9x50 RACI finder or Skywatcher ST 80??

[Moonshane]

Hi all

I am in need of finding a used 9x50 finder of the RACI variety but they seem thin on the ground. I could buy a new one for about £65 but this got me thinking that as it is for my 16" dob (so weight is not really an issue), and I don't have a travel scope currently, that it may be an option to fit a ST80 to my scope as a 'monster finder'.

Has anyone else ever done this and if so any comments/advice?

I presume that the ST80 optics would be every bit as good as a 9x50 finder and obviously the ST80 offers more flexibility.

Ideally I'd like a 72 Megrez but funds will not allow at the moment and I would have to sell my Ethos probably to fund one. The ST80 will also be lighter too so better for the purpose above.

Presumably if I fitted the ST80 with two standard finder dovetails and made a suitable bar then this would work OK assuming I could get the alignment correct? Perhaps I could tap some holes in the tube rings to effect a little movement for this?

Anyone know the weight of an ST80?

Just an idea currently.

Thanks

Shane

[John]

I think an ST80 weighs a little over 3 1/2 lbs Shane. A 40mm plossl would give you 10x and a 4+ degree FoV which would be great combined with a Telrad.

PS: Astroboot often has guidescope rings to mount it with.

[Psychobilly]

I suppose the ultimate mounting system would be soemthing like this...

First Light Optics - Skywatcher Guidescope Mount

Peter...

[MjrTom]

Hi Shane, The ST80 should make a great super finderscope although I suspect that getting a low power EP might be a little difficult.

A 24mm Panoptic would give you ~17x magnification. Its shortish focal length will work in its favour for this kind of usage. Will the ST80 take 2" accessories?

I would say a standard pair of guide scope rings and a suitable dovetail bar would suffice. Get a rough alignment then bolt it to the Dob then use the guide ring screws to align it perfectly.

You thinking also of getting a prism so it is still functions as a RACI finder?

[Moonshane]

cheers John

sounds like a plan. I can set the ST80 a little further back down the tube than normal to help with balance and possibly use a GSO 32mm plossl to give the same field as the 40mm but more mag and a smaller exit pupil. the 32mm plossl would also work well in my 6" f11.

mmmmm

[Moonshane]

I suppose the ultimate mounting system would be soemthing like this...

First Light Optics - Skywatcher Guidescope Mount

Peter...

very nice Peter but I could buy a 72mm Meg for that plus a ST80. it has given me a DIY idea though as I have a Vixen type dovetail clamp of this sort.

[John]

A decent 32mm plossl is always a nice item to have in your kit anyway - not expensive really either

[Moonshane]

Hi Shane, The ST80 should make a great super finderscope although I suspect that getting a low power EP might be a little difficult.

A 24mm Panoptic would give you ~17x magnification. Its shortish focal length will work in its favour for this kind of usage. Will the ST80 take 2" accessories?

I would say a standard pair of guide scope rings and a suitable dovetail bar would suffice. Get a rough alignment then bolt it to the Dob then use the guide ring screws to align it perfectly.

You thinking also of getting a prism so it is still functions as a RACI finder?

hi Mark

I think a 32mm plossl would work well and probably only cost maybe £15 too. 12.5x mag and 6.4mm exit pupil will be OK in a finder I think. plus 3.9 degree field.

I am pretty sure the ST80 is only 1.25" and I think comes with a 45 degree diagonal and I may just use that or get a 90 degree one and live with the right left inversion for the benefits of having the ST80 for other things too.

[Psychobilly]

Thats why I said somethign like that ....

You should be able to make something as you wont be adjusting it all the time... If had done similar things using pairs of screws - usually a grub scew as the jack screw and a normal screw working against each other to give the adjustment...

The ST80 OTA kit came with a 45 degree correct image diagonal...

Peter...

[MjrTom]

Yeah I suspect the Plossl will be great, I suggested the 24 Pan as I know its the widest 1.25" EP so maximises the FOV.

Cant remember if you said you had one or the Nagler 22

Not that you would necessary want to use a great TV eyepiece for finder work!

[Moonshane]

Thats why I said somethign like that ....

You should be able to make something as you wont be adjusting it all the time... If had done similar things using pairs of screws - usually a grub scew as the jack screw and a normal screw working against each other to give the adjustment...

The ST80 OTA kit came with a 45 degree correct image diagonal...

Peter...

ha ha thought so Peter. I have in mind something along the lines of what you suggest

[Moonshane]

Yeah I suspect the Plossl will be great, I suggested the 24 Pan as I know its the widest 1.25" EP so maximises the FOV.

Cant remember if you said you had one or the Nagler 22

Not that you would necessary want to use a great TV eyepiece for finder work!

a 24mm Pan would be lovely but I have a 26mm Nagler / 13mm Ethos so am well covered for the main scope (I sold a 22mm Pan to part fund my big mirror) but a cheapie 32mm plossl can live in the finder.

