PST 10mm blocking filter/ Denk Spectrum 60

langejcarl · Post by **langejcarl** » Mon Feb 06, 2012 6:15 pm

I have what I consider one of the "good" PST's. I have a Denk Spectrum 60 tube that I have used to replace the original PST tube. Other than that, my PST is not modified. The image scale is quite a bit larger than the standard PST, so I would like to make this work out. The problem is that the FOV is very tight. I do only visual work and no imaging and do not use a motorized tracking mount. I have a tough time seeing the whole solar disc even with a 40mm ep. If I take a Coronado BF10, can it be screwed in as an exact replacement for the 5mm blocking filter?

swisswalter · Post by **swisswalter** » Mon Feb 06, 2012 8:36 pm

Hi John

welcome to that wonderful TOS free site. I can't help you, but just wait a minute and you will get answers from other members

Post by **Merlin66** » Tue Feb 07, 2012 7:24 am

https://www.denkmeier.com/index.cfm?fus ... N=10857669

Welcome on board.
My understanding is that the Spectrum mod includes an upgrade of the PST BF5 to a BF10.
Can you confirm the size of the current blocking filter?

langejcarl · Post by **langejcarl** » Tue Feb 07, 2012 1:40 pm

Thanks for the welcome!

The info on the Denk site where the BF 10 is mentioned is basically a review of the upgrade, but does not indicate that a bigger BF currently is part of of the upgrade. If you read steps 1-5 where Denk describes what they do for you it does not include a 10mm BF upgrade. In any event, I purchased the bigger Spectrum 60 tube on the used market. The seller said that he questioned Denk and was informed that the BF mod is no longer part of what they do. I have not independently confirmed this with Denk, but it really doesn't mater whether they do or don't for my purposes since I still have the standard BF that comes with any PST. Therefore, the question still stands. To answer the question does not require anyone's experience specifically with the Spectrum 60. Anyone who may have switched out the standard PST BF with a larger one can answer the question.

What I really want to know is, if I get a BF 10, does it just screw into the PST when I remove the original eyepiece holder which contains the stock BF? If it does not just drop in with typical Eli Whitney simplicity, is it difficult to remove the stock BF from the eyepiece holder without ruining it? If I can put a BF 10 in the PST then are there any problems with it "matching" up and being compatible with the other components of the system?

John
Detroit

Post by **Merlin66** » Tue Feb 07, 2012 1:49 pm

Hmmm.
As the "normal" larger BF filters come pre-fitted to a diagonal (Lunt/ Coronado) the BF would have to be removed from it's cell..the current PST eyepiece holder dismantled and a "new" larger cell machined to accommodate the large BF filter.
A lot of work, I think.
It would be easier to dump the PST "black box" and fit a couple of spacers and then a new BF diagonal to get the benefits you're looking for...
What do you think?

langejcarl · Post by **langejcarl** » Tue Feb 07, 2012 2:10 pm

See the attached pic that I got from a German website. It shows the eyepiece holder (which contains the BF) removed from the PST next to the BF 10 from the diagonal. The person at the German website did the swap, but when I tried to contact her to ask specific questions my email kept getting kicked back to me. Does a Coronado diagonal BF simply unscrew and if so does anyone know if the threads match up with the PST threads? I was just hoping to find out if someone has this info for me before I put down the money for a BF 10 diagonal. If I do that, is it anticipated that I will have any compatibility problems with the other elements in the PST system?

Attached files

Post by **Merlin66** » Tue Feb 07, 2012 2:31 pm

John,
I've just pulled off the eyepiece holder (with a BF10 fitted) from a Coronado diagonal and removed the eyepiece holder from the PST, and I can positively say the threads are identical!!
I'm surprised, but yes you can easily swap them over.
(the "mini-ERF" built into the base of the PST eyepiece holder would still be OK for the larger blocking filter)

langejcarl · Post by **langejcarl** » Tue Feb 07, 2012 2:51 pm

I would be curious to find out what your impressions are if you look through the PST with the BF 10 installed.

Post by **Merlin66** » Tue Feb 07, 2012 3:32 pm

John,
Sorry I can't help you with that...
My PST has been Modded to a 88mm scope with a Baader D-ERF up front...I use a BF15 on a Stage 2 Mod
(I have a 6.5Mb write-up available "Modifying the Ha PST" just drop me an email for an copy)

Post by **marktownley** » Tue Feb 07, 2012 9:04 pm

Well, isn't this interesting! Some exciting implications...

earl · Post by **earl** » Wed Feb 08, 2012 1:39 am

I am the one that sold him my Denk 60 upgrade.

