Baader Ha, OIII, LRGB filters

[Andyb90]

Hi everyone,

I have a couple of questions about my new set of Baader Ha, OIII and LRGB 36mm filters which I'll be installing in my SX USB filter wheel.

Which way round do the filters need to go? Or does it not matter which side of each filter is facing the telescope?

Secondly for maintenance can the filters be cleaned? I have Baaders own optical wonder fluid and their matching cloth. Would it be okay to use them?

Andy.

[Tim]

Hi Andy.

The filters go with the shiniest side facing outwards, to the front of the scope, that is, on the side of the filterwheel furthest from the camera.

The filters have very hard metallic coatings, and can be cleaned, but as with all optical surfaces try to keep this to a minimum. Usually just gently blowing the dust off will suffice, with a slight mist of Wonder Fluid should you accidentally touch the surface or something.

[SkyBound]

8 hours ago, Tim said:

Hi Andy.

The filters go with the "front" facing outwards, to the front of the scope, that is, on the side of the filterwheel furthest from the camera.

The filters have very hard metallic coatings, and can be cleaned, but as with all optical surfaces try to keep this to a minimum. Usually just gently blowing the dust off will suffice, with a slight mist of Wonder Fluid should you accidentally touch the surface or something.

I think he realises that, but as they are 36mm filters I assume they are unmounted and so which side is the front....? I asked this question a while back, and was told that there should be a very small v on the side of them, which should point towards the incoming light.... 

hope that helps

Edited November 28, 2016 by SkyBound

[Andyb90]

1 hour ago, SkyBound said:

I asked this question a while back, and was told that there should be a very small v on the side of them, which should point towards the incoming light.... 

Will look for the '<' . I just found the below info in an FAQ on the Baader website, which mentions the arrow, but has a caveat too:

"Always put the more reflective side towards the telescope side. To guide you we already put a small arrow on the filter rim, on those filters were the position matters. This arrow indicates which face of the filter should be directed towards the sky (telescope-sided). All cell-mounted filters are already oriented in a way that the most appropriate filter face is facing the sky when the filter would be mounted directly onto the front end of the nosepiece of a camera.
If you mount your filter the other way, any reflected light would have a short way to the camera sensor, resulting in a higher risk of getting some kind of back-reflections inside the camera field. Many sensors have highly reflective areas near to the light sensitive area, also the area with the bonding contacts is sometimes highly reflective.

But: this is true only for instruments without optical elements near to the focal plane. If you have f.e. a coma corrector, field flattener, focal reducer, focal extender (to a lower degree due to concave surface), or in extreme cases a whole lens group for more complex field corrections a few centimeters in front of the filter it could be useful to flip the filter against the rule from above (thus having the arrow pointing away from the telescope). Cause in such cases the likelihood of reflections from the sensor could be lesser then fort- and back- reflections from such glass-surfaces. If in doubt, it helps to make some test images from a star field with bright stars, using the filter in both ways for comparison."

I'm using the matching field flattener with my Esprit 100 and the filters. So I'll experiment with the '<' filters both ways round to see if there is any difference.

Andy.

[SkyBound]

Very interesting, I also use a focal reducer / field flattened, so will have to check this out..  thanks

[ollypenrice]

7 hours ago, Andyb90 said:

Will look for the '<' . I just found the below info in an FAQ on the Baader website, which mentions the arrow, but has a caveat too:

"Always put the more reflective side towards the telescope side. To guide you we already put a small arrow on the filter rim, on those filters were the position matters. This arrow indicates which face of the filter should be directed towards the sky (telescope-sided). All cell-mounted filters are already oriented in a way that the most appropriate filter face is facing the sky when the filter would be mounted directly onto the front end of the nosepiece of a camera.
If you mount your filter the other way, any reflected light would have a short way to the camera sensor, resulting in a higher risk of getting some kind of back-reflections inside the camera field. Many sensors have highly reflective areas near to the light sensitive area, also the area with the bonding contacts is sometimes highly reflective.

But: this is true only for instruments without optical elements near to the focal plane. If you have f.e. a coma corrector, field flattener, focal reducer, focal extender (to a lower degree due to concave surface), or in extreme cases a whole lens group for more complex field corrections a few centimeters in front of the filter it could be useful to flip the filter against the rule from above (thus having the arrow pointing away from the telescope). Cause in such cases the likelihood of reflections from the sensor could be lesser then fort- and back- reflections from such glass-surfaces. If in doubt, it helps to make some test images from a star field with bright stars, using the filter in both ways for comparison."

I'm using the matching field flattener with my Esprit 100 and the filters. So I'll experiment with the '<' filters both ways round to see if there is any difference.

Andy.

...which confirms what Tim said. I'm sure you're both correct.

Olly

[SkyBound]

1 hour ago, ollypenrice said:

...which confirms what Tim said. I'm sure you're both correct.

Olly

Ok , Olly fair enough....

Edited November 28, 2016 by SkyBound

[steppenwolf]

Quote

But: this is true only for instruments without optical elements near to the focal plane. If you have f.e. a coma corrector, field flattener, focal reducer, focal extender (to a lower degree due to concave surface), or in extreme cases a whole lens group for more complex field corrections a few centimeters in front of the filter it could be useful to flip the filter against the rule from above (thus having the arrow pointing away from the telescope). Cause in such cases the likelihood of reflections from the sensor could be lesser then fort- and back- reflections from such glass-surfaces. If in doubt, it helps to make some test images from a star field with bright stars, using the filter in both ways for comparison."

What a fascinating revelation - surely this must also apply to Baader's mounted 1.25" filters as well assuming that the coatings and substrate are the same?

[SkyBound]

20 minutes ago, steppenwolf said:

What a fascinating revelation - surely this must also apply to Baader's mounted 1.25" filters as well assuming that the coatings and substrate are the same?

Hmmm, yes very true....first time I have ever heard of having to, maybe turn the filters round depending on set up, used...