Baader 1.25x GPC with PST Mod, How to Mount the GPC?

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Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

Hey all,

I've seen this mentioned a lot, and saw one photo of it disassembled but no way to tell how it was assembled and mounted. I have the Baader 1.25x GPC to take F8 to F10 on scopes for PST mod use. However, how in the heck has anyone mounted this GPC securely in front of the front collimating F10 lens before the etalon?

Very best,


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by Rusted »

Hi Marty

Assuming you are using the AOC Swiss adapters you can fit the 1.125 GPC directly in front of the etalon.
The problem is having to turn the baffle in the front AOC to fit the GPC nose through it.
The baffle hole is slightly too small. I used a lathe but you could file it with a large, coarse, round file.
The back of the flange on the GPC is packed out with anything you have to hand.
I used large rubber washers because I happened to have some.
Cardboard rings might do. Cork mat is easy to cut.

You use the face of the etalon housing + packing rings to trap the GPC in front of it and inside the AOC front adapter.
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H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

Thanks,

I have the AOK Swiss adapters. So I could just slide it into the baffle. Good to know!

That said, I may need to figure something else out. I extend my collimating lens forward with extensions, beyond the AOK Swiss adapter, so that I can insert deep into a scope's focuser to avoid needing to cut a tube. I have to find a way to get this 1.25x in front of the collimating lens, but behind the D-ERF, on an extended 2" nose of the AOK Swiss adapter.

It doesn't look like the corrector unthreads from its mounting, other than the lenses, the cell its in seems to be one piece with the back flange. So I'm wondering if I simply need to take the glass out of it and put it in another cell, like a standard barlow nose cell, which would make it easier to mount.

Very best,


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

Hrm,

I wonder if this would do it:

https://www.highpointscientific.com/zwo ... oTEALw_wcB

If that will thread into a standard 2" threading, like barrel extenders, the 125x corrector inserts into this 1.25" filter space perfectly. And just glue it there or blue tac it there. Then thread it into the barrel extender behind the DERF but in front of the collimating lens.

EDIT: Doh, that's T2, it will not thread into M48, it's M42. I need to find something that will thread into M48 (2") and take a 1.25" filter.

Something like this:

https://agenaastro.com/blue-fireball-c- ... -v-06.html

That would thread into a 2" extension barrel and allow something to be mounted to it, like this corrector. But C/CS-thread is not 1.25". Not sure the corrector would fit through that hole. Then again, could just glue it to it and not care.

Edit: Wait, C/CS thread is just a hair bigger than 1.25, so this would work it seems? I don't need the threads, just the hole big enough to center and glue it to it.

So.... this:

https://agenaastro.com/blue-fireball-c- ... -v-05.html

Those two combined should give me a M48 male threaded ring with an internal 1.25" female threaded ring. This will let me easily mount anything internally to a 2" barrel with M48 threads for internal mounting. Right? Hrm, maybe not right. This is 1.25" on the outside, C on the inside. So that means the 1.25x corrector cannot insert into this or the above adapter as its smaller? Bleh.

Very best,


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

Ok, maybe this will work. Any confirmation would be awesome:

This:

https://www.highpointscientific.com/zwo ... oTEALw_wcB

With This:

https://www.highpointscientific.com/zwo ... HUEALw_wcB

The T2 1.25" will thread into the T2-M48. The Corrector fits in the 1.25" hole perfectly (not threaded though, will glue it there) and is centered and collimated there. The whole thing will thread into the inside of a 2" extension barrel that is M48 threaded.

Think this is right?

Very best,


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

I think I found one that does it with one adapter:

https://www.ebay.com/itm/M48x0-75-male- ... Swx4BdnirK

Very best,


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by bart1805 »

If your telescope you are using it with has 16cm backfocus or more, why would you put the glasspath more to the front? Just mount it in the nosepiece of and right before the etalon.


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

bart1805 wrote: Sun Jan 19, 2020 4:07 pm If your telescope you are using it with has 16cm backfocus or more, why would you put the glasspath more to the front? Just mount it in the nosepiece of and right before the etalon.
Hi Bart,

So my front collimating lens is currently extended forward so that I don't have to bother with shortening an OTA to allow me to get that collimating lens to the -200mm point. If that point is an F7.5 or F8 light cone, should that be where the corrector is to become F10 and then the collimaging lens? If I put the collimating lens back in its original place in the etalon housing, and the GPC right in front of it with the AOK Swiss adapter, to achieve the -200mm focus point, I would have to shorten the OTA, right?

