8 replies to this topic

[Apnee44]

I just bought two Lumicon filters, one h-beta as I always wanted to test one, and one OIII to compare with my Astronomik one. Both in 1.25inch, new condition at 50 euro each.

I will try the h-beta in my Dobson 200 f6 and my refractor 80ED f7. The only eyepiece that can give me more than 5mm exit pupils is a Vixen LV40. My ES24/68 will give too less IMO.

If you have tried one in equivalent equipment, what was your best eyepiece? I was thinking maybe a simple Plossl?

Edited by Apnee44, 05 December 2024 - 04:34 PM.

[Starman1]

The best eyepiece?  Whatever gives you the right exit pupil.

Light transmission differences in eyepieces at this wavelength differ by at most a few %.

[CrazyPanda]

I just bought two Lumicon filters, one h-beta as I always wanted to test one, and one OIII to compare with my Astronomik one. Both in 1.25inch, new condition at 50 euro each.

I will try the h-beta in my Dobson 200 f6 and my refractor 80ED f7. The only eyepiece that can give me more than 5mm exit pupils is a Vixen LV40. My ES24/68 will give too less IMO.

If you have tried one in equivalent equipment, what was your best eyepiece? I was thinking maybe a simple Plossl?

In my 70mm F/6 refractor, I frequently pair my H-Beta filter with a 31N for viewing the California Nebula.

 

In my bigger dob, I'm usually going after targets like the HH nebula or the propeller nebula. I use a 5.5nm H-Beta filter which is much, much better than a typical ~12nm H-Beta filter for my skies. It really likes exit pupils in the 6-7mm range, but lately I've been using a 5.4mm exit pupil with a 25mm Plossl on the HH nebula and it's been quite good. With your H-Beta filter, a 5mm exit pupil should be just fine, but I recommend letting your eye adapt to the darker view for several minutes for best effect.

 

So far, the Tak TPLs do the best job at getting light into my eyeball. They really do have unbelievably good transmission. However, I primarily use Plossls on the HH nebula for the narrower field of view just to keep the glare of Alnitak away. A good quality full multicoated widefield is perfectly fine with any filters if you need the extra field of view (such as when I'm viewing the California nebula).

 

That being said, having tested a few different ~30mm eyepieces against the ultra-faint Propeller Nebula, it's quite clear that the 33 TPL delivers the brightest view and helps show the nebulosity in this region the best. A close second is the 32mm Tele Vue Plossl. Visibility of the blades depends more on transparency than eyepiece.

[Apnee44]

The best eyepiece? Whatever gives you the right exit pupil.
Light transmission differences in eyepieces at this wavelength differ by at most a few %.

I can read that lot of people talk about an exit pupil equal or superior to 5, but I suppose that it is depending also of the sky and the diameter of the instrument (Easy to see that when I use both of my scopes at the same time). Means a good Plossl between 30 to 40 could be the right choice. I will see what gives the LV40. I will try also the 24/68 as it gives 4mm with my Dobson.

Edited by Apnee44, 06 December 2024 - 02:05 AM.

[j.gardavsky]

In my H-beta 1.25" filters arsenal these are:

Astronomik Profi Line, bandpass 12nm: a pair

Baader #2458425, bandpass 8.5nm: a pair

Baader #2961080, bandpass 5.5nm: a pair

 

I choose the bandpass according to how much the sky background should be suppressed to get the best contrast of the nebula.

During the recent observing sessions, my choice used to be the 5.5nm

 

Clear skies,

JG

[Starman1]

The thing I'd be afraid of, with a 5.5nm bandwidth, is the bandpass shift that occurs in fast f/ratios like f/4 scopes would shift the bandpass right off the 486.1nm H-ß line.

[j.gardavsky]

The thing I'd be afraid of, with a 5.5nm bandwidth, is the bandpass shift that occurs in fast f/ratios like f/4 scopes would shift the bandpass right off the 486.1nm H-ß line.

The Baader H-beta 5.5nm filters have a shifted bandpass, similarly to the other professional grade filters, like the Astrodon OIII 5nm, I also have.

 

This can be easily checked with a calibrated hand spectroscope,

JG

[CrazyPanda]

The thing I'd be afraid of, with a 5.5nm bandwidth, is the bandpass shift that occurs in fast f/ratios like f/4 scopes would shift the bandpass right off the 486.1nm H-ß line.

Baader recommends it down to F/3.5: https://alpineastro....-cmos-optimized, but it's unclear if that means it's still within the peak transmission at F/3.5 or not, or if it's partially cut-off.

 

I've got an F/3 mirror on the way. If I put the filter after the Paracorr it will be 3.45. I guess we'll find out how well the Baader 5.5 works at F/3.45.

[Starman1]

Baader recommends it down to F/3.5: https://alpineastro....-cmos-optimized, but it's unclear if that means it's still within the peak transmission at F/3.5 or not, or if it's partially cut-off.

 

I've got an F/3 mirror on the way. If I put the filter after the Paracorr it will be 3.45. I guess we'll find out how well the Baader 5.5 works at F/3.45.

Hopefully your eyepiece won't use setting A or B.  There isn't enough room for a filter below the eyepiece until you get to setting C.