field rotation?

[Galaxyfaraway]

Thanks so much for taking the time to look at the spacing.

According to this link: http://www.firstlightoptics.com/reducersflatteners/william-optics-08x-reducer-flattener-6-gt81.html

and the image/drawing below: the distance between the glass and the camera sensor is supposed to be 64.38mm. Or am I reading this incorrectly? Above it, it does also say the distance is supposed to be 55-57mm "suggested distance". Do you or anyone know how one is supposed to interpret it?

Maybe 55-57mm takes into account included adapter which is 9.7mm? (marked with the blue arrow).

I arranged my spacing according to the 64.38mm diagram and am not using the supplied adapter. Loosing 7-9mm will be difficult. The T2 spacer I currently have adds 5.2mm so without it, I will be out by a few mm.

This is my imaging train: Atik 490EX (13mm) + EFW2 (22mm) + OAG (24mm) + M54 to M42 (1.3mm) + Delrin spacer (1.2mm) + M42 extension ring (4mm) + WO reducer

This gives me 65.5mm (minus 1mm for the Astrodon filters). Do I have this wrong???

I spent about 4 hours experimenting with spacing yesterday (my next refractor will have a built-in flattener! This is too frustrating. Although I read that 5-element refractors are extremely difficult to collimate correctly, if something is wrong). And I also noticed that the star shapes varied a little according to slight focus shifts. I read this about Takahashis (which are faster: where you are supposed to focus off-center) but have not expected this with a William Optics at f4.7.

I can't detect any tilt in the imaging train and everything is as tight as it can be....But i need to nail the spacing first before I start excluding other things, like camera sensor tilt etc.

Lastly: perhaps I am expecting too much from this (relatively) budget scope?

Grateful for any suggestions/comments. 

[ultranova]

I have the Z71 and the matching R/F it says on mine that its 68.32mm

according to the sheet you put up but.

I use mine at 56-57 mm, I cant remember where I got the info I shall

try and find some info

Just found the info lol, it was on the link you put up read it to the bottom

, I still think its a bit of tilt but your main problem is your chip distance

its not the scope, you are not expecting to much its just you have not seen

what it is capable of, I think once you have dialled in this scope it will

meet your expectation's

[Galaxyfaraway]

Do you use the reducer with the supplied adapter? (The Canon EOS adapter ring, which adds about 9.7mm and would explain the difference between 55mm and 64.38mm). I must be crazy but the drawing on the picture seems to say to me that the distance should be 64.38mm!!

Or do you have an earlier version of the reducer?

 

[ultranova]

I know very misleading isn't it, I got confused when I got mine but 56-57 is the way to go

which will probably make it awkward for you as you will probably have to loose the OAG,

O don't use the adapter just straight onto the thread on the back of the R/F

[ultranova]

I have the flattener 6 which you can see on the FLO site

which is made for the Z71

[Galaxyfaraway]

Oh wow. Ok. What is the reason to mention the 64.38mm at all? Is it referring to something else in the picture?

I have been tearing my hair out over this...

[ultranova]

This is with the flattener 6 and Z71 last year,

For a very small cheap Scope it don't do bad,

Your Gt81 should be a bit better once you get it dialled in

 

[ultranova]

I have no idea, but I think you will be surprised by the results if you can

get it to 56-57mm, I am surprised your pics came out as well as they did

what you will get in the corners is a squashing up of the stars, which makes it look

 like field rotation,

[Galaxyfaraway]

Great picture but to my eyes (and maybe I have been staring too much at stars from my own images that is giving me astigmatism...) the top left and bottom right corner stars are slightly 'eggy' towards the centre. For some reason, this only happens to small to medium-sized stars.

Here's a 100% crop from your image. It's probably much too mild (and certainly much better than my stars in the the corners) and might have to do with the fact that WO can't decide whether it should be 55 or 57mm....

Someone should adjust the 64.38mm figure. I will write to WO to clarify this.

It's a shame I will have to ditch the OAG and get some sort of guiding scope. There will probably be flexure to contend with now, as the next pain in the behind...

[ultranova]

yes stars are not perfect in all corners due in part to tilt I have 1.6 kilo's of camera and filter wheel hanging off the back of this tiny scope,

and most systems will show a tiny bit of distortion when viewed at 100% some where on the pic when doing 10/15 minute subs,

But in saying that you can get paranoid about the whole thing which then starts to take the fun out of it if your not careful.

At the end of the day we all want to get the best out of our kit with our hard earned cash, and us Uk living people don't get enough clear

nights to experiment with our set ups,

The best corners I have ever had has been with the SW 80 ed pro, with there 0.85 R/f but at f6.3 its a tad slow for the British weather, 

as all the connections to the scope are screw on which makes for a slightly better connection.

hope the info helps and you get to the bottom of it,  

Paul

 

[Galaxyfaraway]

Thanks! It wasn't meant as a criticism; I am trying to work out how far I can take the 'star shape paranoia' (is there a medical term for this condition?

Do they specify how heavy the load can be on the focusers for various telescopes? This seems like an important metric which should be taken into account when purchasing a scope.

I have my eyes either on a Televue or Takahashi sometime in the distant future...But it seems the latter is not without mixed reviews and the former might be a little slow for UK. Plus there probably aren't bad telescopes, only bad photographers

I guess one good thing is that without the OAG, the load shall be (slightly) lighter. I shall try the new spacing at the earliest opportunity.

[ultranova]

Good luck and keep us posted,

looking forward to seeing the results

clear skies to us all

Paul