13 replies to this topic

[ch-viladrich]

Hi,

 

Unexpected clearing this morning, and turbulence was quite reasonnable considering the low height of the Sun. I was a good time give the Altair 393-3 nm its first light :

 

http://astrosurf.com...-3nm-IMX533.jpg

 

The funny thing is that with this kind of filter (this is also true with the Antlia 393-3 nm) you can make out the prominences by changing the visualisation thresholds.
But I must admit the 14 bits of the IMX 533 helps a lot. This is actually the only situation where I was able to see a difference between 8-bit and 14-bit acquisition.

http://astrosurf.com...-IMX533-ddp.jpg

 

And back to the Alluxa Ca K 0.37 nm :

 

http://astrosurf.com...37nm-IMX533.jpg

 

I could not go double-stack after this because the cloud and the rain arrived  ...

 

Clear skies !

 

Christian

[steveward53]

Hi Christian ,

 

Where does one find this Altair 393 3nm ... ?

 

I can only find reference to the Antlia 393 3nm and the Altair G-band 2nm (which is the one I am considering purchasing )

[gstrumol]

Here is a photo I took using the Antlia 393nm wedge, the AT80EDL, and a Canon DSLR:

 

(click to enlarge)

 

I'm curious about what you said about being able to extract prominences through some visualization techniques. Can you elaborate? Thanks

[hornjs]

Great images Christian!  I especially like the Alluxa version.

[Prasad]

 Excellent as always, I enjoyed them.

[UKalwayscloudy]

I've been playing with an early copy of the Altair. I'm only at 120m elevation in the Thames Valley so even half-decent seeing is a rarity, and I'm still learning how to do CaK, but here it is:

 

https://www.astrobin.com/nrx23s/

 

Also Christian - please can I clarify which Alluxa you were using for that stunning image - was it this one (if only to confirm it is outside my budget!)?

 

https://alluxa.com/o...arrow-bandpass/

 

Thanks, William

[timmywampus]

(if only to confirm it is outside my budget!)?

 

https://alluxa.com/o...arrow-bandpass/

 

Thanks, William

whoa.  i have similar constraints...

[gstrumol]

I'm still curious and waiting for a response to this claim from Christian:

 

The funny thing is that with this kind of filter (this is also true with the Antlia 393-3 nm) you can make out the prominences by changing the visualisation thresholds.

 

I have the Antlia 393nm-3nm filter and there are no prominences. The only way I can think of to see prominences (short of during a total eclipse) is with a Ha scope. So how is this possible with a photosphere filter? 

[timmywampus]

The only way I can think of to see prominences (short of during a total eclipse) is with a Ha scope. So how is this possible with a photosphere filter? 

 

it's in the hardness of your squint.

 

joking aside, proms are super dim, but visible in his 2nd image link (4 o'clock/10 o'clock).  the difference between the 1st and 2nd links appears to be tone curve where the limb is kind of cranked up high just to show proms.  whether this is possible on dSLR as you are using or only through astocam+IMPPG (which i am more used to), may be the difference.  not sure what Christian is using.

[gstrumol]

Dang, you're right!  I see them now. (and I only had to squint moderately)

[steveward53]

It's less than 0.45nm , and I assume that "multi-cavity" means it's an etalon not a 'filter' as such , hence the price ... ?

Edited by steveward53, 23 April 2024 - 01:11 PM.

[ch-viladrich]

I'm still curious and waiting for a response to this claim from Christian:

 

The funny thing is that with this kind of filter (this is also true with the Antlia 393-3 nm) you can make out the prominences by changing the visualisation thresholds.

 

I have the Antlia 393nm-3nm filter and there are no prominences. The only way I can think of to see prominences (short of during a total eclipse) is with a Ha scope. So how is this possible with a photosphere filter? 

Hi Gary,

Prominences are visible in a number of wavelengths : Ha, Ca H and H, H beta, etc..

Of course, the visibility of a given prominence depends on its own brightness and on the bandpass of the filter. The contrast increases when of the bandpass decreases. There is also the question of "off-band" blocking, in other words, what the amount of light transmitted by the filter outside the band pass. The better of off-band blocking, the better the contrast of the prominence.

 

On top of that, the visibility of faint prominences (such as seen in Ca K) also depends on the sensor used. I don't think there is any chance to get Ca K prominence with a 3 nm filter and a DLSR (only one "pixel" out four is sensititive to blue light, and I am not sure what is the actual sensitivity of this "pixel" to Ca K).

 

It could be that bright prominences are also detectable with an Ha 3 nm filters. I haven't tried since I have not any 3 nm Ha filter.

 

All of this is of course only for imaging, never try this for visual observation.

 

For the images showing prominences with the 393-3 nm filter,  I used an IMX533 BW sensor which has a huge dynamic range (13.7 bits). This makes an enormous difference compared to a DSLR.

Edited by ch-viladrich, 25 April 2024 - 07:34 AM.

[ch-viladrich]

It's less than 0.45nm , and I assume that "multi-cavity" means it's an etalon not a 'filter' as such , hence the price ... ?

Yes and no

 

A Fabry-Perot filter (= an etalon) consists basically of two identical reflecting surfaces separated by a "gap". This gap can be :

- air, hence "air-spaced etalon" such as Lunt, Coronado,

- mica, hence "mica-spaced etalon", such as DayStar, SolarSpectrum,

- fused silica, such as older Coronado SMn-35,

- or other exotic material.

 

The gap can also be made of dielectric layers (= dielectric narrow band filters).

 

The number of "cavities" is a bit equivalent (but not exactly) to the number of etalons stacked. It impacts the shape of the transmission curve :

https://www.andoverc...s/filter-types/

 

A one-cavity dielectric filter has the same transmission profile as an air-spaced (or mica-spaced) etalon.

 

When the number of cavities increases, the transmission profile converges to a square shape, meaning a better transmission of the expected wavelength, and a better blockage off-band. But ... price increases sharply (just like going from single-stack to double-stack, or triple-stack).

[steveward53]

Yes and no

 

A Fabry-Perot filter (= an etalon) consists basically of two identical reflecting surfaces separated by a "gap". This gap can be :

- air, hence "air-spaced etalon" such as Lunt, Coronado,

- mica, hence "mica-spaced etalon", such as DayStar, SolarSpectrum,

- fused silica, such as older Coronado SMn-35,

- or other exotic material.

 

The gap can also be made of dielectric layers (= dielectric narrow band filters).

 

The number of "cavities" is a bit equivalent (but not exactly) to the number of etalons stacked. It impacts the shape of the transmission curve :

https://www.andoverc...s/filter-types/

 

A one-cavity dielectric filter has the same transmission profile as an air-spaced (or mica-spaced) etalon.

 

When the number of cavities increases, the transmission profile converges to a square shape, meaning a better transmission of the expected wavelength, and a better blockage off-band. But ... price increases sharply (just like going from single-stack to double-stack, or triple-stack).

Thank you Christian .