My first "proper" image with new setup, another Horse & Flame in Ha

[parallaxerr]

You may be right Ian, but agreed, could be image scale.

If indeed I am already into diminishing returns, which is probably the case shooting narrowband through a DSLR and losing data to the bayer matrix, then I guess OIII and maybe even SII data would move the image on to the next level of detail.

I am by no means under the illusion that I'll match the quality of images produced by cooled mono CCDs, but I must say I'm more than happy with the results so far

[Adam J]

Am interested as to how you managed to get a filter wheel between the field flatter and the DSLR or are you not using one? In which case the stars at the edges of your field are remarkable round for an APS-C sized sensor on an flattened refactor.

[parallaxerr]

Hi Adam, I'm using a coma corrector as a flattener which screws on to the filter wheel via an m48 thread, so DSLR>T-Ring>MPCC>filter wheel>focuser...

 

[parallaxerr]

Going back through my data this evening and it looks like I made a bit of an error.

I noticed some eggy stars on the left hand side of the image that I claimed was 6hrs of exposure time, so I manually checked all the frames and none had eggy stars so figured the problem was in DSS.

I reran the images through DSS in the exact same order only to notice that the output file was only 3hrs of exposure!!!

Long story short, I made a few settings changes and got DSS to stack all the subs, so THIS is the full 6hr exposure. Definitely more detail in the cloud structure and the eggy stars are gone, go figure....

Problem - concentric, circular noise pattern emanating from the middle right of the image?

[Filroden]

18 minutes ago, parallaxerr said:

Problem - concentric, circular noise pattern emanating from the middle right of the image?

That's very strange noise. And more noise than I would expect from Ha and 6 hours of exposure. Are the subs calibrating correctly?

[Adam J]

On 11/29/2017 at 17:32, parallaxerr said:

Hi Adam, I'm using a coma corrector as a flattener which screws on to the filter wheel via an m48 thread, so DSLR>T-Ring>MPCC>filter wheel>focuser...

 

I seriously never knew you could use a Newtonian coma corrector as a FF on a refractor. Are you having to crop the images or do you find that its flat across the full APS-C sensor? That focuser must have some serious back focus available.

[Guest]

Hello there, very nice image, and I also am a big fan of Ha.. 

[parallaxerr]

11 hours ago, Filroden said:

That's very strange noise. And more noise than I would expect from Ha and 6 hours of exposure. Are the subs calibrating correctly?

I tried with and without calibration frames Ken and got the same result. If I strectch my earlier results enough, I see it there too, so I don't believe it's a change I made in DSS. I've seen posts on CN about the same thing, but no solutions, Further investigation required...

1 hour ago, artem said:

Hello there, very nice image, and I also am a big fan of Ha.. 

Thanks artem, nice of you to say

9 hours ago, Adam J said:

I seriously never knew you could use a Newtonian coma corrector as a FF on a refractor. Are you having to crop the images or do you find that its flat across the full APS-C sensor? That focuser must have some serious back focus available.

I don't think it's common practice, just something I came across here when I had a WO ZS66SD and couldn't get a flattener to match...

http://www.stark-labs.com/craig/WO66SD/WO66SD.html

No, they're not cropped, they're full frame

[Adam J]

2 hours ago, parallaxerr said:

I tried with and without calibration frames Ken and got the same result. If I strectch my earlier results enough, I see it there too, so I don't believe it's a change I made in DSS. I've seen posts on CN about the same thing, but no solutions, Further investigation required...

Thanks artem, nice of you to say

I don't think it's common practice, just something I came across here when I had a WO ZS66SD and couldn't get a flattener to match...

http://www.stark-labs.com/craig/WO66SD/WO66SD.html

No, they're not cropped, they're full frame

I assume you mean full APS-C as opposed to actual full frame. I also assume that you need to be within the same F-number window as the corrector works for from a Newtonian? So F4.5 to F6 ish? What F number is your scope?

[parallaxerr]

1 minute ago, Adam J said:

I assume you mean full APS-C as opposed to actual full frame. I also assume that you need to be within the same F-number window as the corrector works for from a Newtonian? So F4.5 to F6 ish? What F number is your scope?

Yes full APS-C, not full "full frame" lol. The scope is F5.

[RayD]

Purely for my interest as I have absolutely no idea, does it make any difference having the filters in front of the CC rather than behind?  I've only ever seen imaging trains with the field correction done before filtering and not after.

[Adam J]

27 minutes ago, RayD said:

Purely for my interest as I have absolutely no idea, does it make any difference having the filters in front of the CC rather than behind?  I've only ever seen imaging trains with the field correction done before filtering and not after.

Will depend on the type of filter, how good any anti-refection coatings are and the separation between glass elements. So in normal circumstances it should not make any difference but if it did it would show up more in a broad band image. 

[The Admiral]

1 hour ago, RayD said:

Purely for my interest as I have absolutely no idea, does it make any difference having the filters in front of the CC rather than behind?  I've only ever seen imaging trains with the field correction done before filtering and not after.

My only thought here is that because the light rays are convergent, the closer to the sensor the smaller the filter can be without causing vignetting.

Ian

[RayD]

Thanks Guys.  As I say I have no idea so both make sense, I've just not seen it done this way and didn't know you could.

[parallaxerr]

2 hours ago, RayD said:

Purely for my interest as I have absolutely no idea, does it make any difference having the filters in front of the CC rather than behind?  I've only ever seen imaging trains with the field correction done before filtering and not after.

In my case, the CC has to be behind the filter wheel in order to maintain the correct spacing of 55mm to the camera sensor.

[RayD]

3 minutes ago, parallaxerr said:

In my case, the CC has to be behind the filter wheel in order to maintain the correct spacing of 55mm to the camera sensor.

Thanks Jon.  Yes I understand the spacing, I've just never seen the filters mounted the OTA side of the corrector before.  If it is doable, as certainly seems to be the case here, it could make me rethink what I can and can't fit in my imaging train (OAG etc.).

[Adam J]

39 minutes ago, RayD said:

Thanks Jon.  Yes I understand the spacing, I've just never seen the filters mounted the OTA side of the corrector before.  If it is doable, as certainly seems to be the case here, it could make me rethink what I can and can't fit in my imaging train (OAG etc.).

I just make sure your focuser has sufficient back focus.