Megrez-72 - horribly distorted image? Help?

[rocketandroll]

Hi all

Ok, so, although I wasted nearly two hours unsuccesfully trying to get my Synguider working last night, I did nonetheless get first light on my Megrez-72.

Please, someone tell me this isn't right?

I've used a few scopes now for imaging, triplets and doublets... so I thought I knew what to expect... but the images I got seemed worse than those taken through a achromatic refractor...

Have a look at the below image, this is just a couple of minutes (in 30sec subs) on Sadr unguided...

The focus isn't bang on, I know... but have a look at the star shapes... as soon as you get about 25% of the way out from the center they are horribly distorted and by the time you get near the edge they're lines.

Whilst the Star-Wars 'hyperspace' zoom effect is amusing, it's not what I'm looking for in astrophotography.

Please, someone tell me this isn't normal... is it?

Has anyone else used a Meg 72 with a DSLR? Even through my 32mm ep the stars visually looked very distorted at the edge of the field, far more so than looking through my ST80.

If this is the best I can expect without forking out for a field flattener, having never needed one with any other scope, doublet or triplet, I'm not too impressed :-(

Can anyone offer help or advice? I just don't think it can be right that only the center 25 - 30% of the field of view can be vaguely useable in such a relatively high end scope?

Ben

[brantuk]

Hi Ben - Did you use a flattener? The SW one works a treat and pretty essential with the Meg72 plus it comes with a T-ring thread

http://www.firstlightoptics.com/reducersflatteners/skywatcher-field-flattener.html

Here's what we got (mostly attributable to Glider):

http://stargazerslounge.com/imaging-deep-sky/136441-kelling-heath-28-3-11-flaming-star-nebula.html

See final processed picture at bottom of thread.

[rocketandroll]

Hi Ben - Did you use a flattener? The SW one works a treat and pretty essential with the Meg72 plus it comes with a T-ring thread

First Light Optics - Skywatcher Field Flattener

Here's what we got (mostly attributable to Glider):

http://stargazerslounge.com/imaging-deep-sky/136441-kelling-heath-28-3-11-flaming-star-nebula.html

See final processed picture at bottom of thread.

Cheers Kim.... no, I didn't use a flattener, never needed to before really, with the ED80, or the Meade 127.... never seen any distortion like this before.

Might have to invest in one... pain in the a** as I don't relly have any spare cash at the mo!

Ben

[brantuk]

Yeah - I know the feeling re spare cash lol But the flatenner will turn the Meg into a superb little wide field scope - so maybe when you get paid.....

[rocketandroll]

Yeah - I know the feeling re spare cash lol But the flatenner will turn the Meg into a superb little wide field scope - so maybe when you get paid.....

I get paid in December :-)

Nah, I have some credit with FLO, will use that for a flattener and a 1.25" diagonal to get the Synguider working I think.

Cheers! :-)

Ben

[brantuk]

The flatenner's 2" push fit btw - just fyi

[carastro]

Ben, up until a few months ago the only scope I had was a WO Megrez 72 APO. I always used a flattener with it, and even then the far corners were distorted. However I would say 90% was fine. It's a nice scope, just need to get the flattener sorted.

I used the WO X0.8 111. I've now got different scopes and bought myself a new flattener (which I haven't had a chance to try out yet) so I'm hanging on to the WO flattener until I know all is working well.

Carole

[Psychobilly]

I didnt need a diagonal to get the Synguider to focus just used the cheapo barlow

taht came with the ST80 with the lens removes... this gives 3-37mm extension and the ST's focusser is at roughly 55mm (pic in your other thread)...

I use a Megrez82 with the WO FFIII it was (accordign to Ian King who sold it to me) the best optionat the time which is a few years ago now... for best performance inthe very corners focus is critical... Other recently available flatteners also work well...

Peter...

[ollypenrice]

You've led a charmed life if you haven't needed a flattener so far! I found my Meade 127 wouldn't quite cover a DSLR chip and my TEC140 certainly won't. Doublet or triplet, any refractor needs a rear element to have a large flat field.

Olly

[steppenwolf]

Have to agree with Olly, a Triplet will need a flattener with an APS 'C' sized sensor so I am not surprised by this result to be honest.

[rocketandroll]

Cheers all...

As Olly says, I must have just been incredibly lucky so far?! I've gone back and reviewed the pics taken with the Meade and there is a teensy bit of misshaping to the stars at the very corners, but I've never noticed it before, so it's barely noticable.

I've certainly never had to crop any images from the Meade due to the corners being off.

I guess it varies from scope to scope.

Anyway, a flattener is on order so, fingers crossed, I can use more than a third of each sub after it's fitted!

Cheers folks

Ben