PST Mod question

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PST Mod question

Post by MapleRidge »

Good day all...

I tried to view/image for the first time today with a PST kit that I purchased last month and have been clouded out most any chance I had to view the sun until now.

I am curious about the spacings between the etalon and ccd chip, which I belive are to be 200mm. Where in the etalon do you start the measurement? From the sky side, the back side of the optics facing the BF, or the centre of the tuning ring? Makes a bit of a difference. Same question about teh spacign for the chip to BF...where on the BF do we measure?

I was no where near the 200mm mark...could not reach focus with more than about 150mm but I was able to get Ha and tune the system. I need to either cut the tube more, or find a different focuser that permits more in travel.

I would appreciate any suggestions.

Thanks,
Brian


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Re: PST Mod question

Post by MapleRidge »

Hi, back again...

I did a quick process of some of the images taken with the PST etalon paired with my B1800Ha Lunt BF, which was installed on the C102 (102mm, f9.5 1,000mm fl) at prime focus. The images turned out better than I had hoped for first light...granted the wide FOV shows the off banding that occurs once you move form the centre of the optical path.

A few details...I had a constant stream of cirrus blowing through most of the time I tried to image, but this was the best clear break I've had in close to a month. Due to the clouds, Registax would only combine a 30-50 frames which doesn't help. This also has the etalon/BF spacing far closer than what it should be. The other C102 that the Lunt DSII mod has a shorter tube, but I'm not disassembling it for fear of loosing the alignment I spent all fall trying to fix. I'm going to work on reducing the focuser profile 1st.

So, here are the 2 choice images...one of the disk, secind one of the limb. There is quite a glare in the lower right which changes a bit with tuning...maybe a ghost image. Need to work on this one a bit too.

Oh, this is the etalon that Gary Beal had, and was the topic of the threrad 'PST Mod - Band is very thin' back in early November.

I would appreciate any comment that anyone familiar with the PST mods has on the spacing measurement and the source of the glare in the lower right.

Disk deatils:


Limb details:


These were images with the PGR ICX674 chipped camera (should have use a barlow to clip out the off-band but I didn't bother with the clouds).

Brian


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Photos: https://www.flickr.com/photos/185395281@N08/albums

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Re: PST Mod question

Post by swisswalter »

Hi Brian

congratulations on the first light with your mod. That is a very good start.

I guess there is nothing wrong. Just alignments and tilting needs to be sortet out


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Re: PST Mod question

Post by Merlin66 »

The majic 200mm is basically from the front of the rubber tuning ring.
This point should be inside prime focus by 200mm for the in-built barlow to give a fully collimated beam through the etalon.
The rear back focus will also be 200mm from the rear lens of the etalon assembly.
The positioning of the BF is non critical but should be as close to the CCD image plane as you can make it.
Hope this helps.


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Re: PST Mod question

Post by MapleRidge »

Hi everyone...

Thanks for all the comments and suggestions. The use of the tuning collar will help with judging the spacing, as I was using the back of the optics in the etalon. This gives me a few more mm, but still off by a few cm by my reckoning.

If we get some sun again here I will keep working with it.

Thanks,
Brian


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Photos: https://www.flickr.com/photos/185395281@N08/albums

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Re: PST Mod question

Post by marktownley »

Hi Brian,

Sorry, was slow to reply to this. Ken is spot on with his advice, but there are ways to 'bend'these rules...

When you're talking about achieving focus, in the case of the eyepeice side of the etalon, if you're finding the 'stock' distance the re-focusing lens provides is not ideal, then it is possible to simply replace the re-focusing lens with one of a focal length that is more suited. I tried a 300mm fl as opposed to the stock 200mm. You can get them really cheap from Edmunds Optical http://www.edmundoptics.com/optics/opti ... c#products

If on the other hand you're talking on the OTA side of the eatlon, and you can't get the Etalon at the magic -200mm focal position, then there are 2 things you can do if you don't want to cut down the tube; first remount the front collimating lens on the nosepeice of the Etalon - 2" adapter you are using, this will afford you 25-40mm more infocus than you had before, if this still isn't enough then mount another 2" barrel on the end of the etalon - 2" adapter and mount the collimating lens assembly in this - it has a pretty darn close M48 thread so will just screw in no probs. I've talked about it on the equipment page of my website http://brierleyhillsolar.blogspot.co.uk ... pment.html

Hope this helps!

