WO GT81 Imgaging Help Needed

[groberts]

As suggested in an earlier posting, I am re-posting this as a more specific issue in the hope someone out there with the same set-up can help. To summarize, I am unable to get any image when connecting my camera to the GT81, see here for more detail:

 http://stargazerslounge.com/topic/221464-no-image-what-am-i-dong-wrong/

The consensus seems to be an issue of focusing but maybe not?  Unfortunately I don't have a good line of sight at home to try it out in the daytime and sky has since been cloudy at night!  I would have thought that a WO GT81 & Canon 700D DSLR was a fairly standard combination, so what am I doing wrong?  For example, using the flattener connected to the camera, is it correct just to fix this combination directly into the focus tube and then look to focus?  Do I need an extension tube? What would the set-up need to be without the flattener?

As I say in the OP, there are no instructions with the equipment and it is therefore difficult to know how to use the equipment correctly, which is very frustrating & disappointing.

Grateful for any help.  

[ronin]

Reading what you have put here - didn't follow up what I said in the other - I think you will need an extender. Suspect 1" or 2".

Then the arrangement would be Scope->Focuser->Extender->Flattener/Reducer->T Ring->DSLR.

Hopefully someone will say if a 1" or 2" is preferable.

Alternatively ring up Ian King and ask, they seem to specialise in imaging aspects and at every show they have WO scopes so I would expect them to know. Then be nice and buy one off them.

It sounds that the diagonal is not present and you will in effect have to "put" that distance back into the system.

Starting to realise the advantages of the WO scopes that have the flattener build in now.

[lensman57]

elps

As suggested in an earlier posting, I am re-posting this as a more specific issue in the hope someone out there with the same set-up can help. To summarize, I am unable to get any image when connecting my camera to the GT81, see here for more detail:

 http://stargazerslounge.com/topic/221464-no-image-what-am-i-dong-wrong/

The consensus seems to be an issue of focusing but maybe not?  Unfortunately I don't have a good line of sight at home to try it out in the daytime and sky has since been cloudy at night!  I would have thought that a WO GT81 & Canon 700D DSLR was a fairly standard combination, so what am I doing wrong?  For example, using the flattener connected to the camera, is it correct just to fix this combination directly into the focus tube and then look to focus?  Do I need an extension tube? What would the set-up need to be without the flattener?

As I say in the OP, there are no instructions with the equipment and it is therefore difficult to know how to use the equipment correctly, which is very frustrating & disappointing.

Grateful for any help.  

If the camera is working OK then the telescope should come to focus, there is no way that optics can be none functional. Use a diagonl and an EP of about 12.5 mm, if you have one that is.

Find a bright star, Vega is perfect for the moment. Focus on the star sure that the star is bang in the middle of the EP. Mark the position of the focuser, measure the optical path of the diagonal, this is the distance that needs to be compensated for in the focusing with the camera minus 55mm for Canon. Take the diagonal out and the camera in using a 2" nose piece, do not use the FF/FR for now, set the iso to the highest value and using the liveview bring the camera gently into rough focus ( do not use any filters for now untyou have achieved rough focus ) .  When a star is well out of focus it will project a very dim large circle which is almost impossible to see even using a CCD so a bit of fiddling is necessary to find the position but the movement of the focuser is very very small to bring it into focus so please don't frustrated and make lage movements of the handwheel. Once you have got rough focus you can put the rest of the stuff back together and try again but this time you know that the target is in the middle and should appear. If I were you I'd download the free version of the APT on to a laptop and use the  live view function to get things done properly. Focusing on astronomical targets using daytime photography routines is not a good idea, hopeless in fact. Hope this helps. BTW, don't expect instruction manual in this hobby, internet is your best friend.

A.G

[Alien 13]

As above normally with a FF/FR there is no need to add in any extra spacing but with a FF or the native FL then you will need a 2 inch spacer.

