A quick Dumbbell nebula. My first one.

[pixueto]

I still have to correct the vignetting with Pixinsight. That's 1 hour 46 minutes during a very warm last Saturday night in light polluted south east London.

Details:

SW200P on a HEQ5 Pro

Canon 1100D modified with astronomik CLS clip filter

4 minutes subs at ISO 1600

Guided with an Orion Starshoot Autoguider through a 9X50 finderscope

Processed with Photoshop

Any comments welcomed.

Thanks.

[laser_jock99]

Nice effort- thanks for sharing.

[Jessun]

Yes, very nice. I feel your pain imaging in light pollution.

I took some green out, see what you think !

/Jesper

[James]

...That's 1 hour 46 minutes during a very warm last Saturday night in light polluted south east London.

You got that from London? During this muggy, hazy, hot, generally bad for imaging weather? That's an achievement!

James

[Gina]

Nice

[jezhughes]

For London that's awesome. I say that because i live here and this week its been hard to make out Cygnus!...

[Coco]

Excellent!

[Freddie]

Nice job.

[pixueto]

Thank you all for your kind words. Thank you for the reprocessing Jesper, thank you James for supplying most of my kit. By the way, I just realised that's not from last Saturday but from the Saturday the week before, the 6th of July.

I had a chance to spend a little time reprocessing the image with a more aggressive stretching in Photoshop and finally tweaking the vignetting, noise and gree tinge in Pixinsight. Hope you like it; hopefully a bit of an improvement?

Thanks for looking and fo your comments.

[x6gas]

Looking good - and well done for wringing that out of the light polluted skies.

Do you take flats? I used to correct vignetting in software (or rather try) but I am a recent convert to flats (nothing fancy - I use the t-shirt method) and it makes a huge difference. Don't know why it took me so long to get around to it!

[pixueto]

Looking good - and well done for wringing that out of the light polluted skies.

Do you take flats? I used to correct vignetting in software (or rather try) but I am a recent convert to flats (nothing fancy - I use the t-shirt method) and it makes a huge difference. Don't know why it took me so long to get around to it!

Yes, I do take flats although I never managed to get right the t-shirt method! I struggled with them until I bought an Aurora Flatfield Pannel from Gerd Neuman. In this particular instance, I just took shots of the morning sky. Unfortunately, I removed the camera from the scope before this and had to put it back again in the position I thought it was so I didn't expect miracles with vignetting. However, I find that Pixinsight does a brilliant job removing gradients.

[RobinW]

You have some flex in your setup. See how the stars are eggy from bottom left to top right across the whole image. That shows flex. If you stacked the images without aligning them you'll see the movement, they stars would be streaks.

Your next move is to sort that out to get round stars. The movement may be in the guider focuser or the imager focuser or both or maybe movement between scopes.

Good Luck ....

[RobinW]

I didn't know how to edit the previous post..

The biggest reason to fix the flex is that the movement will also be seen across the target image. That creates blur and puts it out of focus.

The easy way to fix flex is with an off axis guider. However, now you have backfocus issues, distance from sensor to guider issues, etc etc.

Not an easy fix and takes ages to work out. Bolt everything down in the first instance.

Most movement is in focusers and microns of movement causes miles of problems.

Look at that finder you use for a guider and make sure it's solid.

[pixueto]

Thanks Robin, I didn't know much about flexure until some of you guys pointed out that possibility with this image. I think I know why this has happened but I'd love to hear what you think about it. The night I took those pictures, I had trouble screwing the adapter from Modern Astronomy into the finder so I could use the autoguider. I decided to remove the finder from the main scope to do it so I wouldn't risk moving the scope losing the 3 star alignment. I think that, ultimately my guidescope was pointing to a slightly different part of the sky to my imaging scope maybe creating a bit of differental flexure? Is this a plausible explanation? I've been getting perfect round stars until that night. What do you think?

