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Grumpy Martian

Observing Sun in a refractor using a Herschel Wedge.

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I am not quite sure of the rules whereby a Herschel Wedge can be used with a refractor. Am I correct in thinking that you should only use the wedge in a doublet or triplet objective. But not in a refractor that has an additional element/lens to the rear of the refractor telescope tube. 

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 No.

All the manufacturers of Petzval type refractors have confirmed in writing that their instruments are 100% safe to use with the Herschel wedge.

 

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May I ask what the concern was about? I guess the notion that heat would build up. 

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Posted (edited)

https://www.firstlightoptics.com/lunt-solar-white-light-systems/lunt-white-light-herschelsolar-wedge.html

With respect. I have read this listing on FLO's website section on the Lunt Herschel solar wedge. There are five important points listed towards the bottom of the information at this Web link. Point 2  tells us that the Lunt Herschel wedge is not suitable for refractors with rear element Petzval designs. 

Edited by Grumpy Martian
Correction

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Hmmmm

That’s not what the telescope manufacturers have said in writing.

Al Nagler published in Sky & Telescope that the TV Petzval instruments were 100% safe to use with the Herschel wedge. I also have the same response in writing from Williams Optics and Takahashi.......

I think it’s a perpetuation of the urban myth......

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I am planning on buying an f7 refractor. Also getting and using a Herschel Wedge with this telescope. I am trying to understand what the risks are. This is because I would be interested in a Takahashi refractor. But this does have the rear element. Whereby the Williams Optics 103 Zenithstar does not. 

Are there any Takahashi users who use the Herschel Wedge that can relay their experiences? 

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32 minutes ago, Grumpy Martian said:

I am planning on buying an f7 refractor. Also getting and using a Herschel Wedge with this telescope. I am trying to understand what the risks are. This is because I would be interested in a Takahashi refractor. But this does have the rear element. Whereby the Williams Optics 103 Zenithstar does not. 

Are there any Takahashi users who use the Herschel Wedge that can relay their experiences? 

Which Tak are you looking at Martin? The Taks with rear elements tend to be more suited to imaging eg the FSQs etc. I use an FC100DC ie a fluorite doublet and the results with a Baader coolwedge are fantastic, when conditions allow of course.

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Posted (edited)

Hi Stu. I am after a shorter focal length 100mm purely for visual. My initial direction is the Williams Optics Zenithstar 100mm ed doublet. Which I think for visual and a Herschel Wedge would be great. But the Tak FC 100mm or similar had grabbed my attention. But it has a rear element. Perhaps a used one if it became available. 

For visual, would the improved quality of a Tak over the Williams Optics be that wide a gulf? 

Edited by Grumpy Martian
Add text.

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Posted (edited)
1 hour ago, Grumpy Martian said:

But the Tak FC 100mm or similar had grabbed my attention. But it has a rear element.

The FC100 DC or DF is a Steinheil design doublet. When there is a reference to "rear" it refers to the Flourite Element which is now the second (or internal) element. The Flourite Element used to be on the front (outside) element I believe...

It is not a Petzval design. There is no lens at the "focuser end of the tube"... 

Edited by Stargazer McCabe
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1 hour ago, Grumpy Martian said:

But the Tak FC 100mm or similar had grabbed my attention. But it has a rear element.

The FC100 is a fluorite doublet, no rear element.

I think around f7 (it is f7.4) is ideal for a doublet, any faster and you really need a triplet I think. The FC100 handles low power, widefield just as well as it does high power planetary, lunar and solar views. I reckon it's about the best visual 4" scope there is, particularly if you take into account weight and portability.

Not sure of the comparison with the WO, but I do know that when pushed, the Tak keeps on giving at higher power, probably due to the quality of figure and polish. The contrast is fab too, helped by the fluorite.

 

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21 minutes ago, Grumpy Martian said:

Wonder if the Takahashi 100FC's ever come up for sale used?

I'd be interested to hear about this...as would half of the forum!

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They don't come up for sale. The thing is...they are usually the last buy after buying and selling a bunch of scopes :D

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1 hour ago, Grumpy Martian said:

Wonder if the Takahashi 100FC's ever come up for sale used?

FLO had a return recently in think but it has gone now. They do come up occasionally, but most people hang on to theirs once they have looked through it ;)

Mine will be the last scope I sell if the financial wheels come off!

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The Tak FC-100's are quite safe to use with a Herschel Wedge - I'm sure you have seen the pics of my setup with my Tak FC-100DL ?

I can assure you that I'm not going to risk my eye or my scope - it works 100% safely and extremely well.

You might get lucky and pick up a pre-owned Tak FC-100 but you may need a lot of patience :rolleyes2:

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Have I missed something as I thought imaging/ viewing the sun you're looking at 1 wavelength so a simple achromat is just as good as a triplet or a quad or whatever..  a lunt is a achromat for a example..

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1 hour ago, newbie alert said:

Have I missed something as I thought imaging/ viewing the sun you're looking at 1 wavelength so a simple achromat is just as good as a triplet or a quad or whatever..  a lunt is a achromat for a example..

A Hershel Wedge is for white light solar, so all the wavelengths are transmitted and an ED/APO scope is preferable. For HA you are correct.

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2 hours ago, newbie alert said:

Have I missed something as I thought imaging/ viewing the sun you're looking at 1 wavelength so a simple achromat is just as good as a triplet or a quad or whatever..  a lunt is a achromat for a example..

As Ricochet has said, with white light solar you are observing right across the spectrum and will see chromatic aberration if using a fast achro. Using a narrownband filter such as a continuum, you can pretty much eliminate this by only viewing in one tight band pass of green light.

I actually think that spherical aberration is the more significant issue as this can really kill detail at higher powers. That is one of the key reasons I use a decent Apo for white light solar, but something like one of the 102mm f11 clones would do an excellent job too, SA much better controlled and any CA can be removed with a filter.

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3 hours ago, Stu said:

As Ricochet has said, with white light solar you are observing right across the spectrum and will see chromatic aberration if using a fast achro. Using a narrownband filter such as a continuum, you can pretty much eliminate this by only viewing in one tight band pass of green light.

I actually think that spherical aberration is the more significant issue as this can really kill detail at higher powers. That is one of the key reasons I use a decent Apo for white light solar, but something like one of the 102mm f11 clones would do an excellent job too, SA much better controlled and any CA can be removed with a filter.

Thanks for the explanation..

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