Markarian's Chain 27-5-11 widefield

[Carole]

I went to Herstmonceux village in East Sussex on Friday to give an Astronomy talk at my Aunt's club.  As it was a dark site and I was staying with her for a couple of days I took my full imaging rig with me and was lucky enough to get some clear skies on Friday and grabbed 1 1/4 hours.

I decided to use my Megrez this time to get a wider FOV as I was missing some of the chain on my last attempt.  I still plan to get more subs on this so haven't bothered to process out the satellite trails at this stage.

I would appreciate some feedback on why I get strangely shaped stars in the far extremes of the FOV - this has been a permanent problem with this telescope, but in the past have cropped them out.  Could it be to do with the optics, or the flattener, spacing? (I've put it in the gallery so you can see a larger file)

Anyway, the image (I counted 32 galaxies):

17 x 5mins 800 ISO Modified Canon DSLR EOS 450D (no CLS filter)
WO Megrez doublet 72 APO,  WO X.08 Flattener III,
Guided with QHY5 PHD, on EQ6
Processed with DSS and PS CS3

[MarkS]

Hi Carole,

It's looking good - slightly noisy - you might need a few more hours of data!

The WO Flattener III on the WO Megrez 72 will give spiky stars in the corners of the field - just do a Google search  - there are numerous threads on it.  Your spikes are quite symmetrical so it looks like you've got it set up as best as it will go.

I had exactly the same when using one of the WO flatteners on the ED80:  http://forum.orpington-astronomy.org.uk/index.php?topic=5105 (I can see I was already lusting over a Takahashi, even back then!)

Personally I find it quite annoying that one can be sold a "flattener" that whilst technically it probably does flatten the field, it leaves you with a pile of other optical aberrations.   I'm afraid that flatteners are one of my big bugbears.  Manufacturers really should provide test shots that show you exactly what to expect.  I've wasted so much money on flatteners and now I've just bought another: http://forum.orpington-astronomy.org.uk/index.php?topic=7565.0  - well at least this one has some proper technical data unlike the Celestron and Meade versions.

Mark

[Carole]

Thanks Mark, So it looks like there is nothing I can do about the mishapen stars with this set up.  (Must check the corners of the ones done with the ED120 as well). 

It's looking good - slightly noisy - you might need a few more hours of data!

Aiming to do so - dark skies and weather permitting.

Will take a look at those links.

Carole

[MarkS]

I think the ED120 has a flattener/reducer specifically made for it by Skywatcher.  You might find some examples of its performance somewhere.

Mark

[Carole]

ED120 has a flattener/reducer specifically made for it by Skywatcher.

After you suggested this to me before, I looked it up, and the flattener I have is the one they recommend. 

I looked at my ED120 image corner stars last night and the effect is roughly the same, but not as pronouced with the ED120.

Thanks

Carole

[MarkS]

ED120 has a flattener/reducer specifically made for it by Skywatcher.

After you suggested this to me before, I looked it up, and the flattener I have is the one they recommend. 

I see.  Is it generally thought to work better than the "Skywatcher Field Flattener and.85x Focal reducer for Evostar ED120 Telescopes" found here: http://www.iankingimaging.com/show_products.php?category=17  ?

Mark

[Carole]

I see.  Is it generally thought to work better than the "Skywatcher Field Flattener and.85x Focal reducer for Evostar ED120 Telescopes

That I don't know Mark, but see this website under Astro Imaging which is what I used as reference:
http://www.telescope-service.com/Skywatcher/ED_refractors/ED-refractors.html#SKED120

you should use the William Optics 0.8x field flattener for best results.

Think I might have stated the wrong Flattener model above, will re-check when I get home.

Carole

[Carole]

Yes, typo above, my flattener is a WO X0.8 Flattener III. (Original post now modified)

Carole