, if you don't see that haze, flocking is not needed.

..

Edited by yellobeard, 17 April 2019 - 08:14 PM.

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#3 coopman

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Posted 17 April 2019 - 08:20 PM

The baffle tube in a C6 certainly benefits from flocking.  Not so sure about any of the other sizes.



#4 macdonjh

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Posted 17 April 2019 - 08:22 PM

When I had a C11 I did all the modifications that were fashionable at the time: ventilation/ cooling fans, internal dew heater, flocking.  Of the three, the flocking had the least practical impact.  My assessment was Celestron did a good job designing the primary and secondary baffles.  That said, the flocking sure made the OTA look cool, it was BLACK on the inside, which made the mirror look really bright... when looking into the scope instead of through it.

 

The cooling fans helped when I set the scope up at my club's dark site during the afternoon.  It kept the OTA closer to ambient while the sun was out.  By far the best modification was the internal dew strip.  It simplified set-up.


Edited by macdonjh, 18 April 2019 - 07:26 AM.

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#5 Don W

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Posted 18 April 2019 - 03:35 PM

Been using SCTs since 1980. Never saw the need.


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#6 Asbytec

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Posted 18 April 2019 - 07:23 PM

However....

In some cases, the inside of the baffle tube that extents from the central hole in the primary mirror, does need flocking attention.
You can test it by pointing the scope at the sky during daylight, use a high quality, low magnification eye piece, and look at the exit pupil at a distance of some 15 inch. You should clearly see the small illuminated disk, with the black obstruction in the middle. When you look at that disk, absolutely no light should appear around that disk! The disk should be very bright, exactly round with total darkness around its edge!

But! There is one exeption to that 'more friendly situation'.. The Moon! The Moon also is much less 'forgiving' as it comes to internal reflections!

Flocking helps, when applied on the right spots. But the effect will be much less at night.
Test your scope the way I mentioned earlier, a big haze of light around the exit pupil shows that flocking will improve image quality, if you don't see that haze, flocking is not needed.

..

waytogo.gif

 

Identify it and "flock" it. Deaden the stray light in some way. Depending on the application that lends itself to a solution, I used flocking paper and installed strip rubber "knife" edges where appropriate. Maybe some really flat black paint might work, too. In my opinion, too, this is the part that matters. I do not believe, in many cases, it's necessary to flock the inner tube wall itself. None of that is visible from the exit pupil and light would have to perform a miracle to find it's way down the primary baffle. 

 

glare sources.JPG


Edited by Asbytec, 18 April 2019 - 07:30 PM.

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#7 Axunator

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Posted 18 April 2019 - 11:44 PM

I've got nothing against flocking if indicated, but please use common sense while executing it. My second-hand C9.25 came with  a thick (≈1 mm), self-adhesive flocking velvet inside the primary baffle. It was even inserted so sloppily that it was partially detached from the inner wall under the tension from the rolled fabric. Needless to say, it was vignetting the scope like h***, and I couldn't rip it off fast enough... Must wonder if the guy who put it there was happy with the fruits of his labor fingertap.gif

 

On the bright side, it may have been one of the reasons I got the scope so cheap, and that idiocy could at least be undone in a matter of minutes grin.gif


Edited by Axunator, 18 April 2019 - 11:50 PM.


#8 luxo II

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Posted 19 April 2019 - 12:09 AM

I've seen an otherwise perfect Intes M715D spoiled by ham-fisted flocking - it had shed fibres throughout the interior of the scope and had detached from the inside of the OTA and was flopping around to the extent it was intruding into the light cone. Once the flocking was removed and the interior vacuumed, it turned out to be a terrific scope, no flocking necessary.

 

If you are determined to do this, take the time to choose long-lasting materials and do it well.


Edited by luxo II, 19 April 2019 - 12:12 AM.

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#9 yellobeard

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Posted 19 April 2019 - 06:18 PM

I've got nothing against flocking if indicated, but please use common sense while executing it. My second-hand C9.25 came with  a thick (≈1 mm), self-adhesive flocking velvet inside the primary baffle. It was even inserted so sloppily that it was partially detached from the inner wall under the tension from the rolled fabric. Needless to say, it was vignetting the scope like h***, and I couldn't rip it off fast enough... Must wonder if the guy who put it there was happy with the fruits of his labor fingertap.gif

 

On the bright side, it may have been one of the reasons I got the scope so cheap, and that idiocy could at least be undone in a matter of minutes grin.gif

 

Of course, with flocking a baffle tube, I mean flocking in a proper way.

