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8"SCT with Daystar filter

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#1 cptbobrfh

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Posted 21 April 2013 - 03:50 PM

I have a Celestron 8" CPC telescope and was wondering about purchasing a Daystar .4 A Ion filter.Has anyone used an SCT for HA viewing the sun? How is the image thru a SCT compare with a refractor using Daystar HA filter?
Thanks,
Bob

#2 frolinmod

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Posted 21 April 2013 - 08:58 PM

What size offset aperture stop and ERF are you thinking about using on front of the OTA?

#3 old_frankland

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Posted 21 April 2013 - 08:59 PM

The SCT will work fine, but you'll need to aperture the system down to 80mm or 90mm for the energy rejection filter. An 8" diameter energy rejection filter, if you can find one, will be pricey.

#4 markthais

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Posted 22 April 2013 - 01:51 AM

The C-8 works fine. SCT scopes work with an off axis ERF.
The C-8 will be stopped down to 2.5". The filter will need a 1.8deg wedge front plate.
Now the real world,I would keep to around .7Ang. When you use really narrow filters they will have a wavelength shift across the filter. I came across this with an .3Ang filters. So I had a real ray trace to see what was going on
and the computer showed that indeed the angles where there. So with the .6ang -.8Ang bandpass yes, I would not recommend the .4Ang.
Mark W.

#5 cptbobrfh

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Posted 22 April 2013 - 04:32 PM

Thanks,guys,for your info.
Here is my situation and concern:
I would like to use my Celestron 8"CPC not only for nightime,but for solar HA viewing as well.I had a Coronado 60 mm double stacked at 0.5A.According to the Daystar site,I would be purchasing a front off-axis ERF that would have a 63mm stopped down aperture.I am concerned about the heat that would be introduced into the sct,especially the secondary,and if the heat would affect any parts of the sct.
Also,visually,the Coronado DS gave me incredible views of the Sun!If I was to use a Daystar,or Solar Spectrum,.4A - .6A rear mounted HA filter,how much detail/contrast would I see,as compared to the Coronado?Do SCT'S give a "WOW" as my Coronado did,or soft,less detailed image due to the configuration of the SCT?
This question is for Mark:
If you were to buy a .4A,.5A,OR .6A filter for the 8"SCT,which one would you choose and why?
I know you have a lot of knowlede/experience with HA filters,and I value your expertise on this very much!
The heat issue is very concerning for me.I do not want to ruin the Celstron scope.
Can you also,use Plossl eyepieces with the 8"SCT for HA viewing with the SCT?I have a few plossl's.
Thanks to all,
Bob

#6 frolinmod

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Posted 22 April 2013 - 05:50 PM

So long as you have it stopped down with an ERF on the front, heat build up sufficient to damage SCT internals (anodizing, paint, plastic parts) should not be a problem.

Even so, I'd stick with the Coronado DS for Ha.

I'd then use the 8" SCT for white light views with an Astrozap Baader AstroSolar Safety Film full aperture front mounted filter. It'll give very good white light views, granulation and all. Add a polarizer filter or Solar Continuum filter if you like. Don't under estimate the ability of side-by-side white light viewing to compliment the Ha viewing.

#7 cptbobrfh

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Posted 22 April 2013 - 06:01 PM

Thanks for the info on using the SCT for white light observing.

#8 markthais

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Posted 24 April 2013 - 02:18 AM

When you double stack the etalon you are increasing the signal to noise ratio. You are suppressing the side bands. The filter looks narrower. The double stacked 60 will have contrast similar to a .5Ang single etalon.
The advantages of a rear mounted filter on a C-8 is that you will not have any secondary reflection that you had with your 60mm. There will be only one image to see. There should not be a sweet spot caused by the optics either. The thing you would need to worry about is that you will need to line up the wedge on the front of the filter with the off axis of the cover. If you turn the cover or filter it is the same as tilting the filter and the bandpass will shift towards the blue.
For me I liked the .7Ang filter I used with my C-8. It showed the surface detail fine and the image was uniformed.
I used an RG610 but I think RG630 is better. But the Baader D-ERF would be the best by far for reducing the heat factor. As for a reference one time I was testing a K-line and didn't even have a ERF just a 2" hole and the scope had no problem with heat.
The SCT can be used during the day and night. It was the most common scope for filters in the 80's and 90's. Just don't go narrower then .5Ang.
Mark W

