Some advice needed for my Lunt 50mm B600

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Amra
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Some advice needed for my Lunt 50mm B600

Post by Amra » Mon Sep 05, 2016 1:50 pm

I use the Lunt 50mm together with the ZWO ASI174MM. I tend to use a 2x barlow for more image scale.

I'm having a hard time evenly illuminating the disc, sometimes it goes better than other times, like without a barlow it seemed to work fairly well, but then my last session it was very bad (see attached image), I tried to use the tuner to get it more evenly lit, but that just wasn't happening. Is there anything I can do to help it? Is it maybe because the ASI174MM's chip is so large? Or could it be slop in my optical path that's causing it?

Examples of the images I've taken with this setup can be seen on my AstroBin profile

Appreciate any insight you guys might have.
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robert
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Re: Some advice needed for my Lunt 50mm B600

Post by robert » Mon Sep 05, 2016 3:07 pm

Tuning the etalon should move the bright area from one side to the other. You have to chose the best position. It helps to not have slop on the blocking filter too. Is the etalon square onto the scope axis? Or if it is pressure tuned is it sealing properly. Well lubricated o-ring and screw tight inside the adjuster.?
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Re: Some advice needed for my Lunt 50mm B600

Post by Amra » Mon Sep 05, 2016 4:40 pm

robert wrote:Tuning the etalon should move the bright area from one side to the other. You have to chose the best position. It helps to not have slop on the blocking filter too. Is the etalon square onto the scope axis? Or if it is pressure tuned is it sealing properly. Well lubricated o-ring and screw tight inside the adjuster.?
Robert
Hey thanks for the reply.

The pressure tuner is well lubricated and must be sealed well because it becomes noticeable harder to screw it further and further in. To minimize slop as much as possible I tighten the focuser but it's possible there's still a little bit of slop.

It seems that bright area which I can move around with the tuning is smaller than the disc 2x barlowed, when I was playing with exposures there as a small portion on the disc that got much brighter than the rest, but if you look at my AstroBin images, like this one below, it's not perfectly evenly exposed, but it's pretty close.

Image

Maybe the 'tuned area' of the image circle is just so much smaller than the big ASI174MM chip? I'll research into it.

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robert
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Re: Some advice needed for my Lunt 50mm B600

Post by robert » Mon Sep 05, 2016 5:39 pm

That is probably it!
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Re: Some advice needed for my Lunt 50mm B600

Post by marktownley » Mon Sep 05, 2016 8:00 pm

Maybe it is vignetting with the B600 and the barlow on the big chip? Do you have a full disk at native focal length without the barlow?
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Re: Some advice needed for my Lunt 50mm B600

Post by Amra » Tue Sep 06, 2016 6:01 am

marktownley wrote:Maybe it is vignetting with the B600 and the barlow on the big chip? Do you have a full disk at native focal length without the barlow?
Yeah, here's an unsharpened shot of my very first image taken with the Lunt 50mm without any barlow.
SunHalpha_132333_g3_ap131.jpg
SunHalpha_132333_g3_ap131.jpg (131.31 KiB) Viewed 1627 times
EDIT:
And here it is cropped & processed:

Image

Seems nicely evenly exposed. I haven't taken many images with my Lunt 50 yet, so I'm still learning about it, I would certainly prefer to image with a barlow so I could make use of the nice big chip on the ASI174MM and get some more resolution, I have played with a 3x barlow as well, but I wasn't able to get it to focus.
Last edited by Amra on Tue Sep 06, 2016 6:06 am, edited 1 time in total.

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Re: Some advice needed for my Lunt 50mm B600

Post by marktownley » Tue Sep 06, 2016 6:06 am

That looks fairly even to me.
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Re: Some advice needed for my Lunt 50mm B600

Post by Amra » Thu Sep 08, 2016 1:24 am

Good news. Had plenty of sun today, so I actually had an opportunity to play with the tuner & focus a lot, and I discovered that my tuning was just way off the last time, I was able to find the sweet spot and it seems pretty evenly illuminated to me now. I also tried doing a timelapse of the sun disc for the first time successfully.

Here's the shot from today.

Image

And the timelapse:


I intend to do a lot more of these to see the disc change over more time than 50 minutes. It was a fun experiment though.

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Re: Some advice needed for my Lunt 50mm B600

Post by marktownley » Thu Sep 08, 2016 5:56 am

It's all about practice!
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Re: Some advice needed for my Lunt 50mm B600

Post by nickatnight » Wed Sep 14, 2016 8:20 am

Looks like you're on the right track to solaving your issue. I have the Lunt 50 with B600, and have the ASI174MM camera. I also have the ASI120MM-S which I prefer using with the Lunt 50, as the sun just about fills the chip at native focal length. However I think you'll have a bigger final disk going with the barlowed ASI174MM.

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