Tilt Adaptor - Solving the Tilt

[Aidan]

Hey All,

 

I've finally got a Tilt adaptor on my rig to try and get rid of the annoying elongated stars.

The elongation is ONLY on the bottom corners of an image and more so in the bottom left.

The tilt adaptor has 3 sets of push/pull screws.  One set at 10 o'clock, another at 2 o'clock and the 3rd at 6 o'clock.

Would it make sense that adjusting the screws at 6'oclock would probably be the best place to start?      Thats what seems most logical to me, but thought i would just see what other opinions were

Rgds
Aidan

[michael8554]

If the top two corners are okay then you can only tilt the bottom to a compromise between the two bottom corners.

Or get the bottom correct and see how far out the top becomes.

Michael 

[Aidan]

Trial and Error!    Started chasing my tail when trying to get things sorted.  Eventually a small tweak here, and a small tweak there whilst watching the tilt axis in CCDI got me to quite a low tilt in the end.

[sloz1664]

I find ironing out sensor tilt the most annoying aspect of setting up the imaging train. Yes you start chasing your tail and it's only the tiniest tweaks needed to obtain that flat field, and you have a focal reducer then you have spacing & focus issues to contend with as well. Nothing is easy in astroimaging.

Steve

 

 

 

[fwm891]

Quote

 

Best to leave one screw alone and just adjust the other two - same with mirror collimation

[Aidan]

I eventually gave up with the tilt adapter.  Due to my image train and location of the screws when everything is assembled, they are almost impossible to adjust.  

What I ended up doing was looking at the images through CCDI and determined the tilt was all across the bottom of the frame.  Put some insulation tape across the bottom edge of the cmos chip aperture and that certainly seemed to improve things.

However,  after I then slewed from a rich star field which I used for CCDI,  further images showed some pretty bad figures in CCDI?  

So, I gave up on trying to fix it and set about just imaging the elephants trunk.  Which, apart from the bottom edge came out quite nicely.  

I think I am just going to live with having to slightly crop images and make the most of any clear skies with this scope now.  

I dont like defeat, but things seem to keep changing too much 

[symmetal]

Hi Aidi,

I found that CCDI gives misleading results regarding tilt and curvature when using a field flattener as it ignores the orientation of the elongated stars. Stars too far from the correct distance are treated the same as stars too close, so a badly tilted sensor where the centre is at the correct distance will be reported as having no tilt but significant field curvature. I gave up on using CCDI to try and correct tilt as it does more harm than good and you end up chasing your tail.

I found just looking at the orientation and length of the elongated stars in the image corners is a far better way to see where the errors are. I too resorted to 'jamming' objects in the threads to force a correcting opposite tilt with some success but did end up getting a tilt corrector. Luckily it's fitted far enough away from the camera that adjustments are easy with the allen keys and in an hour or so got it to the best it's ever been and even copes with rotating the camera orientation with very little change in tilt.  I'd wasted days before trying to correct it so the tilt adjuster was well worth it for me. I don't know why they can't be made as an option with the adjustment screws on the opposite side so that you can still adjust them easily when it's fitted close to the camera.

You also need to know the orientation of the sensor in the camera and whether the camera software automatically rotates it by 180 degrees, in order to work out whether the 'tilt' corner you need to adjust is the same corner as indicated by the image or the diagonally opposite corner.  On the ASI1600 it's the opposite corner. On my Atik One it's the same corner. It's easiest to just make a large adjustment in one corner and see where the effect occurs in the image to determine what yours is.

Alan

[Aidan]

Thanks Alan,  I didnt know the corners were skewed on the 1600.  I've just re-positioned my highly technical insulation tape to the opposite corner and see what that yields.   I had hoped the tilt adaptor i got would have allowed it to be inserted in the image train.  I think if i get some thinner spacers, i might be able to make it fit..  Typically, i dont have any of the right thread/thickness in my ever growing box of adaptors!

I've currently got two layers of insulation tape on the camera, if i go for a third, i start getting light leakage.  

The images i took last night of IC1396 came out quite nice.. with a bit of cropping it looks ok.  I will revisit the tilt problem, but so far since the clocks have gone back, ive spent more time fettling than imaging!!

Rgds

Aidan

[symmetal]

3 hours ago, Aidan said:

Thanks Alan,  I didnt know the corners were skewed on the 1600.  I've just re-positioned my highly technical insulation tape to the opposite corner and see what that yields.   I had hoped the tilt adaptor i got would have allowed it to be inserted in the image train.  I think if i get some thinner spacers, i might be able to make it fit..  Typically, i dont have any of the right thread/thickness in my ever growing box of adaptors!

I've currently got two layers of insulation tape on the camera, if i go for a third, i start getting light leakage.  

The images i took last night of IC1396 came out quite nice.. with a bit of cropping it looks ok.  I will revisit the tilt problem, but so far since the clocks have gone back, ive spent more time fettling than imaging!!

Rgds

Aidan

I think it's a law of astrophotography that no matter how many spacers and adapters you have you will always need one more. 

Good luck with your tape for the moment. 

Alan

[david_taurus83]

What tilt adapter did you get?

[Aidan]

I bought the ZWO adaptor.   I went for this as it has the knurled heads for adjustment.     I've since looked at the ones which use hex keys,  these would not work either as there would not be enough space to get the hex key to the hex bolts.

I have since proved beyone reasonable doubt that the camera is at fault.   If i remove the 1600 and replce it with my 460ex (nothing else changed in the image train) with only doing a refocus, the image on the 460ex is flat and sharpe stars across the whole image.   Here's a comparison from the two cameras..    When i first got the camera i did notice this and got in touch with the retailer... At the time i thought it was my OAG causing the problem, but time and crappy weather prevented more testing.  So, i have now got back to them saying that the 1600 is at fault and waiting to hear what we can do about it.

 

[david_taurus83]

I've looked at these and the FLO one. Where is yours mounted? Also, is the 460 a smaller chip? If so then it might be that it's ok closer to the centre of focal point. Any way to overlay a 1600 image and 460 image from their centre points to see the extents? Have you seen my thread about adjusting indoors by pointing at a screen of dots?!

[Aidan]

I have tried to mount the tilt adaptor at various places along the image train.   I cant go either side of the OAG as it clashes with the camera holder.  If i put it close to the camera then the bolts it the camera body.  If i go nearer the focuser, again the bolts clash with the focuser draw tube.   The only other option i can think of is putting a spacer between the focuser M48 thread and the tilt adaptor, but i fear i might run out of focus adjustment....  I only have about 20cm of focus draw tube to play with.

Thats a good point about chip size.  Something that i had not really considered..   Still lots to learn in this game!

I seem to recall the post you are refering to, but i dont think i read too much into it.   Is it something which might help me resolve?   Do you have the link to hand?

 

 

[david_taurus83]

Seemed to work for me. But now you've got me thinking about a tilt adapter so I may end up tweaking again!