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60mm PST Mod

Moonshane

By Moonshane
in DIY Astronomer

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Moonshane

Moonshane

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***BEFORE READING THIS PLEASE BE AWARE THAT YOU SHOULD NEVER ATTEMPT MODIFICATIONS TO TELESCOPES FOR SOLAR OBSERVING UNLESS YOU HAVE RESEARCHED THE SAFETY REQUIREMENTS FULLY AND ARE SURE WHAT YOU ARE DOING IS SAFE. MISTAKES CAN INSTANTLY CAUSE PERMANENT BLINDNESS***

 

Given that occasionally, OK constantly, the weather prevents night time observing when I go away, I thought I should try to create an option for Ha solar observing when on holiday in the caravan. The idea is to complement my 80mm f6 apo which is used for white light solar, with a Lunt wedge, and night time viewing.

 

Another side benefit would be that a scope with a shorter focal length than my 100mm f10 Tal would, I hoped, allow me to get full disk views (albeit at lower resolution/aperture) with my 5mm blocking filter.

 

The PST modding system works really well for many scopes but requires a native f10 refractor which of course, the Tal 100mm is. As luck would have it I checked Astroboot and they had a 60mm f10 achromatic refractor for sale at £20 plus £1.50 P&P.

 

I ordered this and it came in good time a few days later. All I needed was the objective, cap, dew shield (which can be removed which is rather convenient for travel) and the tube itself. Therefore I removed the focuser and mount-related items. I decided to also use a 50mm extension tube which will be securely fixed into the end of the tube with a purpose made machined collar (more on this later).

 

For any PST mod, there are three elements in addition to a suitable refractor. The etalon and blocking filter are taken from the PST itself and there is also a requirement for an energy rejection filter (ERF). For my larger mod, I used a Baader D-ERF which is bolted inside the tube around 10” down from the objective. However for this mod, I decided that the almost identical but smaller and cheaper 2” Baader Ha 35nm would be more suitable and absolutely adequate.

 

A wanted ad yielded a very similar Baader Ha 45nm filter (thanks Peter!) which is also perfectly safe and adequate for this aperture, the main purpose being to reduce heat stress on the etalon and blocking filter. This therefore completed the Ha element of the unit. The other advantage of doing things this way was that I know the Ha unit works as is in my Tal mod so will work well in the 60mm.

 

The next step was establishing the focus point for the eyepiece with the most in-focus requirement was situated. This eyepiece is my 17.3mm Delos which I have found to be excellent in the 100mm Ha scope. I simply hand held the PST mod with the Ha 45nm filter on the front end of the extension tube and as accurately as possible established where on the unit the best point of focus was reached. This indicated that 70mm would need to be cut off the end of the tube to ensure the etalon was placed correctly (200mm inside the point of focus) and that I could reach focus with the specified eyepiece.

 

Three more main issues remain.   The first is the machined collar which will slip inside the OTA and allow me to fit a 50mm extension tube to it. A SGL friend (thanks Chris!) has agreed to do this for me and I hope to have this done within a couple of weeks or so. The next is how to fit the tube to the mount. I have ordered from ebay some camera lens rings which have an ID of 66mm (the tube is 65mm) and I am hoping that with a little added felt and a dovetail bar this will work well. Finally, I need to add a standard Synta dovetail shoe for my home made solar finder. – This will be done after the work is complete on the OTA.

 

I will add some photos later and once the other bits have arrived I will add more images and complete the project – hopefully followed soon after with a first sun light report!

 

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Moonshane

Moonshane

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Chris kindly finished the work on the machined collar and cutting the tube down by 75mm to allow correct etalon position and also the insertion of an extension tube. This allows me to put my Baader Ha filter (acting as a ERF only to protect the etalon) on the end of the extension and 'permanently' inside the OTA. The pst stage two mod then goes in the extension and has a helical focuser built in.

