Weird shaped stars.

[emyliano2000]

Hi guys. I seem to have a problem with the shape of the stars. 

After building my light box I decided to have a go at the horsehead nebula to see if I can get rid of the dust doughnuts.

First of all excuse my interpretation and my editing skills as I'm only a newbie but any coments on that would be appreciated too.

Seems that my light box works but now I don't know why my stars are not centered to that circle shaped aura around them.

I collimated my scope with a hutech laser but I'm thinking that when I slide the camera inside the focuser the compression ring from the adapter is pushing it to one side instead of keeping it center? 

I'm using a Baader mpcc with a 9mm OAG for eos. Just to point out another thing, the bayonet adapter from the OAG doesn't fix very tight on the eos so I get a bit of flexure on that too.

15x300sec at 400 ISO and 10x300sec at 800 ISO with 50 flats and 50 bias all stacked and preprocessed a bit in dss.

My equipment is in my signature.

Thanks. Emil

[cjdawson]

There's a few things that spring to my mind about the star shapes.  Here's what I'm wondering about.

1. is there coma in the image?

2. is the camera sensor flat to the focal plane?

3. is the collimation when the camera is in the focusser?

 

The reasons why these are crossing my mind...

coma, looking at the brighters stars, the halos are offset.  top of the image, they're are raised up, on the top right, it's pushed to the right.  This could be an indication of coma or something similar.

Camera tilt can happen when you attach a camera with a thumbscrew.  Personally, I've been attaching my camera with a threaded connection - dead easy with a DSLR, for my Starlight express, I'm using a C-Thread to T-Thread adapter.  This gives a more secure connection too.

The collimation part is because you mentioned using a lazer collimator.  I've not had much experience with those things before, but my personal experience is that nothing beats a good old fashioned star test, in your case this would be done with the camera to ensure that the scope is collimated to the camera, not to a light eyepiece.

[emyliano2000]

3 hours ago, cjdawson said:

1. is there coma in the image?

I'm using a mpcc. 

I replaced the original 2" adapter with the compression ring 2" adapter from flo in the hope that I would be able to somehow center the camera to the focuser draw tube.

It didn't happen so I bought a 35mm self centering 2" extension tube to try and keep it all the time inside the focuser and align everything with the hotech laser collimator  but unfortunately I can't focus the camera if I'm using the extension tube.

It looks like I bought the hotech laser and the 35mm self centering extension tube for nothing.

What would be the solution to center the camera with the focuser draw tube when I'm using the OAG and the Baader mpcc?

This is how my OAG + MPCC look like. Im inserting the MPCC into the draw tube and I tighten the compression ring but I think it's pushing it to one side.

[emyliano2000]

3 hours ago, cjdawson said:

2. is the camera sensor flat to the focal plane?

I hope it is. I don't know how to check it.

[emyliano2000]

3 hours ago, cjdawson said:

3. is the collimation when the camera is in the focusser?

I have to find a way to do it. I bought the self centering extension tube to be able to do it without the camera connected but I can't focus if I'm using it.

[emyliano2000]

How can I align the mirrors with the dslr in place? Is there a 2" low profile self centering adapter out there that I can screw to the focuser draw tube? Do I need to upgrade the focuser to a low profile one to be able to use my 35mm self centering extension tube? If so which one would be good for my 200p without breaking the bank?

Emil 

[alacant]

Do you mean the halos around the stars are not concentric with the star? I think that's a 'feature' of the coma corrector. Do you have a shot without the cc to compare? HTH.

[emyliano2000]

1 minute ago, alacant said:

Do you mean the halos around the stars are not concentric with the star? I think that's a 'feature' of the coma corrector. Do you have a shot without the cc to compare? HTH.

Unfortunately I don't have one. I'll have to try it on my next night out with the stars.

I upgraded my kit al at once and I didn't think of taking some shots without the cc as I only seen good reviews about it. Never thought it might cause a problem.

[emyliano2000]

Thinking about it I can't try some shots without the mpcc as I need an extension tube or something to connect the oag with the focuser and I don't have anything of that sort. At the moment the mpcc goes inside the focuser and removing it won't  leave me with anything to connect the oag to the telescope. 

Can the mpcc really cause this?

I measured the spacing from the mpcc to the camera sensor and I have 55.8mm.

[alacant]

1 hour ago, emyliano2000 said:

the mpcc goes inside the focuser

Hi. Any 2" extension which fits the screw thread on your eos would do.

 

1 hour ago, emyliano2000 said:

Can the mpcc really cause this?

It's the only other variable in the path so before going at the hardware, it may be better to confirm. I see a similar but less pronounced effect with my mpcc. HTH.

