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Eggy Stars


Nicho

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I've been strugling with this problem for a few months now .At first i thought it was that my field edges need correcting on my ed80 so i bought a skywatcher focal reducer but i still had the same problem. Then i looked at guiding i have a st80 piggybacking my ed80 but after playing about with phd and eqmod i still had no joy i was still getting eggy stars ! MY phd graph is good and my PA is pretty good also, but i havnt drift alighned which could be a problem ? I now think i have focuser droop .My Cannon 1100 isnt that heavy but i know that ed80's a prone to having problems with the focurser. Is there anything i can do with the focuser? or is it the case of saving the pennies for a Moonlight ?

Anyway looking at the picture ive posted it's a 1 min shot which i took lastnight of NGC 6960 i am getting eggy stars a little down on the bottom left and it getting slowly more eggy to top right . Ive tried 1min 3 and 5 min shots all look the same so my guiding is ok i think . I have also rotated the camera 90 deg and am still seeing the same problems

IMG_127234.jpg

I hope someone can shed a little more light on what im doing right or wrong

Thx Nick

Heq5 using eqmod and phd

Ed80 with reducer

St80 piggyback with a spc9000 webcam

Cannon 1100 unmoded

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I have struggled with eggy stars in the past and finally got it sorted.

You need to take very short (2-4s) exposures first to ascertain whether the problem is potentially with the scope. If you have eggy stars at such short exposure times, then you have a good indication that the problems lies with the scope, perhaps the focuser is not sitting square, or the camera, for example.

If the eggy stars only appear with longer exposures then it's something else. My cure for it was Polar alignment. Your comment that your PA is 'pretty good' suggests to me that it's a good place to start. I always thought my PA was pretty good, until I downloaded PEMPro and used it on their 60 day trial and I realised how 'good enough' does not cut it and it actually wasn't very good at all.

You can also take a number of 1 minute exposures and then stack them and then look at the movement on the axis. This will give you an indication of where you can start. Craig Stark has a good tutorial for this, which was linked in one of my posts about something similar. If it's not drift caused by polar alignment, then you're onto differential flexure.

Here's a couple of my posts that will be worth a read with all the information people posted.

http://stargazerslounge.com/topic/136176-drift-alignment-or-flexure/

http://stargazerslounge.com/topic/152425-do-these-videos-show-pa-issues/

Hope that helps.

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Well i've done my sums and Differential flexure is not the issue.

Spent most of this evening taking 5 sec shots and im still seeing eggy stars !

I've tried my setup up with the reducer screwed direct to the mount and also with the flo adapter and am getting varried results. I just seem to be having alot of trouble getting the camera to lay flat to the scope. Running out of idears here and am getting mightly confussed :eek:

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If you have eggy stars at 5 second exposures then that points to something in the optical train. The focuser is normally the weakest point, so I'd say start there first. Is there any focuser sag? If you turn the camera around by 180 degree's for example, do the eggy stars change corners?

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Thx sara for your reply and helping me out like this . This forum is great to have such friendly people on here willing to give there time to help other's .

I hope to do the same one day but still alot to learn .

Luckly i did just that last night and rotated the camera 180 degree's and the star's kept to the same dirrection of the chip on the camera .. ie the stars carried on being distorted at the top of the picture in one shot and on rotation the bottom of the picture .So would that make it the reducers fault ?

Thx nick

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I can not get my head around whether that means a problem with the focuser or not - I never worked it out.

Have a read through this thread where I suffered from similar issues and various suggestions there for testing and correction.

http://stargazerslounge.com/topic/120381-one-good-corner-when-not-using-a-reducer-how-come/

Do you have a reducer in the imaging train at this stage?

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Thx once again Sara

Looks like i have the same problems as you had . I will get myself i lasser later and give it a wirl :smiley:

And yes i do have the reducer in my train with a flo adapter also.

Thx Nick

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You're quite sure you have the correct chip distance for the reducer? In theory this should have a concentric effect but in reality it doesn't, you get a bad side or bad corner when it is a little out. (I have to do a lot of experimenting when reviewing scopes so I've seen this in all its forms!)

I think it will be non-orthogonality in the focuser myself, causing the chip to sit at an angle. The laser test is worth a try but it seems flawed to me. If the focuser and the light cone from the lens are on two slightly different axes (which may or may not be parallel) then all you will end up doing by altering the angle of the focuser is pointing the axis of the focuser at the centre of the lens. That does not mean that you have done anything useful. There will still be a tilt affecting the chip.

