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A Celestron C90 & A Lunt Hershel Wedge?

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19 replies to this topic

#1 SloMoe

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Posted 16 November 2019 - 08:45 AM

Morning all, I'm about to receive a C90 for basically the ol' Grab N Go scope. cool.gif

 

I already have a full aperture glass solar filter and a wedge I use on my Orion ST-90, but I'm not sure if direct sunlight will damage anything in the C90 when using the wedge,

 

Will the OTA heat up or the corrector plate be damaged? Mirror coatings heat up and be damaged?  confused1.gif

 

I know the 90 is the bottom end of aperture for detail but it's what I have for the moment.

 

 



#2 junomike

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Posted 16 November 2019 - 09:05 AM

Bad Idea. For safety reasons one should only use Solar equipment as it was intended.

SCT's (Maks)  ARE NOT SAFE using only a Wedge and if using a proper "Full Aperture Glass" with it,

I'm not seeing any real benefit over  the ST90 which is already properly outfitted.


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#3 SloMoe

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Posted 16 November 2019 - 09:10 AM

Well as I'm starting to do my after purchase research I've got a few more easy question, 

 

Is the VB the same as most SCT's ? 

Like can I swap it out for any other VB accessory, like a Bluefire ball compression band VB?

A focal reducer, maybe a Celstron .63?

Would there be any benefit?


Edited by SloMoe, 16 November 2019 - 09:27 AM.


#4 junomike

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Posted 16 November 2019 - 09:15 AM

Well as I'm starting to do my after purchase research I've got a few more easy question, 

 

Is the VB the same as most SCT's ? 

Like can I swap it out for any other VB accessory, like a Bluefire ball compression band VB?

A focal reducer, maybe a Celstron 6.3?

Would there be any benefit?

It (VB and FR) will work however you'll need a Scopestuff adapter. See here for details  (pic in post #3)

How is the C90 easier than the ST90?



#5 SloMoe

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Posted 16 November 2019 - 09:19 AM

More compact, no CA to battle.

 

thanks for the link Mike, wasn't sure if the Mak 90 had the same size for VB's, 


Edited by SloMoe, 16 November 2019 - 09:28 AM.


#6 bobhen

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Posted 16 November 2019 - 09:42 AM

Morning all, I'm about to receive a C90 for basically the ol' Grab N Go scope. cool.gif

 

I already have a full aperture glass solar filter and a wedge I use on my Orion ST-90, but I'm not sure if direct sunlight will damage anything in the C90 when using the wedge,

 

Will the OTA heat up or the corrector plate be damaged? Mirror coatings heat up and be damaged?  confused1.gif

 

I know the 90 is the bottom end of aperture for detail but it's what I have for the moment.

Don’t use a wedge with an SCT or Mak. The corrector will not be damaged as unfocused light will just pass right through but the secondary will probably crack or become dislodged or discolored as the light and heat becomes more highly concentrated.

 

Baader film is the best material for a full aperture, very inexpensive white light filter.

 

Bob


Edited by bobhen, 16 November 2019 - 09:43 AM.


#7 SloMoe

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Posted 16 November 2019 - 09:57 AM

Thanks Bob, I sort of figured the heat would build up in there somewhere, I've got a glass one, also have the film one too, but it's a too small for either of my 90's, fits my 70.

 

I like the softer color of the glass over the white view with the film, don't know if it's because glass was my first filter for solar viewing back a number of years before the film came out or what, but I like the glass filter also because of the durability of the cell, can't accidentally tear glass, and yeah I know, care has to be taken with anything glass too.



#8 Peter Besenbruch

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Posted 16 November 2019 - 04:05 PM

Is the VB the same as most SCT's ?

The threads are different. To use an SCT visual back, or other SCT accessories, you need an adapter ring.

 

 

Like can I swap it out for any other VB accessory, like a Bluefire ball compression band VB?

A focal reducer, maybe a Celstron .63?

Would there be any benefit?

I have the Celestron .63 compressor more or less permanently attached. Not only can I reach lower magnifications, I can do so with less vignetting.


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#9 Bowlerhat

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Posted 16 November 2019 - 11:10 PM

to upgrade the VB on c90 you need an adapter for 2" sct accesories. Not much benefit on citting on 0.63 reducer on c90 though.



#10 SloMoe

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Posted 16 November 2019 - 11:57 PM

Mostly it's to upgrade the visual back to a compression band type, not much for thumb screws on high end glass ya know



#11 PXR-5

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Posted 17 November 2019 - 12:39 AM

I use the FR/C on mine, it does give a wider FOV :)

#12 Peter Besenbruch

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Posted 17 November 2019 - 01:55 AM

to upgrade the VB on c90 you need an adapter for 2" sct accesories. Not much benefit on citting on 0.63 reducer on c90 though.