Good quality flocking paper is quite thin, not vignetting scopes from 8" and up.

Under 8" , you might have to consider letting the flocking stop some 0.5 inches before the baffle tubes end towards the secundary mirror.

The baffle tube of my C90 already is very narrow with its some 16mm internal diameter, making flocking it quite a challenge. But when you succeed, the reward will be at least a highly improved daylight and moonview contrast (in case of the C90)

 

I already wrote it in my first remark in this thread: It highly depends on the scope what flocking will bring you, and there are so many different scopes out there.

So if you have the experience that flocking is not needed, then feel blessed, however, it doesn't mean that there are no scopes out there that do not benefit from it !!

 

..


Edited by yellobeard, 19 April 2019 - 06:23 PM.


#10 gnowellsct

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Posted 20 April 2019 - 06:09 AM

If you flock the baffle you will increase vignetting on a scope that is already narrow field. And you certainly don't want to mess around in there if it is an edge hd with lenses in the baffle tube.

I flocked the c14 but I did so as part of an engineering solution to supporting an internal dew heater. It's all still in place.

However I haven't flocked my c8 and note that its baffle tube is both roughened and blackened. It would be extremely difficult to get something to adhere in there.

Those of us on yahoo c14 that flocked our tubes in the early 00s came away largely unimpressed.

The c8 is one of my preferred scopes with great performance. The ease of using it with a top mounted 80 to 102 mm apo and it's great performance on planets and deep sky means the 5 inch apo often gets left behind.

If you saw a graph on vignetting I bet you'd leave well enough alone. My c8 is a 1989 body with 2015 optics. I admit I haven't opened up a recent vintage one lately.

Greg N
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#11 Asbytec

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Posted 20 April 2019 - 06:24 AM

It would be extremely difficult to get something to adhere in there.

Greg N

I am sure you know, but for the benefit of discussion, a baffle can be flocked by carefully cutting to fit and press fitting it inside the baffle. Mine is done that way and stays put without intruding into the light path (well, once it did, but I fixed it). Adhesive stuff is hard to work with, IME. Press fitting seemed to work best for me.

 

I left it just shy of the upper end of the baffle, however, to prevent that thin piece of paper from narrowing the opening even the tiniest bit. That was the advice in vogue when I did the mod years ago. Truthfully, though, I think it probably should extend to the upper edge of the primary baffle because the bright window/exit pupil test shows some reflection there. And it is the source reflection closest to the exit pupil, which means it's important to deaden any stray light there. 


Edited by Asbytec, 20 April 2019 - 06:25 AM.

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#12 Lola Bruce

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Posted 20 April 2019 - 11:35 AM

I have a Celestron CPC 800XLT and put flocking paper in it. Yes it helped contrast. Most would not notice the improvement but to me it was substantial.

Bruce



#13 gnowellsct

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Posted 20 April 2019 - 11:53 AM

I am sure you know, but for the benefit of discussion, a baffle can be flocked by carefully cutting to fit and press fitting it inside the baffle.


Any way one cuts the cake, one is adding layers to a structure that already vignettes. (It's there even if not obvious) One assumes in doing so one makes the calculation that the gain in contrast outweighs the increase in vignetting. The baffle tube lives up to its name. It is already baffled with a surprisingly rough surface that is more aggressive say, than the black sandpaper flocking used by Televue in its refractors.

Anyhow people can do what they want. I will say that I might consider buying a c8 that had been flocked...the inside of the ota. I would never buy one that had been flocked inside the baffle tube. The c8 is intrinsically challenged with field of view but already has good and even excellent contrast performance depending on collimation and how good a job was done in assembly.

#14 stevew

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Posted 20 April 2019 - 12:47 PM

If flocking made that much of a difference Celestron would have done it and charged us extra for it.

Opening up an SCT has the potential for misalignment when reassembling. I only open them up if it's absolutely necessary.

If you feel the need to flock something then flock the dew shield and see if that makes a difference.


Edited by stevew, 20 April 2019 - 01:02 PM.


#15 gnowellsct

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Posted 20 April 2019 - 01:01 PM

If flocking made that much of a difference Celestron would have done it and charges us extra for it.


Agree with your post and like c8s. But let's not go too far. Celestron has been glacially slow to make some improvements.

But I think the company already has dealt with the inside of the baffle tube.

GN

#16 stevew

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Posted 20 April 2019 - 01:13 PM

Correct me if I'm wrong, but wouldn't adding another layer to the tube wall also slow down the cooling process?



