Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

LADS -Large Aperture Double Stack Ha telescope

Merlin66

By Merlin66
in DIY Astronomer

Recommended Posts

Merlin66

Merlin66

Posted
  • Author
Posted

That's not a stupid idea...There's no technical reason why the ERF coating could NOT be applied to an objective. You could have dichromatic coatings which block the UV and IR as well as providing a narrowband red filter....

Coronado tried it on the early PST's.. but unfortunately the coating was NBG - they never tried it again.

I think it comes down to cost. There's not enough solar Ha observers/ imagers in the world to drive the volume related commercial costs down. Would be interesting tho'......

Link to comment
Share on other sites
  • Replies 138
  • Created
  • Last Reply
Peter Drew

Peter Drew

Posted
Posted

I've also been thinking further about the sub aperture route. It might be possible to use a piece of lightly aluminised "Mylar" to attenuate the incoming light without significantly compromising the brightness of the final image. I have, in the past, seen such material that required several thicknesses to make a safe white light filter, this would be cheap and of suitable optical quality. In the meantime I'm going to fit a sub aperture 80mm ERF to my 150mm f8 Helios stopped down to 125mm f10. The 80mm could be placed halfway from the objective where the heating shouldn't be a problem. If this works OK then those who are buying 80mm ERF's for their Vixen mods, could realistically consider a s/h achromat of 150 f5 for stopping down or a full aperture 125mm f10 with the benefit of the better resolution.

Link to comment
Share on other sites
Merlin66

Merlin66

Posted
  • Author
Posted

Peter,

I'm finding that the light loss in the LADS is significant ( to achieve <0.4A) the exposure times will increase; so a bit MORE light wouldn't wouldn't be a bad thing.

A 150mm f5 unfortunately due to the "aperture stop" effect of the PST etalon would limit it to an f10 system and an effective aperture of only 75mm. IMHO The Helios 6" f8 is a much better bet.

Link to comment
Share on other sites
haitch

haitch

Posted
Posted
Peter,

I'm finding that the light loss in the LADS is significant ( to achieve <0.4A) the exposure times will increase; so a bit MORE light wouldn't wouldn't be a bad thing.

A 150mm f5 unfortunately due to the "aperture stop" effect of the PST etalon would limit it to an f10 system and an effective aperture of only 75mm. IMHO The Helios 6" f8 is a much better bet.

Or a Meade 6" f8 :)

Link to comment
Share on other sites
Peter Drew

Peter Drew

Posted
Posted

Agreed Ken, it's the 6" F8 I'm using stopped to 5" F10 :). I converted it to "LASS" spec this evening for a comparison with its previous full aperture ERF and also to verify the heating effects, hope it's clear in the morning.

Link to comment
Share on other sites
haitch

haitch

Posted
Posted

Well the sale of my second Meade f8 6" with a ready shortened tube has just fallen through so I'm now tempted to keep hold of it to have a play (following some saving up).

Merlin, just a thought - they seem to be able to produce full aperture glass white light solar filters for a reasonable price, surely just a simple IR block or cut would be even cheaper to produce? Or even if they produced a version of this with an IR cut built in... http://firstlightoptics.com/proddetail.php?prod=BaaderTurbofilm . I realise the QC for an ERF has to be top notch and that bumps up the price but all this is for is to kick out a chunk of non-visible light/energy before it reaches the ERF to make it's job easier in a sub aperture set up where the reduction in energy reaching it will help control possible heat build up.

Must admit the thought of applying all the necessary filter coatings to the objective sounds beautifully simple. Is there any background on the Coronado problems with doing so?

Link to comment
Share on other sites
haitch

haitch

Posted
Posted
If it were that simple, don't you think everyone would be doing it..

Coronado thought it was at one time

I think Ken and I have both tested various other "ERF" options...and the Baader beats them all hands down

My original thought wasn't on replacing the ERF - that direction arose out of responses on here.

What I was thinking of is in your sub aperture set up you reach a critical point as you move the ERF closer to the focal plane where heat build up causes problems. What I was suggesting was a simpler lower cost IR filter at the front of the set up. If that could, for example, reduce the heat energy reaching the proper ERF by something like 20% (pure guess) you should be able to move the ERF 20% closer to the focal plane meaning a bigger aperture to ERF size ratio.

Link to comment
Share on other sites
Peter Drew

Peter Drew

Posted
Posted

At last, an uninterrupted sunny day suitable for Ha experimentation. I'm pleased to say that the LASSES arrangement works brilliantly :). I used the 6" helios F8 stopped down to 5" F10 and a 80mm sub diameter ERF placed half way between the OG and the focal plane and after 10mins of sustained exposure the ERF was warm but not hot. I'm now pretty confident that anyone that has a 80mm ERF can SD mod a refractor up to 6" F10 for around £1K (Baader 80mm ERF around £350, PST £500, s/h 6" f8 around £150 on a good day). The 80mm Vixen mod is very good, I have one side by side with the 125mm, the difference is like comparing analogue TV with full HD digital :), however, those who mod the Vixen will not be disappointed. The downsides to the larger apertures are weight, the 6" F8 OTA is very heavy, and the small FOV with the 5mm BF. I'm currently fitting the released 145mm ERF, that was the previous full aperture unit for the 125mm, to the 220 in the expectation that I will not need the air cooling system.

Link to comment
Share on other sites
Merlin66

Merlin66

Posted
  • Author
Posted

Well done Peter!

Another small step along the "giant leap" forward to achieving a Large Aperture solar scope.

(I've just issued an enquiry for a large diameter >80mm UV-IR optical filter....BTW the largest standard "catalogue" diameter is 50mm and that's around 180gbp!!)

Link to comment
Share on other sites
Merlin66

Merlin66

Posted
  • Author
Posted

Need some help!!!

I purchased a StarTech 2 port 6wire FW PCMCIA adaptor (CB1394_2)

Seems to install OK and recognised in Device manager OK

When I plug in the DMK -no beep - and no camera recognised under IC Capture???

Not getting any power? Don't know....

Is there anything I can check???

(I've sent a tech email to StarTech...)

Not looking good....

Ken

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.