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These irritating spikes

Mark72

By Mark72
in Imaging - Discussion

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D_Mike

D_Mike

Posted
Posted

You see the twiggy stick things across the front of your telescope? Chop them off?

More seriously, I don't know, is there some sort of Fourier transform process that can be used to remove them?

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Gina

Gina

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When I saw other images of yours I thought the diffraction spikes didn't look as bad as I've seen with Newts and wondered if the RC design was better in this respect. It's certainly better in other respects - much better image quality and shorter and lighter.

If there were some way of processing these thing out I think it would be very interesting. Some time in the future I may be looking at a bigger scope but I can't stand the spikes - quite a handicap!

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Mike_F

Mike_F

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Posted
Take some subs, rotate the scope in the tube rings, take some more subs which will thus have the spikes at a different angle, and process from there?

Dithering out the diffraction spikes effectively? Nice idea.. Could also just rotate the camera slightly in the focuser - might save a re-balance.

Thinking about it, is rotation necessary at all? Wouldn't just ordinary dithering by a larger than normal amount do it? If all you want is a data source that contains what was behind the spikes to clone from, can't see why that wouldn't work.

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Mark72

Mark72

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Thanks for suggestions guys,

I really like the small spikes but this one was over the top. Apparently too bright a star for too dim a nebulosity around it.

May be I should treat them as satellites trails. Should be a tutorial how to deal with them.

Mark

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IanL

IanL

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No dithering by a larger amount wouldn't work; the spikes move with the stars so it would make no difference. Rotating and using an appropriate pixel rejection algorithm should work, since the spikes will be in different orientations on different subs. You'd have to experiment with the algorithm used though. Some kind of outlier rejection type algorithm would work better than a simple averaging one.

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IanL

IanL

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Should have said; rotate the OTA by 45 degrees, then rotate the camera back the other way by 45 degrees to keep the same framing. If the spikes are are corner to corner (as in your current shot) in the first set of subs, then they will be straight up/down/left/right in the second set. The framing of the field will be the same so you won't end up having to crop down (if you just rotate the camera OR the OTA, then you're only going to end up with an octagonal area in the middle of the frame that is common to both sets).

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Jessun

Jessun

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Move the kit back from Arizona, to more murky skies :p

You could put an Optec Pyxis rotator in the train? Select the star and spikes, feather, and down the curve a bit for the bright? PS content aware fill?

/Jesper

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SnakeyJ

SnakeyJ

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I was reading on the Obsession web site that curved spiders that reduce/eliminate the issue on their big dobs. I think Destiny make a range for retrofitting http://www.1800destiny.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=1D&Category_Code=CVS

Presumably however thin and curved you still have some obstruction and effect, though perhaps this gets blurred out - has anyone had any hands on with these or seen a good review?

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D_Mike

D_Mike

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The curved thingies give you a diffraction 'halo' rather than spikes, so the diffraction is still there just manifested in a different way. I guess the halo could be easier to remove in processing, I don't know (since I know very little).

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ollypenrice

ollypenrice

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I suspect you could make a layer underneath, apply the dust and scratches filter till the spike disappeared, and then erase the spikes from the top layer. You'd then have to replace any stars lying on the spikes with a layer on top.

Alternatively, beg or borrow a refractor colour layer from somewhere, or shoor one yourself, Registar it to fit the new image, paste it underneath and erase the spikes.

No quick fix! I've donated a spike (or actually a flare) - free image to a friend who pasted it underneath and erased his flares.

Olly

Or another idea; maybe put a copy layer on top and then offset the layer underneath by enough pixels to mean you could then erase the spikes from the top layer? Just a guess.

Cracking collimation and focus, anyway, Mark!

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ollypenrice

ollypenrice

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I tried the Dust and Sctratches idea. It has promise. Copy layer and blur the bottom one in dust and scratches then erase the spikes in the top layer. It might be worth adding a bit of noise to the dust and scratches layer. This was just from a screen grab of yours. Hope that was OK. How well it would work on a serious quality file I don't know. One down, three to go!

Olly

mark%20one%20down-M.jpg

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