Filter threads....Are they meant to be standardised?

[Marmot]

Hi

The title explains my question, but I will give a little more detail so that people understand why I ask.

 

I recently purchased (used) a Revelation Astro 2x 2inch Barlow. I have one 2 inch eyepiece, a Skywatcher Aero ED. I purchased the Barlow as it has an element that unscrews allowing it to be screwed into the eyepiece filter thread giving a lower magnification (approx 1.5). This appealed to me as although I didn’t feel the need to double the mag of my Aero ED, I did feel that the slight increase in mag using the screw in element would be useful and would be more cost effective than purchasing another eyepiece. Unfortunately the element does not screw on, but sticks after about a turn. Both threads appear clean and not blocked by any debris so I can only assume the threads are different. So I ask the question to see if this is a known issue or if I am unlucky and have a defective thread?

 

Unfortunately, as my initial plan seems like it won’t work I may have to sell on the Barlow☹️

Edited June 12, 2021 by Marmot
Add picture.

[gabs]

Hi,

 

I really would like to help you with your questions but unfortunately I am not very expert about Barlow lens.

 

I always found very difficult to get a nice focus when I use a Barlow lens but I think that was due to my scope which has some issue with the focus knob. As soon as I use my new scope I would be able to tell you more.

 

sorry! 

[Nightspore]

The 'Revelation' 2" Barlow is actually GSO. GSO threads are not always compatible with Synta or Baader eyepieces. I believe they're M48x0.75. Quite a few 2" eyepieces use this size. 

 

 

Although Synta, Baader and Tele Vue threads aren't compatible with M48x0.75 in my experience. 

 

 

2" threads have much less compatibility than 1.25" threads. There has been a bit of an effort in recent years to make 1.25" threads more compatible with each other. This just hasn't happened with 2". Half of my 2" filters won't thread into half of my 2" eyepieces. The first thing I do when I buy a new filter is check which of my eyepieces it will actually fit.

 

Astronomy Threads Explained

[Marmot]

Thanks to both of you for the replies.

Nightspore, yet again you have answered my question in some detail. At least I know it’s not a problem with my eyepiece thread but more a case of incompatible threads.

It’s a shame as I really like both the eyepiece and the Barlow, but combining them in the way I intended (screwing the element onto the filter thread) just won’t work. I sought out this Barlow in particular as it not only had the removable lens but it also got great reviews. 

Seems like I may need to sell it on and have a re think🤔 .

[Nightspore]

1 hour ago, Marmot said:

Thanks to both of you for the replies.

Nightspore, yet again you have answered my question in some detail. At least I know it’s not a problem with my eyepiece thread but more a case of incompatible threads.

It’s a shame as I really like both the eyepiece and the Barlow, but combining them in the way I intended (screwing the element onto the filter thread) just won’t work. I sought out this Barlow in particular as it not only had the removable lens but it also got great reviews. 

Seems like I may need to sell it on and have a re think🤔 .

 

I hope you can find a solution. Eyepiece barrel and filter thread incompatibilities have been a huge pain in the arse for astronomers for years lol. 

 

I once had a 1.25" Celestron eyepiece kit. The Plossl eyepieces in it were pretty good (BST/Barsta), but the filters that were bundled with the kit were basically incompatible with most of the eyepieces. Some worked with individual eyepieces but not others. A Green #58A didn't fit anything!

 

 

I still have three of the Plossls left, but the case was the most useful thing. 

[Marmot]

I had no idea that the thread issue was a known problem.

it seems that much in this hobby is trial and error and I accept that I won’t always get it right. It’s for just that reason that I get a lot of stuff from the used market, especially when I am not sure if it will work out, so I can avoid any large losses if I have to move it on. The Barlow was purchased ‘used’ so if I sell it on there shouldn’t be much of a loss if any. 

[Nightspore]

32 minutes ago, Marmot said:

I had no idea that the thread issue was a known problem.

it seems that much in this hobby is trial and error and I accept that I won’t always get it right. It’s for just that reason that I get a lot of stuff from the used market, especially when I am not sure if it will work out, so I can avoid any large losses if I have to move it on. The Barlow was purchased ‘used’ so if I sell it on there shouldn’t be much of a loss if any. 

 

Interestingly, GSO 1.25" threads are normally compatible with most things. As most OEM's are situated in Japan, Singapore, the PRC or the ROC it's difficult to get them to agree on a standard. Japanese threads had a reputation for not being very compatible for a long time.

 

 

My one and only Circle T seems to be excellent though. It has a beautifully made chromed brass barrel (only marred by the undercut) and its filter threads seem to be compatible with everything. 

 

 

 They utilised Ohi glass but I don't know where Tani San sourced the barrels and housings from. Apart from the undercut they were perfect.

[MarkAR]

There's also some not standard adapters I believe, can't remember what they were exactly but for the same diameter some had 0.5mm pitch and other had 0.6mm.

[RT65CB-SWL]

All my filters screw to my 1.25” e/p’s without problem. The only e/p that I do have an issue with filter threads is my TeleVue 6mm Radian.

[Nightspore]

8 minutes ago, Philip R said:

All my filters screw to my 1.25” e/p’s without problem. The only e/p that I do have an issue with filter threads is my TeleVue 6mm Radian.

 

TV threads are renown for incompatibility.