2" Aero ED / TMB clone filter threads

[badhex]

Hello all,

Why on earth have the 2" Aero ED / TMB clones got a filter thread that is not the same pitch as standard 2" filters? 🤯

More importantly, is anyone aware of an adaptor that may exist so I can use my expensive Oiii filter in it without fouling up the threads on the filter? I have no clue what pitch the Aero ED is using though.

[John]

I've owned the 30mm and 40mm Aero ED's and found they worked fine with my Lumicon and Astronomik filters

[badhex]

23 minutes ago, John said:

I've owned the 30mm and 40mm Aero ED's and found they worked fine with my Lumicon and Astronomik filters

Ah - mine is the 35mm which I understand is technically a 'new' eyepiece and not a clone of the original TMBs. Could it be that the thread is different on the 35mm? Not sure if they use the same bodies or not but seems odd that they wouldn't.

I guess it could also be that thread blackening paint is causing the issue but there's definite resistance after a partial turn which feels like a threading mismatch, and I've not been willing to risk tightening it further!

I actually have a cheap skyglow which I could perhaps use as a sacrificial lamb. I guess I'd better have a look at it in the daylight which I haven't yet done.

 

Edited October 12, 2021 by badhex

[Pixies]

I have both the 30 and 35mm. I'll test them out once I get the dog to bed!

[Andrew_B]

Apparently there isn't exactly a standard 2" filter thread. Most manufacturers seem to use M48x0.75 but some use M48x0.6 and Baader have adopted a pitch of just under 0.75mm to try and maximise compatibility with the range of M48 threaded products on the market based on detailed measurements of hundreds of examples.

[Pixies]

For info. I tried my 2" UHC (no name) and it fits both 30mm and 35mm Aero ED eyepieces.

[badhex]

1 hour ago, Andrew_B said:

Apparently there isn't exactly a standard 2" filter thread.

I did not know that. Seems daft not to to be following a standard for something so widely used as filters!

54 minutes ago, Pixies said:

For info. I tried my 2" UHC (no name) and it fits both 30mm and 35mm Aero ED eyepieces.

Hmm, weird. Thanks for checking - surely mine must be the right pitch as well then and maybe it's paint on the thread or something else.

Looks like I will have to get everything out tomorrow and do some testing! Will report back.

[badhex]

Had the EPs and filters out today to do a bit of testing, and also did a bit of research online.

The issue seems to be that the Astronomik filter is M48x0.75 per Astronomik's website, but it might be that the Aero ED is actually M48x0.6 - and also, it turns out, possibly the Televue Panoptic - although this is unconfirmed. As per SGLers comments earlier in this thread, it does seem that most manufacturers are broadly using 0.75mm pitch standard, but not always, and manufacturing tolerances etc. mean some accessories just don't quite fit with other accessories.

I tested a number of my 1.25"-2" adaptors and diagonals which were all fine, but both the Aero ED and Panoptic start to bind after a turn or so, and leave a gap between the filter and the barrel:

 

The filter, on closer inspection does have a small manufacturing issue/blemish where the very last part of the thread is a little malformed, however I do not believe this is the problem as the filter has no problem with the adaptors and diagonals, and it starts to bind well before that part of the thread is in contact with the eyepiece barrels.

Looking at the barrel interior itself, I crudely measured the thread as best I could and it definitely seems more like 0.6 than 0.75:

 

I also tested other filters I have and what I did find was that the cheapo skylight filter (none-astro, picked up as part of an ebay bundle) not only fits all of the eyepieces/adaptors perfectly, but will stack and accept the Oiii perfectly as well. With that I mind, I fashioned a lens spanner and removed the filter glass from the skylight filter, and can use it as a 'universal adaptor' of sorts. It will add a few mm onto the optical train but I don't envisage it being a problem.

[Don Pensack]

Several years ago the people at Lumicon tested almost 200 2" eyepieces.

They found so much variation in diameter that they realized that if they held their filter threads to extremely tight tolerances

that they could only fit about 50% of the eyepieces.  25% were so large the filter would simply push in without catching a thread or be so loose it would fall out.

25% would thread in maybe 1/2 thread or not go in at all.  And some were not round!

The rest varied from extremely tight to extremely loose, but at least the filter would stay on the eyepiece.

48mm x 0.75mm is the standard, but just like when you use a tap, there will be a big difference between threading the tap in part way or all the way through.

