800mm focal length refractor

[Merlin66]

Can any one recommend a suitable refractor for solar work.
Needs a focal length around 800 - 850mm

[Merlin66]

Hmmmm
No suggestions, no recommendations???

[MortonH]

Does it need to be ED/apo? Is 900mm too long? (thinking ED100 f/9)

[Merlin66]

Just needs to be a good achromatic.....
900mm focal length would be too long, say 850mm max.

[rustigsmed]

hmmm there really aren't many refractors around 800-850mm!

[bojan]

Try one of Rubinars.. after glass relaxation, my Macro 10/1000 is diffraction limited.
Ops.. I had a look at ebay (https://www.ebay.com.au/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=rubinar&_sacat=0), prices went up 5-fold from times I bought mine (from rugift.com)


I also have this one (https://www.ebay.com.au/itm/143717981520?epid=6052061315&hash=item2176425d50:g:SG4AAOSw4iVfU S1A&amdata=enc%3AAQAHAAAAoMQUBqF35KZ5A8 LimNZvdWJNZhWWMUl%2BrkvrsM3kqM6AIau zDaDWrSfOzB8UrVVUIo%2BTypAeJ2z9vPQL fTkvHzoGxXKv9WC4A9w7FUaWQG2m3orIJd% 2BCSQbnoSP8ad10KKtxyhDS61sdDhm%2BBO zQk1ivbhS14DCFj75vd%2FFL4EjSgX%2FzH ntgwfU4GHXsfu96D3xTYyJ2yFxl%2B56rg% 2FUMHOI%3D%7Ctkp%3ABk9SR57h5sv8YA). . not bad as a visual telescope, not too many CA.
When Sun is up, atmospheric turbulence will be a dominant problem anyway.

[Merlin66]

Bojan,
Looks much longer focal length than what I need.
850mm is around the max.

[bojan]

Opteka (MZ-5000) has adjustable FL, 650-1300 mm.

Rubinars 8/500 would be good.. sometimes they appear on ebay for less.

[Eldest_Sibling]

It has a dovetail-bar, for placement onto other mounts, but no tube-rings, and rings for this one would be virtually impossible to find online...

EDIT: http://www.saxonoptics.com/products/product-details.php?productid=10011

...however pipe-clamps served for this "de-forked" 50/600, at f/12...

297571

...a bit of DIY.

Only a safe solar-filter can be attached, at front over the aperture; no Herschel wedge or other, as the telescope is plasticky. Achromatic refractors from 40mm to 76mm were once of all-metal, the focusser and the doublet's lens-cell in particular.

[Merlin66]

Alan,
Thanks, but I think the costs to ship from the US to Australia would far exceed what the scope is worth.

[MortonH]

Ken,

Probably a silly question but does the scope need a native focal length of 800mm or could you use a shorter/longer one with some kind of focal extender/reducer?

[Eldest_Sibling]

I've edited my post, and with the Saxon equivalent.

[Merlin66]

Morton,
Not a silly question.
Using a Barlow, they have limited backfocus spacing which can put the optics close to the prime focus. Not a good situation when working without filters Solar imaging with larger apertures.
I’m looking at the x0.75 GSO reducer (to use with a 1000mm refractor) - it has a working back focus of 80mm .

[Eldest_Sibling]

If the Saxon 608 seems viable, I cannot find the model among the three vendors I searched. It may be discontinued, or available as a special order.

Oh, I almost forgot: my own 4" refractor has an 820mm focal-length.

[Nikolas]

Bresser makes some of that scale
also nat geo?
I know they are cheap but they are an achro of that focal length


Or something like this? (https://www.amazon.com.au/SVBONY-Dispersion-Achromatic-Micro-Reduction-Astrophotography/dp/B0928CPN65/ref=sr_1_12?crid=3JL21F2TZ818G&keywords=svbony+telescope&qid=1666925238&qu=eyJxc2MiOiIyLjg4IiwicXNhIjoiMi4y NSIsInFzcCI6IjAuMDAifQ%3D%3D&sprefix=svbony+telescop%2Caps%2C265&sr=8-12) it's 714mm or is that too short?

[anj026]

Hi Ken,

I see that the Scopetech 80mm lens are now available from FLO.
The 80mm f10 lens works out to approx $210 AUD inc postage.

https://www.firstlightoptics.com/scopetech-telescopes/scopetech-80mm-lens-and-cell.html

Andy

[Merlin66]

Andy,
Appreciate, but I need a bit more aperture.
A 120mm with a focal length of 900mm (not necessarily an ED version) would be ideal.

[anj026]

How about the Explore Scientific AR 127 f6.5, 826mm focal length?

http://www.frontieroptics.com.au/Explore%20Scientific%20AR%20Doublet %20Series.htm

Andy

[Merlin66]

Looks good what about price?

[Tropo-Bob]

Occasionally, there is Vixen 140mm SS in the classifieds. Its focal length is exactly 800mm. The going price seems to be a little over a $1,000 ($1200 to $1,400).

[Merlin66]

Andrew,
Thanks but more than I’m prepared to pay.

[gbeal]

If you can live with just 63mm, a Telementor is 840mm. I use mine with a Quark occasionally, and years ago all the time with an SM60,
.

[Merlin66]

It’s for use with a MiniSHG for solar imaging. I need the aperture for increased resolution and the focal length to match the slit gap height.

[Eldest_Sibling]

That would be this one... http://www.saxonoptics.com/products/product-details.php?productid=10201

Synta also offers a 120mm achromat, under the "Celestron" marque, and "Saxon", but at f/8.3; 1000mm.

https://groups.io/g/astronomicalspectroscopy/topic/85664508?p=Created%2C%2C%2C20%2C2%2 C0%2C0

[Merlin66]

Alan,
The ED refractors are overkill and seem to be very expensive.
I’ve found a 120mm SW achromat 1000mm fl for trials……
Stay tuned.