I can see the scope in my images

[sidelight]

Hi,

I'm fairly new to astrophotography but have been bitten by the bug.

I've just done a full spectrum mod of my 450D, and taken a set of 200 second subs (iso 400) on stacking I am seeing the reflection of a of the focuser tube and scope.  I have an IR filter, coma corrector and IDAS filter (all external to the camera) fitted.

I recently flocked the scope as the weather has been so poor in the UK so that filled an evening, but I thought the collimation was good

http://www.flickr.com/photos/92021206@N03/10857202413/

Any ideas what is causing this?  How to fix?  Could it be collimation?  

Regards

Ross

[sidelight]

I've just had a thought, like I said I recently flocked the scope, but never did the dew shield (a home made affair from a piece of black foam from hobbycraft).  I am wondering if the foam is bouncing the light down the tube sufficiently to get this effect?  The moon was quite full a couple of days ago.

Cheers

Ross

[tdmodels]

Looks like your focusser is protruding into the light path.  Do you have any spacers/adapters that could be removed so that the focusser can be racked out further?

[RogerTheDodger]

Yep that is the focusser drawtube. I had the same problem on my 200PDS and changed the focusser for this one http://www.firstlightoptics.com/skywatcher-focusers/skywatcher-dual-speed-low-profile-1252-inch-crayford-focuser.html the drawtube is in two sections so you can adjust the total length of the tube, and ensure that at prime focus for the camera that the drawtube doesn't protude into the OTA.

[sidelight]

Thanks,  I'm more worried that suddenly I can see the extra brightness around the stars - this is a stacked and stretched image but I've not seen that before with this scope.  Is this usual, and I've just been lucky up to now?  

Even on the lights this is quite noticeable.  I'm not sure how I would stretch the image without getting the effect above.  

Sorry to be asking questions but I'm stumped.

[lensman57]

Hi Ross,

Something is blocking the light path, I don't have a NEWT but others are correct in suggesting that it could be the draw tube although this is unavoidable with most NEWT designs.  I also think that your collimation could be a bit  off as the stars and the halos are not concentric to each other.

A.G

PS: As you have stacked the filters externally  ( increasing the sensor distance from the focal plane )   you will have to bring the the draw tube in further to compensate for the filters  thickness, I am sure with internal filters or without the filters the draw tube will not be in the light path as much as it is now.

[sidelight]

Hi all,

First thanks for the replies Tim, RogerTheDodger and Lensman, You help is greatly appreciated because this is new and one day I will learn to change one thing and check it before making another change.  Although in my defence the weather in the UK this year means I would have pretty much worked out how to polar align, and thats it this year ;-)

Thanks for the thoughts.  The filters I have fitted to the front of the coma corrector (A Baader MPCC) and fits inside the draw tube so hopefully other than the effect of the glass on the focal place the focus point should not have moved much.

I am wondering about the "halo" around the stars, I've just never seen such a huge difference in the area around the stars and the rest of the background which I can only describe as the scope (as you say you can see the draw tube).  This is fairly obvious in the individual light frames as well which means that stacking exaggerated the effect.  It's not something I've seen before so was wondering  if its an effect from the fairly full moon and that I have flocked the scope, or that collimation is way off.  It does look like it is a little off

I've put individual subs from M42 on the same night up so you can see what I mean (the bright area above)

https://dl.dropboxusercontent.com/u/16050702/M42_LIGHT_200s_400iso_%2B7c_01249stdev_20131113-00h43m22s157ms.TIF 

and the raw cr2

https://dl.dropboxusercontent.com/u/16050702/M42_LIGHT_200s_400iso_%2B7c_01249stdev_20131113-00h43m22s157ms.CR2

Cheers

Ross

[sidelight]

Trying again tonight after flocking the dew shield as well.  So far so good, so the effect that got into all my lights from the other night hopefully was either light bouncing off the dew shield or the atmosphere seems to have  been a one off :-)

Will know for sure when I start processing though.

[sidelight]

Still getting the "scope halo" around stars.  Re collimated scope today, just in case and still not got rid of the blasted things.  I Just had a thought the DLSR has a full spectrum mod.  There is an external IR cut-off filter there, but it doesn't look like it also filter UV.  Could that be the problem? Hmm this is getting frustrating now.  The focuser tube has never been visible in images up to this point so I think that just allowed me to identify what it was showing.

[tdmodels]

Hi Ross,

I had a similar issue with halo's, which was proven to be the EOS Ha clip filter.  The halos were a lot smaller than yours though.  Hence, I suspect that it is probably your IR filter that is causing the problem.  What filter are you using?

Try taking an image of a bright star, with and without the filter to help diagnose the problem.

 

Cheers,

TIm

 

[sidelight]

Hi Tim,

Sorry for the delay in responding.  My favourite for the cause at the moment is the IR filter - It's a fairly cheap one I bought which reading up on does not block UV.  

I moved to external filters after having all sorts of problems getting the replacement glass in the 450d square when I modded it which was causing all sorts of offset halos.  In the end I decided I would remove the glass and put external filters on to remove the problem.  As is often the way I removed the offset halos and gained a new problem.  What I should have done is changed one thing and tested before changing something else - I flocked the scope so stripped down the newt introducing a multitude of changes.  Oh well live and learn.

I have ordered an IR/UV blocking filter so hopefully this problem will be solved when that arrives.

Cheers

Ross

[Tinker1947]

Why not go back to basic's, prime focus with your camera and nothing else, then add the other bits you have to the image train......1 bit at a time...

[todd8137]

Why not go back to basic's, prime focus with your camera and nothing else, then add the other bits you have to the image train......1 bit at a time...

Your messier list makes my screen go funny on my iPad. As it's so long it shrinks the screen

[sidelight]

Finally a clear night without otehr commitments to try things out.  Started out with the internal filters back in the camera.  Lots of combinations later and it looks like it was the external IR filter I had originally purchased was not blocking UV.  New external 2" Baader UV/IR cut filter and everything is fine.  Just need to clean everything and knock the dust off everything after tonight, ready for a proper imaging session which hopefully doesn't involve screwdrivers.

Thanks for the help and suggestions everyone 

Cheers

Ross

[sidelight]

Decided that as it was the first clear night I would carry on and try it out as this never really became apparent the first time until I stacked the images.  Seems to be cleared up :-)

Thanks once again for the suggestions, I can get back to trying to get to grips with PI, and waiting for the next break in the weather. 

Cheers

Ross