Front mounted energy rejection filter

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HAL
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Front mounted energy rejection filter

Post by HAL »

Hi,

Question for those using a Quark/refractor combination of more than 100mm aperture...

I'm thinking of upgrading to a 120mm refractor for use with my Quark and understand that I must use a front mounted energy rejection filter. I'm wondering what others are using for this? I have seen the Baader ones which need to be ordered with a custom housing. I'm wondering if there's a less expensive way to do it...

Thanks!

HAL


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Re: Front mounted energy rejection filter

Post by Dennis »

HAL wrote: Tue Mar 07, 2023 5:39 pm Hi,

Question for those using a Quark/refractor combination of more than 100mm aperture...

I'm thinking of upgrading to a 120mm refractor for use with my Quark and understand that I must use a front mounted energy rejection filter. I'm wondering what others are using for this? I have seen the Baader ones which need to be ordered with a custom housing. I'm wondering if there's a less expensive way to do it...

Thanks!

HAL

Hi,
for cheaper solutions others may provide infos, but if you want the best results i recommend a full aperture d-erf.
Reasons are potential tube currents that can soften your results if you go for a internal erf-solution. It also protects your Quark blockfilter better if there is less heat load on it.


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Re: Front mounted energy rejection filter

Post by AndiesHandyHandies »

Hi

It can reduce tube currents. But the large filters pass more light than smaller filters. As its not economic to lay on as many coatings, one the cost and two the rejection rate.

If you are doing a bare etalon mod you need a KG3 to stop the long IR, protect your eyes for visual, and make images a bit sharper.

The modern dichoric coated filters reflect the rejected light so do not heat up.

I use a dichoric UV-IR and a dichoric red rgb filter as an internal ERF on a 180mm Mak. The insides are no hotter than a Daystar Quark etalon when heated. And a KG3.

Cheers. Andrew.


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Re: Front mounted energy rejection filter

Post by DeepSolar64 »

According to DayStar literature a front mounted energy rejection filter is required on anything larger than 80mm while using a Quark.


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Re: Front mounted energy rejection filter

Post by marktownley »

I recommend a full aperture ERF.

To make it cheaper just order the DERF and make your own holder.


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Re: Front mounted energy rejection filter

Post by cte »

I purchased a full aperture daystar yellow filter as a front erf for my 130 mm refractor. It comes in an aluminum cell which securely clamps around the dewshields. I tested it on the last sunday and it works fine, although it still lets red and infrared wavelenghts in. Probably baader filters are better, since they are mirror like filters which only let a narrower band in, but, so far I'm happy with that anyway. Just for extra safety I added an internal ir rejection filter (a 2 inch astronomik uv/ir cut) to my imaging train, before the barlow and the quark, but really it should not be necessary.


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Re: Front mounted energy rejection filter

Post by Martin_S »

I tried a sub ERF filter in my SW 120 refactor (2" 7nm H alpha) and got shocking tube convection currents. So I made an open frame refractor that fixed all those issues at the fraction of the cost of a full aperture ERF.
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Re: Front mounted energy rejection filter

Post by Simon2940 »

There are 2 ways to do this -

Get the Astronomik L-3 filter and be done with it

https://telescopes.net/astronomik-l-3-u ... ilter.html

or get the ERF from Hutech

https://astrohutech.store/product/hutec ... n-filters/

If you go with the L-3, make sure it's as far forward as possible. With this filter you can go up to 150mm which i have been using for a majority of all my solar work.

The ERF is a lot better when it comes to tube currents but if you are on a budget, this may not be the best.


HAL wrote: Tue Mar 07, 2023 5:39 pm Hi,

Question for those using a Quark/refractor combination of more than 100mm aperture...

I'm thinking of upgrading to a 120mm refractor for use with my Quark and understand that I must use a front mounted energy rejection filter. I'm wondering what others are using for this? I have seen the Baader ones which need to be ordered with a custom housing. I'm wondering if there's a less expensive way to do it...

Thanks!

HAL


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Re: Front mounted energy rejection filter

Post by HAL »

Thanks so much for the helpful replies everyone.

I did not really consider the issue of tube currents which was a big oversight, so thanks to those who mentioned this.

Andrew - I wondered if you could say more about your filter set-up, I'm not sure I'm fully understanding it - you have 3 filters all internally?

Martin - your set-up looks incredible but far beyond my practical skills unfortunately!

Simon - you say the Astronomik L3 filter is good as an internal filter up to 150mm, I'm already using one of these on my 80mm (but L1). I'm told that this absolutely isn't enough when working over 100mm, is there any literature anywhere stating that you can use these up to 150mm? Do you find tube currents to be a big problem when not using the ERF?


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Re: Front mounted energy rejection filter

Post by AndiesHandyHandies »

Hi

I have only been observing visually so far.

MAK180.

This is a Santel F10, ex Intes staff, which is all metal construction. I use it for a PST Mod2. I cannot afford a 180mm front DERF for possible 4 days a year when the seeing would be good enough.

