2" Thread = ?mm

[BlueAstra]

Can anyone tell me the mm equivalent for 2" filters? I assume its 49mm, but 2" = 50.8mm? I need to get a step down ring for my Canon (58mm) so I can use my 2" SW LPF.

[riklaunim]

So you need T2 to 2" focuser reduction with a filter thread on it T2 side goes to DSLR without a lens. Like this one: Adapter von 2" Steck auf T2 Aussengewinde - Teleskop-Express: DER Astroshop + Fotografie + Naturbeobachtung so you will be able to use a 2" filter

If you want DSLR + Lens + Filter then you have to check which M** thread has the lens (like M48), and then M** to T2, and from T2 to 2". Or directly M** to 2" if any shop has such.

T2 to 2": Adapter vom T2 Gewinde auf 2" Steckdurchmesser - Teleskop-Express: DER Astroshop + Fotografie + Naturbeobachtung

[russ]

You just need a 58mm to 48mm step down ring

You can find them here:

Stepping-Rings

Russ

[Merlin66]

I got a whole series of stepper rings, 48mm to 55mm, 48mm to 58mm etc etc from Vintage. Excellent service! Recommended!

(I haven't found a "stepper" ring that will hold a 1.25" filter -28.5mm in a 2" (48mm) filter holder:( - this would be ideal to allow the smaller filters to be used in 2" fittings [i know about the possibility of vignetting with astronomical filters, but the Star Analyser/ Baader spectroscope gratings don't care!])

Ken

[riklaunim]

You can try cutting diffraction grating to the size of 2" filter cell or your DSLR filter size and put the circle on the filter.

[BlueAstra]

Thanks for the answers. I should have mentioned that I want to put the 2" LPF filter on the camera 18-55 zoom lens, which has a 58mm filter thread.

[russ]

I may still have my 58-48 step down ring. Can you hang on until i get home and check my old bits'n'piece box? You can have it for nothing if i do.

Russ

[Merlin66]

Riklaunim,

These are "professional" gratings mounted between glass, so unfortunately the size is fixed.

The majority of cheap replica grating sheets are too inefficient to use for stellar spectroscopy.

[riklaunim]

I've seen Star Analyser. If you get that blazed grating type/quality - then it will do the same. Only a good company that makes them needed (and they could cut proper shape too )