16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

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16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by davidem27 »

Hello eveyobody,
this is the Sun, today on 16th of July showing in h-alpha band took with a simple Lunt LS50THa that does not want to get in focus with a simple ASI 178MM sensor camera.
2021-07-16-1329_Ha_FD_COL_pistr.jpg
2021-07-16-1329_Ha_FD_COL_pistr.jpg (895.54 KiB) Viewed 1047 times
2021-07-16-1329_Ha_FD_BW-pistr.jpg
2021-07-16-1329_Ha_FD_BW-pistr.jpg (599.93 KiB) Viewed 1047 times


The only way to reach focus is to put the optical element of a small barlow in the eyepiece holder and to screw the camera without its nose.

But these situations drive me crazy because I'd like to put a small power barlow to pump up a little bit with sampling.
focusIssues.jpg
focusIssues.jpg (584.03 KiB) Viewed 1047 times
The most upsetting situation is in picture no.1 with the normal use of Lunt, without any accessory.
The picture no.2 says to me that I could not able to use any barlow lens with Lunt 50 etalon module...
The picture no.3 is the last non focus situation before I insert the small barlow lenses in the ep holder...

And I would like to put a barlow on future situations (planning to frankenscoping) with Lunt 50 Pressure Tuner etalon module...

What are your experiences with Lunt 50 reaching focus?


White light: Skywatcher 120 ED and Borg 76 ED with Baader Herschel Wedge and filters
H-alpha: Lunt LS50T Ha BF600, 120 ED modified by Lunt etalon. Thousand Oaks 0.9 Å Prominance filter
Calcium II K: Lunt B1200

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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by DeepSolar64 »

Your images still look good though.


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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by EGRAY_OBSERVATORY »

Hello David, I can't see anything wrong with your two images as far as focusing is concerned.

I have the Lunt 60mm Ha as well as their CaK scopes (with double-stack available if required) and have never any issues with adding Barlows, although certainly Newton Rings can be a problem in some cases when using Barlows. I also now use two ZWO ASI-178mm cameras in the Lunts.

For White-Light though - I have just received a new SkyWatcher ED80 triplet and subject to it's first-light on the Sun, will likely get another camera for Full-Disk captures.

To tell us which Barlow(s) you use and their manufacturer(s) might assist us to give you better advice ??
There's been numerous posts on the subject too..

https://astronomy.tools/calculators/field_of_view/ for FOV

https://astronomy.tools/calculators/ccd_suitability for camera/pixel size recommendation.

These two web-pages might also assist ..



Clear skies
Terry


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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by davidem27 »

Thanks for the reply Terry!
My two images in this post do not have severe focus issues*
But just because I've inserted, in the eyepiece holder, the optical element of the barlow by William Optics binoviewer (shown below)
opticalElement.jpg
opticalElement.jpg (111.51 KiB) Viewed 1003 times
Without it, no focus can be reached.

The only barlow I have now is the Baader VIP that cannot grab focal plane because of its mechanical design (optical element is at the end of the far side of the nose, shown in the upper image). So I'd better borrow a classic barlow from a friend and have a try.
EGRAY_OBSERVATORY wrote: Fri Jul 16, 2021 5:32 pm I have the Lunt 60mm Ha
The Lunt 60 has a quite different design despite of 50: you'd have the 2 inches Blocking filter that can be fully inserted or fully pulled out to let grab focal plane with camera either with an eyepiece.

Sorry for my english, if I cannot explain myself better.

* (maybe the edge at 8 hours is slightly unfocuesed due to the tilter)


White light: Skywatcher 120 ED and Borg 76 ED with Baader Herschel Wedge and filters
H-alpha: Lunt LS50T Ha BF600, 120 ED modified by Lunt etalon. Thousand Oaks 0.9 Å Prominance filter
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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by rigel123 »

You might give Lunt a call but I believe most of the folks that I have seen using the 50 mm have replaced the helical focuser with something like a moonlight or feathertouch.


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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by MAURITS »

David the above images looks good to me.


