Sun HA 15.8.17 (+ Frankenscope Test!)

[Macavity]

Here's the usual "combination" -- Lunt50 Disk + Proms:

As previously remarked, I've had an interest in making
 a "Frankenscope", and finally got around to putting a 
TEST rig together! No HUGE magnification yet, but I
had all the requisite "bits" from a trusty old ST102!

I am expecting delivery of a Baader ERF tomorrow, so 
for initial testing, I stopped the ST102 down to 50mm!

Here are the images showing the Frankenscope (last!)
compared to Lunt50 (standard config. & Barlowed 2x).

1. Lunt50 (f=350mm; d=50mm)

2. Lunt50 with 2x Barlow: (f~700mm; d=50mm):

Throwing caution to the wind, I *increased* the stop
size on the Frankenscope to 70mm for a preferred f/7.
No sudden *cracks* or smells of burning thankfully! 
(I suspect it is wise to be *cautious* re. such tests...)

3. Frankenscope with 2x Barlow (f~1000mm; d=70mm):



I have managed to convince myself that the 2x Barlowed Frankenscope is showing
a real advantage over the 2x Barlowed Lunt! Not sure where to go with a possible
DONOR scopes yet! Anyway, I will have the ERF to play with, albeit with a fair few
quid *less* in the Bank! But you're only young once... Eh, Readers?  

[Pig]

Nice one Chris, the Frankenscope is certainly showing much better detail ? For a start you can easily see the spicules all the way around the limb of the disc, the plaged area is also more substantial ?Much better all round in my opinion.

[Paul73]

Looking good!

Also, looking forward to following Frankenscope's journey to Solar domination!!!! Cue the manic evil laughter.....

I'm a bit late on this build. Are we talking a sawn off Lunt 50mm, mated with a bigger frac (with a decent ERF etc)??

Suddenly, I feel the need to upgrade.

Although, the views through my ham fisted 100mm PST hybrid were lovely earlier???

Paul

 

[David Smith]

Nice Chris, Frankenscope looks promising. Adding the ERF shoudl give you a nice hike in aperture for not-too-much cash outlay.

[Macavity]

Hi Folks --- Thanks (as ever) for your collective enthusiasm!

***************************************************
As a quick SAFETY thought, I should perhaps remark that I do
not personally observe visually much... But anyone who *does*
should bear in mind the important considerations re. modding
scopes... Keep your eyeballs safe from excessive heat / light!!!
*************************************************** 

The Baader ERF arrived, so here's an (obligatory?) picture:

Since I was already beginning to "sweat a bit", just handling it,
I decided to put it in a *padded* container for safe keeping! 

To clarify the construction method - With *limited* facilities,
I am making various "Anuluses" (?!) from hardboard & MDF
for the OTA "Bung" and EDF cell... "King of the hole saw"? 

FWIW, I simply LEFT the Lunt OTA attached at the ERF end,
removed the objective, and am just sliding the *whole thing* 
into the ST102 OTA using "wood-technology" rings to hold it
(roughly) in place. As the others who followed this path, I'm
using a canonical guide scope ring to allow for "collimation"!

As someone else ELSE noted, I also include a BOLT as an
"End Stop". Heaven forbid my Lunt 50 should fall out!!! 

ASIDE: As I survey the market of potential Donor Scopes,
I note there aren't many candidates! With the 90mm ERF
I am almost tempted by the ST120 OTA (only). At under 
£250, they are as good as many of the ilk? Removing the
odd internal baffle is no problem! lol. Stopped down from
f/5 to f/7 should help *spherical aberration* a fair too... 

I already KNOW how to Barlow a Lunt 50 *Four* times.
(I sense the limit is more like 3x for a 50mm objective!)
But with focal length 600mm, field stop 86mm (for f/7)
f=1200 mm, with 2x barlow, and maybe even more... 

P.S. Ah, so those are the famous Spicules? I had been
dismissing them as processing "artifacts" up to now! lol. 

[Pete Presland]

Lovely set of images.

[Macavity]

Just as a final amusement, I was (theoretically!) able to compare
the result of masking the scope by 50mm (f/10) and 70mm (f/7). 

A 1/2hr gap between images, but everything else is the same...

  

The image on the LEFT is 50mm, that on he right is 70mm!
And it *seems* indeed that 70mm has "better" resolution?

But this brings me to a QUESTION -- I may be thick, but... 

For an Frankenscope based on the Lunt 50 f/7 it seems most
natural to chose a donor scope matching the focal ratio, f/7!
BUT why isn't it possible to use (say) an f/10 Donor Scope? 

As far as the Etalon etc. is concerned, the f/10 light cone is
simply the central portion of the f/7 light cone? I plan on a
90mm f=600mm (f/7) scope, but I have seen the use of a  
90mm f=900 mm (f/10) scope! It seemed to work as well!

Before I choose, ANY thoughts would be most welcome...

[Macavity]

Don't worry folks... Got is sussed now (I think)!
All down to "similar triangles", but you do have
to make allowances for adding the solar image
dimensions to the (point source) light cone etc.

[GreatAttractor]

Quote

And it *seems* indeed that 70mm has "better" resolution?

 

Yes, a very good demonstration there.

 

On 16.08.2017 at 20:50, Macavity said:

BUT why isn't it possible to use (say) an f/10 Donor Scope? 

It's definitely possible, however, the usable field of view will be smaller than with f/7. The linear size of sweet-spot stays the same (so it covers the same portion of your camera's sensor), but (due to the longer f.l.) the image now has larger scale (i.e. less arc sec/pixel); if at f/7 a solar feature encompassed n pixels, now it's 10/7·n =  1.42·n pix. Aperture stays the same, so the level of details visible is the same (they're just bigger). In effect, it's best to stay as close to f/7 as possible.

On the other hand, using a smaller F-number would clip the incoming light cone and reduce the effective aperture.

[Macavity]

Heheh... Worth a bit of "wriggling", but no free lunch?
So f/7 it is then! In the interim, I'll *reclaim* my ST102! 

Thank you for your reply - Liking your ideas and images!
As for the Frankenscope: "I have a cunning plan" now. 

https://youtu.be/AsXKS8Nyu8Q