LADS -Large Aperture Double Stack Ha telescope

[Merlin66]

Hmmmm

How the devil do I get the additional power to the card???

I have the original small 4 pin plug with the 5mm (?) 12V socket which then goes to the larger 6 pin for the camera....do I need a 6 pin to 4 pin socket - then use the old cable???

[GazOC]

Mine has a power inlet (similar to the on an EQ6) next to the firewire ports. I use a 9v power supply from the mains and a straight 6 pin firewire lead to the camera.

[Merlin66]

OK I get it now!

Can I ask make and model#

Lindy don't seem to have one or Maplin...

So much for the Firewire having power available on Pins 1 & 2!!!

ken

[GazOC]

I've just checked an theres no make or model number Ken, thinking back its probably an Ebay purchase from China.

Similar to this one (note the power inlet on the left)

1394A Firewire PCMCIA Laptop Cardbus Card 3 Ports on eBay (end time 13-Nov-10 14:45:52 GMT)

[GazOC]

So much for the Firewire having power available on Pins 1 & 2!!!

I may be wrong but I've always assumed it was a limitation of the PCMCIA interface on the laptop rather than the Firewire to the camera?

[Merlin66]

Thanks to Gaz I've now managed to get a PCMCIA powered Firewire adaptor which works on the ol' ACER and drives the DMK cameras!

(According to the experts at Lindy not all adaptors are equal! Some only function in 4 pin mode....)

Anyway, now all I need is some clear skies to image with the double stacked PST etalons....hopefully soon - I have to start the "BIG" packing session soon....

[Tim]

How long till you have to move Ken?

[Merlin66]

Don't honestly know at this stage - I do know they want my wife in her new job ASAP!!

I hope by next week to have a fix on the european location (Brussels or Geneva seem to be the favourites) Then find somewhere to live, then move...I'm assuming, to be there before Xmas....

[Tim]

Crikey, that IS quick! Sounds like you will be very busy the next few weeks.

[Merlin66]

I hope you guys are sitting down and took your tablets this morning...

I got the quote for 100mm and 150mm diameter broadband UV-IR filters with a bandwidth of 600-700nm (similar to the Baader D-ERF)

8mm thick, 1/4 wave/inch surface, un mounted

100mm - 2048Gbp + VAT

150mm - 2325Gbp + VAT

If anyone wants to order (!?) I can forward the quotation.

[NickH]

Similar to numbers I got from a certain scientific glass supplier

You get why the Solarscope's are pricey now?...they use higher than 1/4 wave too!

[Merlin66]

Fatal flaw???

Not much more results...weather and packing have limited me.

The double PST etalon is very touchy to tune, but they certainly seem to be able to reduce the bandwidth and still provide a good focus (200mm behind the rear etalon)

I've been looking at the next step - sub diameter ERF and it's placement in the OTA.

When I started a dimensional layout it become obvious that if the ERF is positioned 1/2 way along the focal length ie use a 100mm ERF on a 200mm aperture, that the reflected beam from the front of the ERF will be focused on the rear of the objective!!! Bearing in mind that the majority of the energy is reflected I'm concerned that this will have a detrimental effect on the objective.....

I'm looking at the tilt required to allow the beam to clear the objective, but then we have the cooking of the inside cell or tube....

I need to put the ERF on the spectroscope and see how the bandwith varies with tilt; it maybe possible to set it at 45 degrees and dump the energy outside the tube. (This will effectively reduce the diameter of the ERF to x0.7 actual ie a 100mm diameter ERF would cover a 70mm beam so it would be placed closer to the etalons...no big deal but awkward....)

Any other ideas???

[brianb]

if the ERF is positioned 1/2 way along the focal length ie use a 100mm ERF on a 200mm aperture, that the reflected beam from the front of the ERF will be focused on the rear of the objective!!! Bearing in mind that the majority of the energy is reflected I'm concerned that this will have a detrimental effect on the objective.....

I'm looking at the tilt required to allow the beam to clear the objective, but then we have the cooking of the inside cell or tube....

Yes, it sounds like a potential issue.

Tilting the ERF will mess with the bandwidth, possibly fatally, but also increases the size of the ERF to intercept the converging beam from the objective. The "classic" approach (as used by e.g. the Lunt CaK module) is to have the ERF (mounted at the front of the diagonal) tlited slightly but not enough for the beam to hit the tube wall; because in this case it's way beyond the halfway point the reflected beam is already divergent when it reaches the objective, where it makes a "hot spot" about 30mm smaller than the diameter of the objective.

With your "halfway" problem, I think the tidiest method would be to intercept the convergent beam from the ERF with a small 45 degree mirror mounted in the manner of a Newtonian secondary and divert the energy out of the tube through a hole cut in the wall. The mirror needn't be optically flat and could be made of polished metal so as to avoid cracking from the heat.

[NickH]

Surely the ERF reflection energy is no worse than the energy pass through an objective with a Herschel Wedge though? Or am I missing a trick here? ERF is a uniformly spread energy reflection, not a focussed beam

[brianb]

Surely the ERF reflection energy is no worse than the energy pass through an objective with a Herschel Wedge though?

But with a wedge the excess energy either goes out through a hole or gets hit & absorbed by a heat sink which is away from the optical path.

