BST starguider moon filter size

[Orange Smartie]

Hi. I've been out tonight with my my Heritage 150p and two new BST starguider eyepieces. Unfortunately, the moon filter (make unknown) i had for my old plossl eyepieces (also make unknown), is too small for the BSTs, despite having the same outer barrel diameter. 

Could someone with BST starguiders point me in the direction of a neutral density filter that would definitely work with my new eyepieces. 

Thanks in advance, 

Pete

[Tiny Clanger]

Most screw in eyepiece filters simply come in 1.25" or 2" sizes to fit the standardized threads on most eyepiece barrels as far as I know ... my Celestron £10 moon filter and cheap Chinese variable ND polarizing filters are 1.25" , and they fit my BST starguiders  just fine , so you should be OK with any that claim to be 1.25" . Mind you, they fit my plossls too !

Strange that your plossls & filter have a different thread to standard, did they come as a set perhaps ?  While you wait for a new ND, you can try perching the filter on top of the eyepiece instead of screwing it into the bottom of the barrel in the proper way.

Which makes me wonder .... you were screwing them into the bottom of the barrel in the proper way, weren't you ?!

Heather

[Orange Smartie]

Hi Heather,

Yes, I believe I'm doing it right - both lens types have an internal thread at the base, but the one in the old eyepieces is maybe 0.5mm smaller diameter so the filter simply doesn't grip in the BST thread. It's so long ago (like 25 years or more) that I bought them, that I really can't remember how they came, but as you suggest, may have been as a set.

No matter, I'll get a new one to fit 1.25". And good idea about using the filter above rather than below the eyepiece.

Pete

[Tiny Clanger]

50 minutes ago, Orange Smartie said:

Yes, I believe I'm doing it right - both lens types have an internal thread at the base, but the one in the old eyepieces is maybe 0.5mm smaller diameter so the filter simply doesn't grip in the BST thread. I

What provoked me to check was suddenly recalling that when I got my cheap Celestron Moon filter it was via Amazon , and there were very many peeved complaints in the 1 star reviews where folk had evidently attempted to screw the filter into the eyepiece cup ... 

Heather

[Zermelo]

I believe the only standard size smaller than 1.25" is 0.965", so you would know if it were that.

Another thought - are you sure that it's the thread diameter that's different, and not the thread pitch?

Some manufacturers produce 1.25" equipment with a slightly different pitch from the norm, so they're not always interchangeable. I think Meade were one such.