 

So you are merely dealing with +/- tolerances here, and wonderful Chinese quality control (which barely exists, if at all, on eyepieces at this price point).

It isn't just filters, it's everything threaded from China.  

[badhex]

21 minutes ago, Don Pensack said:

Several years ago the people at Lumicon tested almost 200 2" eyepieces.

They found so much variation in diameter that they realized that if they held their filter threads to extremely tight tolerances

that they could only fit about 50% of the eyepieces.  25% were so large the filter would simply push in without catching a thread or be so loose it would fall out.

25% would thread in maybe 1/2 thread or not go in at all.  And some were not round!

The rest varied from extremely tight to extremely loose, but at least the filter would stay on the eyepiece.

48mm x 0.75mm is the standard, but just like when you use a tap, there will be a big difference between threading the tap in part way or all the way through.

 

So you are merely dealing with +/- tolerances here, and wonderful Chinese quality control (which barely exists, if at all, on eyepieces at this price point).

It isn't just filters, it's everything threaded from China.  

I did read about that research somewhere on my travels today.t

TBH I had assumed that the Aero ED had poor QC or weird threading, but thing that is a bit of a shame is that the extremely expensive Televue behaves exactly the same as the Aero ED. The filter was also expensive, so I'd at least expect the two expensive items to play nicely if they both have good QC and follow the standards.

[John]

I've not used a Panoptic 41mm but the Ethos 21 and Nagler 31 seem to fit my Astronomik and Lumicon 2 inch filters well

[badhex]

1 hour ago, John said:

I've not used a Panoptic 41mm but the Ethos 21 and Nagler 31 seem to fit my Astronomik and Lumicon 2 inch filters well

It's very odd John and I am also perplexed that others don't seem to have any issues, although perhaps it's just that specific eyepiece and that specific filter 🤔

[Louis D]

I'm investigating a theory of mine that thread depth is also a factor.  I've noticed on closer inspection of some troublesome male filter threads that they are deeper and sharper compared to less troublesome threads which are shallower and blunter.  I think it's because a lot of female filter threads are not very deep on inspection.  Thus, the male threads have to "chase" the female threads to make them deep enough to thread into.

[badhex]

4 hours ago, Louis D said:

I'm investigating a theory of mine that thread depth is also a factor.  I've noticed on closer inspection of some troublesome male filter threads that they are deeper and sharper compared to less troublesome threads which are shallower and blunter.  I think it's because a lot of female filter threads are not very deep on inspection.  Thus, the male threads have to "chase" the female threads to make them deep enough to thread into.

Interesting theory, I had not considered thread depth but that makes sense as a potential cause. 

One theory I had was that the other filters, (including the one I'm using as an adaptor) all have a shorter thread length than the Astronomik. This means that there are fewer threads mating at any time, and the filter is fully screwed in after fewer turns, so doesn have chance to bind.

Although, this only really applies if the issue relates to the Aero ED / Panoptic having a 0.6mm pitch.

[Don Pensack]

Since the filter is soft aluminum (usually 2014 or 2024), it can be chased using the "Dutchman's Thread Chase".

Basically, you sit in front of the TV and thread the filter in till it stops and tweak it tighter an infinitesimal amount more, then thread it out until it feels loose.

Repeat, each time threading it in a tiny bit more.  After 100 iterations, the filter will be threading in much farther than it did originally.

If you feel like it, keep doing this until it hits the stop (though catching only a couple threads is sufficient to hold the filter in).

I would suggest doing this on an eyepiece with a chromed-brass or steel lower barrel, as doing this to an aluminum eyepiece could be chasing threads in the eyepiece

as well as the filter.  The process is a lot faster in an aluminum barrel, though.

[badhex]

Thanks Don. I've heard of this technique before in another context I think. I suspect the Aero ED is aluminium but it might be worth investigating as an option.

[RT65CB-SWL]

On 13/10/2021 at 19:27, badhex said:

I did read about that research somewhere on my travels today.t

TBH I had assumed that the Aero ED had poor QC or weird threading, but thing that is a bit of a shame is that the extremely expensive Televue behaves exactly the same as the Aero ED. The filter was also expensive, so I'd at least expect the two expensive items to play nicely if they both have good QC and follow the standards.

The only TeleVue e/p that I have an issue with the filter thread is this one…

the 6mm Radian. Not sure though if the others in the series had the same issue.