Baffles

[pmrid (Peter)]

I'm having a play with an 80x900 achromatic and planning to put together a well baffled tube. I am wondering about the number, size and placement of baffles. I plan using standard 1.25 inch EPs. What is the collective wisdom on this?

[Leo.G (Leo)]

I did exactly this with a Tasco 80x900 (I think, I don't remember too well) and found some calculator somewhere and drew the light cone and did the maths. It worked out in the end.
As for quantity, I can't remember but I can go have a look a little later after I hit the sack for a while.

[Leo.G (Leo)]

OK, I found some information, possibly what I used, I honestly can't remember it was several years ago:


https://www.cloudynights.com/topic/1...le-calculator/


Image as used on CN:
Original image as shown by
Mike I. Jones of Cloudy Nights



Another link which may be useful:


http://www.berfield.com/baffles.html


As for baffles, I believe from memory I had the perfect size tobacco tins a friend had given me and I cut the centres out as required based on the maths. I believe they sat in perfectly without any major need to secure them (they would be secured I just DO NOT remember) Did I mention I have an useless memory?


Two baffles and VERY rough photos.
This Tasco is modified beyond standard, Vixen 80mm ED lens cell, William Optics DDG Synta focuser (tube cut down to accommodate my design adapter), self made tube rings.


Sadly I don't really use it but while it's out now I should look into paint for the inner tube and throw it on a mount and take some lunar shots.
The original Tasco 17TR was bought new in the late 80s or early 90s from the only source I could find at the time for telescopes, some photography store. Luckily I had a pro photographer friends tax number and I saved on tax on anything related to photography (22% from memory), whether it was parts for a VHS I was fixing (though I did get asked what a VHS had to do with photography) to any lenses I could afford at the time.
GST RUINED that personal scam!

[pmrid (Peter)]

Hi Leo and thanks. I did a 100% line drawing and placed baffles at the first and second thirds positions and then used a simple micrometer and managed results very near the formula you showed. So I guess I'm on the right track.

All I need to do now is find someone who smokes tinned tobacco!!

[Leo.G (Leo)]

I don't even know if the tobacco is available in tins now. A friend used to smoke it give me tins if I wanted them. I used the empty tins for small screws for projects when stripping anything down.

[pmrid (Peter)]

I found I had a metal tin that had discs for a grinder and it is exactly 4 inch diameter. But cutting a precise shape and size hole has been a real drama. I have bandages on several fingers and thumbs now so perhaps I need to rethink my methodology.

[Leo.G (Leo)]

I'd suggest an accurate centre punch mark and a decent quality hole saw. I have one which has a cutter like a lathe bit and it's on an extendible arm and very accurate compared to the standard type hole saws. It's only suitable for use on a bench/pedestal drill though. I also use a decent flat piece of timber under what I'm cutting when using hole saws on thin material.
I went through numerous options before I found the tins which fitted precisely.
Clamps are optional but advisable if cutting thin material because it goes through fingers like a hot knife through butter.
I have a plasma cutter here which will do 10mm steel but I don't think it (or me) would be very accurate doing something like this. Certainly not hand held, I learnt my lesson after telling my son I was good with an oxy hand guided. The oxy cutting didn't require a full welding helmet which kept flicking between dark and light.
There's always the option of taking it to a local machining place or engineers shop if such a beast exists locally?

[pmrid (Peter)]

Well, it's done! 2 baffles installed; a new 4 inch aluminium tube Matte black inside and white enamel out; a Bintel Crayford focuser installed and only a dewshield/external baffle needed. I have a pair of 120 m guide rings I can use but would prefer a close tight fitting set one day. Haven't decided where to position a guide scope either.

Overall, I'm fairly happy with the optics. I plan using it for lunar/planetary initially but in time, I might try some NB imaging with it.

Thanks for the hints and advice.

[Leo.G (Leo)]

I'm glad my useless information was helpful.
You should get some stunning shots and check Aliexpress for rings, if you can wait they are often cheaper even when you add GST to their price.
I still have the original clamshell thing for the Tasco but prefer a vixen dovetail. I couldn't align the clamshell properly.