Solar 6" Refractor Quandary

[michael.h.f.wilkinson]

I am about to pull the trigger on a relatively fast 6" refractor to use as a dedicated solar instrument. The idea is to place my Beloptik 85 mm Tri-Band ERF halfway down the tube, so by switching between Herschel wedge, Ca-K module, and my Baader TZ4 telecentric/Solar Spectrum H-alpha filter combo, I can image the sun in three wavelengths.

There are two main contenders, the first being the TS 6" F/5.9

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p2229_TS-Optics-RFT-152mm-f-5-9-Gro-feld-Refraktor-mit-2-5---Zahntriebauszug.html

or any of its near identical twins. The second is the Explore Scientific AR 152, which is F/6.5

https://www.robtics.nl/nl/refractor-lens/5115-explore-scientific-ar152-air-spaced-doublet-ota.html

The former has a very good rep with those using Quarks, and I am sure it would work fine in WL, and (perhaps stopped down a little) for Ca-K as well. I have two issues with this scope. The first is that being F/5.9, the Baader TZ-4 will extend this to F/23.4, which is a bit short of the minimum F/25 that the Solar Spectrum H-alpha filter likes. I can stop the scope down a little (as I currently do with my APM 80mm F/6), or could get myself a Quark (but have QC issues really been resolved?). The second issue is the long waiting time (110 days according to TS).

By contrast, the ES AR152 is a bit of an unknown quantity. It gets good reviews, but not specifically for solar. It is considerably cheaper, and at F/6.5 it gets turned into an F/26 instrument, which is fine with the Solar Spectrum filter. Besides delivery would be expected in 3 weeks.

Has anybody tried solar work with the ES AR-152? Is the 6" F/5.9 really that much better?

[johninderby]

I found the TS152 was a good solar white light scope. Used it with a Baader Coolwedge which did get a bit hot but not too bad.

[michael.h.f.wilkinson]

1 hour ago, johninderby said:

I found the TS152 was a good solar white light scope. Used it with a Baader Coolwedge which did get a bit hot but not too bad.

The ERF should take care of the heat, as it only transmits three bands around the H-alpha line, the solar continuum band, and the Ca-K line. The rest is reflected away.

The focuser of the TS looks more solid than the ES, I must say.

 

[johninderby]

The optics of the TS were surprisingly good for a fast achro. I’m sure I’ve read that the ES isn’t as good optically.

[Freddie]

I use an AR152 for my solar imaging with a Quark and think it performs very well. Not imaged for a while as have been moving house but you will find some shots from last year in the solar imaging section.

[Victor Boesen]

3 hours ago, michael.h.f.wilkinson said:

but have QC issues really been resolved?

I can't comment on the choice of scope, but I can add to my experience with a quark chromosphere I purchased a couple weeks ago from astroshop.eu (price matched to teleskop-express' price).

Here's a thread covering my experience with it so far: 

 

Edited May 26, 2021 by Victor Boesen
Typo

[michael.h.f.wilkinson]

I have just found a supplier that claims to  be able to deliver a Technosky version with 2" focuser rather than the 2.5" in the TS version in two weeks. I think I will stick to my old Solar Spectrum filter, and get a Siebert Optics 4.5x or 5x Tele-Centric to compensate for the focal ratio.

[John]

I don't know how relevant this is now but Ed Ting reviewed and compared these scopes (or clones of them) back in 2010:

https://scopereviews.com/page1y.html

 

[michael.h.f.wilkinson]

2 hours ago, John said:

I don't know how relevant this is now but Ed Ting reviewed and compared these scopes (or clones of them) back in 2010:

https://scopereviews.com/page1y.html

 

Thanks for that. The rotating focuser is a point for the TS/Technosky, and I don't need the finder or diagonal of the ES AR152, but then the case is a nice touch. EDIT: they don't seem to mention supplying a case for it any more.

Choices, choices.

