The Synta Wonky, Plastic Objective-Cell Fix

[Alan64]

...and for Synta's entry-level refractors.  Are you really going to trust them to design and manufacture a static, square-and-true objective-cell?  Not a chance. For this fix, I've chosen the only refractor I have of theirs: the Celestron "Astromaster" 70mm f/13; however, this fix might be effected for most any entry-level, overseas refractor...

I do have one other of theirs, a 60mm f/15 "PowerSeeker", but I got it just for its 1.25" focusser to replace the .965" of my Tanzutsu of the same spec.

Isn't that achromatic-doublet a beaut?  However, pretty is as pretty is indeed, and that's what I'm about to find out: is this Chinese doublet just as good, let alone better, than that of a Japanese Towa, et al? 

There are three places where the cell is screwed onto the optical-tube.  But look closely at the image there...yes, that's right, or rather wrong...only two "wood" screws were present upon its receipt!

I had thought about contacting Celestron and requesting a three-pack, but then I realised I could simply find one here at home, or at the local hardware, albeit longer, cut it down to length, and booger up the tip with the Dremel...

No!  I can't!  I won't!

[Alan64]

First, and to get it out of the way, I blackened the edges of the crown and flint elements...

...must keep Synta's expert alignment of the elements intact.

...this, in the hopes of improving the contrast that much more.

[Alan64]

I couldn't use the holes for the "wood" screws, so I drilled new ones...and to my "ISO9001" standard ...

...albeit an unknown.

The smallest standard-size hardware I could find, at the local hardware with the lovely bins, and all of stainless with an extra set of nuts of common zinc-plated steel...

Phosphor-bronze...

 

 

 

[MarsG76]

nice ingenuity.

[Alan64]

Now, you can simply use the aftermarket hardware for a static installation, if you're that trusting.  Mine however will be dynamic, and collimatable.

One side of the bronze tabs and the stainless flat-washers were heavily scored with a wee diamond-bit...

Once the cell is collimated, and the screws with the lock-washers in addition battened down, said scoring will help prevent slippage, and the ruining of the alignment.

The new holes of the plastic cell were slotted, and the bronze tabs have been epoxied into place over them.  I used a steel-reinforced epoxy, as I did for the focusser-fix.  The screws here are holding the tabs in position until the epoxy sets.  All gluing surfaces were roughened up a bit just before...

I couldn't find jam-nuts of the size required, so I've chosen to grind down the common nuts, as they will be on the inside of the tube, therefore no need for stainless there.  There's no room for the nuts at their present thickness.  I can't have them jutting out into the light-path...

I had gotten four of everything, but I'm only using three.

And through this new, slotted hole, one of the old holes just beyond...

[Alan64]

30 minutes ago, MarsG76 said:

nice ingenuity.

Thank you.  I had heard of something like this being done before, but I didn't know of the particulars.  It is, therefore, straight out of my head, for better or for worse.

[MarsG76]

Tinkering like this is what makes this hobby better.... I'm about to active cool my DSLR, when that works I'll find much more joy and satisfaction out of it than if I just went out and bought a ready made cooled camera.... like I'm being recommended to do...

When you have your synta rock solid due to your own work, you'll love it that much more....

[Alan64]

Yes, tinkering with this stuff is great fun, and rewarding like no other.

I see that you're in Sydney; a bit of an illuminated dome I'm sure.  I wish it were otherwise.  When I lived in Memphis, I had only the brightest objects to observe, and not very many of those.  I now live about 25 miles south, here in Mississippi, and have for about 25 years.  Back then, the sky was filled with stars, but there are not quite as many now.  The third-largest gambling-complex in the U.S. is just to the west, and this area is slowly but surely becoming less rural and more suburban.  Still, I expect to use my eyepieces until my passing.  

Do you take that 14" out to the countryside on occasion?

[MarsG76]

36 minutes ago, Alan64 said:

Yes, tinkering with this stuff is great fun, and rewarding like no other.