Mark :)

PS - dont forget to try double stacking the PST etalon with the Lunt DS module - results could be fun ;)


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Re: PST Mod question

Post by MapleRidge »

Hi Mark...

Thanks for the hints, and I will get a look at the video clip one day when I can think straight.

Biggest issue at the present seems to be that when the etalon/CCD distance is fixed at 200mm, the focuser will not rack in enough to reach focus. I have to look at the focuser, and see if I can pare some space out of it before I try to cut the tube.

Now, to DS the PST with the DSII is exactly what I had hoped to be able to do. I believe that the focus travel will be a equal issue with the DSII in the path, but I want to see the PST working on its own before I go on form there. I think the next mod will be to fit the DSII or PST to a 6", f8 OTA...but one step at a time. Will need sunny skies to test anything out right, and right now sun has been at a premium.

My biggest question is if the PST/DSII were to be stacked, is there any magic spacing between the etalons?

Brian


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Photos: https://www.flickr.com/photos/185395281@N08/albums

10'x15 Roll-off Roof Observatory
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Re: PST Mod question

Post by Merlin66 »

Brian,
The front element of the PST etalon by design MUST sit at -200mm inside the prime focus of the donor. The final focus will be +200mm behind the rear element of the PST etalon. This is a nature of the assembly...whether a Stage 1 or Stage 2 mod.
I use the DS60 front etalon double stacked with the PST etalon....makes no difference to the positioning and the final focus. Just fit the front etalon in the T-max tilt ring securely to the front of the donor.
Using a front mounted etalon (ie SM40/ SM60 etc) on any scope - you're not restricted to f10 etc and using a BF10/BF15 will give fantastic views of the Sun.
Hope this helps.


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Re: PST Mod question

Post by marktownley »

Biggest issue at the present seems to be that when the etalon/CCD distance is fixed at 200mm, the focuser will not rack in enough to reach focus. I have to look at the focuser, and see if I can pare some space out of it before I try to cut the tube.

Got a picture you can post up? I'm sure with some visual clues we can come up with a work around... One way could be to remove the rear collimating lens from its current position and mount it further back...


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Re: PST Mod question

Post by MapleRidge »

Mark and Ken...

I snapped a few pics of the assembly today, but I had to wing the whole thing as it was raining all day.

The pic below is the setup wit the PST etalon and Lunt B1800BF. I use a number of T-spacers to get to the 200mm mark. The BF attaches with a female/female t-thread collar. When I have the system set up this way, I cannot rack the focus in far enough to reach focus...probably 2+ cm short. The images I posted had the spacing in the 150mm range.


I have the ability to change the focuser to on that is slighter lower profile, so I can test this the next sunny day.

I guess the first question is have I assembled the elements correctly...or have I botched the my perception of the assembly. If this is basically correct, then I'm down to shortening the tube/lower profile focuser.

The pic below shows the DSII installed on the other scope, and the PST assembly fitted behind it. This was where I questioned the spacing of the etalons. I have copied the camera/B1800 and inserted them below to give an idea of the focus position of the DSII mod alone.


The last pic is the PST and adapters.


This is where Mark lost me a bit. If I follow, you mean to remove the collimation lens from the PST housing and re-mount it closer to the objective...in the tip of the 2" adapter? Did I get that right?

I hope the pics help to shed some light on the problems. The weather has only provided me at best a half hour to work wit this, so I've barely scratched the surface of getting it set up.

If I've got the assembly wrong let me know...or any where to help improve the system.