Or wait, duh, it has to do with it being the focus point in an F8 scope is not the same as F10 so I only have to get the GPC to the F8 or -160mm point and it becomes F10 from there and I'm able to focus?

*******************

I would just test it, but because I'm off and want to test a piece of equipment, of course, "Sunny Florida" is just not considerate today. Literally just need 30 seconds of a break in these clouds to know it will focus. Sigh.

Image

Very best,


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

Ok, so I got my 30 seconds to test it finally. Sheesh had to wait through a lot of clouds.

It was able to focus with room to spare.
Contrast was great. Visible detail was great.
Image scale definitely was increased (finer).
Seems to be working?

I didn't have to mod the AOK Swiss adapter. I just placed the corrector on the collimating lens holding cell and centered it with the AOK Swiss adapter's internal baffle, and then gently starting threading it down. The inner cell of the corrector's holding cell lines up with the baffle in the AOK Swiss adapter and it self-centered is square to everything, I didn't tighten it too tight, just enough to hold everything and its still plenty sturdy as it threaded around a few times before getting any tension.

I was able to get focus and got a great view through my ED80 operating at the 80mm F7.5 with no mask, internally it's being stopped down to approximately 75mm aperture due to the F9.38 focal-ratio with the 1.25x corrector, but this is still a great aperture and view from this scope. I put the camera on it and it was able to focus too (ASI290MM) nicely and showed great detail. Looked at the new flux region that just popped up today.

When the weather improves, I will test it on my 150mm F8.3 frac next. That scope has been slightly shortened by original owner for bino use, and has a shorter focuser that I replaced onto it, so I'm certain this one will focus easily too.

Good to go it seems. Once I confirm everything I'll get some photos of the arrangement for others that may consider an option like this.

Thanks all!

Very best,


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by Rusted »

Marty

I discovered only today that you can't screw a normal 2" filter into the front, AOK, etalon adapter.
It fits, but not without displacing the etalon away from the objective by the thickness of the filter body.

I was going to add a Baader 35nm filter to the AOK nose but had to move it forwards between my 2" Ø extenders.
No idea if this impacts your GPC mounting ideas above.

I also discovered that the focal plane hadn't moved noticeably as a result of the 1.125 GPC being placed up against the etalon.
You may not get your desired focal plane shift [at all] unless you move it well forwards.
Then you might start vignetting due to the limited GPC's clear aperture.


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H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

Thanks,

Here's what I did. Nothing permanent. Worked it seems from my test on the sun both visually and with camera. After I test more later on a day with good enough weather, I will determine a more permanent and stable way to set the GPC here and keep it centered without "luck." The outer ring and cell thread of the GPC is clearly seen through the AOK Swiss baffle aperture and its concentric rings, so its pretty much centered like this. I'm just sandwiching it between the AOK Swiss adapter and the cell holder of the front collimating lens as it enters the PST housing. From there, a Baader Red CCD-IR Block filter serving as the sub-aperture D-ERF threads right onto the AOK Swiss adapter.
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Very best,


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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by Rusted »

Hi Marty,

You have added the filter precisely where I tried and found the etalon moved backwards by the thickness of the filter housing.
Not sure this matters but I just preferred a more stealthy filter setting which did not push the fittings apart.


http://fullerscopes.blogspot.dk/

H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
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Re: Baader 1.25x GPC with PST Mod, How to Mount the GPC?

Post by MalVeauX »

Rusted wrote: Sun Jan 19, 2020 8:44 pm Hi Marty,

You have added the filter precisely where I tried and found the etalon moved backwards by the thickness of the filter housing.
Not sure this matters but I just preferred a more stealthy filter setting which did not push the fittings apart.
Thanks,

Ideally I will put the filter through the baffle, I just wanted to test it first. I will likely open up the baffle aperture to allow the GPC to come through so that it doesn't touch anything behind it, for reasons like you stated you observed.

Very best,


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