8 replies to this topic

[Spectrum222]

Well, not sure whether I should post this here, as I KNOW there will be a LOT of variable achromat vs APO comments, and some disparaging ones re: using achromats for solar under continuum "white-light" full/reduced spectrum observing. Oh well... here we go!

 

I post this mainly as encouragement for those with these or similar scopes who may wish to do solar observing and kick it up a notch or two from maybe what they are currently doing now. These are my "quick set-up, solar scopes"; I have several APOs also, but these are currently the two largest refractors I have (not counting my APM 120-45SDs, which are just nuts on Sol...). Both are employed with the following filters:

 

1. Lacerta Lac-2s 2" Brewster angle Herschel Wedge (used/shown in pics below), <OR> APM 2" Herschel, <OR> Baader Mk1 2" Herschel wedges. Current favorite is Lac-2s...
2. Baader ND3.0 on wedges, exc. APM which has its own integrated filters.
3. Hoya 2" polarizer, plus Baader SA filter. (120mm scope - ST120)
4. In lieu of (#3), with 152mm RFT scope, use a Player One UV/IR cut (OD4.0 outside vis range) filter, THEN Baader SA (semi-Apo), then polarizer (linear Hoya, B+W, or Baader, usually latter)

My Skywatcher ST120: on Oberwerk TR3 Maple Tripod, using Skywatcher AZ5 head...

 

 

My TS Optics 152 f/5.9RFT on Stellarvue M2C (alt-az) mount, on Oberwerk TR3 Walnut tripod:

 

 

So... how DO THEY do?

 

Well, pretty amazing, actually! The ST120 has been up to 86X in excellent seeing, but usually to 60-71X, depending upon conditions. The 152 has yet to go over 80x (only seeing limited as of late, had to repair the tripod before using this week with my newer Lac-2s Wedge), but handled 69x in very good seeing so far... No issue going higher on either, just seeing limited so far.

 

In the ST120, the tint of the sun is a pale straw yellow color, or deep cream. (due to the SA filter blue reduction); in the TS152RFT, the sun is a pale cream-white - very close to but NOT quite pure white. 

 

Using the wedges, esp, the Lac-2s and Baader Mk1, I do see a very small amount of CA residual on the limb. very thin pale blue on the ST120, with a VERY thin pale yellow. Same on the RFT, though the outside fringe is more of a pale mauve-deep blue. Estimated to be approx 1% or less of the disk. Very low. On axis, the fringe disappears - so this is more of a field curvature-related OOF color fringe. It can be nulled by either positioning the limb more mid-field, or by eye placement within the field when observing that region. 

 

However, during viewing of disk detail, spot groups, plage, pores, spot penumbrae, etc. The views are sharp and not at all plagued by color fringing. During arcsecond to sub-arcsecond seeing, level of granular details are very close to my APM 120-45SDs, which ARE APO binoculars. I'd say the 152RFT beats out the ST120 by a bit, which is expected since it is a larger scope, with a longer f-ratio.

 

When NOT using the wedges, I use in the ST120 an APM 2" BK7 prism, with a custom CA-reducing filter stack (SV MV2+Astronomik L-3) on the diagonal, and full aperture Kendrick 120mm filter. (AS Film). On the RFT, I use a Euro-EMC 144mm aperture filter w/APM "blue" mirror diagonal (has additional violet/blue partial cut for SCT/Achromats) and the same filter stack. I can also use just a SA semi-apo, or a Hoya L44/Baader UVIR cut filter in lieu, which also does well, though the tint is admittedly a pale straw in that last stack - the SV/L3 combination is very close to pure white, and only maybe 1/3 (if) of the residual fringing seen in the wedges as described above. 

 

Nonetheless, these scopes deliver serious solar views, and work very well. The A-A mounting allows some nice "scans" over the sun during nominal field drift as these are manual, unpowered/non-motored mounts. 

