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Old 13-08-2019, 01:00 PM
RussellH
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The horror of cheap T-Rings

So as you do when starting a new hobby, I tried to minimise startup gear costs where I could. One of these corner cutting measures was purchasing a cheap T-ring from eBay. The one I got came with a 2” adaptor, which was hard find, as everyone else only had 1.25” adaptors.

When I went to mount my DSLR for the first time last night, the camera connection was fine, but screwing the adaptor to the ring took multiple attempts as it kept sticking in spots as I screwed it in, and the last half of the thread to seat the adaptor flush with the ring took considerable force.

But it was together and working, so i gave it no more thought, until this morning. In my last 5 minutes before heading out to work, I decided to check the mounting of my Ba’ader MPCC Coma Corrector, the last piece of my imaging train to install.

So I removed the T-adaptor from the T-ring, and started to screw in the coma corrector. It started getting tight at the half way point again, so I unscrewed it until it came off, at which point I realise that I had not removed the corrector from the ring, I had unscrewed the thread adaptor of the corrector, and it was now stuck in the thread of the t-ring!!!

With no way to grip the now stuck thread adaptor, panic started to set in. Cutting the rest of the story short, I did finally manage to get it back out again, no harm done (I think). I’m now stuck in with a dodgy t-ring, and wondering how much I have to spend to find a decent replacement, as prices weekly wildly different with no way to tell you high ones are decent quality. I am also stuck without being able to use the Ba’ader until I find a replacement.

So, while I probably would play eBay bingo again if I had to do it all over again, sometimes there’s just no avoiding coughing up the big bucks for the right gear. Any suggestions on a good supplier that doesn’t charge the earth?

Thanks. Russell.
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Old 13-08-2019, 02:11 PM
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billdan (Bill)
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If you want to buy locally within Aust', Bintel has a kit of T-Rings for $49.00, that may be suitable for you.

https://www.bintel.com.au/product/bi...v=6cc98ba2045f
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  #3  
Old 13-08-2019, 02:38 PM
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Joshua Bunn (Joshua)
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Hi Russell.


I make custom adapters for the good people here on IIS. check out my forum post in the equipment discussion section 🙂


Regards
Josh
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  #4  
Old 13-08-2019, 03:22 PM
RussellH
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I’d actually love to get a low profile one for a bit more focus travel and to pull the focuser out of the tube a bit more, even if only a couple mm. Will check your post when I get home Josh.
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Old 14-08-2019, 05:43 AM
RussellH
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I just had an epiphany. When using the MPCC, I can’t use a low-profile T-ring as the MPCC requires 55mm back focus, so I need the standard 11mm T-ring still. The MPCC is not supposed to change the focus position when in use is it, so it will have no effect on my Camera focus position?

I’m wondering if it’s a bad idea to consider lubricating my existing T-ring to see if it’ll free up the binding. i certainly don’t want fluids flowing down into my camera body, or back into the scope, but is a gentle wipe with a lubricant infused piece of cloth still a bad idea? If it’s just bad threading, it’s not going to help, but if it’s rough threading, it might.

Thanks. Russell.
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Old 14-08-2019, 02:56 PM
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doppler (Rick)
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I've come across this before, some Chinese scope adapters and filters etc have the right sized thread but it's at a different pitch. I would tread with caution here it's pretty easy to destroy alloy threads.
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Old 14-08-2019, 03:06 PM
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Careful lubrication with right lubricant (syntetic grease for example) always helps, especially preventing stucking...

BTW, focusing threads of all lenses are full of lubricant, and there are no ill effects.

Last edited by bojan; 14-08-2019 at 03:30 PM.
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Old 14-08-2019, 03:34 PM
RussellH
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Quote:
Originally Posted by doppler View Post
I've come across this before, some Chinese scope adapters and filters etc have the right sized thread but it's at a different pitch. I would tread with caution here it's pretty easy to destroy alloy threads.
Very odd when they supplied both piece though and they still don’t mate. The listing said m42 x 0.75

As for lubricant, any specific recommendations then? Any particular silicon grease?
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Old 14-08-2019, 03:43 PM
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Silicone grease (Dow Corning vacuum grease for example) is not good lubricant for metal (Aluminium), it is actually worse than nothing.
I use Litium grease (green stuff - and very little of it).
Also, vaseline (petroleum jelly) is good
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Old 14-08-2019, 05:08 PM
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"Very odd when they supplied both piece though and they still don’t mate. The listing said m42 x 0.75"


