Scaling advice sought

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
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DJD
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Scaling advice sought

Post by DJD »

Dear All,
I am currently experimenting with a SolarMax II SM40 DS unit on the front of an 80mm F6
refractor. The back end uses a Baader 35nm Ha filter a UV-IR cut filter and a BF10.
Obviously I am losing some aperature due to the 40mm SM40 and a little bit more due
to the central obstruction of the DS unit , but basically it seems to work very well with my
DSLR.
The cost of the DS units alone are substantially cheaper than the full blown units of comparable diameter.
Is there something I am missing ? Could I not buy a 90mm DS unit for example and utilise more of the
full aperature of the donor scope if I used the same back-end or do I need more filtration of some sort ?
Best wishes,
David


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Re: Scaling advice sought

Post by GUS »

Hi David, the double stack units are only cheaper when compared to a full scope, which also includes a BF, which alone are relatively expensive . Usually the price of a DS(external) unit plus a BF costs about the same as a scope with an Internal etalon and BF.

You could use a larger DS etalon unit with the BF10 and it would work fine(would be limited by the 80mm objective if you used a 90mm Etalon) you would not need any further filtering.(out of curiosity, why are you using the IR/UV cut and the baader 35nm filters, is it because of your camera, as usually for visual and imaging you only need the BF).

In Australia, the cost of a Lunt 60mm PT/BF 1200 is about $2800, and the cost of a DS60f etalon plus a BF 1200 is about the same price, plus you still need a scope and an adapter to mount the filter, so its not really cheaper when you look at all the other things needed to make it usable.

Since you already own the BF10(which could be used with both Lunt and Coronado etalons) you would only need an external etalon and an adapter to fit it to your scope.

GUS.


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Re: Scaling advice sought

Post by DJD »

Thanks Gus.
We can not buy separate components over here in the UK for some reason. Have to buy from the US
or pay the importers mark-up. Makes a big difference.
The scope I use as a terrestial telephoto, I see no need to buy another one.
The back-end I use on an existing PST mod but want something with shorter focal length.
The reason I use the UV-IR cut is laziness. Don't need it for the camera, but do swap in an eyepiece
when I want a quick peek, so erring on the safe side. It does not seem to make any image degradation. I believe that that use of the IR-cut filter is the recommended addition on threads that discuss ITF replacements ( for visual use ).
Despite being fabulously interesting, solar observing is very expensive. I am just trying to make sure
I have done the necessary leg work before selling something to generate the funds.
Thanks again,
David


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Re: Scaling advice sought

Post by GUS »

Sorry David, so you are using the UV/IR and the 35nm as replacement for a rusted ITF.


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Re: Scaling advice sought

Post by DJD »

Exactly, sorry I was not clear. When I said BF10, I meant the actual blocking filter screw in/out section
from a PST.


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Re: Scaling advice sought

Post by marktownley »

You need to make sure it is the single stack etalon and not the double stack unit that you get. Double stacks are deliberately designed to sit on the red side of 656nm so they work. You risk getting banding and potentially it not getting on band at all. The images you are getting with that 40 are very even and on band and suggest to me it might not be a secondary double stack etalon, rather a primary etalon.


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Re: Scaling advice sought

Post by DJD »

Thank you for that Mark. I did not know about Double Stack (DS ) units being different.
The unit I am using was sold to me as a DS unit for a PST, came with the appropriate documentation
and screws onto the PST objective as expected. It was imported from US by the previous owner
but I had no reason to think it was anything other that what it appeared to be. That said I have not
really used it as a DS unit as the image with it in place is pretty dim. I have had much more success with
it as a front mounted etalon unit. You may very well be correct or I could just be very lucky?
Either way it does make my inclination to just buy a larger DS unit somewhat of a big gamble.
You might have just saved me from making an expensive mistake, I owe you a pint.
Best wishes,
David


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Re: Scaling advice sought

Post by marktownley »

Regardless of which ever it is it works which is the important thing :)

Yup, definitely don't get a double stack if you import, get the ss etalon.

I'll be up for that pint later on ;)


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Re: Scaling advice sought

Post by swisswalter »

marktownley wrote:Regardless of which ever it is it works which is the important thing :)

Yup, definitely don't get a double stack if you import, get the ss etalon.

I'll be up for that pint later on ;)
Hi Mark

bring the pint with you next week, so we can share it ;)


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Re: Scaling advice sought

Post by marktownley »

We'll bring more than a pint Walter ;)


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Re: Scaling advice sought

Post by GUS »

I bought a 40mm DS unit originally for a PST which also works with my own scopes no problem, and had three different Coronado DS 60mm filters(Solarmax II) that worked well together in DS mode, and SS mode on several different scopes I own, adjustments to tuning were made by relocating the side pin into a different hole to allow for differences in altitude, and with a combination of Richview and T max tuning, getting on band can be achieved. I think the problem was with the original solarmax filters that only had T max tuning and not RV tuning.(when I ordered the filters I didn't specify how they were going to be used).


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Re: Scaling advice sought

Post by DJD »

That is good to know Gus. ( But it does confuse me more than ever now as it reinforces my original
position)
I guess that I will have to buy a "SM unit + BF" filter kit and sell-on the BF assembly just to be
on the safe side. Which is a shame.
Best wishes,
David


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Re: Scaling advice sought

Post by GUS »

Yes, probably better to be safe than sorry, why not keep the new BF as well,(it has the proper ITF for visual use) as a spare.

GUS.


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