 

AR 3828, the newest active region's spot could be seen at 23:25UT (Sept16/24) showing easily its "notch" in the umbra plus a forming plage or light bridge - pretty shallow angle, with limb CA nulled, and was very fringe-free/CLEAN and visible during arcsecond- level seeing. Several small pores in the mid disk were easily seen also, and AR 3825 had amazingly well-shown plage and granular deep structure during this time. Also, the small group above AR3824 nearer mid disk, but to the west wide, had two bright hot spots, one next to a small spot/pore. Was very obvious during examination of that region at 69X in the 152RFT. 

 

Solar altitude was about 20 degrees altitude here in Edmonton Alberta at that time. So even below 25 degrees, with seeing this wedge system and the 152 did a superb job! There was lots more visible, but I think the point was made here...

 

So, yes, not an APO... got it... but worthy of exceptional solar details? Absolutely, with proper execution and use. EPs generally used are APM UFF 15/18mm or TS UWAN 7/10/13/16mm (really like them!) or TV Nagler Type 6 in similar f.l.: 9/11/13mm usually. 

 

Today and over the weekend, the UFF 15mm (60X) or UWAN 13mm (69X) were used in the RFT, with the Lac-2s Wedge. The biggest surprise to me is the level of detail despite having FOUR filters in the chain. That was a lot!

 

I used my 152 on the April eclipse from Edmonton with my Baader wedge and it did a dandy job as well. What I like about the Lacerta *Lac-2s is both its wider brightness range, and the more complete polarization of the light, which, when paired with a good linear polarizer, REALLY makes the plage and granular structures very deep - even mid disk, when present. Also Penumbral filamentary details really pop as well during excellent seeing (in all refractors - incl. my SV/TMB105 and SV90T Apos). 

 

*the Lacerta has been modified/augmented: I replaced the stock 2" eyepiece system with a TS 15mm adapter ring, and ZWO 4mm m54-f48 insert ring (to place a 48mm ND3.0 filter into the body, similar to a Baader wedge. This way I get deeper room for various stacked filters and eyepiece barrels. Works very well, and IMO better for general visual use. I can always revert to stock if I wish to, but why?!

 

If anyone has questions, or comments they are welcomed. I would prefer not to have any disparaging arguments here. The reason for the post is information gathering, and to use an Achromat when it is required or perhaps the only scope one has. Not in my case, but this testing has yielded very superb results - in both scopes, which also do superbly on planetary and lunar with the mods mentioned above. Again, no not an APO, but they do VERY well regardless. 152RFT has been well over 200X on planets and ST120 from 150X to 200X when seeing permits with v.good to even dare I say, excellent, results. 

 

Clear skies and wishing you lots of good detail!

 

Darren 

Edited by Spectrum222, 17 September 2024 - 01:29 AM.

[steveward53]

I know the Sun's orientation is often misaligned but there's definitely a 'right way up' here on Earth ... 

[Spectrum222]

Funny!!! lol!

 

Yeah for some reason my photos when taken with my iPhone almost always mount sideways on the posts! Weird. 

 

That WOULD be a tough way to look at the sun... sideways! 

 

Darren

[Spectrum222]

See my new posting on a killer solar combination with the 152RFT! Just in from 70X on the sun!

 

https://www.cloudyni...o=new_post&f=87

 

Darren

[gstrumol]

See my new posting on a killer solar combination with the 152RFT! Just in from 70X on the sun!

 

https://www.cloudyni...o=new_post&f=87

 

Darren

Uh ... that just brings you to a way to make a new post! 

[Spectrum222]

lol yes, but it is worth it (?) and still typing my observations and so on. stay tuned. 

 

This sort of counted as a "special case" of the RFT system - totally knocked me over today! Should be done the first writeup by 1800 EDT or sooner. 

 

Darren

[Spectrum222]

Since I did that, I'll repost this here for those wishing "continuity"...

 

No, not trying to hog bandwidth here lol...

[Spectrum222]

So here's what the "new" RFT system does!!!

 

Well, I have been doing solar for many (nearly 30 now) years, and today was one of those days where I just could not process mentally ALL the details available in my instrument I have owned. Came close with my Baader Solar spectrum in H-alpha on my 80mm ED, and with full WL in my 120mm APM SD Binoculars, but this exceeded those levels of general details by quite a bit - today!

