Modernising a 70s Towa 80mm F15

[philj]

I posted this on the classic scopes groups but thought others may be interested as it doesnt just apply to classics, these mods can be done on any scopes

These scopes hail from the 70s and were renowned for having superb optics. After making an 1 1/4" adapter to fit modern eyepieces I can attest to that. For an achromat the views of Mars recently were astounding. At one point I was pushing 300x on Mars with bags of detail to be seen and little to no colour.

So I decided to treat the scope and me to a new focuser. The old focuser although functional was looooooonnnnnggg resulting in droop even though I repacked the draw tube felt.

I decided to fit a 2" Dual speed Crayford which would be man enough to handle binoviewers and the extension tubes that would be required to reach focus with 1 1/4" diagonals and eps

The Towa tube is 79.5mm ID and there are no direct upgrade focusers that will fit so an adapter would have to be made.

I plumped for the Antares dual speed focuser which normally fits the 120mm fracs. The tube adapter was removed and a new one to fit the Towa made up by a local machine shop to my dimensions was fitted to the tube

[philj]

The next step was to fit the focuser to the tube. This was easy as the tube is drilled with 3 off holes equispaced around the focuser end. Jobs a good un.

Before fitting the focuser I matted the single tube baffle face to improve contrast. Towa must have run out of matt black paint on my scope because the black was very patchy.

This mod is designed solely for making the scope compatible with binoviewers tehrefore the new focuser will fit directly onto the tube in place of the old. If I want to use ordinary diagonals and single ep the scope needs at least 5" of extension tubes fitted to the draw tube to reach focus. One day I will make up a tube extension of about 6" for use when I do not want to use the binoviewers.

Next was the finder. The Towa one is a long bodied 6x30 and very useable so it was going to stay but it need a new fixing as the original bracket fitted onto the focuser which I had removed. A rumage in my scope box found a Synta 30mm finder bracket and shoe which did the job nicely.

The next job is to fit a couple more baffles. The Towa has one in teh tube and one on the end of the focuser draw tube (how that works I dont know). I want a minimum of 3 and I am in the process of designing these on Turbo cad at the moment using a ray trace diagram to get the optimum size. I shall update when these are made

[dweller25]

Looks great, well done.

[philj]

1st light after the mod was spectacular. Mars was high and conditions were steady. With the binoviewers I was pushing 200x with filters. The view was a little dim due to the light loss in the binos and filter but it was superb, Syrtis Major, the polar cap and even some atmospherics on the limb were easily visible.

With binos the focuser was about half way, (my calcs were right phew). I fitted extension tubes and a 2" diagonal and was able to push teh scope to 300x on Mars filtered. The view with the #12 filter was almost 3d.

The mod had not only improved the handling but the lack of focuser droop and the better contrast due to matting of the tube helped contrast and definition. Lets hope a couple more baffles will improve things further.

Philj

[AndyH]

Amazing wot these wee scopes will handle, magnification wise.

Shows the quality the Japanese opticians could figure, on the long focus lenses.

Cheers,

Andy.

[argonaut]

A very interesting thread Phil,thank you.

What would we do without these small jobbing shops?

[philj]

Heres the 1st baffle pre painting. Knocked it up on the mini lathe last night from 6mm ali plate, not the nicest machining Ive done but seeing as its gonnabe covered in paint and stuck down a tube finish doesnt really matter. I took some of the meat out of it to reduce the weight.

This is the back baffle closest to the focuser, I calculated this to be 1.27" hole dia and would fit 4" in.

Its a nice slide fit in the tube and when positioned will be glued in place.

[Towa]

Eagerly awaiting a report on how well the baffles work Phil.

It's interesting that Towa only fitted the one in the tube, but the quality of the views through these scopes speak for themselves.

My Kenko 3 inch scope has 4, but then Kenko thought it was not necessary to paint the middle two and tube section.

One day I will re-paint the inside of my Towa with flat black paint, and will probably put an extra baffle in.

[AndyH]

Good job Phil !!

Andy.

[philj]

Eagerly awaiting a report on how well the baffles work Phil.

It's interesting that Towa only fitted the one in the tube, but the quality of the views through these scopes speak for themselves.

My Kenko 3 inch scope has 4, but then Kenko thought it was not necessary to paint the middle two and tube section.

One day I will re-paint the inside of my Towa with flat black paint, and will probably put an extra baffle in.

From my experience Mike just painting the insides with proper black, especially the tube baffle will give a great deal of contrast enhancement.

If you look down the tube from the objective end of mine the tube is only properly painted for 6" in the rest was only shown the spray gun:D The same at the other end, so my painting the single baffle the otehr night helped alot

Philj

[AndyH]

Out of interest.....

What type of glue will you be using?

Andy.

[Towa]

If you look down the tube from the objective end of mine the tube is only properly painted for 6" in the rest was only shown the spray gun:D The same at the other end, so my painting the single baffle the otehr night helped alot

Philj

They might have wanted to bunk off early that day to watch Godzilla.

I think the phantom paint sprayers apprentice was let lose on mine, judging by the 14 inch paint run inside my tube.

[philj]

Just put the scope away dripping with dew after a couple of hours testing whilst the main rig is imaging.

I sprayed the new baffle and temporarily fitted it for the test. I want to flock the tube inside so the baffle will be coming out again soon.

