80 mm What is wrong?

[xelasnave]

I was in a rush to beat the clouds and thought I was polar aligned or at least reasonably so. ..but lookinh at my few images this morning the stars are elongated badly near the edges (which is probably why I did not notice last night).
It is an 80 mm espirt with a nikon 24 meg camera.
Any ideas what my problem is.
In the central area stars look reasonable but at edges they are terrible.
Alex

[xelasnave]

Here it is...

[N1]

Field curvature?

[luka]

Yes, it is field curvature. A field flattener will solve the problem.

[brisen]

There should be a flattener in the case with the scope, I have recently upgraded to the Esprit 120 and a flattener was included. I am using a CCD with it, but the stars are round to the edges with the flattener in place.

Brian

[xelasnave]

Thats the problem the field flattener is on????
Must need adjustment...
Alex

[brisen]

Have you got the spacing right - there is a DSLR adapter that comes with them - should be 55mm back focus from the flattener to the sensor.

Brian

[xelasnave]

The flattener is instaled see photo.
Alex

[brisen]

The flattener is right and it looks like the DSLR adapter is there - there looks to be a bit extra on yours after the adapter though which might be taking the backfocus back too far. I have a canon t ring with mine and it looks thinner but not sure if the Nikon one is different. The ring screws straight onto the adapter with no extension tube. The other thing - is it the correct flattener for the 80 mm. I know some inadvertently got the wrong flattener. On the flattener mine has 120 - might be worth checking as this can cause issues.

Brian

[bigjoe]

Theres elongated stars even in this nice image near center ..not just edges ..tracking needs be a bit closer to pole perhaps..thought if spacing is not within even half a mm that can cause problems ..nice go Alex..gives us all an idea of what can happen.
PS:this unit has an extra spacer? is it needed?
bigjoe.

[xelasnave]

I dont know the distance to the chip when Michael put it together I think he took the front of the flash plate as where the chip face was ..its supposed to be 61 mm but looking at it and with crud measuremeants to determine where the chip is at this stage it seems it could be too far out. But looking at the bits I have I cant see something I missed...I probably have.

Maybe it is the wrong flattener I will try and get a beeter alignment..also maybe the camera is not ligning up ..its just such a strange arrangement for the stars.

And the old (new) 8 inch out of the box worked...It must be me...

Thanks everyone I will have a play to night hopefully ... But other than my current problem I was happy with the image in so far as 30 seconds at 800 iso in the city is ok by me... And I think much longer captures will be possible...If nothing else I will see how long I can expose for and not worry about trailing for the moment ...Settings iso plus need to get a dedicated focuser mask ...so much to do.

alex

[xelasnave]

I will work on the alignment but I think its more than that..Its like what I expect as coma would be like in a reflector...

I think the camera needs to be closer ... but cant change that at the moment but maybe I will adjust before the flattner between flattener and objective... a bit see if that changes anything...

There is no spacer or any thing that allows me to put it together differently.



I will have a look on utube for someone setting up a rig like mine ..there must be one out there.

Alex

[xelasnave]

I must check mount level something may be different.
If it has gone out of level..how I dont know but thats what it looks look somehow...as well.

I love problem solving I love problem solving.1...2...3...4...

ANyways the way the clouds are rushing past I will have to go for 10 second captures...maybe the sky is the problem,...because I think even though it looks clear there must be a lot of water vapour so maybe clouds refracting the light???
Alex

Alex

[xelasnave]

From the ruff mesurements so far I think back focus is too short...maybe there is a ring I have misplaced...as it seem needs to move back.
I am not sure where the chip is and dont realise want to poke aroung with a probe of any kind ...but I will try and find the distance .
The back focus is 61mm and

[JA]

Hi ALex,

You don't need to poke anything inside the camera body (unless you really want to), since the Nikon F mount has a sensor to lens mounting flange distance of 46.50mm.

Best
JA

[xelasnave]

Continuing
But the chip seems past that so it needs to be closer MAYBE.
I think it could be the mount not level ..I cant look until dark as I dont want folk seeing me play telescopes...
The mount not being level could give this effect I would think...

Anyways start on it later.
Alex

[xelasnave]

Thanks I will get up and look with that in mind.
My legs are not happy that I am back into astronomy.
But what a good reason to get out of bed...its bed or astronomy maybe food but its secondary.
Alex

[xelasnave]

I got the scope and have it laying in the bed to love at some measurements and all I have is a plastic thirty year old dress makers tape..the decent stuff is in the garage but the stairs.. so far it seems off. There seems like 5 mm out ..but I will take a few more see if I can get a decent ruler...when I get the level from thr garage...baby steps.

Alex

[brisen]

Hi Alex

You need to have 66 mm backfocus from the back of the flattener to the chip. As the chip is 46.5 mm you need 19.5 mm to meet the exact requirements for focus.