[Waldemar]

What I notice on high magnification is that the stars in all corner are a bit elongated to the middle except in the top right corner.
To me that means first of all the distance to the cc is not exactly right and it is not perpendicular to the sensor, just a tiny bit off. Could be your focuser hangs a bit, or the cc not tight enough in the threads
even a dust particle between connecting surfaces can cause this
The distance to the sensor should be 56 mm, but it may vary a bit. The only way to get ot really right is through trial and error.

The best way to get this right is to use a adjustable spacer like these: http://www.baader-planetarium.com/en/baader-varilock-29-lockable-t-2-extensiontube-20-29mm-with-spanner-tool-(t-2-part-25y).html 
or these: http://www.baader-planetarium.com/en/baader-varilock-46-lockable-t-2-extensiontube-29-46mm-with-spanner-tool-(t-2-part-25v).html

As  far as the halo's concern:  Those are reflections in your image train. Can be a filter or the cc that causes it.  Happens a lot with those really bright stars. Only in the middle of the image they will be concentric with the star itself. The further to the edge, the further out of concentricity, because of the light angle. 

[emyliano2000]

5 hours ago, Waldemar said:

The best way to get this right is to use a adjustable spacer like these: http://www.baader-planetarium.com/en/baader-varilock-29-lockable-t-2-extensiontube-20-29mm-with-spanner-tool-(t-2-part-25y).html 
or these: http://www.baader-planetarium.com/en/baader-varilock-46-lockable-t-2-extensiontube-29-46mm-with-spanner-tool-(t-2-part-25v).html

I have no idea how I would be able to achieve the 55mm (+/-1) from the mpcc to the sensor with the oag in between them.

[Uranium235]

Compression rings.... the work of the devil!!!

It would have been better to drill and tap a third hole in your original push-fit adaptor for another thumbscrew.

To help with the slop between your bayonet adaptor and camera, cut out a thin plastic ring with a notch in it (to accomodate the locking pin) from an ice cream container lid (tesco own brand is ususally quite thin plastic) and insert that between the bayonet adaptor and your camera - that should take the play out of it.

In regard to the off axis halos, do your collimation with a cheshire first - only using the laser to check or make minor adjustments. When using the self centering adaptor, dont do it up too tight as that may skew the the collimator - just do it up enough so you can still just about rotate the laser in the adaptor. While rotating the laser, check the dot on the primary to see if its scribing a circle.... if not, all is good and you can continue with your collimation.

Some degree of off axis halos away from the centre of the field are to be expected on all but the highest quality optics since it is a reflection off a flat surface (ie: filter) on to a curved surface (the rear element of the corrector) and vice versa.

Check the off axis halo on the edge of field garnet star from a Star71:

 

Once you get your collimation nailed, and your adaptors snug - your star halos should look more like this with a 200p / pds:

(btw: the above image was taken with the MPCC).

[emyliano2000]

5 hours ago, Waldemar said:

The distance to the sensor should be 56 mm, but it may vary a bit.

I measured again and I always get my measurements around the 55.8mm mark.

The oag+eos adapter=9.47 and there's a lip on the side where I connect the mpcc which is 2.28mm so from the front of the oag where I connect the mpcc to the back which sits on the front of the camera I have 11.75mm + 44mm distance from the front of the camera to the sensor = 55.74mm

I measured in a different way too. I put the camera with the oag connected on a flat surface and I measured the distannce from se sensor mark on the camera to the flat surface and I get 55.8mm

I don't know why I would have a coma problem if I'm in the 55mm(+/-1) mark.

And this is how they are connected

[Uranium235]

Have you connected that MPCC in M48 mode?

You need to be aware that the spacing distance from the base of the M48 thread is 57.5mm.

[emyliano2000]

11 minutes ago, Uranium235 said:

To help with the slop between your bayonet adaptor and camera, cut out a thin plastic ring with a notch in it (to accomodate the locking pin) from an ice cream container lid (tesco own brand is ususally quite thin plastic) and insert that between the bayonet adaptor and your camera - that should take the play out of it.

Thanks, that's a great idea.

 

12 minutes ago, Uranium235 said:

In regard to the off axis halos, do your collimation with a cheshire first - only using the laser to check or make minor adjustments

I do the cheshire collimation inside the house and the laser outside after I mount the scope. 

 

14 minutes ago, Uranium235 said:

Compression rings.... the work of the devil!!!

It would have been better to drill and tap a third hole in your original push-fit adaptor for another thumbscrew.

I drilled a 3rd hole in the compression ring adapter but I managed to snap a screw inside the hole because I drilled it too small ?

[emyliano2000]

10 minutes ago, Uranium235 said:

Have you connected that MPCC in M48 mode?

You need to be aware that the spacing distance from the base of the M48 thread is 57.5mm.