Anyrode the view of mars was even better than the 1st post mod light last week. No Syrtis this time to spice things up but the image at 200x was clear, excellent definition, no false colour that I could detect. I could even make out dark patches on the polar cap quite clearly at times. The dark areas below the polar cap and in the southern hemisphere were clear with signs of darker areas at times. Sorry Im not a Mars buff (yet) so dont know all the names:D

The real test of the baffle system will be testing it on a bright moon so next month that is on the agenda.

Is this mod worth doing? Yep definately worth every penny and minute spent on it.

Waiting for Saturn now to give it another test once its dried off

Philj

[Towa]

The mods are most definitely worth doing and worth every penny of it. Over the last 40 years I used two scopes that never

cease to amaze me, those two being the Towa and a Takahashi TSA.

I too was out observing Mars last night with the Towa and it is amazing what the little 80mm lens shows.

[philj]

A bit more work internally today.

I got hold of some Protostar flocking material and flocked the rear baffle, the tube internals at the focuser end and 8" in from the objective. I havent made a 3rd baffle yet because I have run out of ali of a suitable width, got to restock.

Heres the flocked baffle

The view of what the focuser sees. The flash makes it look very bright but believe me its dark in there Also the baffle is painted matt black under the flocking so the bits of baffle showing where my poor cutting lets it show isnt too much of a worry.

AND finally the finished articule waiting expectantly for a break in the clouds for a test.

This arrangement with the 2" filter wheel, extension tubes and 1 1/4" diagonal works well. I may treat it to a decent diagonal one day but this is functional

On a final note, flocking a 80mm dia tube internally is not easy:( Thats why I chickened out and did it in sections and have only flocked the business ends so far

So thats it for the moment. Just got to test it again. I think Im going to leave repainting till the warmer weather.

Cheers

Philj

[philj]

Out of interest.....

What type of glue will you be using?

Andy.

Sorry Andy, missed the question, Ive used 3 blobs of clear silicon sealant so if I have to take it out again I just have to break teh sealant. The baffle is also held in by the protostar flocking so its not going to go anywhere.

Philj

[F15Rules]

Brilliant job, Phil! I know how pleased you and Towa are with your 339s. I have decided to keep mine and get the lens cell off with help from an engineer I know (one of the 3 retaining screws is seized).

I need to do this as the lens is cloudy, a kind of milky deposit. I don't know if it is mould or fungus or just grime, but I compared it the other night to my 80mm Pentax and it was a good 25-30% dimmer than the Pen, and not as sharp. I am hoping that a good clean will fix the problem.

Plan B, is this..if I can't sort the lens out, I may buy one of the Carton 80mm F15 lenses from the US, same make as AndyH's new Carton F13 100mm I believe..the FL would be the same, so hope it could be made to work..the rest of the scope is worth saving.

I can heartily recommend the Classic Scopes forum if you are not already a member guys and gals...some great guys over there, who know their "onions":p!

[Astro_Baby]

Thats some lovely scope and some brilliant work. Love it.

[philj]

There's an old saying "Proof of the pudding is in the eating" ;well Friday (brief) and last night I managed to test the Towa on the Moon to see how the new baffle and flocking were working.

I am pleased to say they are working well and have made a considerable difference to the contrast.

Friday was clear between clouds and the 1st viewing showed the moon set against a jet black sky with no flaring against the rim. Small craterlets just popped into view the longer I looked at certain areas.

Last night was a little misty but I managed to get a few hours just drinking in the view. Contrats was a little compromised due to the mist but the view was still impressive. I was amased at what detail could be seen even with 150x.

Anyrode here is a snap from last night using the 1000d not the best image due to the mist but it gives an idea of just what this scope can now do.

Do I fit another baffle???? Yep I think I will, but not just yet, Ive a few other projects on the go at the mo:D

Philj

[Towa]

That's an excellent result Phil.

Come the summer, I think my Towa will be having an internal paint job and extra baffle, amazing to think that the Towa

can give even better views, the ones I get at the moment are fantastic.

[Doc]

I looked through Phil's scope last night at one of our EMS meets and I must say I was impressed. The scope delivered some fantastic views of the moon, the views were packed with contrast and those little cratlets really popped out.

Even when adding more magnification up to X250 the image was still very good.

Well done Phil.

[philj]

Thanks Mick and Mike

Hers a better image of the moon I managed to take tonight through the Towa, slightly less mist tonight early on so contrast was better. The second pic is a closeup on the top view

Philj

[Rob]

Diging up an old thread here.. super telescope. Could you please share with me how to calulate the baffles location?. Thanks Rob

[philj]

Hi Rob

Sorry about the delay in replying but have only just seen it coming to the surface again:)

Its easy and straightforward no maths or formulas involved.

I did my initial rough sizing using turbocad and just did a ray trace diagram. Turbocad isnt necessary a pencil, ruler and paper is just as effective. I measured the actual apeture in the cell also the focal length then drew a ray from each side of the apeture.

I decided to make the baffle position easy to get to, no point in putting it halfway down the OTA if you cant reach it to fit and secure it. You can then determine what size the hole will be from that.

I made the baffle, positioned it and doule checked by sighting down the tube at the fp to ensure the objective could be seen in its entirety but without any of the cell.

I used a cheshire eyepiece as a sighting device for that bit.

Simples:)

Philj

[Rob]

Thanks Phil,

I need to check the current ones as they are not fixed in the tube??.. they are just foam rings held in a preflocked tube..