First Light Report - Towa 339

[AdeKing]

Since FLO started stocking the Scopetech long focal length achromatic refractors, I've had an urge to try an f/15 refractor to see what observing with a traditional long focal length telescope is like as I've seen loads of praise of them even though the current trend tends to be for shorter focal length ED doublets.

I do have an Altair Starwave 102 f/11 already, but it doesn't see a lot of use as I feel that my Vixen GP is about at its limit with this setup due to the weight and long moment arm.  Its just a little too shaky for me and needed a motorised focuser fitting for me to find it usable.

Anyway, @Dave1 posted an Ad in the classifieds for a Circle T 80mm f/15 refractor complete with most of the original accessories and the original mount and tripod in its original wooden storage crate.  After much deliberation, and changing my mind every 5 minutes, I eventually put it out of my mind and decided that I didn't need "yet another telescope" until I noticed that it had popped up on SGL classifieds again recently at a lower price, so I decided to give it a go and got in touch.

I collected the not insubstantial wooden crate and its contents at the weekend, and was surprised to find that despite being probably about 35 years old that the box still contained clouds.

Considering that these telescopes were essentially Department Store telescopes, I was really impressed with the build quality with everything being solid and not a sign of plastic parts anywhere in the construction of the OTA.

The OTA was quite scratched, something that I was expecting from the description in the Ad, but the optics were absolutely spotless.

I knew that the scope had been modified to accept 1.25" eyepieces and I also knew that Dave had flocked as much of the tube and focuser drawtube as was possible.

The focuser only has about 50mm of travel and to reduce the length of the tube the focuser employs a telescoping drawtube which extends the drawtube length by 210mm in addition to the 50mm of focuser travel.  I was quite excited by this as I hoped that the OTA would allow me to use my Binoviewers natively without needing a GPC element, so allowing lower magnifications.

First Light - Terrestrial

First light was to view a group of starlings on top of an electricity pylon about 200m away and I was pleased to see a nice clean and sharp view at 48x using one of the nice Skywatcher 25mm stock eyepieces (not the plastic one) and my Tak prism diagonal.

Next I removed the GPC from my binoviewers and put them into the diagonal and confirmed that I could just reach focus on the clouds, but needed a proper astro target to confirm.

Second Light - White Light Solar

Early yesterday evening saw some relatively large clear parches between the clouds so I added the GPC back into the binoviewer and put in my Lunt 1.25" wedge to view the sun.  After adjusting the focuser to a point at mid travel I then adjusted the extending drawtube to get a sharp image and was blown away.  The detail visible was impressive, three small spots in an arc (AR2772) with some associated pores and lots of obvious texture in the macro-granulation with some faint faculae also visible.  This was very pleasing and I can see this OTA becoming a solar favourite.

Third Light - Jupiter & Saturn

It stayed clear last night and I managed to get about an hour of viewing of Jupiter and Saturn in before I nodded off and woke myself by nearly falling off of my observing chair.

Performance on Jupiter was impressive at 48x with the moons cleanly resolved and details visible in the north cloud bands with the GRS being immediately obvious.  I was also pleased to see that there was almost no discernible CA, which was to be expected given the focal length, though CA doesn't actually bother me that much, even in my little ST102 that plenty of people complain about. 

I tend to prefer observing at lower magnifications as the contrast decreases as you increase magnification and although I did get a nice view at 114x through my Pentax XL 10.5mm the view at 48x through the Skywatcher 25mm was somehow more satisfying.

On to Saturn and again, a crisp sharp image presented itself.  I increased the magnification slightly and was able to resolve the Cassini Division but was too tired to put in the effort and try to pick out the subtle bands in the clouds.

Finally over to Capella to do a star test, not the ideal target due to its low elevation but it Was getting quite hazy by this time and Capella was nice and easy to pick out.  In focus there was a nice airy disc and on diffraction ring.  Defocusing revealed a perfectly centred bullseye target pattern, so I'm very pleased.

One thing that I did notice is that the Dewshield is rather short and things did start to dew up at the end.  I shall have to make a foam extension to the dewshield or get another dew strap, but I'd like to keep this setup as simple as possible so I'll try a dewshield extension first I think.

 Here is a photo of the Towa 339, I'll add more photos showing details of the sliding drawtube and clean objective once its stopped raining.

Edited August 20, 2020 by AdeKing
Sunspot number added

[Mark at Beaufort]

Very nice Ade it makes me think why did I sell my 80mm Towa.

[AdeKing]

10 minutes ago, Mark at Beaufort said:

Very nice Ade it makes me think why did I sell my 80mm Towa.

Thanks Mark,

I'm very pleased with it and am amazed at the quality of all parts of it it given that it was a department store type telescope.

Just need to switch the fixed finder for a vixen finder shoe so that I can use my solar finder with it.  The actual finder is lovely though, so need to get some small guide rings with a vixen foot so that I can carry on using it.

Regards,

Ade

[Peter Drew]

I'm just refurbishing one of these.  The tube and fittings were in poor cosmetic condition but no dings, they have been stripped, rubbed down and are ready for painting.  The objective however cleaned up nicely and pre strip down showed an excellent terrestrial image even at 400x.  I have fitted a 2" R & P for future astro tests.     🙂

[johninderby]

This fits a 6x30 finder just fine and I’ve used the bracket with a couple of scopes although slightly modded into a low profile bracket by leaving out the centre part. Replaced the nylon tipped acrews with shorter M5 x 10mm nylon screws.

https://www.amazon.co.uk/gp/product/B088WRYFXT/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Edited August 19, 2020 by johninderby

[DirkSteele]

To quote a famous jedi - "An elegant weapon for a more civilised age"