The eggy saga continues

[rubecula]

Well, it wasn't an issue with the modified Canon 550D, which I thought was the most likely.  The sky was clear for a short time this evening and I managed to run a 600 sec exposure with the 7D and got exactly the same eggy stars in the top corners of the image. 

Now that's ruled out, from the help you gave me previously it seems it may be the collimation or a problem with the focal reducer.  My next guess would be collimation.  But having got the last guess wrong I'm not so sure.

I looked at removing the focal reducer but it looks as though I'll have to buy another fitting to connect the OAG to the back of the scope and I need to look up what backfocus is required.

Does anyone have any ideas as to what is most likely, the reducer or collimation? Here is the original 550D image, the distorted stars are the same with the 7D:

 

 

[PhotoGav]

Hi, is this problem with your EdgeHD 800 and 0.7x reducer?

[PhotoGav]

Reading your earlier thread and looking in your signature, I presume this is with the edge. In which case, I am having a very similar problem with my EdgeHD 800 and 0.7x Reducer. Have a look at this thread for more details: 

As you can see from that thread I have eggy stars on the left side of the image. It seems to be much better without the reducer. Your thread makes me think that it must be an issue with the reducer. I did try another similar reducer courtesy of FLO, but the problem persisted. I ruled out the reducer, but I'm beginning to think that perhaps these reducers aren't very good!

As an aside, it does look like your collimation is out. You should definitely have a fiddle with that. Use an eyepiece, much easier than trying to do it with a camera - that's my experience of it anyway!

[rubecula]

Photogav, yes it's an image taken with the 8" EdgeHD and the focal reducer.  Next clear night (Thursday possibly but I'm not holding my breath) I'm going to check the collimation visually with and without the focal reducer to see if I can spot the problem. 

I'm not sure if the 13mm eyepiece will give me enough magnification to check the collimation visually.

If that doesn't show an issue then I'll have to do a 600 sec exposure without the focal reducer to compare with the image above.  I think I need to buy another adapter to get the right 133.35mm backfocus without the reducer.

[PhotoGav]

Hello Robin,

Thought I would let you know that FLO very kindly sent me a new reducer to try on my Edge. Tonight is the first night I have been able to give it a try and the first sub has just come in... It looks much much better, to the point of being perfectly acceptable. So, my problem appears to have been a dodgy Reducer. Perhaps you will find the same.

Clear skies,

Gav.