Flocking Advice

[Dave882]

The flocking on the inside of my c14 dew shield is coming adrift and I was considering to replace the flocking material rather than just re-sticking it.

At the same time I want to flock the outside of my 2600mc (I get bad reflections when using the hyperstar). And do you think its actually worth doing the inside the c14 tube as well??

Just wondering if anyone's got an opinion on the best material / supplier? And in particular if you think there's any benefit doing inside the tube (in particular for planetary viewing contrast).

Much appreciated...

[croweater]

Hi David. For the inside of your c14 you can get flock board from First Light Optics. It may be a bit pricey but you dont have to glue it to your tube. It come as a roll and snaps open against your tube walls. I like the sound of that. Anyway have a look on their site if interested.
Cheers Richard

[mura_gadi]

no idea about being a competitive price, but Astrodog in QLD also sells flocking.

[oska]

I've ordered some of this (& black 3.0), not exactly cheap for paint.

https://culturehustle.com/products/black-v1-0-beta-the-world-s-mattest-flattest-blackest-art-material?variant=41435474657438

[DarkArts]

You could try this: Taskmaster BLACK FELT ADHESIVE VELVET ROLL (https://www.ebay.com.au/itm/262839835037). It used to be available at Bunnings, but they don't seem to have it anymore.

I'd be nervous about putting anything with out-gassing potential inside my OTA. Richard's advice might make me re-think flocking the interior, though.

I use EVA75 foam (6mm) as a dew shield for my C14 - it's lightweight and naturally matt black. My next move is to re-do it with 1.2m wide foam to insulate the OTA as well (with a one-piece foam roll) in a bid to stop tube currents. Alex (of Astro Shop) has been talking about that for a while, so I figured I'd give it a try. I don't know if that's any use to you.

[Startrek]

Dave,
Maybe run the idea of painting the 2600MC black on the ZWO forum
I joined as soon as I bought my 2600MC back in August 2020 and the forum answered most of my questions in a timely manner ( either by ZWO admin or other members , especially Chen , who is the guru of 2600series cameras )
Painting the camera may inhibit some thermodynamic properties ( warming / cooling ??)
Who knows ?
Cheers
Martin

[Dave882]

Thanks Richard- I definitely like the idea of NOT sticking flocking inside the tube. I shudder to think how you’d deal with that if it starts to deteriorate. Cheers

[Dave882]

Yes I saw that- be interested to know if anyone’s got any experience (especially long term) with the stuff

[Dave882]

Thanks John- that’s an interesting product I’ve not seen that before. Thanks

[Dave882]

Yes flicking inside makes me a bit nervous too. I’m keen to know if anyone’s found a visible difference with flicking inside? I’ve already got the ota insulated but might look into the foam idea for the shield…

[Dave882]

Don’t think I’d ever paint the camera. If anything I’d probably make a sleeve to slip over. Got to be very careful not to interfer with the cooling. Cheers

[DarkArts]

Ah, the felt stuff is still available at Bunnings, but they changed the brand name: At Home 450mm x 1m Black Felt Adhesive Roll (https://www.bunnings.com.au/at-home-450mm-x-1m-black-felt-adhesive-roll_p3970145)

[mental4astro]

I've been using the Bunnings stuff for several years on multiple dewshields with no problem. My dewshields are made from Coreflute. I cleaned the dewshield section really well, finishing it of with some isopropyl alcohol before applying the stuff. When I'm done for the night I bring everything into my man-cave which has a dehumidifier running to dry everything off.

I emailed the people who make Black 2.0 & Black 3.0 about its water fastness considering an astro specific application. They were very helpful, explaining that neither product is water proof and not water resistant - these paints are not designed for being subjected to water, dew in our case. They are also extremely delicate, meaning they do not take well to being rubbed, finger or otherwise, as this will alter the surface finish that is attained by the drying process. If you are going to use either one of these paints, best only applied to closed surfaces, such as the inside of a Mak or SCT as these are very unlikely to have dew form on the inside of the OTA. Certainly do not use these paints on any surface that will be subjected to dew or movement, such as a dewshield. These are specialist paints designed for a specific purpose, not with astro in consideration.

Alex.

[Dave882]

Yes I think that Bunnings felt will be a very quick and easy solution for the dew shield (maybe even create a slide-on sleeve for the camera with it too).
Regarding the paint the more I think about it I’m not so sure I’m confident enough in my painting abilities to do a good job ;). That FLO material looks very interesting for the inside of the tube though. I’ll report back…

[oska]

Thanks for the heads up Alexander ;)

[mental4astro]

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.

[By.Jove]

I’ve seen that APM scope. It l certainly has exceptional contrast. No flocking. Though on the night I saw it, it had insulation extending out the front as a long dewcap and that probably also helps to keep stray light out.

[mental4astro]

A properly designed dewshield will help reduce stray light too. Certainly. But what is more critical is how the inside of the OTA is dealt with. A dewshield is token.