If you are lucky and, with the scope vertical (for the sake of argument), the lens is centred directly above the focuser then the laser test seems valid it me. But if the focuser does not sit directly below the lens then my flaw seems to apply. I'd be interested to hear what others think and have no guarantee that I'm right here.

There are so many of these threads that we begin to see why having an expensive focuser is a good idea. The manufacturers are trying to cut costs too far and offering dreadful focusers, many of which just don't work. We should give them our collective permission to charge a bit more and get Baader Steeltrack quality. That is a good focuser at a decent price, even if it is a Crayford!!

Olly

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Nick,

The sample image you posted seems pretty good to me! (perhaps the elongated stars can be seen by zooming in?)

I suggest that you don't get yourself bogged down with trying to achieve perfection - go out an image instead! One can become obsessed with this kind of stuff and before you know it another imaging season has passed!

Happy imaging,

Paul.

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Zooming right in it seems that it's the fainter stars that appear to be most affected - and then the very faintest ones show only a very faint bit below what might the main portion of the star. So it's sort of reminiscent of a double image due to movement.

So I'm wondering - do you operate the camera by hand or use an external shutter controller? (You could try the free 30 days of Backyard EOS)

Have you tried setting mirror lock to up?

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Just had a quick scan through this post & I think I may have posted some info in one of the links Sara posted ( sry havn't followed it through) Anyway, I had pretty much the same issue with my ED80. The focusser wasn't square to the tube & after using the Hotech laser to fix that I found the lens cell wasn't screwed in quite right either. I unscrewed it and cleaned the threads of paint flakes and refitted it. It fixed the problem in the corners with the stars. I also now use one of these to get a much better attachement of the reducer/flo adapter.. well worth it.

http://www.365astronomy.com/2-clicklock-m56-clamp-for-celeston-skywatcher-telescopes-p-1913.html

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Nick,

The sample image you posted seems pretty good to me! (perhaps the elongated stars can be seen by zooming in?)

I suggest that you don't get yourself bogged down with trying to achieve perfection - go out an image instead! One can become obsessed with this kind of stuff and before you know it another imaging season has passed!

Happy imaging,

Paul.

Paul your quite right i really shouldnt beat myself up about it . 6 months ago i would be over the moon with this shot !

Maybe im being too pickie ,it certainly got me frustrated last night .

I just thought i would get a better picture for paying £165 for the reducer instead of more problems :shocked:

Thx Nick

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Zooming right in it seems that it's the fainter stars that appear to be most affected - and then the very faintest ones show only a very faint bit below what might the main portion of the star. So it's sort of reminiscent of a double image due to movement.

So I'm wondering - do you operate the camera by hand or use an external shutter controller? (You could try the free 30 days of Backyard EOS)

Have you tried setting mirror lock to up?

Thx for your comments squeaky

Yes ive used backyard eos in the past didnt really get on with it but i do recall it can setup a mirror lock in the routine ? as the cannon 1100 does not have a mirror lock built in .

Thx Nick

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Just had a quick scan through this post & I think I may have posted some info in one of the links Sara posted ( sry havn't followed it through) Anyway, I had pretty much the same issue with my ED80. The focusser wasn't square to the tube & after using the Hotech laser to fix that I found the lens cell wasn't screwed in quite right either. I unscrewed it and cleaned the threads of paint flakes and refitted it. It fixed the problem in the corners with the stars. I also now use one of these to get a much better attachement of the reducer/flo adapter.. well worth it.

http://www.365astron...pes-p-1913.html

Thx Sp@ce_d i will look into that .

I've never taken off the lense cell is it as simple as screwing it off ? or is there any more too it ?

Thx Nick

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Yes, BY EOS has a mirror lock option - but I don't know if that will work if the option is not already available on the camera.

So you are operating the camera photo button by hand? If so... you could try setting a ten second delay before the camera takes the photo. It "might" be that no matter how gentle you are there's a bit of shake that takes a while to subside?

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You're quite sure you have the correct chip distance for the reducer? In theory this should have a concentric effect but in reality it doesn't, you get a bad side or bad corner when it is a little out. (I have to do a lot of experimenting when reviewing scopes so I've seen this in all its forms!)