I am glad to hear that it looks like the BF10 will screw directly into the PST.

The mini-ERF filter is not needed since the 60MM lens is coated with ERF. I had a lot of discussion with DENK before I purchased the upgrade and I was pleased with it but getting the 90MM required that I sell the upgrade. Part of the deal with the wife.

Keeping the mini-ERF in place is not hurt anything but if you find that you do not have enough focus you can remove it and screw the BF5-eyepiece into the black box. That is what I had to do to be able to image with my DMK41 and when I used barlows with my eyepieces.

Enjoy ...

Post by **marktownley** » Wed Feb 08, 2012 5:33 pm

Ken, I don't suppose you have a transmission curve for this mini ERF? I'm curious as to how 'narrow' the bandpass is on it...

Post by **Merlin66** » Wed Feb 08, 2012 5:43 pm

Good question Mark!
I'll put it on the list to measure with the spectroscope....

Post by **marktownley** » Wed Feb 08, 2012 5:51 pm

Good question Mark!
I'll put it on the list to measure with the spectroscope....

Thanks!

This is the bit that 'rusts' so would be interesting to know the specs to see what is commercially avaiable to repair failed units. I know Robert arnold completely removed his when it rusted, and without it the result was positive for imaging...

Post by **Merlin66** » Wed Feb 08, 2012 6:10 pm

I have a collections of "horror" images of various "mini-ERF" failures in the PST!!!
My answer has been to dump the erf and carry on as usual.
EDIT (I'm sure it's only there to add protection to the more sensitive BF filter)- certainly doen't help the etalon!!!!

Post by **marktownley** » Wed Feb 08, 2012 6:22 pm

EDIT (I'm sure it's only there to add protection to the more sensitive BF filter)- certainly doen't help the etalon!!!!

Yes, would agree with you there Ken. Maybe because the Coronado ERF has very little (read no) blocking in the IR?

Cor-SM60-log by Mark Townley, on Flickr

Richard · Post by **Richard** » Wed Feb 08, 2012 9:46 pm

Very interesting, so in effect it should work the other way round aswell...If you unscrewed the PST BF with the mini ERF and fitted it into a standard diagonal, you would have a BF5 Diagonal?..
Just thinking as then you could use it with a SM40.....
I have both and would be interesting to play with them on the ED80 to see if it would work before buying a BF10....

langejcarl · Post by **langejcarl** » Wed Feb 08, 2012 10:19 pm

Can you explain to me what you mean by the "mini ERF"? Also, Mark said that "this is the bit that rusts."I thought only the objectives on the PST's had the "rust" issue. Please straighten me out on this.

Thanks.

langejcarl · Post by **langejcarl** » Wed Feb 08, 2012 10:21 pm

Here is something interesting. Anacortes has his language in its PST description:

"The PST uses a 5mm blocking filter that cannot be removed or changed."

I wonder why they thought that was necessary to include that info.

Post by **Merlin66** » Thu Feb 09, 2012 12:16 am

A couple of things.
1. I don't know if the PST/ Coronado eyepiece holder will fit "any diagonal"
2. When the "gold" objective on the early PST's was replaced with the "blue" objective, Coronado added a small "mini-ERF" to the front of the eyepiece holder.
3. This "mini-ERF" like the original objective, is subject to deterioration, and can "rust" and fail in other ways.
4. We've just proven that the BF5 in the PST can be replaced with a BF10/BF15 from a Coronado blocking diagonal.

Post by **marktownley** » Thu Feb 09, 2012 6:47 am

Here is something interesting. Anacortes has his language in its PST description:

"The PST uses a 5mm blocking filter that cannot be removed or changed."

I wonder why they thought that was necessary to include that info.

Lol!

I guess it is to try and put people off messing with stuff, however they didn't count upon us lot having a party here and spending far too much of our time wondering how we can take things apart to improve on existing designs

Post by **marktownley** » Thu Feb 09, 2012 6:48 am

Very interesting, so in effect it should work the other way round aswell...If you unscrewed the PST BF with the mini ERF and fitted it into a standard diagonal, you would have a BF5 Diagonal?...