In the back of the primary mirror baffle, on a push up tube, I was using just a 1.25" UV-IR filter but I have now added a Red Meade rgb type filter behind it.

There is plenty of filtering after that in the PST Mod2.

TS 90mm Triplet.

I am now using 2" UV-IR and 2" Red rgb Dichoric in the front of the diagonal. Plenty to protect a Quark blocking filter and for visual use.

In a second option I am using a 2" Red rgb Dichoric followed by a 2" Beloptic KG3 UV-IR. I have to put the KG3 second to reduce the heat on it.

I cannot comment on tube currents for imaging, though I hope to start imaging this year.

Another option for heat dumping is a perforated diagonal 'mirror' in a baffle after the objective/secondary mirror to reflect the unwanted heat out of a side aperture/window. You can mount internal ERFs on this to reduce the heat in the beam you need to fully illuminate the focal plane. See Hinode Space Telescope.

If you are using a cheap refractor and have already chopped down the tube to increase back focus as required, cutting a side hole near the top will not really reduce its value further.

Cheers. Andrew.
Last edited by AndiesHandyHandies on Wed Mar 08, 2023 9:43 pm, edited 1 time in total.


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Re: Front mounted energy rejection filter

Post by HAL »

That's helpful, thanks Andrew.


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Re: Front mounted energy rejection filter

Post by AndiesHandyHandies »

Posted in error.
Last edited by AndiesHandyHandies on Thu Mar 09, 2023 11:17 am, edited 1 time in total.


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Re: Front mounted energy rejection filter

Post by marktownley »

I'm just going to throw a caveat here based on my own experience.

I've been the sub aperture ERF route with my 5" frac and Quark; after a couple of years the 12.5mm blocker in my Quark died, I replaced it with the 25mm version of the same blocker mounted high in the light cone. After a couple of three years that died and i'm on my second 25mm blocker replacement.

All these filters that use soft coated elements (Quarks, Lunt CaKs) will fail over time. Using sub aperture ERFs at apertures over the recommended aperture will just accelerate the process. Fact.

The only reason you will know the coatings are failing is that one day you will start questioning why contrast is becoming less and exposure time is becoming longer, then, the day you are brave enough to take the unit apart you see the filter has failed.

Now it is a question of economics - you may prefer to pay say £1k for a 6" DERF for example and get longer filter life (the blocker will still fail ultimately!) or stick to a sub aperture ERF and change the soft coated blockers (maybe £0.3k) more often.

You pays your money and takes your choice! ;)


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Re: Front mounted energy rejection filter

Post by Dennis »

My Quark is several years old and it doesnt show problems yet, i always used a full aperture d-erf solution, so did the previous owner. I think its the cheaper and better solution because you can resell the front d-erf relatively easy once not needed anymore. Apart of that, reading some proposed solutions here i can only appeal to the sense of selfpreservation if you will use this visually.


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Re: Front mounted energy rejection filter

Post by Valery »

Dennis wrote: Thu Mar 09, 2023 9:01 am My Quark is several years old and it doesnt show problems yet, i always used a full aperture d-erf solution, so did the previous owner. I think its the cheaper and better solution because you can resell the front d-erf relatively easy once not needed anymore. Apart of that, reading some proposed solutions here i can only appeal to the sense of selfpreservation if you will use this visually.
My first good sample of Quark now is 7 years old. No signs of degradation of it's EDF filter. It always worked in telescopes equipped with a full aperture DERF. Also my oldest DERF now is 11 years old. So far for signs of degradations.

In the same time I have experimented with subaperture filters which are purposed for DSO imaging. They all were damaged.

All subaperture ERF filters deliver softer images. Never reached the resolution and clarity delivered in scopes equipped with a full aperture DERF.

The results: several $$$ loss, a lot of observing time loss, a lot of time for image processing loss, a lot of efforts loss, a lot of nervouses loss.

All these substitutions are like alchemy. However, not for free, but for a fee. It is better to learn from someone else's experience/mistakes than from your own.

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Re: Front mounted energy rejection filter

Post by HAL »

This has been a useful discussion thank you all.

After reading and thinking through all of this I think I will go for the front mounted ERF.


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Re: Front mounted energy rejection filter

Post by sebalbion »

Hi all
I am new here but have been following this discussion and other threads as I want to adapt the etalon module of my Lunt 50Ha to a Skywatcher Evostar 90/660 f:7.3. I wonder if in your experience the same conclusion is true for that mod, i.e. a front mounted ERF is the way to go, as when using a quark. The etalon unit of the Lunt 50 has an internal ERF in front of the first collimating lense, so the question is mostly whether it can survive the more intense beam from the 90mm lense, and whether it will create currents that will affect the image?

Sébastien
Last edited by sebalbion on Sun Mar 26, 2023 2:02 pm, edited 1 time in total.


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