Once I have rings etc I'll add some pics and explain how it all fits together. An initial squint today in very poor conditions showed reasonable levels of detail albeit naturally not comparing favourably with the 100mm aperture.

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Moonshane

Moonshane

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Here's some initial pics of the thing put together other than rings/dovetail - I have ordered a couple of these which are about 1mm bigger in diameter than the tube 

http://www.ebay.co.uk/itm/131340161087?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

trouble is they are on the way from China - hopefully here soon though.

Full OTA bar the rings/dovetail/finder shoe.

Stage two PST mod unit - also just fits straight in the back of my 100mm mod.

Not much light getting down the OTA to the etalon!

Rear of the filter looking down the extension tube.

 

 

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Moonshane

Moonshane

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On 19/04/2016 at 09:33, Gina said:

I would like to do Ha, but imaging - too afraid of doing something wrong for observing, I'm afraid.

I think Ha observing is actually safer than white light observing - not that either are dangerous if you follow simple rules. With Ha you are looking at only the narrowest band of light in Ha with all the dangerous UV/IR removed well before it gets anywhere near your eyes.

 

 

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Moonshane

Moonshane

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I am sure you know James but for the benefit of others, as I understand it the Ha filter/ERF is there simply to protect (or reduce stress) on the etalon/blocking filter (not to protect the eyes/camera) and I understand is the same coatings 'formula' as the Baader D-ERF, just smaller and thinner (2mm thick I believe rather than 8mm).

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Moonshane

Moonshane

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I think you can use the Baader Ha filter as a ERF for any aperture in theory as there's not a lot of heat assuming it's set forward of the focus point (think of a magnifying glass on your hand, just out of, and exactly in, focus) but personally anything larger than this 60mm and I'd be using a Baader D-ERF.

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Gina

Gina

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35 minutes ago, Moonshane said:

I think Ha observing is actually safer than white light observing - not that either are dangerous if you follow simple rules. With Ha you are looking at only the narrowest band of light in Ha with all the dangerous UV/IR removed well before it gets anywhere near your eyes.

That sounds logical :)  I won't risk observing in white light either.  Quite the opposite - I'd be more likely to risk observing in Ha than white light for the reasons you suggest.

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Moonshane

Moonshane

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I have made some steps towards finishing this project. Further pics will follow when I have a bit more time on the laptop at home.

Did some recalculation on the correct etalon position and feel that a 35mm extension will be more like optimal. I therefore replaced the 50mm one with a 35mm and also managed to remove the helical focuser from the train.

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This did not quite have the travel / total length I required and I have ordered a 1.25" helical from 365 Astronomy (I hope). Just need to get a step down ring from M48 to M46 to allow me to screw Baader fine tuning rings onto the focuser so I can insert it into my 2" adapter. This should all fit together well.

I am still awaiting delivery of my tube rings from China but have a dovetail now.

Further pics to follow.

 

 

 

 

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  • 3 weeks later...
Moonshane

Moonshane

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Well it's finished! Looks a little more steampunk than I planned. There's a couple of stages out which I will add pics of but here's the finished article.  don't really need a finder shoe as I seem able to just point it.

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Stu

Stu

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3 minutes ago, Moonshane said:

Hi mate cheers

Only tried it hand holding as I only got the rings and fixings recently.  indications are good though. Will report back soon.

The c/w is a taxi sign holder

E.g.

http://m.ebay.co.uk/itm/271121678995

Signholder looks useful. Dumb question, I assume its not heavy in itself but you attach weights when you need them??

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  • 2 years later...
astrorg

astrorg

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I know this is an old thread, but it would have been useful [for the tick ones like me!] to see an image with all the bits dismounted and in line - to give an idea.

I was thinking to do something similar and I am a good DIYer, I am just not less tick enough to grasp the whole concept - I am not asking to dismount it, if you still have it!

Once I grasp it, I can make it.

Is there a website where I can see the whole project or similar one using the PST 'bits' ?

Thanks
M

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