[Dave882]

Alex that’s a very helpful input thanks for sharing your experience.
So if I’m understanding correctly, if I were to use that matt black 2.0 on the baffle tube (inside & out) and on the secondary mirror holder there should be a noticeable increase in contrast for the imaging/viewing of brighter targets?
This would be quite a challenging project (and a level of risk involved too) but if the results are substantial I’d be very tempted to give it a go

[By.Jove]

There’s potentially another issue affecting contrast as well - glare off un-blackened edges within the eyepiece.

[mental4astro]

David,

This is the sort of thing that SHOULD be done in factory. Yet for their own reasons they don't and it has consequences for the end user. Yes, there is an element of risk for us as end users to do this and as a result it is up to the individual to decide if they want to undertake this and if they are then planning is important so to reduce the risk. There are ways to reduce the risk to the optics (not getting paint on them, etc), such as masking in ways that does not involve getting sticky stuff on the optics, or even leaving a short distance between base of say the baffle and where the paint starts. It may leave a short unpainted gap of a couple of mm, but will improve things in a significant way.

It is not just the outside of the baffle tube but the inside too. Look up the tube from the back end of the OTA and you will see a series of bright edges - these are the edges of the machined and black anodised aluminium. These also introduce stray light/scatter that impacts on contrast.

Eyepieces are less problematic. Even many inexpensive eyepieces come with blackened elements and good coatings to control internal reflections. There are some problematic eyepieces due to their design, but problematic eyepieces can be ferreted out quickly by doing side by side comparisons with the same scope. And this too may be a product of stray light from internal reflections from the scope if these have not been tempered. I have come across some contemporary (not cheap either) eyepieces that have internal reflection issues with small bright objects such as Jupiter and Venus, but these eyepieces thankfully are the exception.

The scope is the first point in the optical train, followed by the eyepiece and even your eyeball can have an impact as light reflects off the cornea from a bright source. Just don't fall into the trap of blaming a convenient scapegoat. It took me a long time to come to recognise the shortcomings of naked black anodised aluminium and how this impacts on contrast WAY MORE than we think, blaming the poor secondary mirror instead... When you look through other scopes of similar design and how their contrast is significantly better you need to look inside to see what THAT scope is doing different and not think it just because it is Brand "X" that that is the reason why. Brand "X" is not doing anything unobtanium-like. So what are the differences... It may surprise you how "simple" what they do is, though doing the fix is not necessarily easy as the end user.

Black 2.0 & Black 3.0

Remember that these are specialist paints designed for a specific purpose with artworks. These may not have the same adhesion properties that we expect the paint on our scopes to have. On bare anodised aluminium I would hazard a guess that there would need to be a primer used to ensure better adhesion of these specialist paints.

With this in mind, I looked back to my correspondence with the maker of these paints and I have emailed them today asking them about this aspect of using a primer first on bare metal. I'll report back on what they say.

Alex.

[wayne anderson]

Around 6 years ago I flocked the inside of my 12 inch Meade LX200, the resulting increase in contrast was not that noticeable, however when I painted the inside of the baffle tube with ultra-flat black paint the increase in contrast was indeed very noticeable, much less scattered light from the sharp edges of the baffles resulted in much better contrast on all objects, take note of the potential for scattered light from the sharp edges of the internal baffles in the photo.

[Dave882]

Alex- thanks so much I’ll be interested to hear what they say. I agree it makes perfect sense to tackle the biggest issues first. If there is a noticeable gain in contrast to be had with planetary viewing I’m keen to give it a go.

[Dave882]

Wayne that’s very encouraging to hear. Can I ask how you went about painting the inside of the baffle tube and what paint you used?

[wayne anderson]

There were many threads on the Cloudy Nights forum stating that krylon 1602 ultra flat black paint was good to use but very hard to find
even in the USA, this is just one of many discussions on krylon 1602 ultra flat black paint

https://www.cloudynights.com/topic/801030-black-30-or-krylon-ultra-flat-black-1602/

However I realised I already had a business account with an Australian supplier CRLaurence that stocks krylon 1602 ultra flat black paint , so I purchased a few cans.

https://www.crlaurence.com.au/crlapps/showline/offerpage.aspx?ProductID=6680&GroupID=4314&History=39324:4307:4312&ModelID=4314


The painting process was a little tricky, I did not want to go through the detailed process of removing the primary mirror or baffle tube so after
carefully removing the corrector plate I made a protective donut shaped cover for the primary mirror out of card board and tape then using
card board, cling wrap and tape I carefully masked off all other areas so only the inside of the baffle tube was exposed. Then I cleaned off any
oily residue inside the baffle tube with a cloth and isopropyl alcohol and allowed to dry.

I starting with several light coats of paint until the inside of the baffle tube was fully coated then I allowed a further 14 days for a complete
outgassing of the paint before re-assembly, this paint is very smelly and gassy.

All went very well and there has been no issues with it for 6 years and it should do very well for many years to come.