 

Before getting into some of the highlights, here's the basic setup: (You who've been on this post thread have seen my scope and wedge already, so... )

_____________________________

 

TS Optics 152mm f/5.9 RFT doublet (f=900mm)
APM 15mm UFF (60X in the scope), and TS 13mm UWAN (69.3X).
Lacerta Optics 2" Brewster-angle Herschel wedge (Lac-2s) - modified a bit - more later*
Filters after prism surface: 2" Baader ND3.0, B+W Linear polarizer (46mm), Custom** 589nm D-line filter, FWHM ~8nm, ~68%T, 2mm thick x 37mm dia., mounted in custom 37mm cell, adapted to 48mm on back side, 46mm front (for mounting polarizer)
Mount: Stellarvue M2C mount (alt-az) on Oberwerk TR3 Walnut tripod.
I had been meaning to try this filter in the RFT for some time, I won't get into why now for brevity, had some mods to do on the mount that were needed. Now good to go. 

 

I mounted this D-line filter into a 37mm cell and used adapter rings many years ago, and it does very well in most scopes I have (using mostly wedges - my Baader Mk1 Herschel and APM Wedges, both 2" format), but I generally prefer the full spectrum as a rule. Even the lime-green of the Baader Continuum filter, which works well, was not my ideal - and this 589nm filter shows more, BTW, than the Continuum. With an Achromat, using a narrow filter like these nulls out the CA issues totally. I have ways to use CA reduction, but certainly these DO help noticeably when seeing does go less ideal - for sure... But, not the case today! Seeing was superb!!!

 

It is sort of a perfect storm here; optically, the RFT doublet is optimized coincidently to the Fraunhofer d-line, one of the quirks of this optic. It has best monochromatic Strehl at 589nm. As my "luck"  would have it, mates ideally with this filter in the chain. Atmospherically, we had sub-arcsec seeing with the sun near apex and just a light wind, which really steadied the view today. Sol was between 32-36 degrees during my observational window of Sept 17 18:20-19:50 UT. (lunch break basically) If I had NO work to do today, I'd still be out - almost missed my 1pm Teams meeting!

 

So... how did it do, and what was visible?! Let's refer to today's active region HMI view:

https://www.spacewea...p24/hmi1898.gif

 

I am still honestly reeling from the amount of details - not many times do I get SO much at once that it is hard to fully process, but here are the highlights:

 

First, imagine taking the sun, have it like a ball of yellow colored dough, and rolling it in ultrafine ground pepper! That is sort of the level of granular detail seen today all over the disk - exc. where facular plague and other details were seen over this. Granular cells were alternating DARK and light (in sodium yellow tint of course), which is VERY easy for our eyes to see optically, contrast-wise, one of the better combinations of tints for this. I could NOT not see this even when not specifically looking. It was SO obvious! Seeing had me well below an arc-sec for resolution. I will confirm this later, but I am 99% certain of it (talking like in the 0.85" regime, or possibly slightly lower at best - pretty much near the optical limit or very close for this 152mm optic).

 

Facular Plage details were DEEP - about 2x deeper in estimation than seen in a Baader 538nm CF. Structural details in granulation, over most of the disk, including the mid-disk portions, had excellent visibility. On spot penumbrae, most of the active regions had fine featherlike appearance (esp. the mid spot group, AR 3825), and excellent rendition of fine structure within them, even to >90% of the disk view. Subtle shading and granular depth (read: temperature and size) variances could easily be made out, within and around the plages too. Imagine sort of a "cross" between a Baader CF and a good Ca-K image, but with yellow and dark tinting instead of green or blue-violet. Best way I can sort of describe this! 

 

AR 3828: Besides being amazing, the primary spot had some discernable structure, seen yesterday evening in this scope in white light as it was splitting down the "middle"; it showed last evening as a partial split with a light bridge - The split at the time today has not quite fully bifurcated the spot yet. penumbrae were "featherlike" surrounding this spot, and superbly deep plage seen throughout this area into AR 3825, and also really nice between it and AR 3827, including some small pores dotted about as well between them. WOW.

 

AR 3827's penumbral region also was very "featherlike", with ultrafine filamentary details seen in it. read - VERY fine! I even saw a few porelike specks on the S leading edge, just within it, for a bit anyway, before they either merged with the adjacent filament (thickening), or stabilized to nominal average temp...