I do think I am leaning towards the Technosky I can get in 2 weeks or so. Until the Siebert Optics 4.5x tele-centric arrives, I can always stop the scope down a little. It will still be a huge step up from the 75mm aperture I currently use for H-alpha. I might even get a 1.3x 1.25" tele-centric while I am at it, for use with C8 and ASI183MC and planetary/lunar imaging

[michael.h.f.wilkinson]

7 hours ago, Freddie said:

I use an AR152 for my solar imaging with a Quark and think it performs very well. Not imaged for a while as have been moving house but you will find some shots from last year in the solar imaging section.

Had a look, and those images are very good indeed.

[Highburymark]

Think my decision if I were ever to contemplate such a large scope (with a Solar Spectrum filter- fantastic!!) - I’d be governed by weight/mount issues first, and then whether my seeing was up to  6” scope. But if these are satisfied, and as you say you can stop down the aperture, Tecnosky does seem to be well regarded, not just for optics but for build quality and attention to detail - at least from what I’ve read. Looking forward to seeing the first images Michael.

[michael.h.f.wilkinson]

Bit the bullet and ordered the 152 mm F/5.9 version. It will probably arrive in September at the earliest. Just sent an enquiry to Siebert Optics to see when they can deliver a 2" 4.5x tele-centric Barlow.

[michael.h.f.wilkinson]

The telecentric Barlows from Siebert Optics now also ordered. They should arrive in 2-3 weeks (and then be held up in customs, no doubt)

[Solar B]

I think with these type of scopes it's more the build & mechanics than optics that

could waver a decision , however mechanically all are superior to the SW option.

Brian 

[michael.h.f.wilkinson]

13 hours ago, Solar B said:

I think with these type of scopes it's more the build & mechanics than optics that

could waver a decision , however mechanically all are superior to the SW option.

Brian 

The degree of spherical aberration is of particular importance here as is focal ratio. The Skywatcher 6" F/5 is too fast to my liking, and suffers more from SA than the others I was considering. The F/8 is too long and cumbersome. F/6.5 hits quite the sweet spot with my Baader TZ-4, F/5.9 is a touch short, but with the 4.5x telecentric underway, that is not an issue. Mechanically and optically the Technosky/TS 152mm F/5.9 edges out the ES AR152, apparently

[michael.h.f.wilkinson]

On 27/05/2021 at 02:34, Highburymark said:

Think my decision if I were ever to contemplate such a large scope (with a Solar Spectrum filter- fantastic!!) - I’d be governed by weight/mount issues first, and then whether my seeing was up to  6” scope. But if these are satisfied, and as you say you can stop down the aperture, Tecnosky does seem to be well regarded, not just for optics but for build quality and attention to detail - at least from what I’ve read. Looking forward to seeing the first images Michael.

The Technosky/TS is apparently a touch lighter (but that may be because the ES includes a finder and star diagonal). Both my Vixen Great Polaris and GP-DX mounts should be able to handle the scope easily. Seeing might not be ideal in Ca-K, but I have had god white light results with the C8, so I don't worry too much about the seeing in white light and H-alpha

[Solar B]

10 hours ago, michael.h.f.wilkinson said:

The degree of spherical aberration is of particular importance here as is focal ratio. The Skywatcher 6" F/5 is too fast to my liking, and suffers more from SA than the others I was considering. The F/8 is too long and cumbersome. F/6.5 hits quite the sweet spot with my Baader TZ-4, F/5.9 is a touch short, but with the 4.5x telecentric underway, that is not an issue. Mechanically and optically the Technosky/TS 152mm F/5.9 edges out the ES AR152, apparently

Yes perhaps with a more sensitive etalon for imaging the SA will matter , I used

my SW150 with a Quark and it was a good match , but have long since given up 

on the solids as I call them ! , I'm sure the Techno will be great however none of 

the given optics can be described as well configured , I still hanker after a really 

good APO for WL but it would only be for solar use.

Brian 

 

[michael.h.f.wilkinson]

32 minutes ago, Solar B said:

Yes perhaps with a more sensitive etalon for imaging the SA will matter , I used

my SW150 with a Quark and it was a good match , but have long since given up 

on the solids as I call them ! , I'm sure the Techno will be great however none of 

the given optics can be described as well configured , I still hanker after a really 

good APO for WL but it would only be for solar use.

Brian 

 

I will be doing WL only in the solar continuum band, so an APO isn't really necessary