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Alternative for the PST mod crew

NickH

By NickH
in DIY Astronomer

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NickH

NickH

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Skywatcher Evostar 80

Cheap as chips, same focal length, same OD, (F11.25), and on an EQ mount with tracking, under £200 (way under typically on the tracking mount for around £178.

For those with the 90mm ERF, the Evostar 90 should also work (F10), both will obviously need a tube chop to get the <200mm back focus, and then fit a 2" focuser

Not personally tested it, but...I know someone using the old SW909 (almost the same spec) and getting staggering results..

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NickH

NickH

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ST102 at F5?

You aint seen nothing Jamie unless you move to F10 which is the optimal cone for the etalon

I thought the WO80ZS was good on mine, until I moved it to the Vixen...

DIfferent ballgame...trust me

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Jamie

Jamie

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Nick

I can only imagine how good the view through the F10 version is.

If you mange to get to SGL 5 i will have to get you to have a look at and through my HA solar bins.

These things have given me better views than an 0.5 60mm Coronado and beat the pants off a 50mm Lunt for viewing quality....

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Jamie

Jamie

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The only mod i do with this set up is i bring one of the scopes down to 0.5a ...

This way you get great surface detail along with superb prominences...In the same field of view at the same time....

The last time i did a side by side comparison, my set up was able to show a CME in action as where we couldn't make it out through a 50mm 0.5a Lunt.

There is also a hint of curvature on the solar limb when using these bins.....Though i can't wait to look through what ever set up you choose to bring with you Nick...

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NickH

NickH

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ah...now that's a neat idea...I love that in fact, using the brain to trick the eyes into merging the combination image...plus double the light path

Having used a few Lunts now, I have no doubt it will beat it...

What I'm now thinking, is can this be done at 80mm :-)..

Been looking at the possibility of getting a PSM40 for the 80mm, and using that to double stack, as it's a pure etalon, with no relay lens system.., though how to integrate it in to the light path is the trick

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Jamie

Jamie

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That's when you have to take the whole set up to a trusted engineer and have the "cell" for want of a better word custom made to make it integrate in to the light path....

I do like your train of thought though Nick.....

Now you have gone and done it......The thought of 80mm HA solar bins is running around that massive gap between my ears.....:D

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NickH

NickH

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Ken (Merlin66) is the man on the light path (we've had a chat about this) and I know DaveG is also interested in this possibility. In terms of making a relay lens cell, I am sure I know a few very good engineers who could sort that out.

Hmm..telecentric lens ahead of the DS module, light path through that is then parallel, and remains so until it hits the PST etalon, then it will converge down as before..

So, in effect a module to hold the PSM40 as close to the PST etalon, with a telecentric in front of it. You'd also go some way to negating the sweet spot effects...though how much, I am not sure

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Ibbo!

Ibbo!

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i cannot decide whether to buy a new scope as you have mentioned above

i quite fancied the idea of a tal 100 if i could find one at the right price

or i do have a 100mm f13 in the garage with a chip out of the edge of the objective that i could mask off i suppose

i will think about it while my shoulder recovers from the op and look at what the rest of you come up with

i did use the short f/l mod today and it was very frustrating as the clouds scudded past and the wind blew then as the sun disappeared over the neighbours garage we had a spell of about 3/4 hour

but not before i some good views of a prom and a surprising for me bit of surface detail

steve

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Merlin66

Merlin66

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Re the SM 40 double stack option..

I did some "trials" last year using a x2 Big Boy barlow behind a 90mm f10 into a SM40 then into a un modded PST. Later tried a Wollensak from Surplus Shed as well. This gives the double stacking but I found the TV barlow VERY fiddly to set properly and had limited success. I think my additional beamsplitters ( to allow the system to work without the $$$ of an ERF) made it very complicated and required accuracy beyond my limited hand tool construction.

The real solution would be to remove the barlow lens from the front of the PST etalon, THEN double stack the SM40/ etalon.... the rear end to the BF would be unchanged.

Up front an ERF, 90mm f10 objective and a -150 to -200 doublet barlow ( clear aperture >40mm - Edmund Optics) positioned just in front of the double stack....

The "key" would be to see if the PST etalon barlow can infact be removed...Anyone have one available? I'd be very gentle and carefull with it!!!!!

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NickH

NickH

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Okay...here's my exact distances for the setup I image with (i.e...it works!)

A80M - Front objective distance to etalon front 740mm

Etalon to prime focus on BF10 - 200mm (exactly 200mm!)

Etalon clear 86mm to 80mm objective

Etalon to rear adapter (before the BF10 is inserted) 115mm

Hope that helps

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Merlin66

Merlin66

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To do the job "properly" you'd need:

80mm D-ERF approx 400 gbp

BF10 ( Blocking filter) 500gbp

nosepiece adaptors etc 80 gbp

The alternative is to start with "Mod 1" and continue to use the PST black box, then you only need the ERF and adaptors..

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