[Quatermass]

That's a great dumbbell pix very nice indeed,I am getting the urge to start imaging again but need too get a replacement dual axis control box. Last image was the sculptor galaxy back in october must have gone astray some where ;-)

Sent from my Nexus 7 using Tapatalk 2

[pixueto]

That's a great dumbbell pix very nice indeed,I am getting the urge to start imaging again but need too get a replacement dual axis control box. Last image was the sculptor galaxy back in october must have gone astray some where ;-)

Sent from my Nexus 7 using Tapatalk 2

Thanks quartermass. I missed your posts here in the forum. It's been a while.

Nevertheless, I must say you didn't miss much imaging this winter as we could hardly take the scope out. I got a SW ED80 and despite being desperate to image Orion and the Horsehead with it, I did not manage to find a single night with the right conditions to do it.

When I took this photo of M27, my mum was with me and I was showing her what is involved in an imaging session...well, can you believe that I had forgotten how to attach the adapter to the camera? Shocking. I don't think she was impressed.

[Quatermass]

Yes last winter was pretty grim and after October I just wanted a break from everything plus I became obsessed with making German model aircraft. I sold my ED 80 as I felt it was never going to get used that much without an atik camera and I actually like my 200p more.

Once I can get a hand control unit for my dual axis motors I will get back to doing some imaging again. Had a reprocessing session of my shot of m31 and boy am I rusty good job I kept a detailed note book of my Photoshop methods. So hopefully I will join you all again soon buddy :-)

Sent from my Nexus 7 using Tapatalk 2

[jezhughes]

Thanks Robin, I didn't know much about flexure until some of you guys pointed out that possibility with this image. I think I know why this has happened but I'd love to hear what you think about it. The night I took those pictures, I had trouble screwing the adapter from Modern Astronomy into the finder so I could use the autoguider. I decided to remove the finder from the main scope to do it so I wouldn't risk moving the scope losing the 3 star alignment. I think that, ultimately my guidescope was pointing to a slightly different part of the sky to my imaging scope maybe creating a bit of differental flexure? Is this a plausible explanation? I've been getting perfect round stars until that night. What do you think?

Doesn't matter so much what part of the sky your guiding scope points to (within reason), as long as its in the right region you won't notice a difference. In fact my guide scope very rarely guides on a star close to the target.

Flexure's a mechanical error. What do you use to mount your guider? The main culprits are the guide scope's mounting and the focus tube slopping, although it can be your main scope too (although if your guide scopes attached directly to your scope, this reduces the possibility a bit). If you haven't got a rock solid (and i mean rock solid) mounting you can get a bit of flex. If your focusing tube is extended right out and wobbling all over the place, that's a sure sign. Its a tiny amount but can make a difference.

As someone's suggested, an OAG is the best thing to eliminate it, hence why I have 2 after getting fed up with flex. For some its not an option though, so look for a more solid mounting for your guide equipment, make sure you have a solid focusing attachment (without breaking anything).

I used to use a ST80 guide scope with my setup, i managed to cut flex down by doing a few things: I used to use a Skywatcher guidescope mount - got rid of it. Even when tightened up it was extremely sloppy and introduced a lot of movement. I went on to attaching straight to a saddle. I also upgraded my dovetails from the skywatcher ones to ADM which are far more robust, i didn't trust the stock Skywatcher ones. The ST80's focusing tube was also really sloppy, so i decided to use a t-thread extender to achieve focal length rather than use the draw tube its self. This meant more of the draw tube could sit within the scope tube and be locked in to place. This made things a lot more solid. After that i didn't notice much flex at all in lower f/l, but still a tiny amount in longer f/l (1200mm+), so decided to grab an OAG which has helped guiding at longer f/l

Sorry that's a bit long winded.

[jezhughes]

(Having said all that, i wouldn't let it bug you - I think your image is great and it will only improve)

[pixueto]

Thank you Jezhughes. Nevertheless, I think the finder scope was pointing to a very different part of the sky. I'll align it properly and see what happens during the next imaging session; I think that will be the acid test before I go mad chasing gremlings