Baffles vs Flocking?

Lo all,

Got a question for anyone with a little more knowledge than myself on the matter. I have the Orion 10" F3.9 'Astrograph' OTA. I am in the process of making a few upgrades to it and have had the primary and secondary out for the mounting of a new Moonlite Focuser assembly & placement of a CatsEye center spot. While having the mirrors & mirror cell out I reached in and did some inspections of the "baffle system" Orion has in the tube. This is what I found, there are 13 baffles all .5" with a 2" separation spacer that is part of the baffle. There is no sizing difference from the first baffle to the last they are all .5", really that is all that can be the baffle size as the tube is only 11.25" ID with the tube ends off. Using about any Newtonian configurator this setup comes back as "design does not allow for baffling" as the required front opening for what is considered to be proper for baffling would be about 12.25".

So here is where my questions come in. I pulled three of the "baffles" out from the rear of the tube, how I got the measurements, each one of the 13 weighs in @ .375 Lbs. each. This means the 13 baffles add nearly 5 lbs. to the weight of the OTA, I'm sure they are having some positive effects in maybe stopping down the OTA a little and helping to improve contrast in this fast Newt with a 31% secondary obstruction. My question is, do you think pulling the 13 small identical baffles and replacing them by flocking the tube would do the same as the current series of 13 .5" baffles 2" apart from the primary up? Just thinking about it as a possible way to fairly easily shave 5 Lbs. off the OTA without damaging the performance of the OTA. By everything I've managed to find on baffling a Newtonian OTA the 13 identical size baffles just don't seem like they would be doing a great deal of baffling & being plain plastic might even cause some possible thermal balance issues with the metal tube. It seems kind of like having a 26" long plastic inner liner about .063" sitting inside the tube against the metal wall of the tube, I can imagine that might cause some internal tube thermal problems. Maybe not. But I was just wondering if the flocking would be a better choice while reducing the tube weight some. Any thoughts or input would be welcome. Over all the OTA has given a pretty fair performance for a $650.00 ten inch fast Newt, just wondering if doing the flock vs 'baffles' change couldn't possibly increase the over all performance, given the smaller I.D. of the steel tube.

Thanks & CS!

Mark Jordan

http://www.thestardeckobservatory.com

If I were trying to reduce some weight I would keep the baffle nearest the diagonal and replace all the rest with flocking material. It's a short tube so, easy job. But how much are you REALLY going to save when you add the weight of the rolled .06" plastic. Maybe reduce the thickness to .032 would be better. I like Lexan® which is available in that thickness. But WDIK (what do I know). wait for a better answer.

The original question was about reducing weight while keeping some sort of baffle system, yes? And what you say is true about the 13 baffles (useless). Extending the tube works to reduce stray light. I would use a 24" .018" aluminum flashing for the (removeable) extension. $65 from the building supply for 50 ft. Try hitting up a contractor in the business for 38" or so, you will need some charm to get it free. Still have to ultra flat in inside. Piece of polycarbonate .030" alternative. Might still have to keep two baffles for tube strength down the thin steel tube. Tube currents might be a problem.
Doesn't look like it's going to save much weight after all but stray light will be reduced.


Mark Jordan said:
[SIZE="Small"](So here is where my questions come in. I pulled three of the "baffles" out from the rear of the tube, how I got the measurements, each one of the 13 weighs in @ .375 Lbs. each. This means the 13 baffles add nearly 5 lbs. to the weight of the OTA, I'm sure they are having some positive effects in maybe stopping down the OTA a little and helping to improve contrast in this fast Newt with a 31% secondary obstruction. My question is, do you think pulling the 13 small identical baffles and replacing them by flocking the tube would do the same as the current series of 13 .5" baffles 2" apart from the primary up? Just thinking about it as a possible way to fairly easily shave 5 Lbs. off the OTA without damaging the performance of the OTA. By everything I've managed to find on baffling a Newtonian OTA the 13 identical size baffles just don't seem like they would be doing a great deal of baffling & being plain plastic might even cause some possible thermal balance issues with the metal tube. It seems kind of like having a 26" long plastic inner liner about .063" sitting inside the tube against the metal wall of the tube, I can imagine that might cause some internal tube thermal problems. Maybe not. But I was just wondering if the flocking would be a better choice while reducing the tube weight some.)[/SIZE]

Thanks all,

Some good points, but the secondary & focuser while not set back a whole lot more than a regular Synta 10" Newt are set back 7.5" from the front of the tube. The regular set back for Orion has been closer to 4 inches, so no you cannot see the opening of the front when looking straight down the focuser. Don't have too many complaints on the contrast I get from the OTA, just as was said feel the "baffles" are pretty much a useless cosmetic widget not doing much at all but adding 5 lbs. to the tube weight. The end extension thing has crossed my mind a time or two, not really too concerned about the weight as it is sitting on a G11. I just like to get rid of things that might just be useless weight. Thought about replacing the baffles with a Protostar Tube Liner, it's cheap enough & a lot less hassle than going the flocking paper route. The pursuit of some free aluminum flashing such as the box building supply places sell is not a challenge. Being a FT career FF/EMT-P I can put the word out I'm looking for some & likely have more than I would ever need. About 1 out of every 5 FF I know or work with does contracting, several do roofing so the flashing wouldn't be tough to find.... It's a thought.

Right now I will have plenty of time to work on the tube if I want to as of the February the mirror is going to be bound for Steve Swazye. When I had it out I found a defect in the aluminum coating, it appears to be breaking down under the protective coatings. It's a very small spot about 2mm x 1mm in a tear drop shape, but under a 4x magnifying glass it looks like tiny flecky edges around the spot, but the protective coating appears unbroken. Not a good sign, possibly some kind of contaminate when it was coated. It's not a real problem right now doesn't really effect the images due to flat frames, nor does it seem to effect anything visually... Just a small defect, my concern being it may continue to grow. Orion was "understanding", but not much they are or can do about it as the OTA was purchased in December of 2012 new by the original owner, who sold it to me May of 2013 due to it being too heavy for his setup.

In Orion's defense, the OTA is "second hand" and out of the 1 year warranty period. Orion did respond to my hard copy letter sent to express my disappointment in a 2 YO primary mirror showing reflective coating deterioration. Just let them know it was happening & I was completely honest about the purchase history on the OTA. They did give me a call and expressed their regrets, wanted me to continue to monitor the defect & see if it continued to grow, but basically didn't know if they could do anything for me about it. I just told them fair enough, but I was likely going to go ahead and get it taken care of as I would not sell it with an uncertainty on the primary, likely just get it recoated & keep using it for a while. Thought I might as well have it refigured if possible before the recoating, Steve said he could get to it end of February!

Mark Jordan

http://www.thestardeckobservatory.com