Missed focus again!

[Rustang]

I'm starting to get a little annoyed with how finicky the WOZ73 is to get focused correctly, I never had any issues with the SW80 what so ever and just used to eye ball it with my B mask every time. Having initially had issues from the start, the next night out I used the B mask function in APT to correct it, I did the same last night and got it even better so why do my stars look out of focus yet again? Because the B mask reading was even better than the first, I was to lazy to fully check the subs, well that was a mistake! Its another case of worked fine now doesn't again! 🙄

A really crude stretch below of last nights image

Edited September 28, 2021 by Rustang

[Shimonu]

Did you tighten the lock screw for the focuser? Not that I've ever experienced any slippage though. In my experience I've had to look quite closely at the spikes to find the center, they're not sharp themselves. If you're using the built-in mask I've heard claims that it's not really the best performing mask and I'd say there is some merit to that.

[Rustang]

2 hours ago, Shimonu said:

Did you tighten the lock screw for the focuser? Not that I've ever experienced any slippage though. In my experience I've had to look quite closely at the spikes to find the center, they're not sharp themselves. If you're using the built-in mask I've heard claims that it's not really the best performing mask and I'd say there is some merit to that.

Yeah I'm using the built in mask so it could be that, I used the sharpstar one with the SW80 so may order another. Yeah the draw tube locking screw was tightened.

[Clarkey]

I have used a focus mask and the focus was never perfect. (Admittedly a home made version). I tried using the Bahtinov APT tool to improve it and the results were still not good. I now run the autofocus routine on my focuser which gives a much better result. From memory, APT has a focus aid program which measures the FWHM of a given star - have you tried this? The other thing is to check your subs individually - did it start ok and get worse or was it out from the start? It go fairly cold here last night and the temperature drop could have had an effect.

[Rustang]

28 minutes ago, Clarkey said:

I have used a focus mask and the focus was never perfect. (Admittedly a home made version). I tried using the Bahtinov APT tool to improve it and the results were still not good. I now run the autofocus routine on my focuser which gives a much better result. From memory, APT has a focus aid program which measures the FWHM of a given star - have you tried this? The other thing is to check your subs individually - did it start ok and get worse or was it out from the start? It go fairly cold here last night and the temperature drop could have had an effect.

Cheers, its similar advice Ive had before, I try to take one step at a time though. I was informed about using APT's b mask tool so first I did this and it worked on my last image so that's why i went back to using that again which has now failed!! I will now try what you and others have stated in regards to the FWHM value but I'm new to really understanding this, all I know is that I need a small value but how small is best?. I've been told about temperature changes etc etc changing focus but its something I've never suffered with before, ever with the SW80 and always just crudely used the B mask by eye so why this scope is so fussy I don't know, never mind, Il try and find a new routine that works. I will now definitely check each sub, I was lazy the other night and assumed wrong due to the good APT b mask result that everything was ok, so thats my own fault for not checking the subs.

Edited September 29, 2021 by Rustang

[geeklee]

1 hour ago, Rustang said:

I will now definitely check each sub, I was lazy the other night and assumed wrong due to the good APT b mask result that everything was ok, so thats my own fault for not checking the subs.

When you tighten the focus lock, do you then set off another focus check sub?  As you mention above, whatever process you end up being happy with definitely needs the extra check when the mask comes off.  Just fire off a 30s sub to check, then if all looks good run a longer one too.  I don't think the scope is that fast so surprised you see such an out of focus image from using the bahtinov mask that might be a tiny bit off - as you've said before, it's served you well.

I remember on my ED80, I got used knowing which way the focuser lock would nudge the focus (ever so slightly) so got used to leaving it a tiny touch off, then locking, then checking focus again.

It's definitely locking and there's no slippage?

[david_taurus83]

I think the WO acrylic B masks are really good. Never have an issue with them. I only ever eyeball the spikes though. Don't trust any of the software that analyses the spikes. Also, if your locking the focuser after adjusting this can also move it slightly if you over tighten.

[Clarkey]

2 hours ago, Rustang said:

all I know is that I need a small value but how small is best?.

It will depend on the seeing. Basically adjust to the lowest number you can get on the night.

[Rustang]

1 hour ago, geeklee said:

When you tighten the focus lock, do you then set off another focus check sub?  As you mention above, whatever process you end up being happy with definitely needs the extra check when the mask comes off.  Just fire off a 30s sub to check, then if all looks good run a longer one too.  I don't think the scope is that fast so surprised you see such an out of focus image from using the bahtinov mask that might be a tiny bit off - as you've said before, it's served you well.

I remember on my ED80, I got used knowing which way the focuser lock would nudge the focus (ever so slightly) so got used to leaving it a tiny touch off, then locking, then checking focus again.

It's definitely locking and there's no slippage?

Yeah definitely re testing once locked as I know it moves when tightened. It is strange how out it is and the spikes and reading looking really good, I just hope its not the scope but then what could it be if it were so! Its really annoying having to deal with something like this but I guess if your not hardened to deal with the fact this hobby is just very frustrating then its best to take up another   I'm pretty sure there's no slippage. I know a few people have mentioned that there are lots of factors that can alter focuser but I had simple no issues that I was aware of with the other scope, I never even re focused after a filter change!! so this scope is definitely fussy for some reason! at least the stars are nice and round though

Edited September 29, 2021 by Rustang

[geeklee]

3 hours ago, Rustang said:

It is strange how out it is and the spikes and reading looking really good,

Was there a different process you took each time.  For example the times you've had issues with focus you slewed to a star far away to pick as your focus star, then slewed back to target?  Whereas (for example) the "good session" your focus star was very close to your field...  or do you put the mask on the field you're targeting and pick a star+pattern you can see there?

