impossible refractor?

[graham.hobart (Graham stevens)]

Having issues with getting distance right with FLI +FW+OAG with coma corrector and also have a small SV 60 which has a native flattener which needs the same back focus (55mm).
Are there any flatteners/ refractors which have longer back focus (apart from hideously expensive ones?) . Something around 300-600mmfl . Maybe a frac+ flattener combo which allows for CCD +FW +OAG or a corrected flattened frac which doesn't need an additional flattener?
pipe dream?
cheers.
Graham

[rustigsmed (Russell)]

How about this one graham?
http://www.teleskop-express.de/shop/...r-Astroph.html
not sure if it would effect the ability to reach focus - that is a lot of spacing.


for the newt I would recommend the baader Rowe Coma Corrector.
http://www.teleskop-express.de/shop/...-distance.html

best of luck,

cheers

[gregbradley]

There are quite a few actually. You won't need the coma corrector on a refractor you need a flattener perhaps. The 8300 chip is not that large so some refractors may not require a flattener and are good up to APS sized sensors (25 x 18 approx, KAF8300 is 18 x 14 approx).

TEC140, TEC110. Perhaps the William Optics similar scope 110mm triplet. Early versions used a TEC lens. Tak TOA, Tak TSA are all likely to be just fine.

An AP130 would be a good match to that camera.

Just about any Tak scope except FSQ106ED which is probably just short of backfocus for the camera, filter wheel and an OAG depending on which OAG and filter wheel. FSQ106ED may work. You have to add the distances and see what the listed backfocus is for the 106ED.

Stellavue have a number of refractors. I am sure some of them would work fine.

I don't know about the chinese triplets but its likely some are fine with that setup.

Its better to express the setup in length in mm rather than the components as adapters, filter wheels, OAG all vary in lengths.

My standard setup for 3 refractors was:

Proline or Microline, FLI CFW, adapter, adapters MMOAG, adapters Tak 4 inch Flattener (an older Tak FS152 flattener) adapters scope focuser.

That worked on TE180 and AP140. On TEC110 I had an adapter made to attach the MMOAG to the TEC flattener but sadly sold the scope before I ever got to use it. I used to use a guidescope which worked well although I always prefer an OAG for guiding as its way more reliable.


Greg.

[graham.hobart (Graham stevens)]

Hi Greg- yes sorry I was meaning coma corrector for my Newt.

[graham.hobart (Graham stevens)]

The combo would be about around 60mm -if I don't use the OAG its less but still the distance is not right for it in the newt with the mpcc.
And all those scopes are a bit steep Greg!
I have a WO FLT 132 which is a beauty but that with the imaging train is just a tad too long for comfort in my obs.
That's why I mostly use my newt now- its much shorter and lighter - and I was looking for a small FL scope to go on top.
Maybe I will just try the SV60 without the flattener and see how I go.
Rusti-I saw hat TS flattener also- has quite a lot of back focus and could suit myf5.5 60mm but will try a few things first.
I have that Rowe corrector on order for the newt!

[graham.hobart (Graham stevens)]

I also wondered about just getting an ED 80 or one of its clones and spending big on the flattener -like a Televue one, but I don't know the back focus is any different than most others i.e 55mm ?

[rustigsmed (Russell)]

yep I hear you on the MPCC, I used it with the TSOAG9 for a while and it just snuck in. the RCC should do the trick, to make up the space TS have adjustable spacers that might be worth looking into

I like this one as it has the M48 thread rather the narrower T2 options.
http://www.teleskop-express.de/shop/...-17-23-mm.html

With your 'frac if you are guiding on the newt with an OAG at the same time you won't need the OAG in the 'frac imaging train? Im also considering putting a small refractor (or camera lens) on top of my newt so interested to hear what options you end up with.

cheers

[gregbradley]

What about the FLT110. It seems to be a very nice scope.110mm is also a good aperture for imaging.

60mm, hmmm a bit small for a decent widefield machine. I know there are some fairly good Tak FS60c images around. But you are nudging good lens territory there.

Perhaps a Pentax 6 x 7 300mm F4EDIF. About US$1000 when they come up. Have a look at the awesome shots Marco has done with one. Beats most scopes and there are quite a few super wide areas one can image.

Greg.