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Solarscope SF70DS

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#1 pao

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Posted 20 November 2019 - 06:40 PM

Hi guys,

I’m wondering what I can really see with a Solarscope UK SF70 double stack filter.

There are so many solutions out there for high resolution solar observation: quarks with giant optics attached, Lunts for every taste and pocket, Daystar quantum, Baader, etc...

But what can I really see, in “the real world”, with a small scope like my Televue 76 + SF70 DS solarscope filter? Anyone had direct experience? Is it worth the price for a so small filter? Low detail and low magnifications useful only for full sun disc observing?

Thank you

pao

Edit: I’m referring only on solar observations not photography.


Edited by pao, 20 November 2019 - 06:43 PM.


#2 MalVeauX

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Posted 21 November 2019 - 10:23 AM

Heya,

 

You can see see lots with a 60mm aperture in solar. You'll see the same features you see in high res, just smaller, but they are resolved. The sun is huge, so we benefit in that sense. 70~80mm shows even more. You'll see the spicules, fibrils, plages, filaments and prominences no problem. Also, daytime seeing is very limiting, so I wouldn't go larger than 102mm (4") on aperture for visual anyways unless you know your seeing is very good and have lots of experience and deep pockets to go bigger. Also depends on the quality of the filters you want to invest in. But you can certainly see virtually everything with the apertures you're looking at.

 

Very best,


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#3 George9

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Posted 21 November 2019 - 10:15 PM

If money is no object, then that is a nice portable choice, and it is likely to work well for its aperture. I am guessing that Solarscope on average produces a great filter, but everyone has variation among units, and threads report problems with every single brand, even the most expensive. Many people are very happy with it.

 

The TV 76 is very capable of carrying those filters on the front, so that is a nice match. (My 70mm TV Pronto carried my Isle of Man ASP-60's well, and the Pronto is the 76 predecessor, and the ASP-60 is in a sense a 70mm predecessor, although it had a central obstruction.)

 

The 70 DS will show more than other companies' 60 DS (extra 10mm plus no central obstruction), but a good 80 or 90 DS will show even more at a fraction of the price. (I think the price of the SolarScope 70mm DS is around $16K. Of course, that may include a steep US markup. And I guess it is just hard to produce an unobstructed 70mm precision etalon.)

 

So yes there is plenty to see. My 80mm can get to 150x in good seeing, so the 70 should be pretty high, too. Whether it is worth the price is obviously a personal choice.

 

George


Edited by George9, 21 November 2019 - 10:25 PM.

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#4 BYoesle

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Posted 22 November 2019 - 02:49 AM

I am guessing that Solarscope on average produces a great filter, but everyone has variation among units, and threads report problems with every single brand, even the most expensive... The 70 DS will show more than other companies' 60 DS (extra 10mm plus no central obstruction), but a good 80 or 90 DS will show even more at a fraction of the price.

With larger diameter etalons a central obstruction spacer system becomes necessary. My limited experience was as described, and a DSF100 (~$32,000) did not perform better that a Tucson Coronado DS SM90 (~$12,000), and required some additional tweeks to perform that well: Due to lack of a central spacer system, and insufficient IR blocking on the ERF, it was not as thermally stable: 

 

Caompare Image2 enhanced comp.jpg

Click for larger image.

 

Due to the smaller aperture of the 70 mm a lot of this might not be applicable, and some who have used both note the high quality of the Solar Scope filters is worth the premium price.

 

However, beyond a 80 or 90 mm DS system, note the Lunt 100 mm front etalon uses the "root 3" spacer system for thermal stability/gap uniformity, and a LS100FHa double stack system and blocking filter would appear to be less expensive than the 70 mm DS Solar Scope filter system. Just something to think about...


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#5 Doug D.

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Posted 22 November 2019 - 11:26 AM

I own a DS SF70 filter set that I have dedicated to a TV76 with dual speed focuser.  In no particular order I can add the following:

 

-Pairing these filters with a TV76 is in many ways ideal although somewhat overkill in that a decent achromat would likely more than suffice.  With a Solarscope supplied adapter, I can screw directly onto the OTA with dew shield retracted. I love the solid and secure feel of this configuration.

 

-You can reach the tuning rings of both SF70 filters easily with a TV76, even a TV85 put them at an uncomfortable distance for me.

 

-The SF100 without central spacer constitutes a heroic manufacturing effort but as Bob (and others lucky enough to have used an SF100) points out, thermal stability can be a problem.

 

-I use binoviewers (Baader Maxbright) for >90% of my visual observing using primarily Pan 24's, Zeiss 25mm equivalent microscope eyepieces, and other 16-18mm simple eps from my collection. Binoviewing is the single most important upgrade once you decide on a filter system and scope, at least IMHO.

 

-Hard to argue with Bob's comparison of the Coronado 90 and the SF100 although visually I doubt most of us could tell much of a difference at the EP.  Sample variability also definitely matters - Bob's Tucson Coronado filters seem to me to be particularly good examples.

 

-I agree that daytime seeing is more limiting to higher apertures and may not allow you to realize as much bang as you think you'd get at >90mm or so.  To me, the SF70 is in the Goldilocks zone for unobstructed etalons or their equivalent.

