Eggy stars - Not sure why. - Forums

Hi All.

I’ve just stated imaging on my Skywatcher 190MN and ASI533MC Pro and I’ve got to say, I’m not too impressed with these stars. This is just a single 300 second auto-stretched sub straight from ASIAir. Can anyone advise as to what the cause might be? I’m suspecting tilt as I have the standard crayford focuser, which is supposed to be terrible for imaging. Is there some kind of application I can run the image through to give me some insight?

The guide stars don’t look great either despite me using the focus feature to get the star size as small as possible. Maybe this is the cause?

Look up the ASTAP app. Don’t take my word, but my understanding is that phd2 doesn’t need perfect stars to guide due to the math it uses. It looks like tilt to me ¯\_(ツ)_/¯

NINA has the tool (Hocus Focus) but I never used it (in fact I don't do auto-focus). The stars don't look too bad to me, maybe a little tilt upper right - lower left.

Sean’s suggestion is a good one. You may have tilt/sag in system. Stars on left edge of frame look less “eggy” than the right.

The stars don't look too bad to me either, but I see as starfield mentioned that the right side look the most eggy.
The ASTAP app as Sean mentioned, is great. This is my first time looking at tilt with this tool and this is what I see in your image.

I looked at a bunch of my images and I see varying amounts of tilt in all different directions, but the stars look good.

EDIT: Just want to mention. BlurXterminator will help correct some of the eggyness.

Jim

I saw Eggy Stars in '74 opening for The Who at Hammersmith.

But seriously (mostly), where you have eggs, I have the whole bird. I will be definitely checking out the Astap inspection feature. I've only used Astap for plate solve.

Thanks for all the replies. I've just downloaded ASTAP and opened a random FITS file from the other night. This doesn't look good to me. Anyone know where I need to start looking? I suspect the focuser as it has a lot of wobble. Could collimation be out?

BlurX usually does a fantastic job but I was reading about IOTD and the first in the list of criteria was perfect stars. Although I don't think I'm at a level where I should be submitting images yet, it seems like a good thing to work towards in terms of a target.

On another note, are there any 190MN users here that can recommend a better focuser? I've read about the Moonlite and feather touch but both are nearly impossible to get hold of. FLO recommended a Baader Steeltrack

This a Maksutov-Newton so intrinsically aplanatic, i.e., no coma, so collimation requirements are rather weak but tilt still needs to be corrected in order for everything to work out as it should. If the focus extraction is large enough then the Baader should do the trick if you suspect that the stock focuser has unacceptable slop (that is if it is wobbly). If it is a more a matter of focuser tilt then your best bet is to add a tilting unit to your existing imaging train.

I just finished working thru a tilt issue with my system (Esprit 100 refractor). On thing I did was to look at images at zenith to try and eliminated any tilt coming from sag/slack in the focuser/imaging train. I found that the tilt did not really change, so this let me focus my attention on the OAG/Filter Wheel/Camera connections and not have to worry so much about the focuser.

I'm not sure how to test the focuser/image train contribution on a MN. I'm thinking that you might learn something if you run ASTAP on frames captured low on the horizon and at zenith. I would think any sag/focuser slop would get worse as you get closer to zenith and the imaging train becomes parallel to the ground with more strain on focuser.

Maybe some MN or Newt owners can chime in here.

Steve

I just finished working thru a tilt issue with my system (Esprit 100 refractor). On thing I did was to look at images at zenith to try and eliminated any tilt coming from sag/slack in the focuser/imaging train. I found that the tilt did not really change, so this let me focus my attention on the OAG/Filter Wheel/Camera connections and not have to worry so much about the focuser.

I'm not sure how to test the focuser/image train contribution on a MN. I'm thinking that you might learn something if you run ASTAP on frames captured low on the horizon and at zenith. I would think any sag/focuser slop would get worse as you get closer to zenith and the imaging train becomes parallel to the ground with more strain on focuser.

Maybe some MN or Newt owners can chime in here.

Steve

*(since I'm both a MN and a Newton owner)

I'd test for focuser sag the way you suggested, but in more progressive fashion: from 30 deg above the horizon , then 45, 60 and finally 90 (zenith).

I have the MN190 and use it with a 2600MC, a filter drawer, and an OAG. Optically, the design has a lot of advantages, but the stock focuser is not robust enough for AP. I bit the bullet and replaced mine with a FeatherTouch (FTF2020BCR) and been very happy with it since. FT makes an adapter so you do not need to replace base of the stock focuser, which makes the whole process a lot easier: https://www.starlightinstruments.com/product/a20-mn190-adapter-2-0-for-mk190-maksutov-newtonian-intes-alter-mn84-mak-newton-es8-astrograph-w-cf-ota/

Christopher Dietz:
I have the MN190 and use it with a 2600MC, a filter drawer, and an OAG. Optically, the design has a lot of advantages, but the stock focuser is not robust enough for AP. I bit the bullet and replaced mine with a FeatherTouch (FTF2020BCR) and been very happy with it since. FT makes an adapter so you do not need to replace base of the stock focuser, which makes the whole process a lot easier: https://www.starlightinstruments.com/product/a20-mn190-adapter-2-0-for-mk190-maksutov-newtonian-intes-alter-mn84-mak-newton-es8-astrograph-w-cf-ota/

Thanks for this. A feather touch would be great but they seem to be impossible to find, especially in the UK.

