What's causing this diffraction type pattern?

[sheeprug]

I took a few images of some star clusters the other night.   Below is an enlargement of small section conatining NGC457 after stacking,some stretching and increased saturation.  I suspect it's  a little over exposed at 60s.  

I'm wondering though, what is causing the diffraction type effects around the brighter stars?   Equipment was WO 110FLT refractor, field flattener, Canon 750d on an HEQ5 guided with PHD2.  I'm guessing it's internal reflections in the DSLR since that's the only square item in path,  but does anyone have any suggestions?   It would be nice to lose it.

Best, 

SR

[Peter Drew]

Bahtinov mask left on?  

[souls33k3r]

pinched optics by the looks of it mate

[RayD]

Firstly I would just have a look down inside with a torch just to make sure nothing is obstructing the sensor.  The reason I say this is that I had a very similar thing, and it turned out one of the rings form my Hotech FF had popped off and was rattling around inside the tube without me knowing.

[MarsG76]

Something in the optical path perhaps... is there a screw that holds something in place that might have gone through and can be just slightly captured by the FOV??? 

 

[MarsG76]

3 minutes ago, RayD said:

Firstly I would just have a look down inside with a torch just to make sure nothing is obstructing the sensor.  The reason I say this is that I had a very similar thing, and it turned out one of the rings form my Hotech FF had popped off and was rattling around inside the tube without me knowing.

WOW... we have to keep an eye on every aspect of the imaging train.... EVERY SINGLE BIT.... Murphys Law, what can go wrong, will go wrong.

 

[RayD]

49 minutes ago, MarsG76 said:

WOW... we have to keep an eye on every aspect of the imaging train.... EVERY SINGLE BIT.... Murphys Law, what can go wrong, will go wrong.

 

Yes exactly.  Took me by surprise, and I only looked as I'd checked everything else I thought it could be.

[MarsG76]

16 minutes ago, RayD said:

Yes exactly.  Took me by surprise, and I only looked as I'd checked everything else I thought it could be.

It's always the last place you look....

 

[ollypenrice]

I've read several explanations for the refractor 'inverse light house beam' effect, blame being laid variously on lens clips and pinching. Since it is more than normal in most Takahashis and other high end refractors, and since it doesn't send spikes flying half way across the image, I've never let it bother me.

There is a simple way of minimizing the effect in Photoshop;

- Copy layer, bottom layer active, top layer invisible.

- Curves. Pin the background sky level near but clear of the star's outer glow and put another fixing point below that.

- Drag down the curve above the fixing points and restore it higher up.

- Top layer visible and active, erase the top layer artefact to taste.

Olly

[fireballxl5]

I had odd diffraction spikes once using my Borg refractor/DSLR combo in the past. It turned out to be a loose baffle in the OTA that had spun around and was obstructing the light path. Easily fixed but spoilt some images until found. 

Andy

[wimvb]

4 hours ago, ollypenrice said:

I've read several explanations for the refractor 'inverse light house beam' effect, blame being laid variously on lens clips and pinching.

I believe to have read a post on this issue where the solution was to make a ring that covered any lens clips. This decreases the aperture somewhat. In reflectors this is a more common solution, as mirror clips almost always get in the light path.

Btw, I assume that you don't use an off axis guider.

[sheeprug]

Thanks for your comments everybody. I'll have a closer look at everything in the optical path. I fear though, that the Christmas 'interruptions' may have started already, so it may be in a few days!

Best,

SR.  

[swag72]

In my FSQ85 I have this similar pattern....... I have to say that it's never bothered me. 

[tooth_dr]

13 hours ago, MarsG76 said:

It's always the last place you look....

 

Generally... because most sane people would stop looking after they found it 

[sheeprug]

12 hours ago, ollypenrice said:

I've read several explanations for the refractor 'inverse light house beam' effect, blame being laid variously on lens clips and pinching. Since it is more than normal in most Takahashis and other high end refractors, and since it doesn't send spikes flying half way across the image, I've never let it bother me.

There is a simple way of minimizing the effect in Photoshop;

- Copy layer, bottom layer active, top layer invisible.

- Curves. Pin the background sky level near but clear of the star's outer glow and put another fixing point below that.

- Drag down the curve above the fixing points and restore it higher up.

- Top layer visible and active, erase the top layer artefact to taste.

Olly

Thanks for that - definitely looks worth trying, though my PS skills are rather elementary at the moment!

SR

[MarsG76]

1 hour ago, tooth_dr said:

Generally... because most sane people would stop looking after they found it 

Most sane ppl wouldn't be spending thousands of dollars on gear to take pictures you can download that are much higher res Hubble images either, but sanity is boring... :-D haaaaaaa

[iapa]

12 hours ago, wimvb said:

I believe to have read a post on this issue where the solution was to make a ring that covered any lens clips. This decreases the aperture somewhat. In reflectors this is a more common solution, as mirror clips almost always get in the light path.

Btw, I assume that you don't use an off axis guider.

I think it was @Skipper Billy did this on 10" reflector a couple of months ago.