[RikM]

Olly uses, or has used, an ST80 as a finder on his 20" dob. Perhaps a PM in his direction would be fruitful?

[Moonshane]

cheers Rik

will do.

[michael.h.f.wilkinson]

Maybe you should check out this for 2" crosshair EP

TS 26mm Fadenkreuz Okular 2' - 70° ERFLE - Eigenfokussierung

This gives 4.55 deg FOV

They also stock a 32mm, but that gives a rather large exit pupil

You would also need a 90 deg 2" Amici prism (expensive)

I use a 70mm F/5 achromat as a 16x70 45deg CI finder

[Macavity]

Checkout the Baader Variofinder. Better than some (most?) of my scopes.

Mind you, at that price... Cute though.

[John]

Does anyone use a small newtonian as a finder on a big dob these days ?.

Years ago Astro Systems and Fullerscopes used to market 3.5 inch newts for this purpose. The 76mm Skywatcher Heritage is less than £50.

Just a thought.

[michael.h.f.wilkinson]

Does anyone use a small newtonian as a finder on a big dob these days ?.

Years ago Astro Systems and Fullerscopes used to market 3.5 inch newts for this purpose. The 76mm Skywatcher Heritage is less than £50.

Just a thought.

Have not seen them, but I did once try out a 4.5" F/4.4 Newt as a mammoth finder (3 deg FOV) on my C8 . I will see if I can dig up pics and scan them.

[John]

There is a 130mm F/5 Skywatcher newt OTA on E.Bay with a 2" focuser at the moment for £50 delivered - that would be a BIG finder !.

[michael.h.f.wilkinson]

There is a 130mm F/5 Skywatcher newt OTA on E.Bay with a 2" focuser at the moment for £50 delivered - that would be a BIG finder !.

True, but getting a Newtonian to show an erect image is awkward, and erect images makes finding things much easier. Besides, using a Nagler 26mm would put the price up a bit;), and you would need something like that to get a decent exit pupil and you would just get 3.28 deg FOV (not very much). The Erfle with crosshair would get you 2.8 deg FOV. Or you could go for an Ethos 21 with 3.23 deg FOV

:D

[Moonshane]

funnily enough John I have just looked at the Celestron Firstscope at £28, I could not go far wrong. I bet I could move the fitting point round by 90 degrees and it would then be at a better angle.

I'd prefer an upside down newt image to a right left inverted image as that's what I am used to as I prefer turning the book upside down to trying to interpret the detail backwards.

might give it a try. it has a 300mm focal length too so very wide field of view, especially with a Telrad and maybe a 25mm plossl to keep the exit pupil down to 6.3mm and with a 4 degree field and 12x mag.

I need to think of the benefits of a bigger finder against just biting the bullet and buying a 9x50 RACI one for about £65.

I could even consider the 70mm Celestron Travelscope which you can get for about £50, comes with a 45 degree diagonal, flimsy tripod and carry backpack).

might be a better option and would be a lot lighter too I suspect.

[michael.h.f.wilkinson]

funnily enough John I have just looked at the Celestron Firstscope at £28, I could not go far wrong. I bet I could move the fitting point round by 90 degrees and it would then be at a better angle.

I'd prefer an upside down newt image to a right left inverted image as that's what I am used to as I prefer turning the book upside down to trying to interpret the detail backwards.

might give it a try. it has a 300mm focal length too so very wide field of view, especially with a Telrad and maybe a 25mm plossl to keep the exit pupil down to 6.3mm and with a 4 degree field and 12x mag.

I need to think of the benefits of a bigger finder against just biting the bullet and buying a 9x50 RACI one for about £65.

I could even consider the 70mm Celestron Travelscope which you can get for about £50, comes with a 45 degree diagonal, flimsy tripod and carry backpack).

might be a better option and would be a lot lighter too I suspect.

The travel scope would be very close to my set up. TS also stock a 1.25" 20 mm erfle with cross-hairs , which gives 4 deg FOV. You can always add that later.

[Moonshane]

I think my mind is made up. it's going to be the 70mm Celestron. One reason is the focal ratio at f6 is better on exit pupil and the 32mm plossl will be even better in that giving EP of 5.6mm a field of 3.9 degrees and magnification at 12.5 (although you get a 20mm cheapie eyepiece with it giving mag at 20x and field of around 2.5 degrees.).

[Psychobilly]

If it's the travelscope you'll have the "bonus" rucksac for the flask and sarnies

[Moonshane]

ha ha and it may even fit a used 72 Megrez (or even a TV Pronto yeah right - surely only to be removed from your cold dead hand ) if it does not come with one and when I can afford one without sacrificing my 13mm Ethos.