Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_solar_25_winners.thumb.jpg.fe4e711c64054f3c9486c752d0bcd6f2.jpg

Jammy

Strange Diffraction Spikes

Recommended Posts

Does anyone know what the strange diffraction spikes are in this image?  I know the star Alnitak is pretty bright but wasn't expecting this.

I've never seen this happen before.  Is it an SCT thing, or a MY SCT thing?

I've seen straight diffraction spikes, but never curved.

Is there anything I can do to stop this?  Could it be a collimation issue?  I did check before I started imaging, but thought everything looked ok.

My scope is a Celestron C9.25 XLT, and I'm using a f/6.3 corrector/reducer with modded Canon EOS 600D.

Thanks in advance :)

IC434 second try.jpg

Share this post


Link to post
Share on other sites

Not a collimation issue judging by the other star shapes. Most likely a reflection from something internal or external.   :icon_biggrin:

  • Like 1

Share this post


Link to post
Share on other sites
32 minutes ago, Jammy said:

Is there anything I can do to stop this?

Frame the picture differently. This is a lens flare, surely taking place inside the reducer. Bright stars are bound to cause this effect at certain angles, but especially near the edge of the lenses. It's the first time I see such a long flare, though. Do not discard the pic, everything unusual is interesting, and it might prove artistic when you look at it with an open mind. The flare frames the Horsehead pretty well.

  • Like 2

Share this post


Link to post
Share on other sites

Thanks guys.  I did wonder if it was from the focal reducer.  I've never seen a flare this long either, thats what made me ask.

I did try to move the star out of shot, but then struggled to find a guide star in the OAG.  I might have done better moving it into the middle.

Next time I'm out I'll try imaging a bright star, central in the frame, to see if there is any flaring.

As you say, keep an open mind.  I'll try processing it again and see if I can extract some detail :)

Edited by Jammy
spelling

Share this post


Link to post
Share on other sites

That's a great example of the effect.

Altinak is probably the star that causes more weird effects than any other!

Mark

Share this post


Link to post
Share on other sites
On 12/21/2017 at 10:27, newbie alert said:

Did you clean the reducer beforehand? I get this on my sct sometimes..

No I didn't.  Should I clean it, and what with?  I try to touch these things as little as possible.  It looks clean when you hold it to the light and look through.

Share this post


Link to post
Share on other sites

Like I say I get this now and then with my sct and reducer...cant pin it down to after it's been cleaned as it's not every time..

Share this post


Link to post
Share on other sites
On 12/21/2017 at 14:06, sharkmelley said:

It could be internal reflections inside the baffle tube:

https://www.cloudynights.com/topic/565539-strange-arcs-of-light/?p=7688737

Mark

That's ineresting.  Have you ever had any problems like this with your SCT Mark?

I'm wondering where the reflections can be coming from.  Possibly the secondary housing?  I'm not entirely sure how to check, or if I want to.  I don't really want to start dismantling the scope.

Share this post


Link to post
Share on other sites

Id bet it's a internal reflection from the reducer..seen them on a couple of others images and the common denominator is the 6.3 reducer..i try to find an image of mine,unless I've deleted them already..

  • Like 1

Share this post


Link to post
Share on other sites

I'm thinking its down to the reducer.  Unfortunately I don't think Celestron put as much effort into this reducer as they should have done.

Would a different brand f/6.3 reducer work with my C9.25?  I'm thinking they're probably all the same with a different brand name on the box.  

Share this post


Link to post
Share on other sites

Try flocking paper in the baffle tube. Roll it up, slide it in. It will probably stay put  by itself (without glue) when it unrolls itself. A thin material is best.

If it solves the problem you may consider fixing it more permanently.

Share this post


Link to post
Share on other sites
11 hours ago, Jammy said:

That's ineresting.  Have you ever had any problems like this with your SCT Mark?

I'm wondering where the reflections can be coming from.  Possibly the secondary housing?  I'm not entirely sure how to check, or if I want to.  I don't really want to start dismantling the scope.

No I haven't seen this with my SCT but it's a long time since it has seen active service except for planetary work.  To be honest I can't really visualise exactly how this effect is caused, however I think it is significant that this "reflection" passes through the star.  I have often seen these artifacts when the star is outside the field of view, when  the star's cone of light will be reflecting off various optical components.  But for a star within the field of view, the cone of light should not be hitting anything en route to the sensor. 

I will set up an experiment sometime after Christmas to see if I can make it happen.

Mark

  • Like 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By astronomer2002
      I am selling a JMI focus motor for Meade SCT's.
      It has a replacement controller as the original was lost many years ago. Works fine on a LX200.
      Asking £40 for complete unit and controller plus £5 if you need it posted.
       
