baffled about flocking

[Leo.A]

Can anyone advise me on fitting baffles and flocking to my 80mm, 900mm focal length refractor.

I would like to use the scope to do some photography and while I've taken numerous reasonable quality photos of the moon (both projection and straight through with 35mm film camera), I'd like to take it beyond this level.

I know how to fit the baffles, have done the cone of light under a cone of silence without the influence of any other cones (a little humour) but all my searching hasn't answered a couple of concerns.

1: Can I use tin inside an aluminium tube?

These materials will both have differing expansion/contraction rates, so will it cause any problems?

I have some old tobacco tins which can have the bottoms cut off to provide a lip to fit them (using the base as the baffle) and they are a good interference fit into the tube.

2: Do all my baffles have to be equidistant from each other or can I place them anywhere provided the aperture is correct?

3: I already have one baffle in the tube assembly itself and one in the focus draw tube, but am unsure of exactly where the focal length is measured. Is it from the inner face of the objective lens to the eyepiece with a fully extended draw tube and focuser?

I'm considering fitting one more towards the front of the tube as the original baffle is approximately 2/3 down the length of the tube nearer the focuser.

Would it be beneficial to fit more than one extra baffle?

I was contemplating possibly fitting 2 between the existing baffle and the objective and 1 more between the existing baffle and the focuser for a total of 4 in the tube and the small one in the focus draw tube.

I guess It may be more trial and error, but I don't have the weather conditions to trial it during winter. It's the wettest on record I believe.

Now to my flocking problem.

Can I use a non reflective, matt black, adhesive felt?

Is it better to fit the flocking in one circumference (not easy to roll it and apply it since it's self adhesive), or would it be easier/better to cut it into strips and apply individual strips length wise?

I'm trying to make the best of what I have and what I can afford, which is very little as a single dad and a disability pensioner.

Any advise or links to relevant information would be greatly appreciated.

Thanks!

[philj]

Having baffled myself a few times (pun) I shall try and answer you qs

1 Tin. I see no reason why not, many scope manufacturers over the years have used pressed steel baffles in ali tubes. I use ali myself because Im set up for machining ali and am lousy at cutting circles with snips in tin.

2. No

3. Thats exactly what I have done to a scope where I changed the focuser and lost the baffle in teh focuser draw tube. I made a new baffle and fitted it about 4" in from the focuser end of the tube.

Now the 6 m dollar question - Is it beneficial to add baffles. Yes. I found immediate improvement in contrast particularly on bright objects like the moon when adding a flocked baffle just 4" in from the focuser end. The benefits of more baffles will diminish with the number you add, however I suppose if you had one perfectly sized and positioned with 0 reflectivity then you would only need one I should imagine but nothings ever perfect.

Flocking

I use protostar flocking which is basically sticky backed black felt and works superbl. However fitting it into a small refractor tube all the way through can be a pain as the inside dia of the tube does not let you get your hand down to smooth it out and as ever with anything sticky backed it sticks everywhere, so you may have to do it in stages. I actually flock the face of the 1st baffle from the focuser as well because invariably the flat black paint used is not dead flat.

Hope that helps, I did a thread awhile back in the DIY section on here on doing just this to my 80mm Towa refractor. A full write up is on my web page http://philjay2000.tripod.com/classic/Modernising_the_Towa_339.pdf

Phil

[rfdesigner]

I baffled my smaller newt.

I drew up a diagram 1:1 scale and plotted the offending light rays and the wanted light rays, it was easy to see where the baffles cast shadows and where they didn't, thus setting the position of the following baffle. It made a significant improvement to the apparent skyglow visible at the eyepiece. (remember to allow the wanted rays to cover a field of view suitable for your widest eyepiece)

Refractors are much easier to baffle than reflectors so you shouldn't have too much trouble.

Derek

[Leo.A]

Thanks for the very helpful replies.

I'm considering fitting a different focuser in the not too distant future as my current tube only accommodates 1" eyepieces. A 2" unit is too big for the 80mm tube I believe (or I've looked at the wrong ones), so I will probably get one that takes 1 1/4" eyepieces. This should relate to better eye relief unless I'm misunderstanding the meaning of the term, and am just curious if my baffles would have to be changed again when I fit the new focuser?

If so, it would be beneficial to hold off on my current upgrade plans till I can find a reasonable quality affordable focuser instead of going through all this twice?

My current original Tasco focuser has been shimmed with brass to remove the slop and prevent movement of the scope when the motor drive for the focus nears the end of its travel. Prior to this when using the focus motor drive the tube would jump considerably and necessitate both realignment and locating whatever object I had been viewing.

So many plans, so little cash!

[rfdesigner]

As the focusser doesn't move the image plane then any baffling or flocking will be suitable for the new focusser or the old one. The only issue is field of view, which will increase if you do end up with a 2" focusser. Optimising the baffles for the larger focusser will then cover all eventualities.

Derek

[philj]

I fitted a 2" Antares Crayford to my 80mm Towa with no problems, the OD of the crayford was just a couple of mm under the od of the tube so a new adapter was made and it all fitted nicely.

No need to change the baffles as its the objective you are working to cut stray light from and this doesnt move.

Crawmach in the states do a nice 1 1/4" replacement crayford focuser for smaller scopes, they have a very good reputation and I understand a modified version is fitted to teh new Skylight Mini.

Philj

[Leo.A]

Thank you Phil and Derek, much appreciate the responses.

Hopefully, soon my scope will provide some better viewing and with the new EQ3 GOTO I should be able to find plenty I haven't seen before, plus my son has now taken an interest due to the driven mount, so it's a good thing.

@Phil, I have a nice little adjustable hole cutter which goes in my bench drill and providing care is taken not to force the cutter, it's very accurate. If I still had my metal lathe I'd turn something up but I only have a wood lathe now, had to give the Myford away due to space limitations.

[theodore]

hi,

I think baffles are over-rated. Its easier to fit flocking - I use sticky-backed black velour from a habidashers. I always find it easy to fit and completely eliminates internal reflections. I've used it for 127 and 80mm refractors and 150 and 300mm Newts, no problems. You can cut it into 1/2 circumference strips and overlap the edges a bit if you find it hard to fit. Don't forget to also flock the focuser back plate. I also put a flock disk on the internal edge of the focuser tube, which on my scopes is always shiny and can reflect back to the objective / primary.

Theo

[Leo.A]

Edited title and first post?

Sorry, I'll try not to offend anyone in the future!

I am however aware I did not use offensive language, just a play on words to describe my knowledge on the matter (or lack there of).

I've already done a test fit of my first baffle and it fits well so I may as well add it now and see how it goes and once I find my can of stove black to paint it with I will refit it. As for the sticky tube lining stuff I will start laying that between the baffles today.