Thanks,
Brian


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Photos: https://www.flickr.com/photos/185395281@N08/albums

10'x15 Roll-off Roof Observatory
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iOptron CEM70G Mount carrying:
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Re: PST Mod question

Post by marktownley »

Hi Brian.

When you say you cannot rack the focus in far enough are you talking about altering the spacings on the t-thread spacers or altering the focus on the moonlite?

Mark


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Re: PST Mod question

Post by MapleRidge »

Hi Mark...

With the 200mm spacing as shown, the moonlite will not rack in...it bottoms
out before the sun comes into focus.

I was able to focus when I took one of the spacers out form between the
etalon and blocker, but this cut the spacing down to about 150mm.

I have another adapter that will mount the camera very close to the t-thread
on the back of the Lunt blocker, but the camera spacing isn't that critical
(say within 25mm or so) or is it?

Brian


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10'x15 Roll-off Roof Observatory
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Re: PST Mod question

Post by marktownley »

I was able to focus when I took one of the spacers out form between the
etalon and blocker, but this cut the spacing down to about 150mm.

I have another adapter that will mount the camera very close to the t-thread
on the back of the Lunt blocker, but the camera spacing isn't that critical
(say within 25mm or so) or is it?

Brian

I would have a play around, and if it works and images well then so be it... ;)


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Re: PST Mod question

Post by Merlin66 »

Hmmm
Looks like you're at least 25mm out.
The final focus +200mm should be from the rear of the PST etalon body.
I'm sorry I didn't realise you were talking about a LUNT DSII etalon...
I don't know about setting that up. You may need to check where the focus is with the DSII in place then seeing if it is possible to achieve the -200mm for the PST etalon......


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Re: PST Mod question

Post by MapleRidge »

Hi Ken...

In your opinion, is the spacing correct in the first pic, or am I measuring form the wrong end of the PST etelon? That is the first hurdle I need to clear.

I'd hate to go so far as to shorten the tube and find out that I had the spacing wrong (either no need to shorten, or should have cut more out!).

The DS with the Lunt DSII is a secondary concern for now.

I can change the moonliet body with another that has a shorter profile...if I need no more an a 1-2cm it may work.


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Re: PST Mod question

Post by Merlin66 »

Brian,
The tape measure should be on the rear of the PST etalon, not the front.
This gives you another 25mm or so to add to your focuser spacers.....
We'll get back to the DSII later.........


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Re: PST Mod question

Post by MapleRidge »

Ken...good to confirm that. I was using the wrong side of the tuning ring. This will require more than the alternate focuser can provide, but I ll try it next sunnt day.

Thanks,
Brian


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Maple Ridge Observatory
Cambray, ON Canada

Photos: https://www.flickr.com/photos/185395281@N08/albums

10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
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Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM

2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
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Re: PST Mod question

Post by sullij1 »

Just observing here but is the 2 inch stainless to etalon adapter common to these mods? Is the inside of the stainless adapter blackened/flocked? This could be the source of the reflection on the bottom right. It seems to me that the bare stainless steel will create a horrible internal reflection.


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Re: PST Mod question

Post by MapleRidge »

Good catch there....I have to flock it yet (wanted to be sure the machining was completed first), and I missed mentioning in my post that was my first target for the reflection.

Brian


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Maple Ridge Observatory
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Photos: https://www.flickr.com/photos/185395281@N08/albums

10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
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Planetary Work - SBIG CFW10, ASI462MM

2.2m Diameter Dome
iOptron CEM70G Mount carrying:
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Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
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Re: PST Mod question

Post by sullij1 »

Good luck with the mod, I will be watching with interest. Happy Holidays Brian! :)


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Re: PST Mod question

Post by colinsk »

Just observing here but is the 2 inch stainless to etalon adapter common to these mods? Is the inside of the stainless adapter blackened/flocked? This could be the source of the reflection on the bottom right. It seems to me that the bare stainless steel will create a horrible internal reflection.

Good catch. Threaded and coated black works very well.


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