For now, just add the sub check or two after you've done focus, it'll save you a wasted night.  If the focus looks off you can put the mask back on then and double check - maybe adjust in and out of focus using the other methods mentioned above (FWHM, HFD etc).  It'll give you a shot at getting focus for the night while learning some new focus methods and hopefully figuring out what's going on.

Silly question, but the imaging train after the focuser is all good?  Is there an adjustable flattener that's not tight or non-screwed connection that's likewise?

 

[tooth_dr]

I'm not familiar with the scope Russ, but like you my ED80 was flawless - just set the focus and work all night.  Since I bought a different refractor, a 4" APM, I have noticed it is temperature dependent.  Focusing at the start of a session will look perfect, but even an hour, once the temp drops, the focus can be out enough to ruin an image.  There is no option but to use autofocus.  Could temperature be affecting your focus?

[Rustang]

5 minutes ago, geeklee said:

Was there a different process you took each time.  For example the times you've had issues with focus you slewed to a star far away to pick as your focus star, then slewed back to target?  Whereas (for example) the "good session" your focus star was very close to your field...  or do you put the mask on the field you're targeting and pick a star+pattern you can see there?

For now, just add the sub check or two after you've done focus, it'll save you a wasted night.  If the focus looks off you can put the mask back on then and double check - maybe adjust in and out of focus using the other methods mentioned above (FWHM, HFD etc).  It'll give you a shot at getting focus for the night while learning some new focus methods and hopefully figuring out what's going on.

Silly question, but the imaging train after the focuser is all good?  Is there an adjustable flattener that's not tight or non-screwed connection that's likewise?

 

So normally I would go to a bright Star, so the Image that worked with the new scope (Crescent nebula) I went to Sadr to focus then to the Crescent neb so they are close to each other. I did the same the other night using Sadr but the Lobster is futhur away, would that really make a difference and why? What if there isant a bright enough star close by to use? I use the WO adjustable flattener that's to my calculation is where it should be and the whole connection is now a threaded, locked connection so I believe its not an issue that end but I guess I cant rule that out the way its going.

[Rustang]

2 hours ago, tooth_dr said:

I'm not familiar with the scope Russ, but like you my ED80 was flawless - just set the focus and work all night.  Since I bought a different refractor, a 4" APM, I have noticed it is temperature dependent.  Focusing at the start of a session will look perfect, but even an hour, once the temp drops, the focus can be out enough to ruin an image.  There is no option but to use autofocus.  Could temperature be affecting your focus?

Sadly I dont have an auto focuser and really dont wont to be adding anything to the set up or extra to think about right now. The scope could well be temperature fussy, it will be a shame if so, kinda wish I stuck with the SW80! I really wish the precious nights could just be with out issue, I fully appreciate I'm not the only one though, its been so mentally challenging to get to where I'am with this hobby and was just about settled with everything to just enjoy it but there are so, so many things that can seem to play up just when you have the hang of it all.

Edited September 29, 2021 by Rustang

[geeklee]

45 minutes ago, Rustang said:

would that really make a difference and why?

It's unlikely but I was thinking could a bigger slew be moving something in the focuser / imaging train.  You're right, you should be able to go to wherever you like to focus and back without an issue.

43 minutes ago, Rustang said:

The scope could well be temperature fussy

If you look through your Lobster subs, they'll likely start fine and start to drop off if it's temperature so at least something you can check (if not done already of course).

48 minutes ago, Rustang said:

I really wish the precious nights could just be with out issue, I fully appreciate I'm not the only one though,

I understand and sympathise.  With the lack of clear skies, everything can become doubly frustrating and can (for me in the past anyway) keep nagging away at me until I can test again the next clear night.

[Rustang]

50 minutes ago, geeklee said:

It's unlikely but I was thinking could a bigger slew be moving something in the focuser / imaging train.  You're right, you should be able to go to wherever you like to focus and back without an issue.

If you look through your Lobster subs, they'll likely start fine and start to drop off if it's temperature so at least something you can check (if not done already of course).

I understand and sympathise.  With the lack of clear skies, everything can become doubly frustrating and can (for me in the past anyway) keep nagging away at me until I can test again the next clear night.

Thanks again for your help, it looks like the subs were out from the Start so once I can get out again and achieve good focus, I will keep an eye on the subs during the session to hopefully rule out temp issues. I'm really hoping its just finding the knack to achieving focus with this scope, and away that continues to work so I can keep things the way they are then il be happy. I'm sure I can get there, I stress alot through life and have many mental demons I have to battle with so things can get frustrating very quickly but I always keep fighting on, the hobby hasnt got the better of me yet.

[Clarkey]

On 29/09/2021 at 19:24, Rustang said:

I really wish the precious nights could just be with out issue

If it is any consolation I spent 3.5 hours a couple of nights ago trying to get decent star shapes with a new scope and coma corrector - and failed! We all share your pain☹️. Now waiting for the next clear night to try again....