My PST - TAL100RS mod

[allcart]

They're not ha filters luke. I think they are ITF filter and blocking filters. You need them, but Merlin66, peter drew, or Markt will know the answer.

[lukebl]

Here's what the two bits look like after removal. So how important IS the filter in the spacer, I wonder, and if it's vital where and how should I reinstall it?

[JamesF]

I'm amazed you managed to split those. I had a look at mine and was not in the least convinced I could do so without breaking it.

James

[nytecam]

Luke - nice image - presumably seeing is more critical via larger aperture and fl? What is the size of the reduced fov via the longer scope fl? TIA

[lukebl]

I'm amazed you managed to split those. I had a look at mine and was not in the least convinced I could do so without breaking it.

James

I managed it with a big Boa Constrictor after breaking the smaller 'Baby' Boa in my earlier attempt. I didn't think it would be possible, but it was easy with the big Boa.

After all the expense of all the optical stuff, I didn't factor in the purchase of additional tools that I would either break, or probably never use ever agin!

Luke - nice image - presumably seeing is more critical via larger aperture and fl? What is the size of the reduced fov via the longer scope fl? TIA

No idea yet. I'll let you know when I manage to try it out properly.

[JamesF]

So how important IS the filter in the spacer, I wonder, and if it's vital where and how should I reinstall it?

My understanding is that the filter in the spacer is a mini-ERF and that the filter in the eyepiece holder is a blocking filter. I think Merlin (possibly?) has suggested that the ERF is not actually required, but may be there to increase the lifespan of the blocking filter.

James

[Merlin66]

In a system with no other ERF in place, both these filters are required.

The "mini-erf"/ ITF, as said before, reduces the energy loading, and blocks the IR from getting to the even more sensitive Ha blocking filter in the eyepiece tube.

I haven't tried it but, it should be possible to remove the ITF and re-glue it (at a very slight angle) in front of the blocking filter element in the eyepiece tube....

For limited imaging work you can operate without the ITF -the image will be much brighter.

[lukebl]

Cheers, guys.

So, it should be OK to image without the mini-ERF in place? The biggest problem I can see with that is that the image is already so bright that to get surface detail with my QHY5 have to use exposures too short (i.e. faster than about 5ms) for the cam to cope with without getting banding on the image. Capturing prominences are OK, as you can expose at 25-30ms which avoids the banding. Could I use, say, an Ha filter to reduce the brightness of the image to get a more workable exposure (I don't have an ND filter, and don't really want to spend any more!).

[Merlin66]

Luke,

In the trials I'm currently doing, a Ha filter (Baader 35nm CCD) doesn't attenuate much of the light, the filters are very efficient! But they do a good job with the energy reduction.

If you wish to continue using the QHY, then you will probably need a ND2 filter....

[JamesF]

Am I understanding correctly that with an f/10 1000mm stage 1 mod you lose the ability to take full-disc images because the image of the Sun is larger than the filter in the eyepiece holder?

James

[Merlin66]

Yes and no....

The image of the solar disk (about 10mm) will be vignetted by the final blocking filter...

[lukebl]

Hi all,

A bit of progress on my PST Stage 1 mod. I've now replaced the PST black box (which is awful to try and focus, and anyway won't reach focus with a camera) with a spare Dual-speed focusser from my old unused 200mm Newtonian.

I managed to get an engineering mate to fabricate a threaded metal plate, so that I could fit the etalon from the PST to the focuser. I must say, the improvement in image quality is amazing. The feeble focusing method of the PST black box is so prone to misalignment, and so fiddly to use that it was a real pain. Views are now really crisp, and it's so easy to focus properly. It's neat how the eyepiece holder from the PST has the same thread as the SW diagonal.

Hope to get some images next.

[JamesF]

Really pleased to hear you've got this sorted, Luke.  Looks like a very nicely done mod, too.

James

[moriniboy]

That's really great, my next mod will be just the same.

Are you still using the BF5?

[Luke]

That's fantastic news, Luke.

I was disappointed for you that it wasn't doing the business before. Look forward to your images!

[Merlin66]

Glad to hear it's finally there!

I'm sure you will appreciate the difference....

Now all you need is a DMK camera, the larger the better ;-)

Onwards and Upwards

[Psychobilly]

Congrats luke. .. I'm lad you have got it sorted. and look forward to your reports and images

Having read the thread again perhaps I need some more lessons on how to use the PBK LOHA as it has a Borg helical and two speed motorised focuser fitted...

Peter...

Sent from my GT-P7300 using Tapatalk 4

[moriniboy]

Hi can anyone confirm the thread size shown on the attached, its the one which goes in the black box.

Thanks Nigel

[Merlin66]

Nigel,

The PST etalon has an M50 x 1 female at the front and an M50 x 1 male  thread at the rear.

HTH

[moriniboy]

Decisions decisions, I have a relative going to the US in November, I am considering the following diagonal / BF combinations for use with the above crayford mod

LUNT

B1200d1
B1200 Blocking Filter in 1.25″ Diagonal with T2 connection
Retail Price: $648.00

B1200d2
B1200 Blocking Filter in 2″ Diagonal with T2 connection
Retail Price: $648.00

CORONADO

Coronado BF10 - 10mm Blocking Filter

Retail Price: $499.00

Coronado BF15 - 15mm Blocking Filter

Retail Price: $699.00

I have a concern that if I go for the 2" version then the magic 200mm Etalon dimension may be exceeded.

Also can anyone advise if any of these diagonals contain an ERF as well as the final BF

Any comments?

[Peter Drew]

Nigel. The Coronado diagonal mounted BF's do include a blue mini erf. Not sure about the relative virtues of the Coronado/Lunt units but would have thought the Coronado would have the better chance of compatibility. 

[Merlin66]

PST Modders have successfully used both the Lunt and Coronado blocking filters.

Each separately supplied blocking assembly (Lunt/ Coronado) are fitted with the ITF (Interference Transmission filter) element in front of the final Blocking filter (trimmer). The reason for that is to compensate for the variable bandwidth of the ERF's used in the front etalon assembly. Also, unfortunately these ITF filters are very prone to failure - the side seal breaks down due, we think, to thermal shock and this allows the ingress of moisture to the internal multi-coated surfaces. The deterioration then "creeps" in from the edges...

No solution so far.

HTH