#17 stevew

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Posted 20 April 2019 - 01:17 PM

I've got nothing against flocking if indicated, but please use common sense while executing it. My second-hand C9.25 came with  a thick (≈1 mm), self-adhesive flocking velvet inside the primary baffle. It was even inserted so sloppily that it was partially detached from the inner wall under the tension from the rolled fabric. Needless to say, it was vignetting the scope like h***, and I couldn't rip it off fast enough... Must wonder if the guy who put it there was happy with the fruits of his labor fingertap.gif

 

On the bright side, it may have been one of the reasons I got the scope so cheap, and that idiocy could at least be undone in a matter of minutes grin.gif

I would never buy a used SCT that someone had flocked. Only because I would have no idea if the person who flocked it actually aligned the corrector plate properly.

Was it radially aligned properly, where the spacer put back in the proper place?


Edited by stevew, 20 April 2019 - 03:00 PM.


#18 Axunator

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Posted 20 April 2019 - 04:22 PM

I would never buy a used SCT that someone had flocked. Only because I would have no idea if the person who flocked it actually aligned the corrector plate properly.
Was it radially aligned properly, where the spacer put back in the proper place?

Well, I bought it from a vendor (specialized in selling second hand gear) from UK, so overseas for me (Finland). The fact that it was flocked was not disclosed to me at the time of purchase. The scope had some other issues as well. Once the scope arrived, and I realized the sorry state it was in, the vendor support was abysmal. Of course I could have returned it even without any vendor support (mail purchase within EU), but in the end decided to bite the bullet and try to fix the scope, because 1) I got it very cheap (no wonder..) and 2) used C9.25’s don’t grow in trees where I live in (the reason to buy overseas in the first place).

The scope alignment was messed up on all possible levels including secondary centering and rotational alignment of both the secondary and the corrector plate, but with patience and help from good CN folks (special thanks to John Hayes who was extremely helpful and patient with my questions) I got it fixed and, I believe, well aligned at the end. Now it star tests well and throws up good images. I’m quite happy for my perseverance. For the record, it’s recent enough model to have corrector centering screws instead of shims.

Sorry for long off-topic post but I felt that I needed to reply...

Edited by Axunator, 20 April 2019 - 04:33 PM.

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#19 Asbytec

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Posted 20 April 2019 - 08:28 PM

To flock the primary baffle, there is no need to disassemble the scope. Just insert the flocking paper through the visual back. There is no real need to clock the inside of the OTA, so again there is no need to disassemble the scope. 

 

Yes, most CATs I am aware of have some form of micro ribbing in the baffles and maybe a knife edge somewhere in the visual back. My current Newt focuser has micro edges, and it's amazing to see how effective they are compared to smooth metal. I cannot say they are completely effective, maybe they are. Maybe not. One can check by looking up the baffle when the scope is pointed at the moon or a streetlight. If those tiny ribs are bright, then there is some leakage. This was my case, especially up toward the upper end of the primary baffle. 

 

One can also check the secondary baffle, however I do not recall seeing any reflections from it and it requires some disassembly to flock. My secondary baffle is removed to reduce the obstruction and vignetting - the secondary was not properly designed. It was designed to be light tight, and it was too tight. It cut into the converging light cone. So, I flocked the baffle and visual back for added security. After much observational testing and probing with a laser pointer, removing the baffle did not allow stray light from the meniscus to strike the focal plane directly. Flocking helps ensure it is attenuated before it get's to the focal plane indirectly. 

 

There may or may not be any real benefit to flocking the primary baffle, at least, but you won't know until you check the baffle and test with flocking in place. Doing that is an easy and perfectly reversible mod, unless you use the adhesive paper. I don't recommend adhesive paper, simple cut and press fit works well. Any benefit will also be determined from the application. When viewing deep sky, the light is so dim any stray light from the FOV is not a problem. The planets, maybe. The moon, probably. Then, the presence of any direct lighting in the area might cause a problem if you're pointed near it. 


Edited by Asbytec, 20 April 2019 - 08:36 PM.


#20 stevew

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Posted 21 April 2019 - 02:07 AM

Well, I bought it from a vendor (specialized in selling second hand gear) from UK, so overseas for me (Finland). The fact that it was flocked was not disclosed to me at the time of purchase. The scope had some other issues as well. Once the scope arrived, and I realized the sorry state it was in, the vendor support was abysmal. Of course I could have returned it even without any vendor support (mail purchase within EU), but in the end decided to bite the bullet and try to fix the scope, because 1) I got it very cheap (no wonder..) and 2) used C9.25’s don’t grow in trees where I live in (the reason to buy overseas in the first place).

