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Does C8 with solar filter also need an Energy Rejection Filter?

equipment beginner Celestron observing SCT solar
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#1 Dave 123

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Posted 01 April 2020 - 12:44 PM

Back in October 2019 I purchased the Solarlite filter S-9187 from thousandoaksoptical.com.

Today someone mentioned that I also need an Energy Rejection Filter to do solar observing with my C8. Can anyone tell me if that is necessary or if it is safe to observe without it? And what if I want to do imaging, would it then be necessary?

 

Thanks in advance,

Dave



#2 Chilihead

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Posted 01 April 2020 - 12:49 PM

I've never used one with mine, I don't know why someone would tell you that.



#3 Hesiod

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Posted 01 April 2020 - 12:50 PM

With white-light frontal filters you do not need an energy rejection filters; you may use a filter at the eyepiece to dim more the view and enhance the contrast (e.g. double polarizer)



#4 Don W

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Posted 01 April 2020 - 12:51 PM

What they said. Energy rejection filters mount on the front of the scope. You already have a filter there.



#5 bobzeq25

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Posted 01 April 2020 - 01:05 PM

Energy rejection filters are used in connection with expensive (they start at about $1000, go way up from there), very narrowband solar filters used for observing solar details like prominences.  You have a wider solar filter for observing sunspots.  They're not used with that.



#6 sg6

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Posted 01 April 2020 - 01:32 PM

Is there a confusion between an ERF and a UV/IR block ?

ERF's sound expensive - I know little about the details. Wheras a UV/IR block is somewhat inexpensive.

 

May not need one with a 10-5 filter at the front. But I bought one for my use on a smaller scope. Reason was just that I had the chance and decided "Why not?"

 

Think, only think, I used it at the Mercury transit. Not exactly sure I did, slight mess setting up and might have forgotten it. At the cost it seemed a reasonable idea. Suppose the approach was: It couldn't do any harm, and might do some good.

 

Also the event was a public outreach event and it sounded better to say the scope had a UV/IR cut filter. Even if I had, maybe, forgotten to put it in. Wish I could remember.

 

For imaging/AP I suspect a UV/IR cut is necessary. CMOS sensors "see" IR so not having it present would be a good idea.



#7 Don W

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Posted 01 April 2020 - 02:13 PM

I have never used a UV/IR filter for imaging or viewing.



#8 Dave 123

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Posted 01 April 2020 - 02:52 PM

Thanks to everyone for responding. Good to know I am set to observe with what I have.

 

But if I wanted to see more detail and prominences would I then need the Energy Rejection Filter and an H-alpha filter? 

 

Would it be cost effective to do this with the C8 or to get another scope?

 

Thanks



#9 bobzeq25

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Posted 01 April 2020 - 04:19 PM

Thanks to everyone for responding. Good to know I am set to observe with what I have.

 

But if I wanted to see more detail and prominences would I then need the Energy Rejection Filter and an H-alpha filter? 

 

Would it be cost effective to do this with the C8 or to get another scope?

 

Thanks

This absolutely requires a big wallet.  <smile>

 

An energy rejection filter for a C8 only uses 2-1/2 inches of the aperture, and is $400.

 

https://www.daystarf...om/energy.shtml

 

Then you'd need a special (expensive) solar filter for ultra-narrowband H alpha (a DSO H alpha filter is too wide a bandpass, and not _at all_ usable.  It's not a question of quality, they just won't work.).  These are $1200, and they're low end.

 

http://www.daystarfi...om/instock.html

 

Then you'd need a Barlow, to slow the C8 down to a higher F number.

 

It would be an unusual scope to use for this.  Since you're not using anything like the 8 inches of aperture, most people go with a small refractor.

 

There are some scopes that bundle everything together.  This is a low priced version, about as low as you can go.  $1750.

 

http://www.daystarfi...com/80/80.shtml

 

This is a lower priced example from a popular company for solar scopes.  $1835.

 

https://luntsolarsys...escope-package/

 

Get a bigger one, and the price soars.  This 100mm is $8000.

 

https://luntsolarsys...vanced-package/


Edited by bobzeq25, 01 April 2020 - 04:27 PM.


#10 Don W

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Posted 01 April 2020 - 04:21 PM

The filter you bought will show you sunspots and little else. Yes, to see prominences you would need an H-Alpha system that would include an ERF and the proper filters by the eyepiece.

 

These systems for  your scope are quite pricey. You would be better off getting something like the Meade PST or a Lunt 50. I think Daystar recently came out with a similar system.



#11 Michael Harris

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Posted 01 April 2020 - 09:31 PM

I have the same filter for my C8 and it is fine by itself for white light visual observing. To see prominences and surface details the Ha scopes are much better and I have found the Coronado PST to be just fine for this although I am sure there are better and more expensive options. Here are two of my solar images, first one in Ha with the PST and the other is a white light view of the recent Mercury transit with my C8 (Without debayering to show colors). If you want reasonably proiced Ha check the CloudyNights classified for a used PST, they show up every so often.

 

Solar 091017 3
Mercury transit screen shot


#12 MalVeauX

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Posted 01 April 2020 - 09:47 PM

Heya,

 

If you look up the transmission profile of most solar filters, you'll find an incomplete blocking range in either UV or IR. Mostly IR. Using a UV/IR block filter with all the long IR blocked, is added insurance for your eyeballs. This usually uses a KG3 filter. If it does not, it probably doesn't block long IR unless it shows it in a graph explicitly. This is why its often suggested. Anecdotal evidence has nothing to do with it. Simply look at the transmission graphs. If one is not available for the filter you're using, assume then it's likely not completely blocking all long IR if you care about long term effects to your eyeballs. Blocking it is a small price to pay for insurance against your vision. It's not just thermal load, or wavelength, its also the radiation. There's more to it. Basically though, if you want to avoid any potential problems, a KG3 based  UV/IR block filter (ie, BelOptik) is the most safe way to ensure your eyeballs and excellent for imaging use. Unless you want to trust your eyes to zero data support anecdotal evidence. Your call. Your eyes.

 

Very best,


Edited by MalVeauX, 01 April 2020 - 09:51 PM.



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