PadrePeace

Rjbram
It’s clear theses images come from good solid subs. I don’t see any guiding issues in either image. The ‘blemishes’ are all normal and will be cleaned up with calibration frames. I suggest you watch any of the many YouTube videos on how to gather Flats, Dark Flats and Darks and how these are applied to your subs during stacking which will transform your stack. 
 

Which stacking and processing software are you using?

Hey, Andy there are those that have and those that will. We are all in there somewhere. F22? Surprised you could see much at all but good spot. Can’t help you with the weather but you may consider using an artificial star. Check it out. I made one from an led torch with the lens covered in about 10 layers of tinfoil lightly pricked with a needle. 

With such a long zoom I’d suggest you get it to focus as close to the end of the travel as you can so that you get as much zoom capacity as you feel you need. I’d expect it to be sensitive as mine was so be methodical in your adjustments as you don’t what to pass through the focus sweet spot as I did. Given that DSLRs are 55mm BF it, by definition, has to be close to that plus the 1/3 thickness allowance for any filters in the optical path. 

Do let us know how you get on. 

Hi Phil, thanks for your kind comments. 

I’m out Horncastle way. It’s been very hard this year as you have found. The NB filters (mostly Ha) help a lot when the moon’s up but I always try to get out before it gets too high so much of my imaging is in 1-2 hr sessions. You have to be on top of the forecast and I use Sat24 web site to see what the cloud is doing. The real world is king.

I thought about getting a Sammy 135 as I do use other lenses occasionally. It’s speed (from F2.8) is very attractive when time is limited. That said, the Askar 180 is a cracking small telescope as this thread is recognising. See AdamJ’s comments on it which are authoritative and backed up by the science behind his deductions. 

Clear skies to you

My latest effort with the Askar180. Still mounted on the iOptron SGP with a mono Atik 460EX and EFW loaded with NB filters. It’s just over 23hrs of integration. Enjoying this wonderful little scope a lot.

Who said?
Evidence for this statement please Licho52?

PS: apologies Licho52, missed the sarcasm in your comment. 

I’d disagree with a £1100 price point as similar market mono versions are typically (ie. ASI294) around £500 over their OSC sisters. I’d expect ivo £1400 even with a small sensor as it’s much improved technically over the 1600 which is getting long in the tooth now. 
The exception seems to be for the high end 2600 series which are both £4k which sort of tells its own story. 

Be smug. Good skills and thanks for bringing this news out to the readership. 

Just re read your opening comment to this thread where you say ‘it works fine on trees during the daytime’ please clarify if you mean the EP or the camera?

what camera are you using?

Google Back focus and pick any of the many YouTube guides to setting this up.

Your camera will have a required back focus distance. This is generally 55mm and is measured from the sensor inside the camera and not the camera case. If you are using a Flattener and/or a reducer on your scope 55mm is measured from the camera side of that device to your sensor. This is where you will need extension tubes/adaptors as you see in my pics. To get an idea of how far your sensor is mounted inside the case you’ll need to find this online or ask on this forum. It’s quite straightforward really.

The reason astrophotographers have to add this additional back focus distance is because scopes are always made to work for visual observing as well and therefore have the focuser optimised accordingly. This is why your eyepieces work but the camera has issues because it’s too close to the scope lens by a significant amount.
 

If you are not using a flattener/reducer you may just be able to extend the focus tube out enough to reach sensor back focus but often that is not the case and you need adapters that screw together to bridge the additional gap.

I’ve had this kind of issue and will guarantee you don’t have the camera back focus set correctly as others have suggested. Replacing an eyepiece with the camera or removing the diagonal and replacing it with the camera will leave your sensor so far out of focus you will get nothing but dark areas or blurred shadows. Follow Adam J’s advice and get your sensor far enough back to focus the light cone into it. You may well need extension tubes to do this as I have scopes that have a lot of additional extension tubes fitted to the back of the focuser to get focus. See examples attached. Do the back focus math for your camera, set that distance and all will become clear… literally.

I’d strip the stars out using Starnet or Straton and then reduce the red and blue equally in PS. 
 

skinning cats here I think.

So it’s the flats adding the gradient. Hope you can resurrect your work and get a good image out. 

What temperatures/humidity are your shooting in?

What temperature are you cooling the sensor down too?

Do you use dew straps on the scope and guide scope?

how good was your polar alignment? 

I ask because I’m seeing stars which are all badly trailing in the same direction which could be bad polar alignment and a lack of corrective guiding. If both your guide and main scope have Dew then that might give the trailing stars which are not guided out effectively added to the issue in the middle of the frame and maybe add this thought to your diagnosis.

I don’t use bias either. 
Took some sky flats today at 2300ADU. Then took some more with my flat panel (not the IPad). Interesting outcomes. 

Sky Flat

Flat Panel (not the iPad)

seems the iPad and the sky flats have significant glow down the rhs which my flat panel does not. The Histogram on the latter looks a lot better as well. 

Budgie

Thanks for chiming in with you experiences. I also cool to -10 to match my subs though I know that’s not necessary. ADU was 23000, Gain was 120 with the offset at 8. I used a white screen on an iPad as the source which has been fine for other CMOS cameras but could be the issue here. I’ll try sky flats tomorrow and report back. 

I'm shooting Sh2-129 (Squid Nebula) with a ZWO 294MC and the L-Extreme Dual Band filter.  Scope is a WO71GT flattened and reduced to 336mm FL (0.8). When stacked in APP I'm getting OIII flats (first image) and Ha Flats (second image) looking as below. Any ideas why the is so much brightness on the right hand side of the OIII and why the Ha looks so different?  The Flats where shot in NINA's Flats tool at 5.63s exposure and the same camera settings as the lights.  I have discounted light leaking into the sensor during FLAT production.  Any other comment on what others may be getting with the same combination would be appreciated. 

Ha Flat

This is the OIII stacked using the Master Flat above:

This is the Ha stacked with the Master Flat above:

Finally, this is the Master Flat in RGB. Hope the colours might give a clue to what is going on here.

This is only 10.5hrs or integration so plenty left to do I guess.......

regards

Padre

Michael, filters in the optical path will always require additional BF to be added, usually 1/3 of the filter glass thickness. You do have a miscalculation here as there is obviously too much distance to the sensor at the moment. Would like to see a sub once you have it sorted.

This shows how stars are impacted by too little or too much back focus. AdamJ is spot on with his diagnosis. 

Planetary nebular? 

Clearly if you have tilt included which may improve or degrade corners further you need to play tunes on the two images above

Agree with AdamJ. This diagram is handy for reference. 

Can I ask given the scope’s  speed and therefore tiny focus window if you are using an autofocuser with you Tac 180? If so, is that on the original Tac focuser or an upgrade?
I’m very surprised that Tac mount a single speed focuser on gear this expensive and fast. how do you find it performs?

Thanks for sharing. I have the same issue with Straton and the spikes. Just hope someone cracks an AI/neural software to recognise and remove those as well as the stars are removed. 

12 hours ago, drivera said:

Thats really interesting. I thought it was 2.93kg so I have been pre-empting my total weighting around 4.3kg with all the stuff. I'm wondering if I do move the guidescope/cam to the counterweight bar it can assist.

It seems you are right on the weight of the new 71GT which seems to have put on some weight since I bought mine(see my attached manual which states 2.2kg). Could be the handle which is a ‘nice to have’ but not essential in my view especially on such a small light scope. 
https://williamoptics.com/download/support/GranTurismo_71_Owner_Manual%2Bver.1.0%2B2017.06.pdf