 

Some variances in tint were seen in AR 3827, 3828 (initiation of another light bridge I suspect), and AR 3825. These showed as spotlike variances in the umbral coloration - since I was basically at one wavelength, this would be a temperature variance within the spot umbra. I have seen these in color before, using my SV/TMB 105 APO, and my APM 120SD Binoculars, showing as a sort of deep mauve-taupe sort of color. That was a few weeks back, and in monochrome, showed as a paler tan-yellow tint, brighter than the deeper umbra region, but within it. This was NOT OOF color, or seeing - seeing was solid. Even when  few times the seeing varied a touch to maybe just above 1 arcsec for a few seconds, this structural feature seen held well, but looked better when stable seeing returned.

 

The biggest HUGE highlight for me was AR3825: The penumbral area was SO detailed! Again, ultra-featherlike details prevailed. I witnessed what I can only call the "bear claw"; this was an extension of 4-5 darker and longer filaments (better than HV movie shows!) beyond the main border of the penumbra of the main spot, facing east and slightly below (reversed in wedge). I've marked this on a Helioviewer snapshot which does not show this well - it was WAY better in 589 D-line light:

 

Here's a movie of this over 6h, most of the structure was in my window I think: https://helioviewer.org/?movieId=9kKW5

 

 

You can see in the above snap a bit of this "claw-like" structure - but it was WAY more detailed and changed in the range of 5-10 minute timeframe. VERY neat to witness this!

 

So... in a nutshell, I have a new favorite: my 152RFT w/Lacerta wedge and 589 d-line filter. The Lacerta Wedge gives a wider brightness range than my Baader or APM wedges, and I suspect part of the reason WHY this was so good, as well as having full polarization in the light coming off the wedge surface. (Definitely the 152RFT is the "Batman" of the Dynamic Duo!)

 

If time had allowed, I wanted badly to go to 100X. I just was having a ball at ~70X, and time was precious. Will do more with this as conditions/weather allow for. This level of detail reminded me of a "live" movie or fast changing photograph. I will look into adapting my camera to shoot this sometime, but not a priority - I just got this running, and it is NOT on a tracked mount - that's on my next list for a mount to handle this 23lb. scope.

 

*The mods to the Lacerta Lac-2s are basically removal of the stock EP/cam mount, which has M54 threads to mate to the wedge body. I added a 15mm extension tube, and a ZWO 4mm thick M54m-M48f ring to mount my 48mm Baader ND3.0 in the unit similar to the Baader wedges. I then use a clicklock and CL 1.25" adapter, and used 3mm extension to the d-line housing to clear any 1.25" EPs I put into the upper section - will fit APM UFFs, TS UWANs, Nagler T6s also. The ring acts as a "stop" to prevent any filters from hitting the ND3.0 filter at the wedge entrance. So I know when I am full length for the 2" filtering. smile.gif

 

**The d-line filter was a surplus (one-of, probably a cancelled order) It is an Omega Optical interference filter, 34mm x 2mm, in 37mm OD ring assembly mount (round). FWHM 8nm, outside of passband blocking of OD 2.0 over 400-1200nm, just ~1/9.2 wave (1/10 wave at 632nm) at 589nm. Mounted 37mm ring Inside a cell (43mm) using graphite epoxy and used step up rings to mate to 48mm (m) and 46mm (f - to mate to B+W Pol filter). Checked alignment during mounting using a He laser I had in 2008 when I got it. smile.gif

 

I am looking at options for other d-line filtering and will update when information presents itself. Also, I may look into a He-line Quark down the road - that might be FUN! The 589nm allowed the BEST this scope can deliver and it did so in SPADES!

________________________________________

 

Clear skies, and good solar - I hope this post was informative...

Darren

Edited by Spectrum222, 18 September 2024 - 03:19 PM.

[timmywampus]

I know the Sun's orientation is often misaligned but there's definitely a 'right way up' here on Earth ... 

judging from the angle, i thought it must be west of me.  then i saw the details said edmonton, but it seems like that would look more top down based my southern us perspective of the map.