PST mods

[spaceboy]

I admit I am more than happy with my LS60Tha for dashing out between clouds but I am currently experiencing a dose of aperture hunger "as you do!" on those clearer days and have been considering a cheap and cheerful PST mod to complement the full disk views in the lunt. Browsing the net for inspiration along with motivation to put my hand in my pocket I came across an interesting set up and wondered if it is actually possible to do a mod that way. The site was unfortunately not in my native tongue so I have probably miss read the images provided on the site.

Now I am aware that ERF filters are required some where along the light path to prevent sunlight burning a hole through your skull. I get that but the thread I found basically used a 2" Herschel wedge to dissipate this energy and the pst 2nd stage mod was then plugged in to the wedge as you would an eyepiece. In my mind I can't see why this wouldn't work as you can view white light in scopes up to 6" safely using only a 1.25" wedge with no need for an ERF. As long as you have a good quality focuser to hold the weight I don't see where there would be any other issue ?? Am I missing something as I would have thought a 2" HW which can be used for white light as well as a potential ERF would be a far better investment that an expensive ERF filter and cell that does only one thing ??

[Moonshane]

I am not sure but suspect it would not work. The wedge would reduce all wavelengths to 5% output including the line you want for Ha. I may be wrong but presume a 5% slice of the Ha would not be bright enough after going through the etalon and the blocking filter to be of use visually. Glad to be proven wrong though.

[Moonshane]

Would it be possible to use the Ha elements of the Lunt you have to insert into a different scope with more aperture?

 

 

[spaceboy]

The lunt was new so I don't want to void the warranty. I do plan on modding the lunt with my evo 150 when the time arises as apparently a 1200mm focal length is needed.

 

Would the wedge still reduce the same amount of light with the ND filters removed? I thought the wedge removes harmful light UV etc and not light, light if that sound right. I find my eyes feel like they are bleached if I don't use a BCF and polariser along with the pre-installed ND filter.

[spaceboy]

If anyone can translate ?? http://www.lightfrominfinity.org/PST/PST.htm

 

What a plum it is translated. Think I need an early night

 

 

[jetstream]

I tried my Quark with my wedge- the result? nothing, zero, no light to my eyes lol!

[Moonshane]

Yes, the wedge takes out 95% of all wavelengths and the ND only allows through 0.1% of this 5%.

[spaceboy]

Thanks guys. From what I can gather from the Bablefish translation on the pre-mentioned site is that the guy is experimenting with it for imaging anyway so no doubt as you say there isn't enough light for the MK1 eyeball to see anything. I did think it might be too good to be true given HW and PST modding have been around for years so someone must have tried it at some point.

[Merlin66]

As already mentioned, the light attenuation with the Herschel wedge is too great to be used as an ERF with a PST type mod.

What you want is to suppress all the wavelengths other than at, and immediately around, the Ha 6563A.

A Baader 30nm Ha CCD filter works very well.....

[Moonshane]

Would 35nm be ok too like this one?

http://www.365astronomy.com/Baader-H-alpha-35nm-CCD-Filter-1-4-optically-polished.html

[Gina]

FLO are cheaper for that

[Moonshane]

Sorry, yes, I'd use FLO but cannot access FLO's site at work.

[Merlin66]

Yeah, that would do the job.

[spaceboy]

While on the subject of PST mods, How exactly does an ERF work ? I see some mods Lunt in particular where the ERF is the focuser end of the scope and the lunt there after. I get that the ERF has to be in the light path but at what point does the focused light risk rupturing the filter ? or are the ERF bullet proof ?? I would have thought if using a smaller ERF than the objective you would want it as close to the lens as possible to reduce focused light increasing the inside temperature of the OTA ??

 

I will look for the image I seen of the lunt set up. It is on SGL but can't put my hands on it straight away. 

 

GOT IT https://stargazerslounge.com/topic/186930-say-hello-to-my-big-fat-solar-lass/

[Merlin66]

Firstly, an effective solar ERF should do what it says on the tin - act as an energy reduction filter to reduce the light and heat loading on subsequent optical elements and eventually the observers eye or camera.

Many of the "standard" ERF designs are no more than a red filter usually with a UV-IR coating. This suppresses most of the visual light - other than the red and the UV-IR coating suppresses the potentially harmful UV and IR radiation.

They are not "bullet proof" and until recently it was common to see the ERF mounted at the objective to provide protection for all internal components etc.

The Baader D-ERF is manufactured from very thick glass polished to 1/10 wave accuracy and then multi-coated to suppress all visible radiation other than a narrow wavelength band centred on the Ha wavelength. Unfortunately to obtain such accuracy these filters although 110% effective are expensive.

To reduce the costs of the PST mods amateurs quickly adopted the use of sub-diameter ERF's in their construction. I advocated that the sub-diameter filter should be >50% the clear aperture to minimise the risk of energy damage.

This 50% "limit" has been adopted in solar telescopes manufactured by Lunt.

The jury is still out on the issue of internal heating within the OTA when sub-diameter ERF's are used and the effects any "thermal tube currents" may have on resolution. Some say it has no or minimal effect, others feel that is does impact on performance.

Hope this helps.

 

 

[spaceboy]

Thanks Merlin. So if in doubt go Baader D-ERF. Changes the playing field a bit as I have seen the prices of their filters in the past although still way cheaper than Daystars filters.

[Moonshane]

Derfs do come up used occasionally.  I got my 90mm for about £200 from memory.  I mounted mine about 250mm behind the objective within the tube.

[Merlin66]

The Daystar ERF say, 80mm diameter is listed as us$400

https://www.daystarfilters.com/energy.shtml

The Baader D-ERF 90mm equivalent is 395 Euro.

http://www.teleskop-express.de/shop/product_info.php/info/p3246_Baader-D-ERF-90mm-Energy-Rejection-Filter---Solar-Observation.html

The Lunt ERF is $325 for the 100mm diameter, $150 for the 75mm.

http://luntsolarsystems.com/product/energy-rejection-filters/

[spaceboy]

On ‎10‎/‎03‎/‎2016 at 22:19, Merlin66 said:

The Daystar ERF say, 80mm diameter is listed as us$400

https://www.daystarfilters.com/energy.shtml

The Baader D-ERF 90mm equivalent is 395 Euro.

http://www.teleskop-express.de/shop/product_info.php/info/p3246_Baader-D-ERF-90mm-Energy-Rejection-Filter---Solar-Observation.html

The Lunt ERF is $325 for the 100mm diameter, $150 for the 75mm.

http://luntsolarsystems.com/product/energy-rejection-filters/

I must have daystar mixed up with another company ? I have been browsing so much I'm confusing myself now, but I know their prices were way over that of Baader.  I don't think it was Istar or Izar ???? Do they even make ERF ? I will have to retrace my steps......