I see that you're in Sydney; a bit of an illuminated dome I'm sure.  I wish it were otherwise.  When I lived in Memphis, I had only the brightest objects to observe, and not very many of those.  I now live about 25 miles south, here in Mississippi, and have for about 25 years.  Back then, the sky was filled with stars, but there are not quite as many now.  The third-largest gambling-complex in the U.S. is just to the west, and this area is slowly but surely becoming less rural and more suburban.  Still, I expect to use my eyepieces until my passing.  

Do you take that 14" out to the countryside on occasion?

I live a bit south off sydney, closer to rural rather than city where the sky is not too bad... actually during the clearest nights the milky way is easily visible.

I did take the 14" A FEW TIMES TO THE MOUNTAINS AND THE VIEWS WERE AMAZING.. but.. MOST of my sessions ended with the mirrors covered in dew. I've put on a dew solution on the 14", just need to find the time during either side of a new moon to take it to the darkest location.

 

[Alan64]

Oh, the sights you must see through it!  One night during a past winter, not only did my 6" f/5 Newtonian dew up, but it froze to boot.  The Moon was bright; but very dim, and almost like a new Moon through the ocular.  That was the end of that session.  I live on a ridge, about 100 feet above the north-Mississippi delta; but still very near sea-level.  The highest mountain in this state is less than 900 feet in height, and I've never seen it.  I wouldn't mind living in the mountains, in neighbouring Tennessee, if I could.  They're a little taller there; and for the panoramic view of the sky.

 

[NGC 1502]

 

Hijacking your thread a bit here......

Great stuff, I like a bit of tinkering and fixing things myself.  I’m definitely no equipment snob, but some of these entry level refractors do have a build “quality” that makes me cringe.......At the moment I have someone elses Celestron Inspire AZ 100. Metal is used very sparingly indeed. The all plastic lens cell is fixed to the tube with wood screws.........the sharp ends can be seen when looking through the glass. But at least it isn’t stopped down, a full 100mm is in use. I’m in the process of doing a few fixes for him, the main one being adapting it with slow motion controls.

Last night I tried it on Jupiter, comparing it with my 35 year old Vixen 80mm F11.4 achromat. I used my own eyepieces. At modest powers 30 to 60x, it was hard to tell much difference between them. But no surprises, at 100x plus, the old Vixen did much better. I could perhaps live with the Celestron’s objective, if the focuser wasn’t so wobbly, and the mount didn’t shake around so much, and it wasn’t so desperately hard to track objects, hence the request from the owner for slow motions.

The most “wonderfull feature” is the lens cap has a smartphone holder that fits over the eyepiece....?

I suppose for around £200 including 2 eyepieces, a red dot finder etc then you get what you pay for. I’m tempted to say I’d rather have binoculars, but they wouldn’t show Jupiters main cloud belts and so clearly reveal the Galilean moons, Saturn’s ring system, loads of lunar features etc etc....so perhaps it’s worth having. But I’d far sooner spend £200 on the classifieds on here or ABS.....

Again, apologies for the hijack.

Ed.

[Alan64]

Not at all, as all comments and critiques are most welcome.

[Alan64]

I decided not to grind down the nuts for the objective's cell, with the Dremel, one at a time, nor on one side only.  I made a jig of oak, and sanded down all three at once, both sides and in order to retain as much of the threading within each as possible, yet whilst still thin enough so as not to intrude into the light-path...

The nuts were then affixed with a steel-reinforced epoxy...

The screws were inserted to hold the new jam-nuts in place until the epoxy cured.

Here, the epoxy has long since cured, the epoxy filed down and tidied up, and the nuts/epoxy painted with ultra-flat black...

The hole in the centre there is original, and all three discarded.  The objective-cell is now collimatable.

It became obvious that the decorative aluminum collar, which fits loosely, would not slide over the new hardware, so I chopped it up into three pieces...

I then added a bit of flair to each, and epoxied them into place, permanently...  

I've decided not to spray the inside of the optical tube with ultra-flat black, but to flock it instead, and given the results of the refractor's second-light.  I've yet to perform a star-test however, but that can wait until after it's flocked.