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Merlin66

LADS -Large Aperture Double Stack Ha telescope

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C'mon guys do a "Sun dance" for me....

I managed a few minutes of absolute rubbish seeing conditions but enough to see the tilt angles of the etalons (about 20 degree difference) and note some VERY interesting results.

I used the 10mm plossl to look at the filament - I couldn't see it...bumma... put it down to the cr**p seeing - then as I tuned the etalons...I saw what initially I thought was another sun spot near the edge of the filament, very dark slightly elongated...as I tuned further it sudden dawned on me that I was chasing the Doppler shift down and along the length of the filament !!! WOW the resolution must be in the 0.3A range...

I had to re-set both etalons to bring the length of the filament visible. Tried this re-tuning three of four times (couldn't believe it!) and yes the results were consistant. (Even with the 80mm aperture when you get down to this resolution the image, visually, is pretty faint.)

I need more than a few minutes broken sunshine to set up the DMK so you can see these results. Nick....you'd love it!!

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It would be VERY interesting to set up the LADS along side the double stacked SM60 and put the spectroscope on to check the actual bandwidth......

(If anyone want's to replicate what I am doing I can supply a sketch (and a possible supplier) for the necessary double PST etalon adaptor)

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The excitement behind this thread is tangible :)

Those pics are incredible Nick, I take it the LS50 is somewhere in the tube?

Just reading your docs Ken, thanks for those, lots of numbers :). Does the reflected energy from the DERF pass unhindered back though the objective then, or is there likely a gradual build up of heat between them? With the ERF on a tilt would one side of the tube blackened inside start to warm up more quickly? If tube currents build up, could they be dealt with by vents, heat sink etc?

If I wanted to double stack the etalon at some point in the future, where do you measure the 200mm inside focus to, the first or second etalon? I'll maybe get an adjustable adaptor made to allow for this if necessary.

Looks like you're going to get some sun to play with later in the week Ken.

Thanks again.

Tim

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It would take more than a "Sun dance" to have cleared today's awful weather Ken. :) On a similar tack to your current DS experiments, do you think that the front mounted DS unit for the PST would stand in for the double internal etalon that you are using? on paper it seems it might be easier to acces and tune as it is normally fitted some 20cm from the internal etalon.

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T-J,

At this stage I'm not to concerned about the heat build up infront of the ERF..."where there's a will...there's a way"

The first etalon must be at the majic 200mm inside the prime focus, the second is placed immediately ie almost glass to glass behind it; the final focus is once again...you guessed it, 200mm behind the second etalon.

Peter,

The front etalon for the DS PST is a "parallel light" etalon ie must be used infront of the objective or in a collimated beam (like our mate in Brazil) - To get a collimated beam for this filter would require additional optics ie a positive transfer lens ( I did trial a 2" Big Boy Barlow in the EC90 design but it didn't work to well). The PST etalon assembly has a built in "barlow" and a "refocusing" lens at the rear.

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Thanks for that Ken, it was just that there was one up for sale. My air blower arrangement seems to cool an ERF efficiently when needed so the "problem" can be got round.

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Got it :)

When measuring, do you go from front, back, or centre of the body of the etalon?

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To the front of the rubber knurled grip on the etalon ( If you look carefully you'll see that it almost aligns with the position of the front lens)

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Can't believe now that I sold Nick Smith another etalon at around 0.7A ....aaagggh

(lol)

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Nick,

If your seeing conditions are better than mine I'll lend you the second etalon and the adaptor so you can trial it also....

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I uploaded perviously on another thread the optical layout which shows the relationship between the two etalons to give a narrow bandwidth outcome. You can see by re-setting the individual bandwiths that it IS possible to further reduce the resulting bandwidth (<0.4A) but at the cost of throughput. To get maximum throughput both etalons would have to already have excellent narrow bandwidths with high transmission.

I attach a copy for reference.

post-15261-133877494082_thumb.jpg

Edited by Merlin66

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oooh magic...thanks Ken..I may get some free time in the next week to take you up on that

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The Gods must really hate what I'm trying to do.....:):(

I had a brief clear patch this morning so set up the LADS and the DMK only to find the trusty ol' ACER couldn't see the camera...well after changing batteries, cables etc etc etc I finally found the problem was the small Firewire connection on the computer had broken (the small plastic tongue which holds the connectors - broken and come out!!)

Looks like I'll have to upgrade and get another laptop - I don't think the 7 yo ACER is worthy of repair.

So, no images until I can find a replacement.

Bumma.

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Yes, I was just looking at them 20gbp for a two x 6pin firewire.

I was getting used to powering the DMK with an external 12V battery....maybe the cheapest and fastest option...

StarTech.com 2 Port IEEE-1394 FireWire CardBus Adapter with Digital Video Editing Kit: Amazon.co.uk: Computers & Accessories

Ken

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Brief opportunity to have a further session with my LASSES (Large Aperture Single Stack Erf Sub-diameter! :). Absolutely fabulous performance, I think I've reached the end of the road in my search for the best Ha results that I'm likely to get, saved me a pile of cash :).

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What between LADS and LASSES we have all the bases covered!!

(BTW can any tell me if its possible to use two DMK cameras at the same time?? ie if I get the dual firewire port can I run two DMK cameras say one for guiding and the other for imaging - I assume by running two versions of IC Capture..or is there some type of internal conflict...just asking...)

ken

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IC capture allows camera selection so two instances would permit two cameras. I would however suggest running on in IC Capture and the other in PHD, as they will have unique PID's anyway, it should work... in theory ...not tested it

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I've been thinking more about this sub aperture etalon idea.

Would it be possible to go further sub aperture if you reduce the wavelengths reching the ERF by using another filter, say a full aperture IR cut filter, in front of the scope partially reducing the amount of energy reaching the ERF? Or would that be just as expensive as a large ERF?

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Haitch,

Consider we're playing with LARGE apertures...the cost of ANY optical flat filter - Wratten #25 (Red), UV-IR or the D-ERF to fit anything above 50mm or so gets VERY VERY expensive.

The solution has to be the size and position of the sub-diameter ERF - how small can it be? and how close to focus can it be?

As mentioned previously a 50/50 beamsplitter mirror can significantly reduce the energy getting through, but the reflected energy still has to go somewhere......

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Thinking about it.... a double firewire connection would allow me to image with a DMK21 on the SM60 double stack and a DMK41 on the LADS at the same time (I can mount them on a dual bar)...side by side direct comparison...

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Haitch,

Consider we're playing with LARGE apertures...the cost of ANY optical flat filter - Wratten #25 (Red), UV-IR or the D-ERF to fit anything above 50mm or so gets VERY VERY expensive.

The solution has to be the size and position of the sub-diameter ERF - how small can it be? and how close to focus can it be?

As mentioned previously a 50/50 beamsplitter mirror can significantly reduce the energy getting through, but the reflected energy still has to go somewhere......

Ok, I thought the cost might be an issue I just thought that IR blocking might have been cost effective as so much glass gets treated to a coating these days.

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getting the optical accuracy is the issue. Most large filters need to be at least 5mm-8mm thick to provide a stable optical base...

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getting the optical accuracy is the issue. Most large filters need to be at least 5mm-8mm thick to provide a stable optical base...

Or...

How about an IR blocking coating applied to the objective?

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