Flared stars

[libraryman]

Hi i tried a 600 sec exposure on M45 @ f/7 , the central stars look very flared, is this a fault with my exposure time, the optics or perhaps the reducer.

the telescope is a Vixen 102 fluorite fitted with a 0.8x reducer.

Also whats the correct description for the (flared) stars

Ray

[ollypenrice]

These are seriously bright stars! (I'm surprised not to see more nebulosity, though. Is the image stretched?) They are a test for any system.

I'm going to guess that this is a one shot colour camera, CCD or DSLR, and that the spikes come from a lensing effect of the Bayer Matrix. I used my OSC and mono cameras on M45 and in the OSC I got some spikes emanating from one of the stars in the group. The mono did not produce this. This has happened on several OSC images but I don't consider it much of a problem. On more normal stars you shouldn't see this effect.

Olly

[Psychobilly]

If its anything like my Vixen ED81S the lens spacing tabs are a bit on the long side and give rise to the diffraction artefacts...<br /><br />Have a look into the scope and see if you can see the three tabs...<br /><br />You can use a front aperture mask slighly smaller than the tabs to get rid of the effect...<br /><br /><br />Peter...<br />

[libraryman]

Hi all and thanks for the coments, yes it is a modified DSLR, however the image is not stretched..it is just one 10min exposure cropped to show the artifacts.

Have to admit i was quite concerned but recognised that i may be asking a lot given..as you say..very bright stars.

i will also have a look and see if the tabs are there.

It does not appear on all the stars, just the very bright ones, if the bayer matrix is indeed the cause how would i go about reducing it, e.g would shorter exposure be the order of the day?

Thanks again Ray

Re:

These are seriously bright stars! (I'm surprised not to see more nebulosity, though. Is the image stretched?) They are a test for any system.

I'm going to guess that this is a one shot colour camera, CCD or DSLR, and that the spikes come from a lensing effect of the Bayer Matrix. I used my OSC and mono cameras on M45 and in the OSC I got some spikes emanating from one of the stars in the group. The mono did not produce this. This has happened on several OSC images but I don't consider it much of a problem. On more normal stars you shouldn't see this effect.

Olly

[Psychobilly]

Here's a test shot of Vega with my ED81S... showing the diffraction artefacts I get with it...

and another of Sadr...

Peter...

[libraryman]

Thanks for the shots; it's great to know i have not got an issue.

Ray

[ollypenrice]

I don't think yours and Peter's have the same origin, but I'm only half guessing. Peter's are more structured whereas yours look like mine in my OSC, fairly random.

Olly

[libraryman]

Thanks again Olly, its great to see the comparison, i just keep learning!!

Speaking of which, M45 is a very good target at the moment i'm not sure how best to image it with my 102 @ f/7, what length subs are best suited to this.

Ray