TAL 100R stage 1 PST mod

[moriniboy]

Finally got round to starting this mod after selling on my trusty 100RS

The D-erf mount is shown inside the tube on the photo below, this means that the end of the tube to the mount is 335mm, does that seem about right?

I could move it forward a bit but I don't want to risk eye damage.

Also would it be better to re-fit the smallest baffle just in front of the mount to stop stray light from passing either side?

I will obviously be flocking the tube as its very shiny.

[keithatrochdale]

I flocked the tube and didn't bother with the baffles.

[allcart]

How many baffles have you removed? You could leave out the baffle in front of the drawtube, not sure about the next one up the tube.

[moriniboy]

The old 100R has 3 baffles, all have now been removed, hence the scratching shown inside the tube on the above photo.

Heres a photo of the ninja star baffles after removal.

I may just use one of them in conjunction with the d-erf mount to try and stop light passing between the mount and the tube wall.

[allcart]

I would be inclined to keep the baffle between the ERF and the objective. It serves a dual purpose. It will stop stray light from passing round the ERF and also help to stop the stray reflected light from the ERF from reaching the Objective again. If you are flocking the tube as well it will also help to control all the reflections inside the tube. I made sure my baffles were matt blacked on both sides. With all my scopes the front of the baffles were blacked out, but the manufacturers didn't seem to worry about the back. With a sub aperture ERF in place, you will have light going in both directions due to the reflected light from the ERF.

[moriniboy]

Been putting the PST through its paces over the last 2 days and I have noticed that the focuser knob can move side to side when focusing, whilst doing this it affects the view through the prism (i.e. sun central when focuser to right, move to left and half of the sun has disappeared)

Has anyone else noticed this?

As I will still be using the black box in the stage 1 mod I decided to open it up. I am now working on a mod to stop this "focuser flop" as I want the focuser to be at its best to take advantage of the larger aperture.

After measurement the focuser shaft is 6.94mm and the hole in the PST body measures 7.96mm, why such a difference?

[Merlin66]

Good question - don't know....

"Commercial tolerances"???

[moriniboy]

Perhaps the over-sized hole is for commercial tolerances however it has not worked with my PST!

I have noticed that the screw thread in the focuser block has not been drilled at the correct height to allow the shaft to pass through the PST body without fouling it.

This means that the whole assembly is out of square (see attached diagram)

I'm going to file out the hole in the PST body and fix a washer with the correct diameter hole to stop the focuser slop noted in my original post.

Might as well paint the top and bottom (sandblasted) sides of the pentaprism with matt paint as well whilst it is dis-assembled.

[moriniboy]

Ok here's the work so far

Focuser shaft mods as above

Painted sandblasted edges of penta prism black

Align the prism as it was not square to the optical axis

Some internal black box flocking (just in case)

Now the sun stays spot on and in focus, a worthwhile mod in my opinion.

All I need to do now is fix a larger focuser knob and its ready for the new D-ERF OTA.

[Merlin66]

Interesting "mod".....

You can use the patented "Vegemite" lid precision focuser - it works very well!!

[moriniboy]

Here is a photo of the inside of the black box when pointed at the sun, have used this to identify where I needed to place the flocking and reduce any internal stray light.

I know we have had very clear weather recently but the view through the PST now shows the area around the sun to be as black as a black thing. May be the flocking, may be the clear viewing conditions or a combination of both, I don't know, but I'm very happy with it.

[StevieDvd]

Here is a photo of the inside of the black box when pointed at the sun, have used this to identify where I needed to place the flocking and reduce any internal stray light.

I know we have had very clear weather recently but the view through the PST now shows the area around the sun to be as black as a black thing. May be the flocking, may be the clear viewing conditions or a combination of both, I don't know, but I'm very happy with it.

Is there a chance the flocking could be combustible in there?

[moriniboy]

The light spots shown come from the pentaprism, it has a transparent gold reflective coating which reflects most of the light (to the ep) but also lets some light through (where it hits the black box walls).

