Please Appraise My Photos - 2 pics now.

[Spacehead]

Hi All,

My stars are looking off depending on where abouts in the photo they are.
My photos are darker on the right than on the left no matter what area of the sky I take.

I have drawn some lines on to show you what I mean by the stars being off - its their shape - like little comets with tails in different directions.

For this pic, I used a Bahtinov Mask for focussing - which I was confident with, as I used a large bright star (Vega) and performed the focussing with live view on my camera at x 10 zoom in.  So that was spot on.
For tracking, I polar aligned using an app which puts a dot on a circle on the screen (it was at 12 oclock), I placed that dot at 12 oclock on my reticle (although I am not certain about that because the cross hairs on the reticle are like an X whereas the crosshairs on the phone screen are like  + so "rotated" if you know what I mean.

The shot is 400 ISO 60 seconds single shot.
Please please please help - I never come in after hour after hour with good shots.

The cam is a brand new eos1300d astro modded - the effects I am seeing are pretty much the same as I got with my old eos 400d - bad.

Here is the image - any appraisal would be very much appreciated.  Its a full size image.


In the image below, taken the night before the one above, ive changed the rgb values in DSS - so you can see something is really wrong here.
It doesnt matter where the scope is pointing, its always the same.  - this darkness to the right - and this pic below is showing something more sinister?


Cheers All.
 

[PeterCPC]

You don't mention that you were guiding so I assume that this is unguided. I just think that you are seeing trailing - do you get this with much shorter exposures?

Peter

[Spacehead]

Hi Peter, sorry - its tracked using a motor on the RA.

I am confident in the tracking (within the limits of tracking that is!) - the overall motion of the stars is "up" the picture over an hour and fifteen mins - only by a bit the so I would expect trailing in that direction of the drift - if any.
but at 1 min shots, its not really showing.  Plus there are different directions in a given shot.
Here is a layered image showing start of session position and end of session position.
Hmm - I would have to try with shorter exposures.

[pete_l]

1 hour ago, Spacehead said:

Hi All,

My stars are looking off depending on where abouts in the photo they are.
My photos are darker on the right than on the left no matter what area of the sky I take.

I have drawn some lines on to show you what I mean by the stars being off - its their shape - like little comets with tails in different directions.

Is the shape of the stars just ordinary "coma"? An optical effect that is quite common on telescopes that are used without a coma corrector

[Spacehead]

Hi Pete, I think that my collimation is waaaaayyyyy out - its 3 years old the scope - ive never collimated it.  I think a combination of the focus and the shading of the overall image could be indications of this.  I am going to have a tinker

 

[ollypenrice]

You do have coma. It's not symmetrical either. It should be possible to improve it but you will need a coma corrector to cover an APSc sized chip anyway. I don't see any evidence of tracking error, at least nothing obvious. So I'd collimate and add a CC and see how you get on.

Olly

[newbie alert]

To my untrained eye it looks like a combination of drift and collimation.. or scope not having enough cool down time..

Your PA sounds like it could be improved..as does the app reticle correspond with your eyepiece.. 

Try sharpcap..or I rate a polemaster very highly

[Spacehead]

Guys - thanks for your replies.

I have just checked (for the first time ever - so it was new to me) the collimation.

It was so far out that I would say a complete 30% of the main mirror was not showing at all in the secondary!!!!!!

When looking through a quick home made cap I made with a hole in the middle - I couldnt initially see the hole in the cap OR the donut on the MM (which actually indicates that they were fairly close so far as I can see as the donut was in the dark area in the middle BUT "somewhere" to start with).  Honestly it was all over the shop.

So I adjusted the back screws until my cap center was in the middle of the donut, then adjusted the tilt on the secondary to bring all that missing 30% into alignment, then went back and re-adjusted the MM to get the dot back in the donut.

I have been using this for three years!!  No dam wonder I can never get good focus - I was going out of my mind - its no wonder half my pics are getting loads more light than the other half! (well - a graded 33% 67% split give or take!)  It all makes sense.

Sure - I understand comma to an extent, and also my failings with tracking.  But at least now my collimation is nailed I can concentrate on those issues.

I am now extremely looking forward to testing this the next fine night!!!!  I look forward to some predictable blurring requiring comma correction, and futher tightening of my PA skills.  (Ill post another query about that).

Cheers