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PST single stack vs double stack

Montana

By Montana
in Imaging - Solar

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Montana

Montana

Posted
Posted

It's slow going at the moment but I am finally processing pictures from last Sunday 21st October.

I took 2 photographs with my PST and DMK41 camera (gamma 100 default). Both had exactly the same processing in Registax 5 with multi point alignment. In wavelets I used wavelet 6 to point 15. Then in Photoshop CS5 a small use of Smart sharpen to taste, then adjusted brightness and contrast in the same way, then levels to colour.

Single stack

8135905778_15f7029ddf_b.jpg

2012-10-21 13-42-37 Single stack f colour by Alexandra's Astronomy, on Flickr

Double stack

8135882761_8cb107cd9b_b.jpg

2012-10-21 13-53-01 DS f Colour by Alexandra's Astronomy, on Flickr

In the single stack the image is clearer and more even, but filaments, plage and prominences are less evident. In the double stack the image is slightly blurred on the left, but more filaments, plage and prominences are visible. Both have their plus points but I hope this will highlight the difference between <1A (single stack) and around 0.5A (double stack) in hydrogen alpha and the difference it makes in imaging and visual in my experience.

Kind regards

Alexandra

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JamesF

JamesF

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Indeed they are.

I wonder if the slight blurring in the second image might be an alignment issue with the filters, Alexandra? Could the additional elements be doing something that causes a slight misalignment of the image plane with the camera sensor?

James

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DrRobin

DrRobin

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To get prime focus with a DMK and a PST, you have to shorten the eyepiece holder. You can either saw or grind about 5mm off the top or you can do what I did which was to go to an [astro] engineering company and get them to make you a new one.

I had a first prototype a couple of weeks ago, but it needed a small adjustment and I am hoping the replacement will be here soon. It is exactly the same as the original, only 5mm shorter. It should become a product (not made by me) in the next few weeks and I can PM you with the details if you like?

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Montana

Montana

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Thanks everyone for all the great comments :)

Yes, I would very much like to know what causes this blurring on one side as it is very apparent when using a 2x Barlow and almost gives a double image effect. This is why I have stopped for the moment taking close ups and kept to prime focus. To achieve focus I use a short shoulderless nosepiece available from Modern Astronomy which didn't cost very much http://www.modernastronomy.com/camerasAstroVideo.html#mintron12v if you scroll down it is the first item under the Accessories for Astrovideo cameras 'short c mount'.

In the DS image the bright red area at top right is the ghost, unfortunately for me this ghost is right over the main image when fully on-band and I have to tease it just out of the way whilst keeping the features OK (compromise) but sometimes I forget.

When imaging the single stack (depending on the seeing which can vary) I usually use around 1/455 second, with the double stack it drops to around 1/150 ish (can't remember the exact figures) so both are taken at the full 15fps. I usually take around 1000 frames and stack the best 100-200. I use the Guassian wavelets and don't change the centre value.

I hope I haven't missed anything, just remind me if I have :)

Regards

Alexandra

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DrRobin

DrRobin

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You are lucky to be able to get a DMK to come to prime focus on a stock PST, I can't, even with a short C nosepiece and butt up against the eyepiece holder. I still had to use a Barlow until I got the shortened eyepiece holder, seems that there is some variance in pentaprism position that means some people can get prime focus whilst it appears most can't.

Even with my short nosepiece, I find it is still too long for my Focal Reducer/screw in Barlow and I get a lot more reduction/magnification than quoted. Ideally, I would like to get my focal reducer a lot close to the chip to achieve a smaller reduction, say about 0.8, rather than 0.5 or less. I noticed that the stock nosepiece supplied with a DMK camera is actually threaded all the way down, so chopped a spare around 20mm off one last night with a hacksaw. It still needs a little tidying up and the FR is a little tight in the threads until they get re-cut, but it looks like it is going to work great.

Interesting as Opticstar (also in the US www.opticstar-ccd.com ), sell two items that might be of interest, the first is a C thread FR ( http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Imagers-Opticstar.asp?p=0_10_5_0_3_510 ) which puts the FR very close to the camera body and the second is a C to 1.25" adaptor, that has a threaded ring, into which a FR or barlow lend could be inserted, again close to the camera body. ( http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Imagers-Opticstar.asp?p=0_10_5_0_3_103). Note that an FR would not work in a PST, but a Barlow lens would.

The latter appears to have a shoulder, so it might not be able to reach prime focus in a PST.

Hope this helps.

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thenews24

thenews24

Posted
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I'm stil confused as seeing how everybody has misinterpreted what I'm asking.

I never asked, how to get prime focus. I'm asking how its possible to get full disc detail on all corners of the disc, while at prime focus. It's pretty much impossible with a rear ended etalon.

I'm at aww you are able to capture detail on all four corners of the disc without doing mosaics.

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Merlin66

Merlin66

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The diameter of the solar disk is approx 1/100 the focal length of the scope.

Compare this wiith the size of your CCD chip - that will tell you if it's physically possible.

(You could use an eyepiece reducer to bring the effective focal length down)

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DrRobin

DrRobin

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Hi,

I haven't tried my DMK41 on a PST, it arrived after I had bought a Lunt. I don't think my PST has a big enough Sweetspot to allow the full disc in one go with much detail and I would almost certainly need to take a flat, to make it work.

My Lunt, which is basically the same design can take a single image of the whole disc with good detail across the whole frame, so in theory it should be possible. I did see one posting where the author rotated the tuning ring whilst taking the video to ensure that the whole of the disc was on-band at least some of the frames.

I have seen some afocal pictures of the whole disc on a PST which show good detail so it must be possible.

I hope this helps.

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Montana

Montana

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Mmmm I'm not entirely sure what you mean? Here is an image I took a while ago as it shows a full DMK41 frame (rather than cropped above) to show the scale. To get the Sun in the sweet spot I always have to hug the right hand side not the middle. This is why I have started cropping to make it neater.

6607290195_c8be5cda05_b.jpg

2011-12-28 11-13-38 by Alexandra's Astronomy, on Flickr

Other than that I have no idea?

Alexandra

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Montana

Montana

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Hi Mark,

In Photoshop go to

Image / adjustments / levels

Change the channel to red, then change the middle value to 1.6

Change the channel to green, and change the middle value to 0.7

Change the channel to blue, and change the middle value to 0.2

Then adjust brightness/contrast to how you like it.

I also have some variations (depends on the picture) with it being 1.7, 0.7, 0.2 or 1.7, 0.6, 0.2

Kind regards

Alexandra

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msh1

msh1

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Hi Mark,

In Photoshop go to

Image / adjustments / levels

Change the channel to red, then change the middle value to 1.6

Change the channel to green, and change the middle value to 0.7

Change the channel to blue, and change the middle value to 0.2

Then adjust brightness/contrast to how you like it.

I also have some variations (depends on the picture) with it being 1.7, 0.7, 0.2 or 1.7, 0.6, 0.2

Kind regards

Alexandra

thanks for that i will give it a go soon let you know how i get on

mark

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robindurant

robindurant

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Hi I am most impressed with your results. I have a PST with a DS using DMK 31 but with my set up I can't get the whole of the Sun in the frame so I am plagued with the sweet spot being on only half of my image so I have to take mosaics which I don't find satisfactory. Do you use a focal reducer to get the Sun well in the frame or does the DMK 41 have a larger FOV. Can a FR be sed anyway?

Thanks

Robin

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