True size of a 2 inch filter in mm?

[skye at night]

Hello,

I am not too experienced in 2 inch filters but need one for a specific purpose.....

The supplier I am considering using lists the filter as available in 48mm round or 50mm round....

Which is 2 inch?

I would generally think 48mm, but often suppliers list 50mm/2 inch as same thing.....

Any definitive answers?

Thanks

Steve

[jgs001]

Steve, I bought a 52mm to 48mm step down ring for my Canon Nifty Fifty (52mm filter threads) so that I can fit my 2" Skywatcher LPR on the lens. It's a perfect fit. So 48mm seems to be the correct size.

[Merlin66]

The standard "astronomical" 2" filter is actually a 48mm filter thread.

The clear "glass" aperture is close to 47mm diameter.

Hope this helps.

( The 50mm round has no mounting frame or threads; ususally fitting into a special mount ie in some filter wheels or adaptors)

[skye at night]

thanks all...

48 should do what I need.

Thanks

Steve

[Saturn1]

Steve,

In engineering terms 1" is equal to 25.4mm 2" being the obvious 50.8 & so on.

For other sizes where you know the imperial but not metric, you tack the first number devided by the second i.e 1 3/8" would be 3 / 8 =0.375 plus 1 = 1.375 x 25.4 = 34.925. Hope that makes sense.

Although the same calcs won't work entirely for astro filters etc, as stated by Merlin, there are minor differences, but this should help you get somewhere close.

Ok, bable over with.

Tony

[callump]

Normally a filter described as 2" is designed to screw into a standard 2" eyepiece filter thread. The outside diameter of the filter including its holder will be about 2". The inside thread, i guess is 48mm.

I don't know if there is a spec for the amount of 'clear glass', but its probably another mm or so less, i would expect.

/callump

[michaelmorris]

Will a 48mm camera lens filter fit in the thread for a 2" filter?

[Jlou]

2" refers to the barrel  diameter of the eyepiece  not the filter thread major diameter.  The filter thread is 48 mm diameter  x .75 mm pitch.  I find it interesting  the large discrepancy  between the low prices  of camera  filter versus  eyepiece  filters. The prices of even the more expensive  camrera  filters rarely %10 of some telescope  filters. 

[fwm891]

This might help clear things...

 

https://agenaastro.com/astronomy-threads-explained.html