Lunt Cak Module

[Dennis]

Hi,
since its hard to find used Lunt Cak Modules im thinking of getting a new one via import, since local vendor prices seem to be a bit "stuck".

Question: which blockfilter size should i choose if i only want to use it for imaging with the f/10 triband c9.25?
I plan to use the imx432 and mostly be in the range of f/20 or f/30. So do i get a gain with a bigger blockfilter or can i stick to the smallest model (b600 straight through)?
Thanks in advance.

[Montana]

Dennis, on this page https://luntsolarsystems.com/product/lu ... k-modules/
Gives you the advice on which size to use (see bottom of page).

If you don't get it right you will get vignetting, which may or may not bother you. However, I looked down Stuart's with vignetting and it wasn't my cup of tea. He eventually bought the next size up

Alexandra

[Dennis]

Thanks Alexandra,
i had it in my mind that these infos are for the visual use of it. I just wonder if the imx432 chip will be vignetted too with the 6mm blockfilter at the focal lenghts that i plan to use.

Dennis

[Montana]

I'm not sure, but Stuart uses a Basler IMX174 which is the same as my ASI174 and the 600 was not good.

Alexandra

[Dennis]

I'm not sure, but Stuart uses a Basler IMX174 which is the same as my ASI174 and the 600 was not good.

Alexandra

Thats valuable info, thank you. Then i guess i also need to get the b1200 version.

Dennis

[marktownley]

I would go as large as you can afford

[Dennis]

I would go as large as you can afford

Hi Mark, thanks for the input.. im thinking and thinking..
you mean even if i will use a 2x or 3x barlow between module and camera (lets put seeing aside for the consideration)?

[marktownley]

The other thing I would suggest is put a sub aperture ERF on m48 extension tubes ahead of the Lunt CaK as high in the OTA as will allow, this will give additional protection and give additional life to the ERF filters on the Lunt CaK before failure occurs - see viewtopic.php?t=39541

[Dennis]

Thanks for the input guys, (pre)ordered the straight through 12mm version.

[Dennis]

Now im wondering if i can also use the module for imaging without the erfs in front of the module, since the front D-ERF would already take most of the energy out (<90%).. i guess i basically just need the actual cak filter in the back of the unit. What do you think?

[marktownley]

Now im wondering if i can also use the module for imaging without the erfs in front of the module, since the front D-ERF would already take most of the energy out (<90%).. i guess i basically just need the actual cak filter in the back of the unit. What do you think?

Categorically it won't work. Been there and got the t-shirt.

Those ERFs in the Lunt module will each provide at least OD3 (possibly more) each of out of band blocking, add together and you are looking at OD5 blocking at least.

[Dennis]

Now im wondering if i can also use the module for imaging without the erfs in front of the module, since the front D-ERF would already take most of the energy out (<90%).. i guess i basically just need the actual cak filter in the back of the unit. What do you think?

Categorically it won't work. Been there and got the t-shirt.

Those ERFs in the Lunt module will each provide at least OD3 (possibly more) each of out of band blocking, add together and you are looking at OD5 blocking at least.

Adapting the Antlia 393 (OD5 from 200-1200nm, OD3 from 1200-1500nm, peak transmission about 80%) instead of those 2 erfs could be worth a try. It looks like the long front part of the module can be easily removed and even has t2 threads as far as i understand. The Antlia alone has worked with my setup without any additional erf or wedge so far without problems.

Here my filter scan:

[marktownley]

I've been chasing CaK nirvana for over 15 years now.

An Antila filter on its own behind a 9"triband SCT is not going to last very long.

The antila filter is completely different than the notch filter on a Lunt CaK (lots of transmission profiles on here, search away!). Put that on it's own on the back of a triband SCT and you will get continuum leakage, you will likely kill the (expensive) filter with thermal load and you will likely kill the camera on the back. I refer you to the blurb at the top of the mods section.

I hear you're happy with the results you are getting with the triband and the Antila, but you will get considerably better ones with a much smaller achromat, and your filters will last a lot longer. SCTS (good sample or not) are nowhere near diffraction limited in the UV unless corrective optics are used (and then you're chasing bespoke unicorns and rainbows).

[Dennis]

Thanks Mark,
i appreciate the infos and opinion.

[OlegLviv]

I want too filter CaK and want buy Quark Ca H and Antlia 3nm but in my mind better choice is Lunt Cak+