Alan

[bruno]

to gain focus with my camera, i bought an extender then focused on a bright star using live view & everything was hunky dory I have since bought a skywatcher FF and i get the same, but now what i tend to do is set the focuser on the scope about 19.5 mm out with the extender and camera & use BYEOS  & take a couple of test shots then you can physically see how your shots are turning out before you start hope this helps

[Davey-T]

As said in original post, get a 2" extension, leave out the f/r for now, focus on a bright star using eyepiece, fit camera take 30sec exposure, iso 800, an out of focus star will still show up as a big blob (technical term for unfocused star) 

If you don't want to pay out for an extension put the camera in the diagonal if it's 2".

If all else fails chuck it all in the car and cart it round to my house.

Dave

[groberts]

Thanks for all the thoughts, much appreciated. I do remember initial problems with focusing with the SW 150PL (found a Bahtinov very helpful) but was hoping that as I had bought this set-up together, it was a case of putting it all together and, with some adjustments, it would just work - clearly not (no pun intended).

Now waiting for a clear night to experiment further; thanks for the offer Davey-T, I may yet take you up!  

[groberts]

By the way - it seems extension tubes come in 50mm & 80mm, which do I need?

[groberts]

Have just found a WO version @ FLO, which I presume is the way to go. Is a spacer still of any use / relevance?

[Alien 13]

You might find these usefull to fine tune the correct FF to sensor distance i know i had to add a little to the standard t-ring with my scope http://www.firstlightoptics.com/adaptors/baader-t2-delrin-spacer-ring-set.html.

Alan

[Davey-T]

Have just found a WO version @ FLO, which I presume is the way to go. Is a spacer still of any use / relevance?

This is the one, nice pics showing what you need to set it up.

Dave

http://www.firstlightoptics.com/reducersflatteners/william-optics-reducer-flattener-6.html

[groberts]

Any comments / observations of this:

http://www.firstlightoptics.com/adaptors/william-optics-2-focus-extender-tube.html

vs this:

http://www.firstlightoptics.com/adaptors/william-optics-2-inch-prime-focus-camera-adaptor.html

???

[Alien 13]

I use the second one on mine it gets my prime focus nicely without excessive draw tube extension however it cannot be used in combination with a FF.

Alan

[groberts]

Progress, of a sort.  I managed to get a couple of hours last night before the clouds rolled in; it was however nice and warm!  Trying the camera ex FF with the diagonal still no success + the same without the diagonal.  However, using the diagonal + x2 Barlow and got a result. Good focus on Altair achieved through live view on the computer (using EOS Utility) which I transferred to M13 to get some images, yet to be processed but Ok'ish.  It would therefore seem that focus is the problem and this will require an extension tube, contrary to the advice of the retailer when I purchased the equipment.  

[Davey-T]

You could pop up to Astronomia in Dorking, open 7 days a week.

Dave

[groberts]

Bingo! With the weather and skies looking good I persevered last night and low and behold a result.  After managing to focus the GT81 + FF successfully on Arcturus using a Bahtinov mask, first visually then through the DSLR camera using the EOS Utility on the computer (see attached image), I manged to get some reasonable images of M13 & M57, not yet processed.  I can now see that focusing with the FF, it is essential to be meticulous, with the focus point very finely established within a fraction of a millimeter; even with the lovely GT81 fine focus control it was difficult.
 
I will now move onto refining the process before dealing with all the other, as yet, unresolved DSO imaging problems (more questions I expect!), chief amongst which is to get a better alignment of the mount (will try and tackle drift alignment when I've recovered from this issue).
 
Thanks to everyone for the responses, thoughts help and patience, I am very grateful  .

[Davey-T]

Congratulations   great sense of achievement and satisfaction  when you get it right.

Dave

[WOGT81Reducerx8]

Please Groberts can you take a picture of your setup. I can.t get the right distance and back focus for my new GT81 with reducer and ASI83pro MM. 

[groberts]

This is what I'm using with my current set-up with a ZWO 1600MM-Cool camera and includes a x0.80 WO Focal Reducer + x7 EFW.

 

If you're using the same Focal Reducer as me this diagram provides the back focus distance, if not you'll need to find it on the manufacturers website:

    Hope that helps, if not let me know what else you need + what you are using.

Regards, Graham

[carastro]

Well done, it's now forwards all the way.  

Carole