Collimation issue or otherwise?

[tooth_dr]

Results from last night are in following my attempts at collimation and the results arent good.  I've had another look at it today - and I feel that it is better that it was, but it isnt easy to get that secondary centered.

I'm seeking help from the experts here - is this a collimation error?

Last night I focused using a Bahtinov mask accurately, and I get double spikes on the stars.  If I focus by merging the spikes (as I thought was also a very accurate way of focusing) then I get larger stars in poor shapes - it appears out of focus.

I've attached a crop from off centre below, and a resized raw sub.

Any advice welcomed and/or swap for Esprit 150.  Is it the primary or the secondary, or both, or the focuser?

 

Thanks

Adam.

 

[sharkmelley]

The star with the double set of spikes is defocused - that's the cause of the double spikes.  Was it in the centre of the image?  Is it the same star on which you used the Bahtinov mask?

I assume this is the Tak Epsilon?

Edit:  I now realise it was a crop away from the image centre.  Can you upload the original raw file somewhere.  I'll do a quick analysis.

Mark

Edited September 24, 2020 by sharkmelley

[tooth_dr]

15 hours ago, sharkmelley said:

The star with the double set of spikes is defocused - that's the cause of the double spikes.  Was it in the centre of the image?  Is it the same star on which you used the Bahtinov mask?

I assume this is the Tak Epsilon?

Edit:  I now realise it was a crop away from the image centre.  Can you upload the original raw file somewhere.  I'll do a quick analysis.

Mark

Hi Mark,

Thanks for the reply.  Yes this taken with the Tak Epsilon 180 and Nikon D800E.  I've attached a sub from last night, 300s exposure at ISO400.  I spent some time collimating the scope yesterday so it will be different from the above image.  Last night I focused using a Bahtinov mask and live view, and then checked with a short exposure to confirm the placement of the centre line on the 'X'.  Despite this I still got double spikes on my stars.  I should have aligned the diffraction spikes afterwards and took a further image for comparison, but I did not think at the time.  It was already 2:30am and I was working at 9am.

If I can get another clear night I will repeat, but with the diffraction spikes as a guide to focus, and ignore the Bahtinov mask.  The diffraction spikes could be due to a mal-alignment of the spider vanes, but that has got to be unlikely due to their thickness and attachment to central secondary holder.

 

Thanks for your help

Adam

 

 

L_0021.NEF

[sharkmelley]

I downloaded L_0021 and I agree it's slightly out of focus.  The stars at the edges have "squiffy" shapes but we need an in-focus example before drawing a conclusion.  How are you connecting the camera - do you have a picture of the camera sitting on the focuser?

Mark

[tooth_dr]

7 hours ago, sharkmelley said:

I downloaded L_0021 and I agree it's slightly out of focus.  The stars at the edges have "squiffy" shapes but we need an in-focus example before drawing a conclusion.  How are you connecting the camera - do you have a picture of the camera sitting on the focuser?

Mark

Thanks Mark. I will get an image with the diffraction spikes aligned as soon as possible and upload it here. 
 

Here is a photo of the camera on scope:

 

[tooth_dr]

[sharkmelley]

Oh, wow! You've changed the focuser! 

Have the stars ever been perfect since the focuser was changed?  If not, it's probably because you have a larger number of degrees of freedom to deal with.  A Tak Epsilon is difficult enough to get right in its normal configuration but the additional complications with a focuser replacement put it well beyond my level of experience.

Good luck!

[Edit:  Is that the standard Tak wide mount Nikon adaptor you are using?]

Mark

Edited September 26, 2020 by sharkmelley

[Allinthehead]

Sorry to see you having such difficulty with your Epsilon Adam, messing with a scope at 02:30 when you're working the next day is no fun at all. If I were in your position I'd get the original focuser back on. Is it a big job to change it?

[tooth_dr]

13 hours ago, sharkmelley said:

Oh, wow! You've changed the focuser! 