There is a significant benefit to using lower power eyepieces with a reducer. A 32mm Plössl goes completely dark in the outer 5-10% of the field without one. Not only to you get some illumination to the edge of the field when using the reducer, you also get real 25x, which is good for birding.


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#13 gustavo_sanchez

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Posted 17 November 2019 - 09:19 PM

Keeping the post on topic, I understand that the Lunt wedges are designed for refractor telescopes, not catadioptric OTAs.

#14 SloMoe

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Posted 18 November 2019 - 07:18 AM

Yes Gustavo, they are,

After starting this thread I've done a bit more research on the Hershel design online .

 

But on another note I did get a few other questions about the scope that I needed some answers for from the members that contributed to this thread,so thank you all for your help.

 

The three major things picked out of this thread for me are that the visual back will need an adapter for it to accept a standard SCT visual back, that my gathering dust .63 reducer/flatterer now has a purpose again, and the full aperture glass filter I purchased originally for my ST-90 again has purpose.

 

And from a thread on the beginners forum, I learned that it can be collimated if need be.


Edited by SloMoe, 18 November 2019 - 07:31 AM.

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#15 Bowlerhat

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Posted 18 November 2019 - 03:16 PM

There is a significant benefit to using lower power eyepieces with a reducer. A 32mm Plössl goes completely dark in the outer 5-10% of the field without one. Not only to you get some illumination to the edge of the field when using the reducer, you also get real 25x, which is good for birding.

I had a different response back then when I asked this, and seems there are mixed response. But you're right, a 0.63 reducer will still have an impact.

 

 

Yes Gustavo, they are,

After starting this thread I've done a bit more research on the Hershel design online .

 

But on another note I did get a few other questions about the scope that I needed some answers for from the members that contributed to this thread,so thank you all for your help.

 

The three major things picked out of this thread for me are that the visual back will need an adapter for it to accept a standard SCT visual back, that my gathering dust .63 reducer/flatterer now has a purpose again, and the full aperture glass filter I purchased originally for my ST-90 again has purpose.

 

And from a thread on the beginners forum, I learned that it can be collimated if need be.

 

You'll need an adapter ring. scopestuff sells it, someone had baader ring instead. It depends on what kind of C90 you have. 



#16 photoracer18

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Posted 18 November 2019 - 04:35 PM

Well the .63x FR still vignettes more of the field than without it however even then the shorter FL does give you a wider field. Its just not really made for something with the F-ratio of the C90.

Intes used to make a similar 0.6x FR for their MCTs that was designed to work on scopes up to F15, and it does have an SCT thread on it as I actually own one of them. I have experimented with it on my LOMO Astele 95 because its the only Mak I have that actually has an SCT thread on the back as my MK67 has fixed optics and a rear focuser. But its baffle tube is not really very much larger than the 90mm scopes out there. I have not measured the change in FOV either. 



#17 SloMoe

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Posted 18 November 2019 - 09:21 PM

I contacted Jim at Scopestuff today, he said he wasn't sure which adapter for which Mak 90 so I have to wait for the scope to get here and measure the baffle tube threads so I get the correct one.

 

Appreciate all the input from you guys, btw what eye pieces were you using when the view edge was vignetting.

1.25" or 2" ?

FOV of the eyepieces?

 

I'm planning on using Naglers, just kinda curious,, 



#18 Peter Besenbruch

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Posted 19 November 2019 - 03:06 AM

Well the .63x FR still vignettes more of the field than without it however even then the shorter FL does give you a wider field. Its just not really made for something with the F-ratio of the C90.

The .63 reducer improves the severe vignetting of the C90. It yields better illumination than not using it, along with lower magnification. Again, with a 32mm Plössl will black out in the outer 5-10% of the field. That outer 10% will have illumination with the reducer.



#19 Peter Besenbruch

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Posted 19 November 2019 - 03:14 AM

Appreciate all the input from you guys, btw what eye pieces were you using when the view edge was vignetting.

1.25" or 2" ?

FOV of the eyepieces?

I was using 1.25" eyepieces in a standard 1.25" diagonal. The worst vignetting eyepiece used was the 32mm GSO Plössl, which uses the entire width of the eyepiece barrel. The C90 has a 16mm opening into the primary baffle. That's why the outer 10% of the field of view gets cut off completely. That's why I use a reducer.

 

Another tip: For day time viewing you may get a bit of  interference from the secondary mirror on a bright day. I tend to use a 27mm Flat Field when that happens. Another alternative is a 24mm wide angle. Naglers should work for higher magnifications, but given the size of the scope, you might want to stay with type 6s.



#20 gustavo_sanchez

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Posted 19 November 2019 - 06:05 AM

Another friendly request to keep the thread on topic... If a new topic discussion is desired, please start a new thread.
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