#9 cptbobrfh

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Posted 24 April 2013 - 06:50 PM

Thanks Mark -
Your info is greatly appreciated!
Does the off axis 63 mm Yellow ERF from Daystar need to be used ONLY with their HA filters,or can you use either Baader D-ERF or Daystar ERF with Solar Spectrum or Daystar HA filters?
It may come down to the .7A or the .6A rear mounted HAfilter.
Would 20-40 mm Plossl's be ok to use?
Thanks again,
Bob

#10 markthais

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Posted 24 April 2013 - 10:31 PM

Hi Bob,
(This is just my opinion) stay away from the yellow filter glass.
1) it block less energy which means more heat coming into you scope.
2) If it's the same yellow glass Del had, it is surplus filter glass.
3) If you have the funds, the Baader ERF is the best. If not go with the red. A good ERF will be about 1/4" thick. If it is much thinner, it won't hold a 1/4 wave on transmission when it heats up.
The 20-40mm eyepieces are good range. I usually use a 40mm because the seeing is never very good here.
Alpine can get you a price for the different ERF's and spun cover for the C-8
Mark W

#11 marktownley

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Posted 25 April 2013 - 03:38 AM

Interesting stuff, thanks Mark :)

#12 BYoesle

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Posted 26 April 2013 - 08:48 AM

If you have the funds, the Baader ERF is the best.


What Mark said! Additionally, the Baader D-ERF's have an IR blocking dielectric coating (not found in a typical red glass ERF - except Lunt ERFs) that will reduce the thermal loading on the downstream filter components, and which may help prevent premature failure of the blocker and trimmer filter components.

#13 cptbobrfh

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Posted 27 April 2013 - 03:54 PM

Thanks,guys!
Having owned a Coronado 60mm externally double stack telescope,I am wondering what what would the sun "look like" visually at the eyepiece using a Clestron 8" with a off-axis mask that has a 63 mm clear aperure using 12-40 mm Plossls and a rear mounted .6A HA filter? I rarely see SCT pictures that show the image seen from the eyepiece of an SCT,mostly,if not always,from refractor scopes.Would I be disappointed comparing what I have seen from the front mounted Coronado,to what I will see from the Celestron 8"?Would spending ~$3000 using the SCT scope be a step down from what I was used to see from my Coronado 60mm DS?Any pictures using SCT would also help.
Thanks to all,
Bob

#14 Tom and Beth

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Posted 28 April 2013 - 01:15 AM

Thanks,guys!
Having owned a Coronado 60mm externally double stack telescope,I am wondering what what would the sun "look like" visually at the eyepiece using a Clestron 8" with a off-axis mask that has a 63 mm clear aperure using 12-40 mm Plossls and a rear mounted .6A HA filter? I rarely see SCT pictures that show the image seen from the eyepiece of an SCT,mostly,if not always,from refractor scopes.Would I be disappointed comparing what I have seen from the front mounted Coronado,to what I will see from the Celestron 8"?Would spending ~$3000 using the SCT scope be a step down from what I was used to see from my Coronado 60mm DS?Any pictures using SCT would also help.
Thanks to all,
Bob


Consider that with an 8 inch SCT you are working at a bit over 2 meter focal length whereas the majority of refractor Ha systems are in the 400 to 750MM range. You're going to want a BIG blocking filter. You'll also want to be around grass or water so the local atmosphere isn't turbulent.

I don't have pics but did use a Coronado 60 with BF15 on a C-8. FoV was as you might expect narrow, but the long FL of the system and being seated allowed phenomenal views of active regions during VERY steady skies. Image was a bit dim (not surprising) and having your head covered was mandatory. While not the system you have in mind, perhaps this experience is enough to give you an idea?

The views were nothing like a 90MM/100MM Luntanado scope, and that's were I am now.

#15 cptbobrfh

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Posted 30 April 2013 - 05:05 PM

Thanks,Tom/Beth-
How did you use the Coronado 60 wITH BF15?
Did you have the Coronado custom spun into the aperture mask of your C-8?
Was the view "soft" on the details on the suns surface?
Thanks,
Bob






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