Have the stars ever been perfect since the focuser was changed?  If not, it's probably because you have a larger number of degrees of freedom to deal with.  A Tak Epsilon is difficult enough to get right in its normal configuration but the additional complications with a focuser replacement put it well beyond my level of experience.

Good luck!

[Edit:  Is that the standard Tak wide mount Nikon adaptor you are using?]

Mark

Hi Mark

I didn’t personally change the focuser. The scope was second hand and came with the Moonlite fitted when I bought it. It was mentioned in the advert that the scope was collimated by Orion Optics just before purchase.  I took this as read, however a year in with the scope and I’m beginning to understand the scope better and realise that it most likely was never right.

I’m lucky enough to have the original focuser and the additional microfocuser.  I’ll fit this tonight (hopefully straight forward) and recollimate.

If you are still able to help me going forward I would really appreciate it.

Wirh regards the Tak wide mount - it came with the scope.  I don’t have a photo on my phone (I’m not at home this weekend) but am back this evening.  The adapter is in a blue box says wide mount on it.  Screws directly into the CC on the scope and looks to be about the right thickness to maintain the 56mm back focus  

 

[tooth_dr]

14 hours ago, Allinthehead said:

Sorry to see you having such difficulty with your Epsilon Adam, messing with a scope at 02:30 when you're working the next day is no fun at all. If I were in your position I'd get the original focuser back on. Is it a big job to change it?

Hi Richard!  You have been saying all along to replace with the standard focuser. Should have listened to you!  Going to try to fit it tonight.  Hopefully I can find the right bolts etc amongst the stuff that came in a box with the scope.  

[tooth_dr]

Removing the Moonlite and refitting the original focuser was pretty simple.

Collimation was way off when the Tak focuser was fitted so hopefully that’s a good sign.  I have recollimated it - a simple task with the Tak collimating eyepiece.

@sharkmelley I’ve attached a photo of the Tak-Nikon adapter box 

 

 

[AKB]

Good luck with the retrofit outcome... would success mean that you have a spare moonlight focuser going?  

Tony

[tooth_dr]

58 minutes ago, AKB said:

Good luck with the retrofit outcome... would success mean that you have a spare moonlight focuser going?  

Tony

Thanks Tony. Yes I think so but just want to make sure this one works.  I might however use the motor with my ED80 and buy a new ML 2” focuser for it.  At the minute that focuser might include a free epsilon. 
 

 

[tooth_dr]

I want to update the saga. I fitted the original Tak focuser yesterday and collimated the scope. I noticed on moving the scope from vertical position (opening towards ground) where I collimated it to normal imaging position in south at say 30 degrees, the collimation was off a good bit.  When I moved it back to vertical, without adjusting anything, collimation was correct again.

This time I repeated the collimation with the tube vertical but the opening upwards.  It was much trickier to manipulate the push pull system but I got there.

No where moved to normal imaging position collimation remained unchanged 👍🏻
 

Now unfortunately the problems continued. There is slop in the focuser suffice to say that collimation seems pointless - when I check the collimation with the collimating tool, with in and out movement it’s different.

Can the Tak focusers be adjusted?

[Stuart1971]

12 minutes ago, tooth_dr said:

I want to update the saga. I fitted the original Tak focuser yesterday and collimated the scope. I noticed on moving the scope from vertical position (opening towards ground) where I collimated it to normal imaging position in south at say 30 degrees, the collimation was off a good bit.  When I moved it back to vertical, without adjusting anything, collimation was correct again.

This time I repeated the collimation with the tube vertical but the opening upwards.  It was much trickier to manipulate the push pull system but I got there.

No where moved to normal imaging position collimation remained unchanged 👍🏻
 

Now unfortunately the problems continued. There is slop in the focuser suffice to say that collimation seems pointless - when I check the collimation with the collimating tool, with in and out movement it’s different.

Can the Tak focusers be adjusted?

I don’t see why not, both my FSQ85 and FS60 focusers can be, there are two or three small grub screws on the top of the focuser housing, so see if yours has those...

One may be under the locking knob, so remove that and take a look...

