An 8 inch Hamburger (looking for help)

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Jockinireland Ireland
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An 8 inch Hamburger (looking for help)

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Post by Jockinireland »


So, despite getting my new short and fast refractor and NEQ6, I have spent some time trying to get my venerable old 8" LX200 GPS to take an image longer than 20s. I've put it on a wedge, done the Petersons Bucks Gears upgrade and added guiding through a guide scope. I got my first image from the set up on Sunday and I think while its promising there are still a few issues I need to resolve. Its noisy and I need to start dithering to get rid of some of the banding. I think the guiding was not awful (total RMS around 1.2" most of the time) but I know I can improve on that.

The biggest problem is what looks to me like horrible field curvature and coma. (Is that what I'm seeing or is it something else) I have a Meade 6.3 FR/FF in place and had really hoped it would be better but I'd like to hear your thoughts. Is this is good as I'm going to get in terms of flattening, or can I adjust (spacing for example) or do I need to tighten up my colimation. Any thoughts anyone?

Anyway here it is (I know its not great but putting it here to get advice)

8" LX200GPS f/6.3 FR/FF, wedged LX200 mount
EOS 1100D (un moded)
Guided in PHD2, Processed APP (this is not a full process - a very slight crop to remove some ragged edges and a quick run through APP- I think it could be improved but I'm not sure its worth the effort)
49 X 180s ISO800
hamburger_with_flats-mod-lpc-cbg-SC-St-first quick psj.jpg
So, thanks for looking and any suggestions or advice you can give (preferably not "stay with the 80ED and stick that hulk in a dumpster". I'm Scottish and therfore am genetically programmed to not throw things away! :lol: )

David
Scope: Skywatcher Evostar 80ED (SW 0.85 FR/FF) on a SW NEQ6Pro
Guiding; SW Evoguide 50ED, ASI 120mm mini
Meade 8" LX200 GPS on wedge (Guided with a cheapo 50mm guidescope and a ZWO ASI 120mm mini)
Sharpstar 61EDPH II (with dedicated 0.8 reducer) with wiliam Optics 32mm uniguide
Camera: ASI2600MC pro. QHY 163M with ZWO 7nm NB filters, Canon EOS700D astro mod
Secondary mount: Skywatcher StarAdventurer

My Astrobin https://www.astrobin.com/users/mackiedlm/
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MariusD69 Romania
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Re: An 8 inch Hamburger (looking for help)

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Post by MariusD69 »


Looks great! Well done, David!
Marius
Mount: iOpton Cem60, HEQ5-for spare
Scopes: newt SW 150/750PDS, dobson SW 150/1200; SW 114/500; TS Photoline 80mm f/6 Triplet APO; SW ST80
Cameras: ASI294MC Pro; ASI1600MM Pro; Atik 314L+mono; Canon 1100D; QHY5III-178m; QHY5L-II-m ; ASI224; Altair GPCAM 290M, GPCAM290C
Accessories: Baader MPCC; GPU KomakorrF4; TS Flat2; TS 0.79x FR/FF
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dritter
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Re: An 8 inch Hamburger (looking for help)

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Post by dritter »


It does look good indeed, but I do see what you mean by the problems out at the edges of the field.

I don't have definite solution but it is probably a good idea to check the collimation as a matter of course. It can't hurt and may well help.

Next up would be the FF/FR. FF/FR lenses usually have a very specific distance that the camera sensor needs to be at in order for them to correct properly. I don't know the specs for either your camera or the FF/FR you are using, but usually these can be found from the manuals or manufacturers websites. Once you know the correct distance setting, you can usually adjust the length of the optical train with appropriately sized spacers.

One other thing to check is the size of your sensor -vs- the size of the corrected light cone coming off the scope. If the sensor is too big for the corrected light cone, the edges will look horrible and there is not much you can do to directly fix it. But to work around it, you could crop the image or use a camera with a smaller sensor.

As for cutting down on the noise, more sub-frames should help that. In my experience, galaxies or detailed nebula need six or more hours before the noise really starts to disappear. Then another six hours to infinity to get more detail.

And your plan for more dithering is good too and should help even out the image somewhat. Plus better guiding always helps too.

So mainly my advice is this: keep doing what you are doing and tackle the problems in a methodical manner. You are on the right track. And the results in the center of the image are certainly showing well already. So, even if you're reduced to cropping, you can still get rather nicely detailed galaxies with the LX as things currently stand.
Dave
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Re: An 8 inch Hamburger (looking for help)

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Post by Jockinireland »


dritter wrote: Tue Mar 31, 2020 8:41 pm It does look good indeed, but I do see what you mean by the problems out at the edges of the field.

I don't have definite solution but it is probably a good idea to check the collimation as a matter of course. It can't hurt and may well help.

Next up would be the FF/FR. FF/FR lenses usually have a very specific distance that the camera sensor needs to be at in order for them to correct properly. I don't know the specs for either your camera or the FF/FR you are using, but usually these can be found from the manuals or manufacturers websites. Once you know the correct distance setting, you can usually adjust the length of the optical train with appropriately sized spacers.

One other thing to check is the size of your sensor -vs- the size of the corrected light cone coming off the scope. If the sensor is too big for the corrected light cone, the edges will look horrible and there is not much you can do to directly fix it. But to work around it, you could crop the image or use a camera with a smaller sensor.

As for cutting down on the noise, more sub-frames should help that. In my experience, galaxies or detailed nebula need six or more hours before the noise really starts to disappear. Then another six hours to infinity to get more detail.

And your plan for more dithering is good too and should help even out the image somewhat. Plus better guiding always helps too.

So mainly my advice is this: keep doing what you are doing and tackle the problems in a methodical manner. You are on the right track. And the results in the center of the image are certainly showing well already. So, even if you're reduced to cropping, you can still get rather nicely detailed galaxies with the LX as things currently stand.
Thanks for that dave, really helpful. I'll try and work out the spacing to see if I can get it closer. I "think" the collimation is ok but i was intending to check it soon. Clear skys are so rare here that I hate spending what little I have on maintenance type issues - but you are right - i should do it.

Thanks again.
Scope: Skywatcher Evostar 80ED (SW 0.85 FR/FF) on a SW NEQ6Pro
Guiding; SW Evoguide 50ED, ASI 120mm mini
Meade 8" LX200 GPS on wedge (Guided with a cheapo 50mm guidescope and a ZWO ASI 120mm mini)
Sharpstar 61EDPH II (with dedicated 0.8 reducer) with wiliam Optics 32mm uniguide
Camera: ASI2600MC pro. QHY 163M with ZWO 7nm NB filters, Canon EOS700D astro mod
Secondary mount: Skywatcher StarAdventurer

My Astrobin https://www.astrobin.com/users/mackiedlm/
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