The "Frankenscope"? (A what if...)

[Macavity]

Solar Forumites sometimes speak of a "Frankenscope" (I think!) for H-Alpha?

My impression is that this is basically where the *objective* of a smaller/cheaper H-Alpha
scope is upgraded with a wider aperture lens (achromat) of the same f/number.

Naively I would imagine such things would WORK! You would benefit from increased
resolution etc. There would be ways and means to secure the "business end" of e.g.
a "Lunt 50" behind a larger objective. Assuming this were mechanically achieved, is
there anything WRONG with the idea? The "light cone is the same? Would *heating*
be a problem with the Etalon though? Maybe a 100mm H-a scope? Just dreaming! 

[Stu]

Nothing wrong with the idea. PST mods seem to be the most popular, an f10 donor scope like a TAL 100 is ideal. There is a bit more to it in that you have to replace the front objective of the PST with either a full aperture or sub aperture (internally mounted) ERF, plus ensuring the etalon itself is correctly positioned relative to the focal point of the new objective.

There is plenty of help around on SGL, quite a few people have done these mods. Mr Drew is a bit of an expert, as is Ken (Merlin66). They will be happy to advice I'm sure if you want to go down this route.

[xtreemchaos]

why not just get a daystar qwark it turns nearly any air spaced doublet frac  into a solar ha scope, that my plan,"but you allready know that"... charl.

[michael.h.f.wilkinson]

I have tried an LS35/ST80+collimator lens + ERF Frankenscope in the past. Although I did get some enhanced views, it was very, very tricky to align properly, and then keep it aligned. I know some people have made very successful LS35 Frankenscopes, but I gave up, especially when I managed to get the Solar Spectrum filter + bigger ERF, so I could use the APM 80mm

[Macavity]

Ah... The above sounds familiar? <G> Optical alignment not for the faint of heart!
Realistically, my basic Lunt 50 proved a *fair* challenge in this respect? Probably a
bad idea to imagine it can SHARE components with some... "homemade" scope.

There is something quite like-able about full disk H-Alpha and WL images though?
Maybe I'll stick to that, and buy a Teleview 2.5x Powermate for the "better days"!

Just about to get to grips with the *new* Lunt Wedge...
Expecting a "quantum leap" on that one. (lol) 

[Peter Drew]

I've made many "Frankenscopes" for solar viewing from 60mm up to 220mm aperture. Provided that you know what you are doing and have suitable facilities it can be quite straightforward. Probably the simplest and "cheapest" approach is a PST mod, the only downside I can see is the basic requirement of a F10 objective to match the original design which leads to a substantial telescope OTA in large apertures. The Quark looked set to be the death knell of solar mods as all you had to do was fit it to the back of a suitable telescope, unfortunately the rather wide acceptance quality of the manufacturer due to the low price for the item has resulted in somewhat of a lottery as to what you would receive and lately instances of unreliability have surfaced.

[xtreemchaos]

thats food for thought about the quark Peter, didnt know it was a lottery if you got a good one or not ,im hoping to get one this month.  charl.

[Macavity]

Thanks Pete!

I suspect discretion will be the better part of valour here!
But I often wonder about certain things...

If I (slightly) dissect a Lunt 50, it seems to be in THREE parts:

1.  An objective lens (achromat?) at the one end of the OTA!

2. The "Middle bit" - Which is also integral to the main RED 
     bit - The pressure tuner... The "Etalon" etc.

3. The DIAGONAL - Containing a "blue bit" and a "red bit"!
    (I assume to be an ERF + additional  H-alpha filtering?)

I guess I don't REALLY understand *why* Frankenscope
constructors often mention need for an additional ERF?

NO OBLIGATION to enlighten me! But just intrigued as
to what exactly constitutes typical (Lunt) H-Alpha scope.     

 

[Merlin66]

In "Imaging Sunlight" http://www.springer.com/la/book/9783319248721

I have a section on commercial solar filters which give an explanation of the various elements used in their construction .

In the case of PST (and other) mods when you enlarge the aperture you also increase the energy entering the telescope.

To reduce the associated risks of damage and injury an ERF (Energy Rejection Filter) is fitted either to the aperture or as a sub-diameter element.

Hope this helps.

[paulastro]

18 hours ago, Peter Drew said:

I've made many "Frankenscopes" for solar viewing from 60mm up to 220mm aperture. Provided that you know what you are doing and have suitable facilities it can be quite straightforward. Probably the simplest and "cheapest" approach is a PST mod, the only downside I can see is the basic requirement of a F10 objective to match the original design which leads to a substantial telescope OTA in large apertures. The Quark looked set to be the death knell of solar mods as all you had to do was fit it to the back of a suitable telescope, unfortunately the rather wide acceptance quality of the manufacturer due to the low price for the item has resulted in somewhat of a lottery as to what you would receive and lately instances of unreliability have surfaced.

I can certainly testify to the quality of the views from Peter's PST Mods.  With 4 inch Mods and larger, and using a binoviewer, it's fairly routine to be able to use x150 magnification and more to have wonderful bright and high res views.  Prominences are particularly impressive.

[Macavity]

Thanks Folks - Yes, that certainly clarifies any uncertainties I had!
Interesting stuff. But I'm now avowed to complete other projects...
Maybe ONE day! (See e.g. setup by our friend "GreatAttractor")? 

An enthusiast for your books, Ken. Re-purchased(!) a diffraction
grating... A return to spectroscopy is among the above projects? 

Pertinent quote, Paul!

Quote

Contentment is not to have what we want, but rather to want and appreciate what we have.

Cheers, Guys.

[Merlin66]

I'm glad to be able to help.....