I had terrible focuser sag and collimation issues with my FS60 and it sorted all that, I realise you have different type of scope, but worth a look...👍

Edited September 28, 2020 by Stuart1971

[sharkmelley]

Well done changing the focuser.

Yes, you appear to have the right adaptor - same box as for my Canon.

The manual shows a couple of grub screws under the focus locking knob.  Unscrew the knob to access them.

Mark

Edited September 28, 2020 by sharkmelley

[Stuart1971]

23 minutes ago, sharkmelley said:

Well done changing the focuser.

Yes, you appear to have the right adaptor - same box as for my Canon.

The manual shows a couple of grub screws under the focus locking knob.  Unscrew the knob to access them.

Mark

Exactly....^ 👍

[tooth_dr]

Thanks @Stuart1971 indeed it did adjust up nicely. I tightened the small grub screws and I now get minimal image shift when checked with collimating tool.

Ive spent 2 hours this morning testing various angles etc and am happy that it’s holding collimation in any position that I put the OTA in. It’s clear tonight so that’s the real test.

Some images of the position I collimated in today, and through the collimating eyepiece with the tube vertical - opening up and opening down.  The Tak Nikon adapter is 9.5mm thick which ties in with a 46.5mm flange-sensor distance, giving the required 56mm Epsilon CC back focus distance.

 

[tooth_dr]

This is an image from last night, so not taking into account the adustments I have carried out today on the sloppy focuser.

Does this look like poor collimation causing coma?  The image i feel is very slightly out of focus too, but I was really up against a very short window of sky last night.  It's looking much better for later.

 

[Stuart1971]

2 hours ago, tooth_dr said:

Thanks @Stuart1971 indeed it did adjust up nicely. I tightened the small grub screws and I now get minimal image shift when checked with collimating tool.

Ive spent 2 hours this morning testing various angles etc and am happy that it’s holding collimation in any position that I put the OTA in. It’s clear tonight so that’s the real test.

Some images of the position I collimated in today, and through the collimating eyepiece with the tube vertical - opening up and opening down.  The Tak Nikon adapter is 9.5mm thick which ties in with a 46.5mm flange-sensor distance, giving the required 56mm Epsilon CC back focus distance.

 

 

great, glad it worked... 👍

Good idea to put a bit of clear nail polish on the head of the grub screw as it stops it moving over time, this is how the Tak fracs come from the factory, it’s easy to remove with polish remover...

I checked mine with a laser in the eyepiece and shon against a white wall, and racked the focuser in and out, and the red spot did not move...but I realise yours is a different type of scope...

 

[sharkmelley]

I've never had stars as bad as those on the right-hand-side.  I can only guess it's the collimation. 

Mark

[tooth_dr]

15 hours ago, sharkmelley said:

I've never had stars as bad as those on the right-hand-side.  I can only guess it's the collimation. 

Mark

Last night i took a few images. There is a lot of coma despite the scope looking fairly well collimated 🤷

L_0037.NEF

[Stuart1971]

30 minutes ago, tooth_dr said:

Last night i took a few images. There is a lot of coma despite the scope looking fairly well collimated 🤷

L_0037.NEF 73.08 MB · 0 downloads

Do you use a reducer or flattener, as that looks like a spacing issue..?

[tooth_dr]

58 minutes ago, Stuart1971 said:

Do you use a reducer or flattener, as that looks like a spacing issue..?

Hello Stuart.  I'm using the tak CC, which is designed to work at 56mm.  I have a tak-nikon adapter than is supposed to be a direct fit, and means that the spacing is predetermined.  The sensor-flange distance of a Nikon is 46.5mm, and the CC looks to be 9.5mm, so this gives the proper 56mm back focus.  Looking at the above, if it is a back focus issue, then where do I need to go with it?

 

[tooth_dr]

On 22/09/2020 at 00:27, sharkmelley said:

...the 3 grub screws on the rim also need to be slackened slightly...

Mark

Mark, do they need to be loosened to do the collimation itself or should they be left tightened up?  How tight do these 3 grub need to be?

Thanks

Adam.