Grey Skies == (Lunt LS50Tha) Scope Tinkerings

[Macavity]

No "rocket science" to the initiates, but my random tinkerings with my Lunt LS50Tha:

https://stargazerslounge.com/topic/269450-improving-the-basic-lunt-ls50-tha-solar-scope/

Real Life, Grey Skies / etc. may intervene, but NO, I hadn't yet "given up" (whatever)! 

[Pete Presland]

A fine solution!

[Davey-T]

Do you get any Newton rings ? I've got a similar setup and just got a tilt adjuster from FLO to fit between the camera and the BF just waiting for another adapter to fit it hopefully before Monday.

Dave

[Macavity]

31 minutes ago, Davey-T said:

Do you get any Newton rings ? I've got a similar setup and just got a tilt adjuster from FLO to fit between the camera and the BF just waiting for another adapter to fit it hopefully before Monday.

Dave

As I said on t'other thread... Sadly yes!

I casually wondered if it might be some property of the ASI120MM filter.
But it (predictably) wasn't! If I remember rightly the ASI120MC (colour)
didn't suffer from such things??? But you lose a factor of two resolution?

Clearly, I can "smear" NRs by playing with EQMod tracking rates, but...

Now I have (famous last words) "completed" my astro setup, I might be
able to squeeze a few more quid for a camera that doesn't give NRs... 

Ah, but which...

[Davey-T]

I get them with the Point Grey BFly Gige camera but not if I use a .5X focal reducer, no idea why, not really clued up about the physical / scientific reason for them

Dave

[Ibbo!]

I get them with the ZWO 120 mono but not with the Blackfly or the DMK 31

[Macavity]

18 minutes ago, Davey-T said:

I get them with the Point Grey BFly Gige camera but not if I use a .5X focal reducer,
no idea why, not really clued up about the physical / scientific reason for them

Heheh. I did look up the "Physics", but decided the formulae might "not reveal much".
A good excuse for getting older!! Could well be interesting to try a TILTER. Frankly, I
didn't come to much of a conclusion either way. But I didn't test it in a systematic way.

Ah, the tribulations of the (DSO & Solar) Astronomer. Either you are stuggling to work
with cold numbed fingers or sweating and straining beneath the UK "blazing sun"?  
 

[Davey-T]

At least it's not raining here ATM

I tried jamming a bit of coke can down the side of the camera and it seemed to help so thought I'd give the tilter a try nothing ventured-- .

Dave

[ArmyAirForce]

I used the female thread from a T-Ring to attach the blocking filter/diagonal. This moved the focus point allowing easier focus with and without barlows. I also made a tilt adapter, and this removed the Newton Rings on my ASI120MM. The angle is about 5 degrees.

[Macavity]

Thanks for the above, AAF. You raise an interesting point, which well
deserves an airing? Comments are (obviously) very welcome on this!
I sense the Mods are Fellow Nerds don't overly mind discussion here?

I was indeed aware that people had rid themselves of Newton's Rings
by introducing a significant Dog-Leg (~5 deg!) into the optical path...
In levity, I remark that my "mild OCD" wouldn't like that idea at all!

I venture that my setup has/had TWO "problems" really?

The FIRST, which I address above is a variation in *tuning* across
the solar disk as it moves around on the chip! At first that bothered
me quite a lot - £1000$ for a "faulty" scope? But now I am relieved 
that I seem to be able to *resolve* this by "clocking" the diagonal
about the axis! But the question remains in my mind though:

Q: Am I the only one who experiences this with the Lunt50? <== !!

(I suspect not) People complain about the helial focusser, but mine
seems reasonably OK! Yet my scope seems to squint? I speculate
that it might be due to the use of a diagonal in the blocking filter...

I sense many of us would prefer a straight-though blocking filter?
Maybe to allow some sort of standard / crayford-style focusser.

The SECOND issue is Newtons rings! I do actually have a TILTER:

http://www.teleskop-express.de/shop/product_info.php/info/p4745_TS-T2-tilting-collimator---compensation-for-field-tipping-in-astrophoto.html

But my (largely unsuccessful) experiment was to place it BEFORE
the diagonal and try to fix the lack of uniformity  issue. I do note
I still have that extra 15mm (T2 spacer) in front of the camera...
This seems the more LOGICAL place to try YOUR experiment in
"Extreme Tilting". Add washers... springs(?) to a Standard Tilter?

You may have a convert, AAF? Anyway another option available!

P.S. I thought this "Solar Astronomy" would be dead simple... lol

[ArmyAirForce]

Changing the pressure tuner does vary the brightness of the image, but yes, there's a sweet spot for detail which also moves with tuning. There's a comparison somewhere on here between the Lunt and Coronado PST. In there in says the PST sweet spot is smaller than the Lunt. I can't recall if it mentioned movement of the sweet spot.

I can get the whole of the Sun on my ASI120MM with the full sensor selected. There does seem to be variation in detail across the disc. Taking 'flats' helps with evening out tone imbalance across the whole sensor. It was the same on my previous Lunt that died after 3 months. When I use my x2 barlow, I cut the region of interest on the sensor to 640 x 480, and the detail seems more consistent over that area.

Here's a recent shot from April 23rd