Poor imaging results with a Barlow

[sdavsky]

Hi everyone, this is my first post on any forum ever so I guess that makes me a forum virgin. Also hi to all those who I met for the first time at the new Tannenbaum dark sky site. I really enjoyed it.

 

My question is this: for the last three nights I’ve been trying to image galaxies with a Barlow and have some very mixed results. In fact thinking back over the last two years I’ve always struggled with focus issues when using a Barlow. With a Barlow my Bahtinov is useless, I don’t get diffraction spikes in fact the best I seem to manage is a weird ‘woodlouse’ shape and I just cant get the stars tight. Its no better with FWHM type focussing.

My scope is an Opticstar ARC127 QUAD. Its basically a five inch doublet with a corrector lens somewhere inside the tube so its nothing special but it seems to work ok – that is, without the Barlow.

I can see that the corrector is refocussing the light at the sweet spot at the bottom of the tube and moving a lens away from there I will start to get refracted light.

I can slide my Barlows a long way in and out of the tube and I’ve just realised the Barlow lens itself may be nowhere near this perfectly focussed spot..

Assuming that this is the case has anyone any suggestions for finding the right amount to push the Barlow in the focussing tube other than laboriously inching in or out millimetre by millimetre while messing with the focus at each point?

I cant tell you whether the corrector is at a fixed position inside the tube or more likely I guess it would be fixed somewhere at the top of the focusser itself.

If the position doesn’t matter then that would suggest using a Barlow is always going to be a poor option because I dont have a second scope to try it on.

Thanks for your time.

 

Regards

 

Dave

[+Ibbo]

How much travel is on the focuser???

[+RonC]

What size eyepiece are you using??

 

Ron

[sdavsky]

20 hours ago, Ibbo said:

How much travel is on the focuser???

There is about 4.4cm of travel left. I should say I have three barlows. One is a Celestron which I got with a kit when I owned a C8 many years ago. The other is a Chinese 2inch supposedly ed glass which I bought from Amazon in a mad moment. It gives the same poor results as the Celestron.

I use Deep Sky Stacker to stack my images and often they are so poor with the Barlow DSS fails to recognise stars as stars and refuses to stack. Without using a Barlow DSS recognises many stars and stacks perfectly.

 

Thanks

 

Dave

[+Ibbo]

I generally only use the barlow on planetary, solar and lunar.

Its not really good for DSO's  as it dims as well as enlarges things.

 

Sound as though you need to go through the small increment excercise to find the sweet spot.

[sdavsky]

23 hours ago, Ron Clarke said:

What size eyepiece are you using??

 

Ron

Hi Ron,

I only use the scope for imaging, I’m using a modded Canon 450d. I have a Celestron 1.25inch 2x Barlow which I got with a kit that came with a C8 I used to own many years ago. More recently I had a rush of blood and bought a Chinese 2inch 2xBarlow, supposedly ‘ed’ from Amazon. To be honest there isn’t a lot of difference between them.

I use Deep Sky Stacker for stacking and with either one DSS really struggles to find stars because the image is poor quality and often I get the dreaded ‘only one frame will be stacked’ message. Without the Barlow I get lots of stars registered and stacking always runs well.

 

As I write I’m thinking sensor orthogonality may be an issue here but I don’t think its the root problem.

I have both a 2inch to T adaptor and a 1.25inch and even though I tighten the screw as tight as I can the camera doesn’t feel it has a rock solid attachment to the scope, to the extent that the camera has fallen off before now. I now routinely attach it to the scope with a small chain.

I’ve just been looking at Baader clicklock adaptors, does anyone have experience of them? It sounds like they would grip a camera securely but I’m not sure which one I would need.

 

Or am I just asking too much of a Barlow? When I image the moon and planets Autostakkert seems to give me pretty good results. Its just that its galaxy season and with an F4.9 scope they don’t exactly leap out of the image.

I should say I image mainly deep sky.

 

So in essence, would a Baader clicklock solve my orthogonality/looseness issues and am I just asking too much to expect quality deep sky images?

 

Appologies for any duplication, while replying a while ago the laptop had a massive update which crashed it.

Many thanks

 

Dave

[+RonC]

My Canon T2 doesn't lock on very well  but It's never fallen off!

Still not sure why you are using a Barlow, I have 3 and I've never used any of them!!

 

Cheers

Ron