The scope alignment was messed up on all possible levels including secondary centering and rotational alignment of both the secondary and the corrector plate, but with patience and help from good CN folks (special thanks to John Hayes who was extremely helpful and patient with my questions) I got it fixed and, I believe, well aligned at the end. Now it star tests well and throws up good images. I’m quite happy for my perseverance. For the record, it’s recent enough model to have corrector centering screws instead of shims.

Sorry for long off-topic post but I felt that I needed to reply...

Glad you made the repairs and brought your scope back up tp specification. 

I only mentioned that I wouldn't buy a used flocked SCT so that the O/P understands that flocking his tube may affect the resale, should he ever decide to sell it.


Edited by stevew, 21 April 2019 - 09:54 AM.

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#21 Gil V

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Posted 21 April 2019 - 08:12 AM

At Criterion, our flocking for the baffles came in the form of a can of Krylon flat black spray paint...
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#22 WadeH237

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Posted 23 April 2019 - 12:54 PM

A long time ago, when I asked someone far more experienced than me, and it was suggested that instead of flocking, the best solution for an SCT was to make a flat black circular mask that is a bit larger than the central obstruction and put it on the front of the scope.

 

The idea is that, by making the CO just a little bit larger and non-reflective, that it makes it much harder for stray light to find its way into the baffle tube.  At the time, I was talking about my C14, and he said that a compact disc is about the perfect size to use for a C14.  You would want something smaller for a C8.

 

Note that I have never tried this, but I wanted to throw it out there as a suggestion.  It's much easier to do, and much easier to reverse, than flocking.


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#23 Cpk133

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Posted 23 April 2019 - 06:38 PM

A long time ago, when I asked someone far more experienced than me, and it was suggested that instead of flocking, the best solution for an SCT was to make a flat black circular mask that is a bit larger than the central obstruction and put it on the front of the scope.

 

The idea is that, by making the CO just a little bit larger and non-reflective, that it makes it much harder for stray light to find its way into the baffle tube.  At the time, I was talking about my C14, and he said that a compact disc is about the perfect size to use for a C14.  You would want something smaller for a C8.

 

Note that I have never tried this, but I wanted to throw it out there as a suggestion.  It's much easier to do, and much easier to reverse, than flocking.

The co is already bigger than the secondary.  I think he was pulling your leg. 


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#24 AxelB

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Posted 23 April 2019 - 09:54 PM

I put protostar in the tube of my C8 but I agree its effect is minimal (but it looks cool ;-)). This was part of a larger project involving a complete dismantling of the ota so while I was at it, I could as well flock it.

I avoided the baffle tube because I didn’t want to install the relatively thick Protostar inside it and risk vignetting the field of view.

If I ever need to open that C8 again, I may build myself a special brush to allow me to apply a few coats of ultra flat black paint (I have a bottle of black 2.0 from https://culturehustl...st-art-material ).

Edited by AxelB, 23 April 2019 - 10:11 PM.

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#25 gnowellsct

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Posted 23 April 2019 - 11:45 PM

c8 baffle tube.jpg

 

This is what the behind of a c8 looks like using a flash + 200 watts of lamp light shooting into the baffle tube.  This is in my opinion a well baffled surface that does not need to be flocked.   Off axis Jovian and lunar light are going to have a hard time making it down this baffle tube, and I doubt anything that one would add after market would be an improvement.

 

So far the discussion has been whether one *should* flock the baffle tube.  My view is, no.  You have a well baffled system and adding anything else in there increases the vignetting. 

 

Now, if one buys a scope that has had modifications to the baffle tube and does not get vendor support, well, that is a different story, and what to do about a non optimal system is a different question.  Depending on my mood, I might fight with the vendor to take it back, I might just remove the foreign material (if it hasn't been totally glued in), or I might just leave it the way it is and see if the scope is acceptable.  That to me is a question different from "should I deliberately stick stuff in there."  Well it's your scope!  By all means.  But I don't think it's going to improve performance.

 

Look folks, I know all about the freedom to mess with scopes.  The reason I have 2015 optics in my 1988 vintage c8 carcass is that I went several steps too far in messing with the older c8 and had to decide between chucking it and giving it new innards--which has been a lot of fun.  So if you want to put stuff in your baffle tube go right ahead, I've done worse, but I don't think one should be under the illusion that it is going to materially improve the image.  

 

Greg N

 

 

 


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