ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

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etatsolarchat

ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by etatsolarchat » Mon Apr 16, 2012 2:48 am

Thinking about a large 127mm PST mod...

Need an ERF, the Baader D-ERF is obviously the best way to go, but expensive and is it overkill?

With the Solarmax 60 for example, the main unit has no external ERF just an internal hot mirror. The 60mm DS unit for it uses a colored filter. If the single etalon unit only needs a hot mirror why did they need a color filter on the external etalon unit?

I realize that I could use a smaller D-ERF inside the tube to decrease the cost but I'd like keep it outside for easy access. Also does having the ERF inside or outside change the optics characteristics in anyway?

I bought a hot mirror on eBay to check out,
http://www.ebay.com/itm/DICHROIC-HEAT-F ... 27a55ff315

Maybe it's not a hot mirror, to test I put it in front of a lens pointing at the sun thinking it would curb the amount of heat the lens made but didn't seem to have any effect (tried both sides 0 and 45degreae angle), any idea why not?

Would standard red color filter would well enough, if so anyone have a good source for them? Thanks.

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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by marktownley » Mon Apr 16, 2012 3:45 pm

I don't think the Baader D-ERF is overkill, infact I think is the standard for ERFs. problem with alternatives for ERFs is that optically they are not very flat...
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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by etatsolarchat » Mon Apr 16, 2012 4:17 pm

Yeah.. probably half the reason they cost so much.

What about the Lunt ERF's? They are a lot cheaper are they just as good? Anyone have a spec or plot on them?

Thanks

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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by marktownley » Mon Apr 16, 2012 6:20 pm

They're half the thickness and pretty much half the optical flatness the baaders are. Much better to save up and get the baader...
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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by etatsolarchat » Mon Apr 16, 2012 9:08 pm

Used C-ERF sounds like a plan...I'll look for a used one at the Lunt price :cheer:

However on the Lunt ERF, I understand they are not as good, but good enough for Lunt right, so seems like they should be just fine for us....

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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by langleif » Fri Jul 05, 2013 7:59 am

Well, I use a Lunt 75mm ERF and it is excellent! What's the point producing them anyway if they aren't up to the job??

Despite the half thickness they are optically 1/4 wave and that's all we need! I also use an old Lumicon 77mm ERF. I don't think its a hot mirror and its even thinner than the Lunt!

I use it on my TeleVue Oracle refractor that is equipped with a 77mm thread inside the dew head for filters. But the filter is then turned upside down.

But obviously that doesn't matter, because its not a hot mirror but very much an absorbing kind off. And it is working excellent too.

In fact, the beam at the focus point is "cool" when the filter is there, but burning hot when its not. So I'll guess, its working all right, then.

And looking at the Sun with both ERFs I see all kind of H-alpha stuff. (With proper Ha filter installed, of course!!) ;)

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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by marktownley » Fri Jul 05, 2013 9:34 pm

Well, I use a Lunt 75mm ERF and it is excellent! What's the point producing them anyway if they aren't up to the job??

Not saying they're not up to the job, just the Baaders are just optically better ;)
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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by langleif » Fri Jul 12, 2013 8:46 am

Right, they are, I just can't see the difference though the scope. And the idea making PST mods originally is for saving money I would say. A 75mm Baader will set you back 255 euro and free aperture maybe 70mm?? A 80mm Lunt 199 euro and free aperture is 75mm.

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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by marktownley » Fri Jul 12, 2013 6:14 pm

Right, they are, I just can't see the difference though the scope. And the idea making PST mods originally is for saving money I would say. A 75mm Baader will set you back 255 euro and free aperture maybe 70mm?? A 80mm Lunt 199 euro and free aperture is 75mm.

I agree, you can't see the difference through the scope. However put a 1/4 wave ERF on a scope such as an AP or a TEC and compare it to a 1/10th wave ERF with a decent CCD and I bet in good seeing there is a difference ;)
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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by Merlin66 » Sat Jul 13, 2013 3:00 am

Langleif,
Caution:
""the idea making PST mods originally is for saving money""

This shouldn't be the motivator...modding PST's can and is expensive!
You'll only do it once (right?) so make the best decisions you can...
To me, the optimum "mod" is a D-ERF on a 100mm f10 OTA and a BF10 blocking filter.
What you achieve is not a Lunt100 or a SM90...it's a good modded PST Ha scope.
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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by langleif » Sat Jul 13, 2013 8:11 am

[quote]Right, they are, I just can't see the difference though the scope. And the idea making PST mods originally is for saving money I would say. A 75mm Baader will set you back 255 euro and free aperture maybe 70mm?? A 80mm Lunt 199 euro and free aperture is 75mm.

I agree, you can't see the difference through the scope. However put a 1/4 wave ERF on a scope such as an AP or a TEC and compare it to a 1/10th wave ERF with a decent CCD and I bet in good seeing there is a difference ;)

Hmm, I'm pretty sure, that owners of a TEC or even an AP doesn't care about the price in the first place.. If they want an ERF they would go for the very best ;)

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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by langleif » Sat Jul 13, 2013 8:35 am

Langleif,
Caution:
""the idea making PST mods originally is for saving money""

This shouldn't be the motivator...modding PST's can and is expensive!
You'll only do it once (right?) so make the best decisions you can...
To me, the optimum "mod" is a D-ERF on a 100mm f10 OTA and a BF10 blocking filter.
What you achieve is not a Lunt100 or a SM90...it's a good modded PST Ha scope.

Well, they CAN be very expensive. Now take a look on the Daystar site:

http://www.daystarfilters.com/inout_art ... Refractors]

This solution is sufficient in small refractors up to app. 4". I do this while imaging but visually I feel save with a front ERF thoug. But this is rather psychological and I DO care for my eyes.

A PST mod from beginning is mainly an imaging device. They are not quite capable as visual because of the bandwidth <1.0A exempt watching proms. Then I would rather use my SolarMax or my DS PST.

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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by Merlin66 » Sat Jul 13, 2013 9:00 am

Sorry mate...
I do enjoy the 102mm modded PST for visual....the 0.7A is OK for me...
Imaging, well I would use the single or double stacked SM60 on the ED80.
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Re: ERFs for large aperatures D-ERF, colored glass filter, or hot mirror??

Post by langleif » Mon Jul 15, 2013 7:02 pm

Well I'm aware of some PSTs out there having narrower bandwidth, but I have not stumbled across one yet. Or to be fair. They were not uniform across the field. Banding and sweet spots and uneven/odd ligting. So if you got one 0.7A and uniform then you won in lottery. The samples I look through never exceed the bandwidth of my SolarMax. But that's another discussion.

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