Yes it's in m48 mode. 57.5mm from the base of the thread? As in the photo?

I have the stop ring that came with the mpcc but there isn't enough thread left to connect it to the oag.

[Uranium235]

12 minutes ago, emyliano2000 said:

I drilled a 3rd hole in the compression ring adapter but I managed to snap a screw inside the hole because I drilled it too small ?

Doh!!

For future reference, drill a hole 1mm smaller than the tap size. Dont worry about it being a bit stiff to tap, the aluminum is quite soft. Take it slow, a few turns in, then a few out to release the swarf, should take no more than 5min to complete.

Re: the mpcc, yes its 57.5 from the base of that thread - so youre looking for another 2.5mm.

 

[emyliano2000]

3 minutes ago, Uranium235 said:

the mpcc, yes its 57.5 from the base of that thread - so your looking for another 2.5mm.

I have no idea how to achieve that and have some thread left to screw the mpcc into the oag. I only have 3.11mm of thread and if I put the 2.21mm ring I'm left with 0.9mm of thread and I cant screw it into the oag.

[Uranium235]

Try this:

http://www.teleskop-express.de/shop/product_info.php/info/p6435_TS-Optics-3mm-Extension-Ring---2--Filter-thread-M48x0-75mm---male---female.html

Its a 3mm M48 extension but you should still be within the spacing tolerances (you can go about 1mm over and still be fine)).

[emyliano2000]

47 minutes ago, Uranium235 said:

When using the self centering adaptor, dont do it up too tight as that may skew the the collimator - just do it up enough so you can still just about rotate the laser in the adaptor. While rotating the laser, check the dot on the primary to see if its scribing a circle.... if not, all is good and you can continue with your collimation.

I'm using a hotech laser collimator as it's self centering too. I don't know if I'm doing it right but I insert the laser into the focuser draw tube, tighten it without tightening the compression ring adapter and do the final adjustments. I'm thinking that it might not be right because when I insert the camera, tightening the compression ring is pushing the camera to one side and messes up the alignment.

The compression rubber on the laser colimator make it a bit hard to rotate it in the self centering adapter. It would be easier to rotate the self centering adapter into the compression ring adapter.

[Uranium235]

Or....

Put the T2 thread adaptor back in the MPCC and convert it to M48 using this:

http://www.teleskop-express.de/shop/product_info.php/info/p2839_TS-Optics-Adaptor-with-T2-female-thread-and-M48--2--filter-thread--male---zero-effective-.html

It has an effective length of 0mm

[emyliano2000]

16 minutes ago, Uranium235 said:

Or....

Put the T2 thread adaptor back in the MPCC and convert it to M48 using this:

http://www.teleskop-express.de/shop/product_info.php/info/p2839_TS-Optics-Adaptor-with-T2-female-thread-and-M48--2--filter-thread--male---zero-effective-.html

It has an effective length of 0mm

I'll have to check on that tomorrow because I think the T2 thread adapter might be hitting the prism. If so I would have to grind it down a bit, the T2 thread adapter I mean.

[emyliano2000]

11 hours ago, Uranium235 said:

Or....

Put the T2 thread adaptor back in the MPCC and convert it to M48 using this:

http://www.teleskop-express.de/shop/product_info.php/info/p2839_TS-Optics-Adaptor-with-T2-female-thread-and-M48--2--filter-thread--male---zero-effective-.html

It has an effective length of 0mm

Isn't the field of view gonna be reduced if I'm using the T2 thread adapter? 

I found something else. M48 fine tuning ring. 0.3mm, 0.5mm, 0.8mm, 1mm and 2mm like the one from the link below.

https://www.astromarket.org/accessories-5/adapters-5/extension-2-5/m48-2-fine-tuning-ring---1mm-5 

So my distance at the moment is 55.8mm. To achive the 57.5mm desired I would need an extra 1.7mm. That's where the fine tuning rings come into play.

The M48 thread is 3.11mm so if I add  1.6mm fine tuning rings I will be left with 1.51mm of thread. I'm wondering if that will be enough to make a secure connection to the OAG.

Even if I would use a 1mm ring it would give me a 56.8mm distance which is inside the 57.5mm (+/-1) mark and I would have 2.11mm of thread left on the mpcc.

[Uranium235]

Your fov isn't decreased by using T2, all that will happen is a small increase in vignetting (at f5, you might not even notice it). To be safe you should have a minimum of 2mm on any threads you use.

Remember that plastic spacer I told you about earlier in regard to removing play in the bayonet? That will also add spacing, not much but it all adds up.

 

Edit: Having said that (regarding the T2), it might not work since the prism would need to intrude further into the light path and may interfere with your imaging chip (ie: leave a shadow).