I'm assuming its relatively low power stuff otherwise the black box would get hotter and hotter with use.

I will keep an eye on it and report back if there is a problem.

[moriniboy]

Just been observing all day, no issues have been found re internal flocking heating up / degrading.

Even took the side plate off and put my finger in the light beam between the etalon and the front face of the prism to check, got slightly warm as you would expect.

[moriniboy]

Apparently the BF5 is the limiting factor on a stage 1 mod, I wanted to see just how big the BF filter was to see if the 5mm hole could be increased and still give the required protection.

There is not much to play with as the filter is 6mm square.

Would it be worth increasing the hole to 5.5mm or even 5.8mm?

[Merlin66]

I don't know of any user who has tried it....

I'd think the improvement may be marginal.

[moriniboy]

Might just give it a go, if the hole is 5.8mm this is a 35% increase in area.

[keithatrochdale]

Hi

Like your fresh view on this subject, it has made me think of areas that can be improved. I know they are little improvements but they all add up!

For the focuser correction, how about boreing out the body a few mm and turning a sleeve to fit the thread of the focus bar, all square and centered of course?

May also be worth checking that the Velcro has not flattered and is still pushing on the side of the case when the cover is in place.

Also what about mat blacking the three sides of the pentaprism to stop light escaping and removing the need for some flocking of the inside body? In fact maybe you could paint part of the other two faces where the light path is not going in and out?

All the PSTs I have seen have the pentaprism tilted slightly forward, never back, so it seems strange that they should all be that way, could there be a reason for that?

[moriniboy]

Drilled out my spare BF5 out to 5.5mm last night and here is the result.

One on left Mexican PST BF 5mm

One on right American PST 5.5mm

If I look through just the BF at a light source the Mexican one shows a red light and the American one shows a green light, does anyone know why, have they changed the coatings and does it mean that they are not interchangeable?

[Merlin66]

Hmmmm - don't know.

The coatings should be very similar, this final blocking filter has a very narrow band pass (only 8A or so) at Ha. There may be "resonance" band passes, but these are usually pretty faint.

They will either work.....or not work....

[moriniboy]

Both colored BF's work with either lower ERF, proms and granulation both visible.

Need a better days viewing to really check as I was observing through haze this evening.

5.5mm BF gives a bit more space and eye positioning seems a little less critical, not a mind blowing change though.

One further thing I noticed is that the American BF is approx 10mm total height less than the Mexican one, this gives more infocus, and I was able to use a 42mm Kellner, until now has never been possible

[moriniboy]

What the heck, now drilled out to 6.0mm, could not resist.

As the filter can move about due to manufacturing tolerances it has now been secured in place to ensure that direct light can not get to the ep

[moriniboy]

Just been out and its well worth it IMO, also flocked the inside of the tube between the lower ERF and the BF6 just to make sure

[moriniboy]

Focuser replacement now completed, all I have to do now is work out where to cut the OTA and we're up and running.

Just in time for the solar maximum.

[moriniboy]

Got first light on Saturday and I now know why people say that the limiting factor is the BF5.

With the PST its possible to get a view of the whole disc, with the stage 1 mod you are restricted to approx 50% of the disc (using the above modded BF6). I was so concerned with the restricted view that I drove over to Todmorden to see Peter Drew. He let me borrow his BF15 and boy what a difference it made, back to full disc viewing, so I'm working out how to get my hands on a BF10 from the US.

Regarding the mod I could see detail on the proms and granulation that would not have been possible with the PST, its a great mod and IMO well worth the cost and time spent.

Lessons learned:

1. TAL 100R scopes use an aluminium OTA tube which has a thicker tube wall in the middle than the edges, this required some more work to the new focuser tube to fit.

2. Remove all baffles behind the OTA internal d-erf, just keep one in front of the d-erf to stop light from passing around the filter mount (see before and after below).

3. Flock it to death.

Finally, enjoy new detailed images and long for a new BF10