In theory, yes...

langejcarl · Post by **langejcarl** » Thu Feb 09, 2012 2:15 pm

That is my thought. If I buy a BF10 and the BF5 from the PST is a perfect fit to the diagonal then I can re-sell the BF5 diagonal and recoup some costs. Assumes I am happy with the BF10.

langejcarl · Post by **langejcarl** » Thu Feb 09, 2012 2:17 pm

So do all of you believe that it is safe to observe with the mini ERF removed?

Richard · Post by **Richard** » Thu Feb 09, 2012 2:37 pm

Hi, from what I can see, the BF5, BF10 etc all have the Blocking filter and a mini erf in them, so the diagonal has both, and the PST BF5 has both, so it would be just swaping the blocking filter bit and not the mini erf as I think the mini erf is the same on all of them (need to confirm this as I havent got a BF10 to check).
And also read somewhere that the new PST with the Blue front, that the Blue lens isnt a ERF???? Also needs to be confirmed by somebody who knows...

Post by **Merlin66** » Thu Feb 09, 2012 2:50 pm

Some clarification:
The "blue" objective PST is not an ERF.
The "mini-ERF" is now housed in the bottom portion of the eyepiece holder of the PST. The top section contains the actual blocking filter.
A Coronado blocking diagonal has the "mini-ERF" mounted on the telescope side of the diagonal body, and the actual blocking filter in the eyepiece holder, identical to the PST.
If the top section of the PST eyepiece holder is swapped for the BF10 in the diagonal, both arrangements would still end up with a "mini-ERF" in the optical path.
I use a blocking filter without the "mini-ERF" - no issues.
IMHO the small ERF is there to provide some protection to the more sensitive blocking filter, not to protect your eye or camera.
(I have a dismantled PST eyepiece assembly and will do a spectroscopy measure of both the ERF and the blocking filter - I've done this before as an assembly....)
Hope this helps.

Richard · Post by **Richard** » Thu Feb 09, 2012 3:11 pm

: Thats super news Merlin. Though as much, but better to get clarification.

Post by **marktownley** » Thu Feb 09, 2012 5:04 pm

So do all of you believe that it is safe to observe with the mini ERF removed?

Only supposition here, but I think it would be safe, but the actual blocker would be feeling the full force of all the leak IR from the main ERF (assuming SM scopes). I think the blockers life would be drastically reduced in this situation. However, with a properly blocked ERF (baader) upfront I think would be fine. Depending on what Kens spectroscope throws back will be interesting clarification.

Post by **marktownley** » Thu Feb 09, 2012 6:09 pm

I think you will find this very relevant and interesting...

http://www.diane-neisius.de/coronado_pst/index_E.html

Post by **Merlin66** » Thu Feb 09, 2012 6:16 pm

Mark,
Thanks for that...nothing new so far...
I need to evaluated the "mini-ERF" and the blocking filter as separate components.....

Post by **marktownley** » Thu Feb 09, 2012 6:59 pm

Well here's a transmission curve for a BF15, this is the whole unit tho. Blocking out to >2500nm.

Cor-BF151-log by Mark Townley, on Flickr

Post by **Merlin66** » Thu Feb 09, 2012 7:11 pm

Mark,
That's good stuff.
The BF10 Coronado diagonal I measured didn't show that transmission peak at 480nm.
It blocked completely the etalon "toothcomb" and only showed a bandwidth of about 4A
(is this the ERF component? It can't be just the BF which must block the etalon???)

Post by **marktownley** » Thu Feb 09, 2012 7:37 pm

showed a bandwidth of about 4A

Wow, surprises me it's that 'wide' - I kinda expected it to be quite a bit lower than that. This is making me think of some possibilities for my scope... hmmmm...

Richard · Post by **Richard** » Thu Feb 09, 2012 8:18 pm

All very interesting stuff, so what does the blue objective filter out on the new PST's then....

Post by **Merlin66** » Fri Feb 10, 2012 5:34 am

Hmmm
Keeps the rain out of the gold tube ;-)
Seriously, it just appears to be a broadband AR coating...nothing special.
Remember the etalon cuts about >90% of the incoming energy, the rest is blocked by the remaining filter.