 

-The Solarscope filters are "worth it" to me, at least at the 2015 prices I paid when I sent back my SS SF70 to get it DS'd. However, given the cost (relative to Lunt or Coronado) you are in the land of diminishing returns with a Solarscope filter set. A look at Bob's posted images more than drives that point home.

 

-it isn't all just about aperture when it comes to viewing or imaging in H-alpha.  What I am struck by with the Solarscope filters I have used (including an SV50 SS scope) is the on band performance across the solar disc/FOV and the deep black backgrounds.  I can't speak to how they compare to something comparable from Lunt or Coronado; I've not had the pleasure of a side by side.

 

- While I like the SF70 filter set, I still miss the SV50 a lot - its performance was outstanding and it seemed to punch well above its weight class. So, no, it is not all about aperture.


Edited by Doug D., 22 November 2019 - 12:05 PM.

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#6 BYoesle

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Posted 22 November 2019 - 12:23 PM

Doug and George are absolutely right. Etalons are incredibly complicated optical devices and even within brands and production cycles there can be samples with great and not so great performance. Plate flatness, lack of polish scatter, gap parallelism and uniformity, quality of coatings, temperature stability, and a host of associated parameters all can significantly affect performance. Generally the principle that you get what you pay for applies.

 

It is unfortunate that the industry does not supply more valid and reliable measures of performance beyond a simple bandpass specification, which can be irrelevant in many circumstances. That leaves one to rely on the reputation of the filter maker to stand behind their products if a concern arises, and keep one's fingers crossed. Those who know someone with experience in what a good system can do, or lucky enough to live close to a manufacturer or supplier with multiple samples in order to "try before you buy," are in the best position.

 

Due to the Solar Scope 100 mm filters having an ERF with a lot of near IR leakage in addition to the lack of a stabilizing central spacer, I don't think the DSF100's as supplied ever became truly thermally stable.

 

Sol-ERF-lin.jpg

Baader-D-ERF.jpg

 

 

Adding a Badder DERF nicely complemented the DSF 100 ERF for IR blocking out to 2500 nm, and worked well to tame the thermal instability and yielded performance almost identical to the SM90s:

 

DERF use cmp.jpg

 

I suggested Solar Scope address this issue and it may no longer be of concern, in which case hopefully all their ERFs might use a better ERF IR blocking coating and have improved thermal stability.


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#7 Doug D.

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Posted 22 November 2019 - 12:43 PM

Great analysis Bob - curious why Solarscope did not address this quickly at the time or even better, have figured it out themselves beforehand?  I also remember reading a report from an SF100 DS user (i.e., Alexandra Hart) that even a cloud crossing the sun would cause the filter to go off band (as it momentarily cooled).  Of course, she did assemble this full disc image using a DS SF100. All I can say is bow.gif

 

It seems like the Baader D-ERF did the trick for you. Don't know what the story is with the SF100 now that Ken retired and the company changed hands (bought by Manx Precision Optics).  I have had an e-mail exchange with new owner, Helmut Kessler, who seems quite committed to Solarscope and even suggested some new scope options coming along in future.  Whether many of us will be able to afford them is another question. 


Edited by Doug D., 22 November 2019 - 01:28 PM.

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#8 BYoesle

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Posted 22 November 2019 - 01:12 PM

The OEM DSF 100's had IR blocking coatings, but no central spacer. Thermal stability (or lack thereof) made the system very frustrating to use.

 

The OEM SM90's have no IR blocking on the ERF, but due to the central spacer are much more thermally stable even without it.

 

For my DS filter system, I removed one RG630 ERF from the DS for improved transmission, and added a DERF for ITF protection.

 

To be as fair as possible, an apples to apples comparison configuration was used for testing the effect of using the Baader DERF (the normal configuration for the SM90 DS) with the DSF 100 equipped with the same DERF, which yielded a more thermally stable DSF100 system. Here's the test set-up:

 

DSF100 v SM90DS DERF comp.jpg

Click to enlarge.

 

Top: SM90 DS w DERF, OEM DSF100.

Bottom: OEM DSF100 w Badder DERF.

Identical ED100/900 OTAs.

 

Doug, I'm sending you a PM ;-)


Edited by BYoesle, 22 November 2019 - 01:18 PM.

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#9 George9

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Posted 22 November 2019 - 02:17 PM

What makes a truly great H-alpha scope is endless hours testing and experimenting (safely) to optimize performance. Bob just showed an example. Forget the purchase price, it's the hours spent fiddling that "cost" the most. That part has to be fun for you.

 

But the main manufacturers do produce good to great filters out of the box (yes always with some exceptions).

 

George


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#10 Doug D.

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Posted 22 November 2019 - 03:06 PM

I very much agree with you George - but it is fun as far as I'm concerned.


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#11 pao

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Posted 23 November 2019 - 07:33 PM

Thank you very much everybody for your contribution. 
Tough choice. I’m not sure Solarscope is still producing the SF100, some times ago I contacted them and they confirmed to me  that only the 70 mm was in production (the SF100 was too long too produce with too low request). 
So, preferring in this moment a 100 vs 70 mm filter (I have also a 100 mm apo waiting...), I think that I have to check somewhere else. Moreover, I am not sure I trust completely on the new Solarscope property. I remember the old and the new Coronado, like two different planets...

pao




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