It can be challenging, I have spent a few weeks trying to get the exact distance on a 120 with a CCD and OAG and it is a tedious process but I think I have it right now.

Brian

[xelasnave]

Is it me...can you see my tape measure and improvised square ...but unless I missing something it looks as if the chip is way off being 61.5 mm away from the marker they give on the flttener.
Alex

[xelasnave]

???? Supposed to be with earlier post.
Alex

[xelasnave]

I am trying to load a photo ???

[xelasnave]

Not working??
Alex

[brisen]

If you are taking the 61 mm from the edge of the paper in the picture you uploaded you should be close to the back focus distance as you need to measure from the back edge of the flattener, so include that ring between the camera and the flattener body in your measurement.

Its a bit hard to read the measurements and I might have misread them.

Brian

[xelasnave]

Sorry that top measurement needs to be 5 mm to the left approx.

But it seems the chip must be 5.5 mm too far out...
Alex

[brisen]

I think you are right so somehow you need to lose 5.5 mm. having been down this road with a new CCD its a tedious task.

Brian

[xelasnave]

Manual hopefuly is wrong.
Alex

[xelasnave]

Having problens wuth photo uplad sorry.
Alex

[xelasnave]

Taking from back of focuser the numbers add up..
Must be the polar align as BigJoe suggested...I was going to put the level on the mount the other day to do the Sun alignment so I sortta think I did it...but I have not checked it...it could be that simple.
Hopefully.
Anyways I dont care if I am out there only talking dark frames.
It depends on the clouds...any time is useful in adjusting stuff.
Should put the 8 inch on and see if it shows similar which would confirm level I would think..
Alex

[xelasnave]

That photo from the manual has to be wrong...
Alex

[Camelopardalis]

The Esprit 80 manual online shows 66mm flattener to sensor distance.

http://skywatcher.com/download/product/manual/esprit-80ed-apo-triplet/

[xelasnave]

Thanks.
I am convinced from all my measuremnts that the sensor needs to be 5.5 mm closer to the flattener..I think Micheal did not get it right notwithstanding he tried...It seems to need a different fitting and hopefully we will sort it out on Monday.
I tried the scope without the flattener and all I can say is it was hopeless with elongated stars almost to the center of the capture...
It will work out I hope.
But such a nice size scope..so much easier to manage than the 8 inch.

alex

[Camelopardalis]

Did your scope not come with the extender that threads on camera-side to the flattener? This is part 3 in the diagram in the manual. Adding the Canon/Nikon T-ring would give the correct spacing, as the Esprits were designed - and shipped with adapters for - DSLR use straight out of the box.

[xelasnave]

Its seems they did not get it right at least in my case or at least when Micheal put the bits together at the shop or when I put the bits tigether at home something was certainly wrong.
Yesterday I removed the spacing and part of the t ring and was able to get the measurements stated in the apparently correct version of the manual (not the one that came in the box).
Now the t ring is held on not by a thread but by the three screws that held in the inner ring and they bite straight into the thread from the flattener.
It does not seem correct but certainly that was the only way I could the the distance.
Last night I gave the scope a run and looking at my image, one hour at 30 seconds on the flame and hotse head region, the stars are as I would expect nice and round.
Hopefully I can post an image of my efforts but I cant get around to processing past a deep sky stack.

And I must say Don from Bintel was most helpful and treated my concerns with respect and kept in contact thru the process.
It is in these situations one appreciates buying from Bintel.
As all could appreciate my heart sank when I first saw those elongated stars and believe me I was very happy to know if there was an unsolvable problem I was dealing with Bintel.

The current set up is not ideal and it makes me nervous that three timy screws hold the camera in place...If I cant get a proper fitting I will literaly glue the thing on...hopefully using a glue that is soluble in something should I ever want a different camera.
But the march is forward and at least last night I got to use it.
Alex

[xelasnave]

Here is last nights effort.
The framing is off but I was not expecting to be able to image so I just had to leave the camera where it ended up after the adjustments.
I thought I would get maybe a couple of test shots but happily the clouds let me get an hour...a little cloud two streaks say a few frames unusable but I present my result with no further excuses.

But the point of this image is to see how the stars have improved..hopefully..
Alex

[Camelopardalis]

Alex, could you post a picture of your flattened and imaging train?

[xelasnave]

Sure.
Alex

[casstony]

My setup worked well with a Canon dslr which has 44mm distance to the chip (from memory). Since the Nikon is 46.5mm a thin Nikon T-ring screwed onto the flattener adapter should work.

[xelasnave]

Thanks for posting your set up Tony.
I have not got to Bintel to see what they suggest...so I havent glued anything yet.
Alex

[Camelopardalis]

Glue :eyepop:

The threaded adapters should make it perfectly secure.

From the back edge of the metal piece on the camera side of the flattener, the back focus is 55mm. I would suggest you find a slimmer T adapter to reach that target backfocus. Tasco should be advise where to source one for a Nikon.