Richard · Post by **Richard** » Fri Feb 10, 2012 8:27 pm

Had a play today, the complete PST BF and mini ERF when unscrewed, have the same threads as a 1.25 inch celestron diagonal. So screw straight into it instead of the eyepiece tube...

So just need an adapter for the SM40 to fit it to the ED80 now....

Post by **marktownley** » Fri Feb 10, 2012 8:31 pm

Had a play today, the complete PST BF and mini ERF when unscrewed, have the same threads as a 1.25 inch celestron diagonal. So screw straight into it instead of the eyepiece tube...

So just need an adapter for the SM40 to fit it to the ED80 now....

That's pretty good! Any chance of a pic of this?

Richard · Post by **Richard** » Fri Feb 10, 2012 8:49 pm

Here you are Mark....
PST BF and ERF attached to the celestron diagonal..

Post by **marktownley** » Sat Feb 11, 2012 7:00 am

pretty darn cool Richard, thanks! B)

Hmmm, I bet the same bit would unscrew from the CaK PST - oh the possibilities... :whistle:

Post by **Merlin66** » Sat Feb 11, 2012 9:57 am

Richard,
Excellent find!
That could help a lot of Stage 2 PST mods to get going....

Richard · Post by **Richard** » Sat Feb 11, 2012 10:03 am

Thats what I thought, saves buying a new bigger BF before you know if its going to work. And something to play with.

Post by **Merlin66** » Sat Feb 11, 2012 10:05 am

Richard,
You know it's going to work ;-)
Just saves the immediate cost of a new BF to get the benefits of dumping the "black box" and penta prism in a Stage 2 mod.
Well done.

Post by **Merlin66** » Sat Feb 11, 2012 3:49 pm

OK Finally got 5 minutes of Sun to test the "mini-ERF" from the PST and the Coronado diagonal blocking filters.
Yes,
It is an ERF and blocks everything other than 600-700nm.
Don't know why it would really be placed AFTER the etalon, other than to reduce the energy loading on the blocking filter.

Post by **marktownley** » Sat Feb 11, 2012 5:07 pm

OK Finally got 5 minutes of Sun to test the "mini-ERF" from the PST and the Coronado diagonal blocking filters.
Yes,
It is an ERF and blocks everything other than 600-700nm.
Don't know why it would really be placed AFTER the etalon, other than to reduce the energy loading on the blocking filter.

That's good to know thanks Ken. Right then, my next project is to remove it from my optical train. My aperture mounted ERF is a 7nm Ha Baader hot mirror, so that is cutting out more than this mini ERF is; all the mini ERF is doing is introducing extra glass and reflections into the scope. I reckon there's a niblet of contrast to be gained with its removal...

Photonist · Post by **Photonist** » Sat Feb 11, 2012 9:00 pm

The Celestron diagonal combined to the PST BF and ERF shown in the picture by Richard is a very good and handy solution to get started and more. Last spring I even chose to use it instead of the Lunt 1200 BF with my PST II mod adapted to a SW150/1200.

I found that the PST BF image was much better and brighter and the smaller PST BF size didn’t matter so much as I generally use a Barlow around 2x with this setup. For now I prefer to use the Coronado 10 BF.
.
Viljo

Richard · Post by **Richard** » Sat Feb 11, 2012 10:07 pm

Hi all, had a play with the PST BF in the diagonal, taped the SM40 to the front of the ED80, BW webcam in and powermate 2.5x and off we go...

First image below...

Post by **Merlin66** » Sun Feb 12, 2012 9:09 am

Very nice!
A little "over cooked" but a good result...

Roel · Post by **Roel** » Sun Feb 12, 2012 12:44 pm

I also use that same old Celestron diagonal to mount the PST ERF an BF and it works great. I had to use a rubber spacer ring between the ERF and the diagonal to prevent screwing the ERF tube onto the glass prism itself, which would almost certainly cause lots of astigmatism!

http://www.roelblog.nl/wp-content/uploa ... rdelen.jpg

Post by **Merlin66** » Tue Feb 14, 2012 2:48 pm

Just thought tthere may be some interest in seeing the MG80 spectroscope I've set-up for filter testing.
The Gerd Neumann filter holder at the front allows me to quickly and easily drop in any filter for testing.

swisswalter · Post by **swisswalter** » Sat Feb 18, 2012 5:39 pm

Hi Ken

great stuff