ERF is a uniformly spread energy reflection, not a focussed beam

The reflected energy behaves as if it had come off a plane mirror. If it's halfway between the objective and the focal plane, a focussed image of the sun will be formed at the centre of the objective, if the ERF is perpendicular to the optical axis.

[Merlin66]

Brian said it all for me!

[NickH]

But with a wedge the excess energy either goes out through a hole or gets hit & absorbed by a heat sink which is away from the optical path.

The reflected energy behaves as if it had come off a plane mirror. If it's halfway between the objective and the focal plane, a focussed image of the sun will be formed at the centre of the objective, if the ERF is perpendicular to the optical axis.

Right... of course, but if it's not halfway just sub aperture (say in a few inches) then mucho less problem. Obviously though this causes other issues in cropping the optical path you're trying to achieve..

Fans on the side of the tube to pull the hot air out? (tube currents??) though how efficient that would be against Brians small beam mirror...with a reflective focal point further in to the tube... but....I don't know what the answer is...

[Merlin66]

Nick,

Yes....but then you need a much larger ERF....

In an f10 beam with say a 200mm aperture (2000mm focal length), if you positioned an ERF about 300mm behind the objective, you'd need a 170mm clear diameter ERF!

I'm thinking now that moving the ERF closer to the etalon say 1500mm behind the objective (300mm in front of the etalon), then you'd only need a 50mm ERF and the energy would be reflected to a point back in the middle of the OTA (1000mm behind the objective) - the width of the return beam on the rear of the objective would be 100mm across which I don't think would cause any major issues...

I'm actually considering a reflector where the secondary mirror cell can hold a smaller ERF between it and the etalon.....

[Merlin66]

Well at long last after the move and clouds...

I managed to set up the LADS - well not exactly - It's a 88mm mod ERF with the double stacked PST etalons.

As I mentioned before its VERY touchy and there's significant ghosting from the etalons. I spent about 20 mins tuning them both to get some very impressive (10mm TV) visual view of the surface the current AR's and filaments etc stand out nicely...no obvious proms (see later)

IMHO it's too fiddly to be a robust solution....

I have the 50mm threaded adaptor to mount the two PST etalons...so if anyone else wants to try it out they can borrow the adaptor.

Ok so I went back to the single etalon and whooooo the sweet spot issues - gone! the surface resolution - not as good but very nice nevertheless but the PROMS - they stood out like the proverbual

someone needs to be imaging NOW!!! There are a couple of really great proms just building....

Summary: unless someone can come up with more ideas I'll can the LADS and trial a SM60 double stacked with a PST etalon....

enjoy the views through the 88mm modded and set up the SM60 double stack to get back to imaging....

[NickH]

Looking at the Lunt models at Astrofest with sub aperture ERF and dual rear etalons, it clearly can be done, but possibly the PST one as you say is just too fiddly

SM60 Ds sounds interesting

[Merlin66]

Hmmm

Did they pinch our ideas or is it a case of "fools seldom differ":rolleyes:

I'll keep you posted with the SM60/PST ds.

[Merlin66]

I can't help myself!!!!!!

The last time I got so excited was when I married Sue!!!

Nick, You GOTTA try this!! I''ve just replaced the 88mm ERF with the SM60+Tmax with the PST etalon as a double stack and the results are mind blowing!!

Honestly they are as good if not better that the results I regularly get from the two SM60 as a double stack.

Easy to tune, no issues with sweet spot and the surface definition...Woooooow

this is why I love this hobby!! I'll sit down now and have my pills!

I've have to say...why oh why didn't I try this before???? The results are fantastic. Highly recommended to anyone who can buy beg borrow or steal the components.

When I stop shaking I'll try and set up the DMK41 so you can all appreciate the spectacular results......

[Peter Drew]

I'm glad this thread has resurfaced. In the intervening time I've carried on with sub diameter ERF experiments. My initial use of a 80mm ERF near the focus of a 220mm F12.5 refractor gave great images but the ERF soon became uncomfortably hot. This was avoided by using a powerfull air blower which kept the ERF cool during a 15mm exposure. A better solution was a 145mm ERF placed much nearer the OG, no undesirable thermal effects were noted. Another experiment was with a 6" F8 refractor stopped to F10 and with a 80mm ERF halfway down the tube, this also worked well with no heating problems so I'm confident that this approach is worthwhile. I have since installed a 125mm ERF before the OG for convenience and this is now my favourite Ha set-up. Although I am very pleased indeed with the performance I've nothing to compare the results with apart from the images posted by the experts, however, I can see all the detail that they show and sometimes finer details so for the relatively little it has cost me I'm well satisfied. .

[Merlin66]

Sounds like the LASS is still worth trying....

I couldn't get the camera set up in time today....but they say we should get some clear skies tomorrow.

I'd like to try a back to back series of test images

a) with the normal SM60/ SM60 double stack set up on the ED80

with the SM60/ PST double stack on the 90/900

It will be interesting to compare these two systems....

[Peter Drew]

The attraction of the sub diameter ERF route lies in the fact that the preferred Baader Cool ERF seems to be available in 90mm aperture as the smallest, this would mean that a "modder" could operate with scopes between 90mm and 150mm aperture with success.