      *****************   SOLD   ******************
       




    • By Fraunhoffer
      lets imagine I wasn't to see a nice DSO about 15' size and I think it should look good nicely framed with a 1 deg field of view in the EP..
      Which would give the better (or higher probability of seeing anything at all ) view from a semi urban light polluted home site (e.g Bortle 6)?
      a) an 100mm f/6 refractor (fl 600mm) and a 10mm EP (60 deg afov, gain 60x = fov pf 1 deg)
      (and exit pupil of 100mm / 60 = 1.6mm)
      or
      b) a  200mm SCT with focal reducer to give f/6 (fl 1200mm) and a 20mm EP (60 deg afov, gain 60x = fov of 1 deg)
      (and exit pupil of 200 / 60 = 3.3mm)
      My gut feeling is that the SCT should give a better view just based upon its 2xaperture - but Im not sure I understand fully the maths why.
      Is the larger exit pupil going to result in a better / brighter / more successful view?
      Or will the view be 'roughly' the same ?
      Or have I got it all wrong.....

      Thanks.
    • By jawja boy
      Wife says to get rid of something before I can buy a new toy!   C6 is in perfect condition.  I am located in North Georgia and would rather not ship.  Scope sells for $800 but will let her go for $500 !
    • By G4EQZ
      Hi, Folks
       I am only a few weeks into astronomy and started off with a Celestron 9.25" Evo on the standard AZ mount. I guess with hindsight this wasn't the best place to start and also with hindsight I would have done better to have bought a GEM mount. Anyway, lesson learned and at 71 years old I have to speed up the learning process compared to younger enthusiasts  I have 2 issues. 1/ Its a pain dragging the scope out into the garden and setting it up every time I think the fickled weather might be obliging. 2/ I now know that the mount I have is useless for long exposures and a wedge is fiddly to get polar aligned.
      My question is, though I gather wedges are a PITA to setup etc is if I was to build or buy a pier for the backyard and use my existing mount + a wedge is this a reasonable way to go? Though it's fiddly to set the thing up once set I could leave the mount, wedge, etc covered up and would just need to drop the OTA on when I wanted to use it.  Is this reasonable or am I missing something fundamental down near the bottom end of my learning curve
      Any advice much appreciated and don't feel you have to spare my feelings
    • By Cosmic Geoff
      I recently acquired a used CPC800 SCT. I thought a 'First Light' report might be of interest.
      First impressions: the tripod is a heavy duty affair with thick legs, a folding lower spreader and a big cast alloy eyepiece tray/steady.  The OTA/fork assembly (not separable) is very heavy (21Kg/44lbs) but has a couple of grab handles. You need to be fit to handle this. ? (I was seriously tempted not to go ahead with the purchase after trying the weight.)
      With the legs retracted it is just possible to pass the tripod through a standard doorway, but it is just as easy to pull up the lower spreader and carry it folded. It is much heavier than a C8SE tripod but more comparable with a EQ5 tripod in weight.  Once in position, I checked the level with the handy built-in bubble level and left it.  I forgot to screw up the eyepiece tray/upper spreader but I don't think this made any difference. 
      Scope stored on a table with faceplate down and rear handle uppermost. Took the weight with my left arm, elbow fully bent, forearm vertical.  Got it on the tripod which took the weight till I got the base to drop over the centre pin, spun it till something clicked into place and then did up the three thumbscrews.   I would not try this with an equatorial wedge unless I had a helper.   Celestron also sell a CPC 9.25 and CPC1100 - if I had one of those I'd need a sheerlegs or a brawny assistant.?
      Fitted the visual back (same as C8 SE), prism diagonal (same as C8 SE), straight-thru 50mm finder, handset (Nexstar+) and handset bracket which holds it facing rearwards (a handy feature not implemented on the C8 SE). Fitted a 25mm X-Cel LX that came as an extra.
      Connected my new lithium powertank and its DC cable, and powered up. It comes ready (CPC Ready) very quickly. Selected 2-star auto align - it whizzed past a time display showing the time ahead of my watch by 1 hour - more on this later.  Aimed at Arcturus and afjusted the finder aim. Selected Capella - it nearly got there and then blackout!  The cable had snagged and pulled on the plug. I ran the cable through the side handle on the fork and tried again.  (It appears that the CPC's supplied cable has a locking ring and the other end has a cigarette lighter style plug.) Capella ... Arcturus .. aligned.  Told it to find Mizar (named star menu).  It did. 
      Also found M48, the Ghost of Jupiter planetary, Gamma Leo (split ), 54 leo, 88 Leo, 90Leo.  The scope appears to be collimated and resolution OK.  GoTo is just accurate enough to drop doubles into the bottom of 9mm X-Cel Lx field.  Even at 200x and a gusty night the view is rock steady. A pier mount could hardly be stiffer than this! And no obvious backlash in use (unlike C8 SE).
      Fiddled with the menu, found the GPS is obviously working, and the time set for daylight saving.   Corrected it to standard time. GoTo still works.
      Teardown: tube horizontal, power off, tube cap on, diagonal off, handset and bracket off, left visual back on and capped it, loosened clutch to point tube straight down.  Got OTA/fork assembly off and back indoors on table, twirled it into position.  Folded up tripod and carried it indoors. I would not try carrying the tripod and scope together.
      Verdict: Very solid mount should be good for planetary imaging.  Some nice features not on C8 SE, otherwise same optical performance.  Alarming weight.
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.