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Maurits

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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by davidem27 »

rigel123 wrote: Sat Jul 17, 2021 10:51 am You might give Lunt a call but I believe most of the folks that I have seen using the 50 mm have replaced the helical focuser with something like a moonlight or feathertouch.
What I understand from my perspection, there are two problem in the Lunt 50 PT telescope.

1. insufficient focuser inward travel for cameras that have sensor to far from the eyepiece holder
2. too much waste of space after the focuser: 31.8mm male nose of the diagonal and thick profile of the eyepiece holder after the diagonal

I purchased this used Lunt 50 with another focuser that should be (as it seems by pictures) shorter than the original helical focuser by some millimeters. But I cannot understand why Lunt has designed a telescope that cannot reach focus with a camera like ASI.

Maybe (maybe) a QHY could reach focal plane: its sensor backfocus is placed at 11mm versus 12.5 of the ASIs.

By using a 2 inches focuser (and changing the male of the diagonal with 2 inches one) the mechanical path gets shorter...
Attachments
NOT MY LUNT, SAMPLE IMAGE WITH ORIGINAL FOCUSER
NOT MY LUNT, SAMPLE IMAGE WITH ORIGINAL FOCUSER
okOPi0C (1).png (159.26 KiB) Viewed 984 times


White light: Skywatcher 120 ED and Borg 76 ED with Baader Herschel Wedge and filters
H-alpha: Lunt LS50T Ha BF600, 120 ED modified by Lunt etalon. Thousand Oaks 0.9 Å Prominance filter
Calcium II K: Lunt B1200

www.volpetta.com

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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by JDJ »

I experienced similar frustrations when I first received my Lunt50. Switching from the stock focuser that comes with the Lunt50 to the 1.25 in feathertouch focuser that Lunt offers helped the focus situation.

https://luntsolarsystems.com/shop/acces ... h-focuser/

My Lunt50 imaging train is: LS50, 1.25in feather touch focuser, blocking filter/diagonal, Powermate 2.5x (with 1.25 T-ring adapter that will thread directly to a ZWO camera), ZWO ASI290MM or 174MM.


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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by eroel »

David:
Those are good FD´s and nice setup.
Best regards,
Eric.


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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by Montana »

It is most frustrating when you can't reach focus. Have you had a chat with Ivan, he seems to do some lovely imaging with his Lunt 50?

These are great full discs by the way :bow :hamster:

Alexandra


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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by Ivan »

Hi,

have you tried the method described here: https://www.cloudynights.com/topic/4984 ... gle-stack/

The bottom line is to screw the zwo camera to the BF (first by unscrewing the eyepiece holder) and then slightly extend the BF.

More options: https://stargazerslounge.com/topic/2510 ... d-sort-of/

Ivan


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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by Rusted »

I don't know if it helps but I shortened the 1.25 nose which screws into my ASI174.
There are further GPCs from T-S including the 2.6x if you want more scale and little more inward travel.
These GPCs push the ASI nosepiece backwards when fitted behind the LUNT BF.
The 2.6x is also shorter than the 2x and 1.6x GPCs. Which also helps.
Though rather oddly, the 2.6x has no filter thread.
Unlike the PST BF, the Lunt projects at the back. Leaving much less room for a GPC.



P1440040 rsz 600 gpcs gpc txt.jpg
P1440040 rsz 600 gpcs gpc txt.jpg (45.53 KiB) Viewed 952 times


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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by davidem27 »

Thanks everyone for the replies, really helpful.

I already though to cut and shorten the camera nose and I think this will be the easiest choice.

Alexandra, I would avoid mosaics as Ivan does, even with his splendid results. :oops:


White light: Skywatcher 120 ED and Borg 76 ED with Baader Herschel Wedge and filters
H-alpha: Lunt LS50T Ha BF600, 120 ED modified by Lunt etalon. Thousand Oaks 0.9 Å Prominance filter
Calcium II K: Lunt B1200

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Re: 16 July 2021 - Ha Full Disc (with some Lunt 50 focus issues)

Post by Ivan »

Before sawing, I would try to screw the camera like this:
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post-43244-0-95487100-1430332482.jpg (125.98 KiB) Viewed 929 times


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