View Full Version here: : How to fix heartshape stars
23-05-2012, 04:56 PM
I took this image last month using 80mm f/5 refrator and canon 300d. Can someone tell me what is the fix for this heartshape stars?
23-05-2012, 09:21 PM
Are you using any other accessories with your scope and camera, for instance a field flattener?
You have some astigmatism in the top left which could be caused by a few things, such as your image plane being tilted.
Your stars look very similar (in the corner) to what i get out of my scope. The problem i am having is that my image plane is tilted (cause still unknown - it is being investigated).
To me it looks almost like you have movement in the image. Are you doing any tracking and how would you rate your polar alignment/drift alignment?
How are you stacking the images, what software are you using or are you doing it by hand?
Your image is also heavily processed which would not help.
24-05-2012, 12:51 AM
I'm getting something similar from my SCT, and I'm not using a field flattener. With/without the light pollution filter I get it. Was wondering if it's due to my Canon sensor being big, 24x36mm maybe (5Dm2)?
I've been looking through recent posts on the forum where someone might have has the same, but all I can find is coma problems in Newtonians? And here a come corrector lens is suggested Arif, not sure if it will help your problem in a refracting telescope? (Click here for some info) (http://www.astronomics.com/main/Coma_Correctors.asp/catalog_name/astronomics/category_name/T6C0K0CAFKES8M95XW91SQQKE1/Page/1)
Advice/suggestions it would be appreciated.
Attached is a low res of what I get. Mine also seem to be worse upper right corner, although upper left also sucks.
24-05-2012, 09:51 AM
I am using LPR filter with color images without fieldflatenner. Both color images are 1 min unguided exposure and converted to jpg and resized to upload. Other monochrome image is only 15 sec exposure taken through starlightexpress hx916. All the images shows similar star pattern. So dont know if the fieldflatener will fix this.
24-05-2012, 10:02 AM
Yours looks like coma problem if you are not using fieldflatener. I am using refractor and I also see people are using fieldflannter with refractor. I just want to confirm if my problem related to that.
I have taken image of NGC5139 with antares f/6.3 reducer/flattener with Celestron C8 SCT. You can see there is no coma effect.
24-05-2012, 11:28 AM
A field flattener will definantly help.
Also if possible, can you try and rotate the camera in the focuser and see if the star trails change direction?
Also as you are unguided, some trails will be promenent.
Also you can get some slight movement if your mount is not very stable, or there is high wind.
My suggestion is to see if you can get a Field Flattener which may solve some of your issues, but if it is a mount problem then you will need to investigate the stability of the mount (tripod legs etc).
After that possibly look into some sort of guiding system, if your mount can handle it.
24-05-2012, 11:34 AM
Arif, the new 3 images show the problem better. All the bubbly tails all the way across the image point the same way. Not radiating out from the center as a coma problem would. Looks like the scope needs to be collimated. Do a google search for "collimate refractor" and you'll find all sorts of info about adjustable lens cells and adjusting the eyepiece/camera holder. Some use bright stars, others use lasers or cheshire eyepieces just like collimating a reflector.
Tanya's problem is coma. My images looked exactly like that with the outer stars showing comet like tails radiating out from the center. I fixed it with a Baader MPCC (Multi Purpose Coma Corrector). It' a bit pricey and you will not know the exact effect until you try it, but your coma almost exactly matches the problem of my scope.
My scope is one of the first Meade LX200 10" Classic running at f/6.3. It was only ever designed to be used with the tiny 1/4" CCD chips available at the time (20 years ago!), so the coma would not have been visible.
Oh, and Tanya, do you have a lightbox? There is vignetting showing up in the corners too. Look for Exfso (Peter) in the Cameras & Imaging Equipment forum section. His are brilliant.
24-05-2012, 11:44 AM
I will check it next time with autoguiding as now i have oag. Mount is working perfect as you can see Ngc5139 photo which was taken unguided 10sec.
24-05-2012, 11:48 AM
And I just remembered. Adding the MPCC to the LX200 required a 2" eyepiece holder as it does not just screw on to the rear cell. So I got a JMI EV-1 crayford focuser with the larger mounting base which screwed onto the larger opening of the rear cell (3.25" diameter thread in my case). All up a rather pricey fix but it fixed the focusing problems I was having anyway. You need to focus to less than 1/3 the thickness of a hair at 1600mm focal length and the primary mirror knob is not up to that and wobbles the whole scope when you try.
24-05-2012, 12:02 PM
Hi Arif, what is the scope you are imaging through? All we know is its an 80mm f/5 refractor. I used the 300D extensively on the Orion 80mm f/7.5. It definitely benefited from a flattener (and reducer). I did a review ages ago that may still be relevant http://www.iceinspace.com.au/93-458-0-0-1-0.html
Since then I've used the WO 72FD f/6 and it also needed a field flattener to illuminate the chip evenly. Its not uncommon to need one.
The other thing you might find is not only is the chip tilted to the objective, but it could also be offset from poorly operating brass compression rings in your focuser.
24-05-2012, 12:24 PM
I am using a Chines brand Aquila 80mm f/5 refractor. It has a crayford focuser. Please see the picture here http://www.iceinspace.com.au/forum/attachment_browse.php?a=115468
One thing might be compression rings as you suggested, may not be able hold canon 300d weight or as Mark suggested about collimation.
I will do further testing using lightweight modified philips webcam and see if it gives any idea.
24-05-2012, 01:48 PM
That's quite likely. You might also want to look at flexure down the track, having the scope mounted on that one small dovetail saddle on a wooden rail, it will eventually start to move.
24-05-2012, 02:05 PM
This setup has not been tested yet. Those photos were taken by directly mounting it on mount.
24-05-2012, 02:27 PM
24-05-2012, 09:12 PM
The image hasn't been processed, so no stacking / flattening which is bringing out the vignetting. (all my other images are cropped to get rid of the coma) .
I thought abt getting a coma corrector but I've also been advised it might be the chip size.
Anyhow - I really need pin-sharp stars so I'll have to try it.
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