I think it will be non-orthogonality in the focuser myself, causing the chip to sit at an angle. The laser test is worth a try but it seems flawed to me. If the focuser and the light cone from the lens are on two slightly different axes (which may or may not be parallel) then all you will end up doing by altering the angle of the focuser is pointing the axis of the focuser at the centre of the lens. That does not mean that you have done anything useful. There will still be a tilt affecting the chip.

If you are lucky and, with the scope vertical (for the sake of argument), the lens is centred directly above the focuser then the laser test seems valid it me. But if the focuser does not sit directly below the lens then my flaw seems to apply. I'd be interested to hear what others think and have no guarantee that I'm right here.

There are so many of these threads that we begin to see why having an expensive focuser is a good idea. The manufacturers are trying to cut costs too far and offering dreadful focusers, many of which just don't work. We should give them our collective permission to charge a bit more and get Baader Steeltrack quality. That is a good focuser at a decent price, even if it is a Crayford!!

Olly

Thx Olly

I talked to Martin @ Flo today and he suggested i started off with a Star test which should tell me if the telescope is out of collimation or not . Which is a great way to start .

Your point about chip distance im not quite sure on .Im still trying to find out what it should be for my cannon 1100 .

My current train in reducer, skywatcher DSLR m48 ring adapter , camera

Thx Nick

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Yes, BY EOS has a mirror lock option - but I don't know if that will work if the option is not already available on the camera.

So you are operating the camera photo button by hand? If so... you could try setting a ten second delay before the camera takes the photo. It "might" be that no matter how gentle you are there's a bit of shake that takes a while to subside?

No at the moment im using the eos utility remote shot with a usb cable

Thx Nick

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Thx Sp@ce_d i will look into that .

I've never taken off the lense cell is it as simple as screwing it off ? or is there any more too it ?

Thx Nick

Yup it just unscrews. threads fairly fine so watch you dont cross thread. If I remember rightly the Sensor to reducer/flattener spacing should be 55mm. Well, at least with my 1000D.
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If I remember rightly the Sensor to reducer/flattener spacing should be 55mm. Well, at least with my 1000D.

What did you have in your image train ? did it differ from mine ?

Thx Nick

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Space-d's point really confirms what I was thinking about myself. You need to be sure that the light cone from the lens is pointing straight down middle of the tube and that the focuser is pointing straight up the middle of the tube. If the beam is not coming straight down the middle of the tube or either the lens or the focuser is shifted off axis then the laser test will not be valid.

So, what about starting with the inverse of the laser test to see if the incident beam is on-axis? Would it be possible to put a translucent centre-dotted screen across the EP holder and then focus a bright light source onto that screen to see if it arrives in the middle? I wondered about putting Baader film over the objective and then using the sun. As for the screen, maybe one could cannibalize an old EP and replace the lenses with a single flat glass (or even plastic) screen. If the beam does hit the centre of the screen than it seems unlikely to me that the laser test would be invalid since I don't see either the lens cell or the focuser being far off axis.

I'm just thinking aloud, not having tried any of this!

Olly

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What did you have in your image train ? did it differ from mine ?

Thx Nick

DSLR - T-adapter/M48 ring adapter - reducer

That should give you 55mm sensor to reducer. Anything else has to go in front of the reducer ie. I have a FLO-adapter with filter then into the focusser via the clicklock m56 clamp ( it really is so much better than using the weedy 2 screws on the factory fitted clamp)

I think Ollys idea is pretty much what I did using the Hotech laser... instead of the Sun. ( I live in Scotland, FLO can ship stuff to me far quicker than it takes light from the Sun to make an appearance.. :rolleyes: )

I found Saras thread I was thinking of yesterday.. There's some pics I posted of how I checked it.

http://stargazerslou...me/page__st__40

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Just a little update

I did the star test buy letting the telescope cool and making sure i wasnt pointing over the house. Found a fairly bright star and defocused it slightly and it all loks nice and round .

So i bought the Click lock clamp (which is an excellent upgrade thx sp@ce_d for the heads up ! It really should be fitted onto all ed80's it is a joy to use over the floppy screws )

Still not getting perfect stars but are looking quite abit better

Here's my first go at ngc7000

10x600

Still got a long way to go on the processing yet . Taking the picture is only half the battle :)

america241.jpg

Thx Nick

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