80mm F12 Towa 339 circa 1970

[philj]

After restoring and modernising my Towa OTA a few years ago I have been left with the mount tripod and wood crate doing nothing but taking up space in my observatory. So when Jules (Nightfisher) mentioned he was thinking of moving his 339 OTA on I couldn't resist making up a full Towa package again.

This was a project with 3 aims

1

I wanted to make the scope as original as possible, so any purists would see an original Towa 339 of the era.

2

It had to work properly with the original focuser and modern 1 1/4" eyepieces. Just putting a 1" to 1 1/4" adapter on and using 1 1/4" eyepieces doesn't work on these from experience because the baffling in the draw tube cuts some of the light path for the new eps, making the image a little dim.

3

The OTA had to be easily converted to fit Vixen DT mounts.

So here are a few snaps of the finished scope. I have just got to tidy a few things up on the mount and do the final star tests (hopefully tonight if the forecast comes true).

I shall post a 1st light once tested but from what I have seen so far I don't think I shall be dissappointed

Cheers

Philj

[philj]

Close ups of the focuser

To make the scope useable with modern eps I had to remove the baffles in the draw tube as these restricted the light path too much

I flocked the top of the OTA near the Objective and also the draw tube, this was to eliminate any internal reflections and make up for the loss of the draw tube baffles

[philj]

This is the full diameter 1 1/4 ep adapter

[philj]

To convert to fit the OTA to a vixen tube, you have to undo 2 allen screws to detach the scope cradle off the old mount.

Then fit a vixen DT bar to the cradle and eh voila jobs a good un

Here it is on my Giro

[JonH]

Nice one Phil, another fine looking scope. Hope you get your first light tonight and all goes well.

[johninderby]

Very nice.

It's funny how a little scope like this can be fun to use despite owning other "bigger & better" scopes. Keeping my fingers crossed for tonight as well.

John

[nightfisher]

See, i knew you were the right person to take on my old towa, these scopes deserve the very best owners, well done Phil, it looks sweet, good luck for the star test

[philj]

I managed a test that night and star images were perfect little bullseyes showing good airy discs indicative of good colimation, however, on bright stars a faint ghost image could be detected. This is usually an objective element spacing issue so I stripped the objective in the dark and the spacer ring between the elements was present but the one between the rear element and the cell wasnt there. Hmm a rethink was called for. The next day I took another look and the spacer was actually 2, so I put them in the correct orientaion and a star test last night revealed all was ok, no ghosting

I then spent awhile looking at a few objects through the mist and wasnt dissapointed, epsilon lyra split into all 4 with ease giving a lovely view. M27, 31, 13, 57 all looked good and the double cluster with a 40mm ep looked really good. The mist stopped a proper look at jupiter but i shall save that for another night.

Im well pleased with how this scope performs, just as good as my other towa

philj

[nightfisher]

really good news to hear the old scope is still good, nice one, here is a little question for you phil, how high can i push the focal length on my vixen 80 f11 with a ccd camera for lunar avi, i half wondered if i might get away with x3 barlow at 2730mm focal length?

This is the scope in question, and im talking on nights of really good seeing!

[michael.h.f.wilkinson]

Nice looking scope. Brings back memories of the Polarex catalogues from when I was a kid.

really good news to hear the old scope is still good, nice one, here is a little question for you phil, how high can i push the focal length on my vixen 80 f11 with a ccd camera for lunar avi, i half wondered if i might get away with x3 barlow at 2730mm focal length?

This is the scope in question, and im talking on nights of really good seeing!

This depends on the pixel size of the chip. On DMK21 and similar chips you could push to about F/30, but not far beyond.

[philj]

I agree Michael. Ive pushed my Towa with a 2x barlow with ease so on a good night I reckon it'll do it Jules

PS nice scope BTW

[nightfisher]

Thanks guys, hope to give it a try tomorrow night with the dmk21