Thanks all of the help. I'm trying to diagnose this tilt issue so I took a quick exposure, then manually rotated the camera approx 90 degrees and took another. Here are the results of the two images from ASTAP. the trouble is, I don't really know how to interpret these results. My thought are that is the tilt is on the same side in these two images, the cause is probably slop. If the tilt rotates as I rotate the camera, the tilt could be on the camera itself. That said, I get very little tilt when I use the camera on my SW 72ED refractor. This has a threaded connection though whereas the 190MN uses a retaining ring.

Another note, I would the scope used and, although I know they hold their collimation really well, I haven't checked this yet. The society I belong to has an OCAL Pro so I'm borrowing this on Friday to check. Could bad collimation be the cause of tilt?

Definitely not the camera. I’m guessing either the focuser/rotator or collimation? ¯\_(ツ)_/¯
I’d love to know everyone else’s opinion as well.

Craig Dixon:
Thanks all of the help. I'm trying to diagnose this tilt issue so I took a quick exposure, then manually rotated the camera approx 90 degrees and took another. Here are the results of the two images from ASTAP. the trouble is, I don't really know how to interpret these results. My thought are that is the tilt is on the same side in these two images, the cause is probably slop. If the tilt rotates as I rotate the camera, the tilt could be on the camera itself. That said, I get very little tilt when I use the camera on my SW 72ED refractor. This has a threaded connection though whereas the 190MN uses a retaining ring.

Another note, I would the scope used and, although I know they hold their collimation really well, I haven't checked this yet. The society I belong to has an OCAL Pro so I'm borrowing this on Friday to check. Could bad collimation be the cause of tilt?

The source is most like located in the focuser connection, which is a likely culprit in most cases. Turning the scope around won't show much if you remove it from the focuser as the tilting will change at random directions. So, either your find a way to use a threaded connection between imaging train and focuser or replace the focuser with one that has (or it is better anyway). Or add a titling unit. If you want to test for focuser slop follow the recommendations some of us gave before in this thread.

Collimation isn't the issue you have here, as far as I can see.

Hi,

I also have the Skywatcher MN190 - which has an extremely good optical design. It is both a good performer in deep sky (with no coma) and on planets, as it is razor sharp on axis.
But I did replace the focusser by a Baader Steeltrack quite soon, as the stock focuser is too tilty. The stock focuser looks much more robust than it really is.
The Steeldrive gives an additional better control, as you do not need to touch the OTA: strongly recommended.
For the Steeldrive, there is a good replacement option for the MN190, whereas for the Feathertouch you need to tinker with adapter material - as I heared. Anyway, the Feathertouch was - for my understanding - way too expensive. So I went the upgrade path with the Steeltrack - maybe not as good as a Feathertouch - but good enough for my deep sky and planetary work.

CS

Markus

Markus A. R. Langlotz:
Hi,

I also have the Skywatcher MN190 - which has an extremely good optical design. It is both a good performer in deep sky (with no coma) and on planets, as it is razor sharp on axis.
But I did replace the focusser by a Baader Steeltrack quite soon, as the stock focuser is too tilty. The stock focuser looks much more robust than it really is.
The Steeldrive gives an additional better control, as you do not need to touch the OTA: strongly recommended.
For the Steeldrive, there is a good replacement option for the MN190, whereas for the Feathertouch you need to tinker with adapter material - as I heared. Anyway, the Feathertouch was - for my understanding - way too expensive. So I went the upgrade path with the Steeltrack - maybe not as good as a Feathertouch - but good enough for my deep sky and planetary work.

CS

Markus

That's really good to hear, thanks.

This is the focuser that was recommended. Is this the one you have?

https://www.firstlightoptics.com/baader-diamond-steeltrack-focusers/baader-steeltrack-diamond-nt-for-newtonians.html

I read online somewhere that you need to but the OTA to get this to fit though so it put me off. Did it just slot straight in when you fit yours and did you have to re-collimate or move the corrector plate?

Yes, this is the focusser I have. But the predecessor version which was not named "Diamond" ten years ago.
But the steeldrive I have is also compatible to the old and the new version.

So, yes, you can go with that.

CS

Markus

Markus A. R. Langlotz:
Yes, this is the focusser I have. But the predecessor version which was not named "Diamond" ten years ago.
But the steeldrive I have is also compatible to the old and the new version.

So, yes, you can go with that.

CS

Markus

I've read a few accounts online of people saying this isn't a direct replacement and that holes need drilling. Did you just literally just bolt yours on?

Mine was attached by TS (my dealer) as a direct replacement, which did not need any drilling. They sold it as optional upgrade, which I let them install appx. 1 year after purchase.
Maybe the new Diamond version has a different base? Could be a good idea, to contact your dealer respectively.

CS

Markus

Is your guiding consistently under .76"?

Is your guiding consistently under .76"?

Nearly always. I'm usually getting about 0.3 total rms.