My 70mm stage 2 PST mod

[Roel]

By the way: I made a simple solar finder from an old useless 5x24 finderscope. I removed the lenses, put in a disk with a hole at the front end and a semi-transparent cover on the other side on which I drew a crosshair. It produces a 5mm "image" of the sun on the cover. I find this easier to use than a normal finder with solar foil because I dont have to look through the finder, but just AT it to aim the telescope. Saves my back!

[james_screech]

I've seen a few PST mods on the web, mostly using 80mm refractors. Is there any reason why other optical systems could not be used?

I've a "spare" 125mm f10 SCT, add a ERF and 2" visual back. Cut short the PST gold tube and pad into the visual back...

[Merlin66]

Hmmm,

With a full aperure ( or reduced aperture?) D-ERF it MAY work, but getting the -200mm spacing from focus to the etalon position may be problematic....

I'd check out the available spacing before getting too excited...

[Merlin]

Here's part of Cloudynight's policy statement on PST mods. For the full read, go into their forums and scroll down to the solar section, then, click on the thread titled: PST safety warnings and modifications. UPDATED. :

"The PST is a very specialized instrument and any changes to a scope like this could be extremely hazardous. Changing the space between the Etalon and the diagonal ( which contains IR blocking ) could result in the light path changing and more energy reaching the eye. The damage would be done without any physical warning."

[james_screech]

Hmmm,

With a full aperure ( or reduced aperture?) D-ERF it MAY work, but getting the -200mm spacing from focus to the etalon position may be problematic....

I'd check out the available spacing before getting too excited...

Having just checked the price of 5" ERF filters I don't think this is going to happen in the near future. Oh well it was a nice thought while it lasted

[Roel]

Well, the other day I got a tip from another PST modder about a cheaper alternative for an ERF. He uses a HOYA HMC R [Wratten 25A] and a B+W #486 UV/IR-Cut filter. He only uses these filters for photograpy, but when you look at the graph below it might work for visual too. (not really a thing for trial and error by the way). The costs are around 10 Euro's for the Wratten #25 and around 50 Euro's for the UV/IR-cut.

[Merlin66]

Roel,

A few years ago I did the same....the problem was getting good enough optical quality filters...the photogragraphic ones' weren't good enough....

[Gina]

Seems to be the way - to get something that actually works you need to spend serious money!

[Merlin66]

Merlin,

I certainly don't want to be drawn into an endless debate, but I need to point out that the Baader C and D-ERF have a very narrow bandwidth (600 - 700nm) and effectively block ALL the UV and IR from even entering the objective...

(I note in the US they tend to use Lumicon type filters which are basically a Wratten #29 red filter and CAN allow the IR through to the etalon.)

As the final blocking filter is only 8A bandwidth - centred on Ha there's no other wavelength getting through - no UV or IR - nothing.

I honestly do believe that the PST mod with a D-ERF filter is 200% safe.