It is a very old inexpensive filter that was sold with a common small telescope about 20 years ago, and it is unmarked (I have no idea who made it). From the way it improves Mars, it looks to be similar to the Wratten #23a but is not extremely high in red transmission. Newer filters are significantly better in their red transmission, as one filter company markets one "Wratten #23a" equivalent with a near 90% H-alpha transmission, so that one might indeed make a good H-alpha filter.
How did you estimate the transmission at Ha?
In any case can you find a W23A/W25/W29 and check again? I Have a W23A, I think that the 29 could be perfect for the assesment of Ha visibility (the 0.2-0,4 nm band as for the Sun is not necessary, and the greater band helps seeing stars and literally finding the way to objects)
BTW you should also check the 23A compared to Ha or the 29... it is very very meaningful (but see yourself).
Previous
Index
Next
Flat
Re: Is it possible to see the nebula with colour?
Edit
Reply
Quote
