Quick white light and CaK images with a 140mm refractor

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thesmiths
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Quick white light and CaK images with a 140mm refractor

Post by thesmiths »

I had my rather sizable 140mm diameter refractor out for "galaxy season" and for the first time tried to do some solar imaging with it. It's a Vixen NA140SSF, a 800mm FL f5.7 telescope that is no longer made. It has a nice traditional Japanese telescope look. I realised it's convenient to actually have a telescope that's nicely polar aligned for solar imaging!

I dropped in my homemade modules for white light (ND3 + Baader Solar Continuum + IR blocking filter) and CaK (Lunt yellow filter from B1200 module + Baader K-line filter) into my Lunt/APM Herschel wedge. Here is a photo of the setup. It's a pretty big telescope! I used a ASI 174MM for imaging (which also gets used for guiding at night time).
vixen na140ssf
vixen na140ssf
752.jpg (269.92 KiB) Viewed 371 times
In general, the images were not as good as I've gotten with my (much more conveniently sized) 107mm f6.5 APO refractor. I guess 140mm is a bit too big for average solar imaging. Conditions were clear but not ideal. First, white light at 800mm and 2000mm FL (using a 2.5x PowerMate). The ASI 174MM was not ideal because of the large pixel size. Taken on April 24, late in the afternoon, with 1ms exposure time. 250 out of 1000 frames stacked.
white light 800mm FL
white light 800mm FL
CapObj_153556_lapl5_ap573.jpg (235.61 KiB) Viewed 371 times
white light 2000mm FL
white light 2000mm FL
CapObj_170020_lapl5_ap203.jpg (237.64 KiB) Viewed 371 times
Here is an image with the CaK filter module at 2000mm FL. This is by far not the best I have ever done. Presumably the telescope is not so ideal for CaK. The 107mm f6.5 APO refractor typically works much better.
CaK 2000mm FL
CaK 2000mm FL
CapObj_164207_lapl5_ap874.jpg (178.13 KiB) Viewed 371 times
Here is a picture of my homebuilt white light and CaK modules (photo was taken for another purpose, to show the nice yellow end caps). The modules have T-mount threads which screw in directly to the ZWO cameras and have 1.25 inch nose pieces that drop into the Lunt/APM Herschel wedge.
white light and CaK modules
white light and CaK modules
784.jpg (196.66 KiB) Viewed 371 times
Finally, here is an image of M51 taken that night using my venerable Atik 460EX monochrome CCD camera. 120 out of 150, 60sec exposures (so total integration time of 2 hours). Deep Sky Stacker and a quick bit of GIMP (the image needs a bit more processing). To defeat light pollution (imaging was done in central London), I used a #29 deep red filter from Lumicon. This restricts the spectrum to red and infrared. As more LED lighting is used, the traditional light pollution filters that block the sodium and mercury lines are becoming less effective. Red/IR imaging is becoming a good way to image broadband objects like galaxies (some colour can be added with narrow band filters like H-alpha).
M51 800mm FL, 2 hours exposure
M51 800mm FL, 2 hours exposure
m51_v3a.jpg (125.68 KiB) Viewed 371 times
The 140mm Vixen telescope does have a nice flat field and good aperture. It's good for deep sky stuff but not the best for solar, I discovered.

By the way, the ASI 174 is 13.3mm diagonal sensor size and the Atik 460EX is 16mm. The M51 image is slightly cropped, while the full disk solar is essentially uncropped. So the galaxy and the full disk sun images are at approximately the same image scale. Camera exposure time, however, is 60,000 times longer for the galaxy.
Last edited by thesmiths on Tue Apr 27, 2021 10:38 pm, edited 2 times in total.


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Re: Quick white light and CaK images with a 140mm refractor

Post by JohnW »

Thanks for posting - some nice images presented, esp. the CaK image and the galaxy. Cheers, John W.


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Re: Quick white light and CaK images with a 140mm refractor

Post by ffellah »

These are very nice, well done !

Franco


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Re: Quick white light and CaK images with a 140mm refractor

Post by p_zetner »

Nice results, Douglas.
It may be that the Vixen objective is not particularly well optimized in the violet.
Cheers.
Peter


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Re: Quick white light and CaK images with a 140mm refractor

Post by thesmiths »

To Peter: I think you are correct about the violet. This Vixen telescope has two lenses in the front and then two lenses at the back to flatten the field. So that's a lot of glass. I was surprised to find that my triplet 107mm did so well with violet. The simple little lens on the CaK PST is amazingly sharp. Quite stunningly good CaK images from that little thing. I must go find it again, now that you remind me.


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Re: Quick white light and CaK images with a 140mm refractor

Post by DeepSolar64 »

I really like the tripod on your Vixen refractor. At one time wooden tripods were so much more common than they are now. I love the classic look and they dampen to vibration quicker than metal tripods do.

All of your images are nice and it's neat that you have assembled your filters on your own. It's probably a bit cheaper that way.

James


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Re: Quick white light and CaK images with a 140mm refractor

Post by MAURITS »

Lovely WL captures.


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Re: Quick white light and CaK images with a 140mm refractor

Post by Martin_S »

Nice captures , well done.

Martin


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Re: Quick white light and CaK images with a 140mm refractor

Post by thesmiths »

DeepSolar64 wrote: Wed Apr 28, 2021 4:27 am I really like the tripod on your Vixen refractor. At one time wooden tripods were so much more common than they are now. I love the classic look and they dampen to vibration quicker than metal tripods do.

James
The Berlebach tripods are amazingly nice! (German company found in 1898) They also tend to be shorter, which I think is generally more stable. Also, my wife says the wood makes it look like furniture so she doesn't mind having it around the house. Don't think she feels the same way about the original metal one.


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Re: Quick white light and CaK images with a 140mm refractor

Post by DeepSolar64 »

I am gonna have to check these out. I have heard of them before.


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Re: Quick white light and CaK images with a 140mm refractor

Post by Montana »

Terrific images and I really enjoyed the galaxies too :bow :hamster:

Alexandra


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Re: Quick white light and CaK images with a 140mm refractor

Post by marktownley »

Hi Douglas,

Nice shots! I wouldn't recommend such a fast large aperture with CaK in it's native form, it will certainly shorten the life of the blockers on there with large aperture / high f-ratio. My solution would be to stop it down, 70mm at 2000mm focal length will give you nice sampling with the 174. it will also be much more suited to your local seeing, which late afternoon, is highly unlikely to support 140mm aperture at 393nm.

Mark


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Re: Quick white light and CaK images with a 140mm refractor

Post by thesmiths »

To Mark: I agree; it was just an experiment since I had the telescope set up for evening use. I should have tried the aperture stop but I ran out of time since it was already late in the day.

Since I was using a Herschel wedge, I doubt the energy from this setup would damage the homebrew CaK filter. Do you not agree?


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Re: Quick white light and CaK images with a 140mm refractor

Post by eroel »

Douglas:
Beautiful images and setup.
Best regards.
Eric.


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Re: Quick white light and CaK images with a 140mm refractor

Post by Carbon60 »

Looking good, even if not yet totally optimised.

M51 looks resplendent.

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Re: Quick white light and CaK images with a 140mm refractor

Post by marktownley »

thesmiths wrote: Thu Apr 29, 2021 1:24 pm Since I was using a Herschel wedge, I doubt the energy from this setup would damage the homebrew CaK filter. Do you not agree?
Ahhh, didn't realise it was after a wedge, it will be fine then.


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