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ERF and UV filter with 152mm f8 refractor and Quark

Posted: Thu Jan 10, 2019 6:09 pm
by RKBerta
I have a Chromosphere version of Quark used on 85mm and 110mm refractors with a 2" ERF/UV filter on front of 2" diagonal. Thinking of using on my 152mm f8 APO triplet refractor. Will the same 2" filter provide enough heat rejection on that combo or would I need to go with a full aperture ERF? That large filter is pricey so want to make sure it is necessary or safer. It will be used for both visual as well as photography.

Re: ERF and UV filter with 152mm f8 refractor and Quark

Posted: Thu Jan 10, 2019 6:16 pm
by Bob Yoesle
Some would say no, and that it's over-kill, but I would go full-aperture for the best IR reduction. Depending on the scope mechanicals, you could also consider an internal ERF such as a smaller ~ 100 mm or so Baader, BelOptik, or Lunt ERF placed within the OTA. I also would consider a 50 mm KG3 filter ahead of the Quark itself. Blocker and trim filter replacement for the regular DayStar filters is about $875:

I don't know if this service is available for the Quark, which if it isn't would mean you'd throw it away and buy a new one.

ERF and UV filter with 152mm f8 refractor and Quark

Posted: Fri Jan 11, 2019 4:32 am
by RKBerta
Thanks! More info ....the filter I am currently using is supplied by Daystar and is a 2" UV/IR Cut ERF. For reftractors the Quark is placed between a diagonal and eyepiece. The UV/IR Cut ERF filter is placed on the scope end of the diagonal. I know that with my BAADER CCS Herschel Solar Priam they warn to not place any filter on the scope side of the diagonal as it might break the glass.
I know that DayStar wouldn't suggest something if it wasn't save but wondering how much energy passes through various aperture size refractors. I suspect that the determination is based on the f stop of the refractor. So a 85mm f8 would have the same energy as a 152mm f8 refractor.

Currently I have used this setup of the Quark Chromosphere model with a 80mm, 85mm, and a 110mm refactor. I am considering using it with my 152mm aperture APO with triplet air spaced lens. That scope is a f8 scope. Needless to say, I want to make sure I don't damage that expensive refractor. Perhaps I am chasing my tail and would be better off staying with the other smaller scopes unless someone can convince me that results might be worth going to the larger scope (resolution?).

Re: ERF and UV filter with 152mm f8 refractor and Quark

Posted: Sat Jan 12, 2019 6:17 am
by marktownley
I think with the 6" triplet it's not the scope that is at risk of damage, rather the Quark. The scope just 'passes' the light, if you think about its perfectly safe (on the scope) using a herschel wedge for example on the sun. As the aperture increases then so does thermal load on the Quarks blocker, and, over time excessive thermal load can cause premature failure of the blocking filter.

Personally I think for anything other than brief views just a UV/IR filter is insufficient with your 6", like Bob says an external ERF is best and not just keeps excess energy off the filter but also keeps thermal currents out of the tube, and bear in mind with increased aperture so comes increased susceptibility to image quality degrading through thermals. However external ERF are expensive, but there is a half way house. I would recommend using a 2" Baader 35nm Ha filter in place of the 2" UV/IR filter. This will prevent excess energy reaching the filter and prolong its life.

Re: ERF and UV filter with 152mm f8 refractor and Quark

Posted: Sat Jan 12, 2019 2:38 pm
by MalVeauX

I have a 150mm F8 that I use. I do not recommend using it without an additional ERF. I find that the 2" UV/IR cut filter with the Quark alone works fine up to apertures of 127mm. But at larger apertures, the tube currents start to become problems and the overall thermal load is too much for long sessions of high resolution imaging and you'll find the Quark itself is getting too hot and will easily go off band.

You can get 150mm ERFs from Daystar that are older, used, yellow glass that are basically UV absorbing filters. They do work better than nothing. They're inexpensive compared to a full on dielectric full aperture ERF (such as Baader). Alternatively you could talk to Valery here on the board about an alternative to Baader (Aires).

Another option is to get a Baader 2" Red CCD Full IR Block filter, around $150 or so new. This filter can actually handle a 6 inch aperture and it is dielectric and will reflect everything except the red wavelengths. It handles the heat. I use the same filter in blue for calcium with the 6 inch aperture and it handles it great. Just put it in front of the Quark. And don't look down into the OTA as that stuff is all reflecting back out.

Overall, I would suggest a full aperture front mounted ERF for the long term. It will cut down thermal load in your OTA's tube which can effect seeing ultimately. Expensive, but worth it and it only hurts once.

Very best,

Re: ERF and UV filter with 152mm f8 refractor and Quark

Posted: Tue Jan 15, 2019 11:51 pm
by RKBerta
Thanks to all....lots of good advice.