You unscrewed the nose piece from the t adapter, so those parts were fitting ok? but then had trouble screwing in the comma corrector? I was thinking that the corrector and t mount threads were not compatible. Find out which has the bad thread and get a replacement, a lot of places don't even want the old one sent back.
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Old 14-08-2019, 05:57 PM
RussellH
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The ebay item I purchased was a combined T-ring and a 2" t-adaptor. They were supplied in a single box, but unassembled. When I first screwed them together, it was rough and jammed in the middle, but with some insistent pressure, I eventually got the adaptor bedded to the t-ring.

I then unscrewed the t-adaptor to try and put the coma corrector on the t-ring. Given it should have had a similar thread and also jammed, I assume it it the t-ring itself that is bad. I only managed to get a $5 rebate from the supplier, as they wanted me to post it back to china for a full refund, which of course it would have cost a fortune to send back. It's still usable if I don't want to use the coma corrector but use the 2" adaptor, so I'm OK with that, but obviously useless for my primary purpose at this stage, unless some lubrication helps, which I will try with some PJ and the cheap adaptor to see if it actually makes any difference or not, before proceeding further.
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Old 15-08-2019, 06:10 AM
RussellH
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I tried some petroleum jelly on the t-adaptor and it now screws into the t’ring quite nicely, although with one or two spots it does get a little tighter, but nothing like it was. I also have a cheap barlow lens with a t-thread. It screws into the t-ring nicely as well.

The MPCC still binds about 2-3mm short of mating with the t-ring. So now I’m wondering if it might be the MPCC? Hard to believe a $300 item would be worse than a $20 item though. I guess my only option left is to try a replacement t-ring and hope it’s a better fit. i found a low profile one and a spacer, so at least it’ll give me some extra flexibility for future use. Just hope the MPCC will fit, or I’ll be throwing good money after bad.

Russell.
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Old 15-08-2019, 07:02 AM
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Maybe the thread was damaged ?
You can try to inspect it with magnifyer or microscope if you have one.
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Old 15-08-2019, 07:12 AM
RussellH
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Hmm maybe. I assumed the t-ring was the issue and didn’t think to check the mpcc. I’m at work now. Will check when I get home tonight.
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Old 15-08-2019, 10:47 AM
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Merlin66 (Ken)
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Russell,
For the past twenty years I've advocated using boot polish to prevent jammed threaded components.
Just a light smear on the threads is all it takes.
No outgassing, heat melting migration etc.
Works very well.
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Old 16-08-2019, 07:33 AM
Wavytone (Nick)
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Another possible lubricant is beeswax or even candle wax. Stays put and no marks.
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Old 16-08-2019, 07:35 AM
RussellH
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Oh I have heaps of beeswax. I have my own beehives.
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Old 20-08-2019, 05:56 AM
RussellH
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The conclusion to this saga is that my new low profile t-ring plus 10mm spacer arrived from Sirius Optics yesterday, and I’m happy to report that the MPCC screwed in smooth as silk, I just hope the spacing is correct. Shame the weather is rubbish, so I wasn’t able to go check it out.
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Old 20-08-2019, 12:25 PM
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LewisM
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Quote:
Originally Posted by billdan View Post
If you want to buy locally within Aust', Bintel has a kit of T-Rings for $49.00, that may be suitable for you.

https://www.bintel.com.au/product/bi...v=6cc98ba2045f
I bought one of those Bintel sets once - every single one of them jammed to the point I had to cut spanner slots on the edges to unscrew them (which is NO fun over a CCD cover glass after it jams in solid!!!). The pitch is cut incorrectly, and there is ample roughness in the grooves and peaks. I always lube my threads with museum-grade micro-crystalline wax, and it still had binding issues, especially with Starlight Xpress and SBIG threads (enough screeching to make my cat go into attack mode!!!).

I solved my issue by having Stefan Buda make me a properly spaced adaptor - those threads are like teflon...
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Old 20-08-2019, 01:12 PM
Imme (Jon)
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I have a little trick that really helps on those dodgy binding threads.
Apply some mild heat (oven at 75'C) then pull them out, wrap a couple big red elastic bands around each piece and twist.
The heats seems to weaken threads a little to allow them to unbind and the rubber bands give a heap more grip.


Has worked for me a few times
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