Do I need to collimate? Or is is something else?

[NallyFace]

Hello

I recently purchase a Celestron 8"OTA - using with a SkyWatcher HEQ5 Pro and SynScan + Safari apps for iOS. My first night viewing I set up and manually slewed to the moon, I had good detail using a 12mm EP. All good, I saw Saturn with clear sight of the rings and could see some details of Jupiter, amazing!

However, since then everything is a blur, the moon, Saturn, the lot. I focus on the moon and get close to detail and then it passes the point and never focuses, same on Saturn and Jupiter.  Now I did slightly, and ever so slightly, knock the telescope when putting it away after the first night, could that have moved the mirrors slightly? Could that be the reason?

I have tried the obvious:

- EP is spotless

- removed and reset the visual back and the right angle thingy for the EP to sit in.

Checked focuser over and over, when setting up finder, the first time I was able to do this on an aerial atop a block of flats about 2 miles away, now that same block is a blur too.

 

The 12mm EP is all I have as I wait for deliveries.

 

Any ideas?

 

Thanks for the advice

[John]

You should get a reasonable image even if the collimation is a bit off. If all you are now getting is a blur it sounds like something else ?

I'd suggest a star test to check the collimation but if you can't get a sharp star image in the eyepiece that's not going to be possible.

Which part of the scope did you slightly knock ?

 

[paul mc c]

Have you tried a star test,this is a sure way of showing it you need to collimate your scope.

[Rob_UK_SE]

Is your telescope an 8” SCT (Schmidt cassegrain)? If so, they hold colimation pretty well and can -usually- cope with a light tap. Continuing this assumption, they provide a focal length of 2032mm so your 12mm eyepiece would be producing 169x magnification - This is certainly achievable on most nights. It is also possible the views might have been affected by thermal currents within the telescope. Whether it is a newtonian or SCT scope, it will require sufficient time to cool down to the ambient outside temperature. An SCT, due to its closed design, will take a little longer to cool. By comparison, newts tend to be a bit quicker. When I had a 9.25” SCT, I used to leave it outside for a minimum of 1.5 hours before considering any meaningful observing time. A Newtonian OTA should be good after about 45 minutes - depending on the temperature difference between where it was stored and that outside.

Newtonian scopes are more susceptible to being knocked out of collimation and should, ideally, be checked each time to ensure the best views. A cheshire eyepiece is the most accurate, but a laser collimator is quicker (at least until you are comfortable with using a cheshire). However, if you have an SCT it is a little more complicated to collimate. This video explains how it works for SCTs: 

 

There is also quite a lot of focus travel on these scopes so it’s worth double checking that it isn’t just really out of focus. Point the scope to a star and keep focusing so that you are reducing the size of the ‘fuzzy blob’ - hopeful it will, eventually, cone into focus. 

...Edited due to incorrect eyepiece focal length initially mentioned.

Edited September 1, 2020 by Rob_UK_SE

[NallyFace]

Hi all,

Thanks for the replies. It is an SCT yes, thanks for the video also, I looked through the scope with the EP removed and the circles look good to me so maybe it’s not in need of collimation. I have, so far, not actually observed outside. I don’t have the garden for it but have a great window from the loft room that has Jupiter and Saturn framed so have been set up there, could the mix of indoor warmth and outdoor cooler air do this? 
 

Its 100% not the focus, not on my part anyway in terms of me turning it, as I’ve had a great view before and know how fine the tuning is. It just almost gets there, needs another tiny turn and it’s gone the other way. 
 

I am taking it to the Lake District next week for a while week so will use it plenty then and try anything suggested as well as have it outside. 
 

 

[Rob_UK_SE]

35 minutes ago, NallyFace said:

Hi all,

Thanks for the replies. It is an SCT yes, thanks for the video also, I looked through the scope with the EP removed and the circles look good to me so maybe it’s not in need of collimation. I have, so far, not actually observed outside. I don’t have the garden for it but have a great window from the loft room that has Jupiter and Saturn framed so have been set up there, could the mix of indoor warmth and outdoor cooler air do this? 
 

Its 100% not the focus, not on my part anyway in terms of me turning it, as I’ve had a great view before and know how fine the tuning is. It just almost gets there, needs another tiny turn and it’s gone the other way. 
 

I am taking it to the Lake District next week for a while week so will use it plenty then and try anything suggested as well as have it outside. 
 

 

Your SCT will be extremely difficult to achieve stable views from inside. At a magnification of 169x it will be particularly tricky. The temperature difference between the air inside the OTA and the air around it will result in thermal currents across the mirror. The air inside needs to match the temperature outside for really stable views. It is quite likely that your issues are, therefore, due to observing from inside and I would certainly recommend a star test from outside to check this. Perhaps the room had cooled right down during your previous success (although views would be greatly improved from outside)? If you are observing through a window the additional layers of glass, given their own thermal characteristics, will also affect views. If you observe with the window open, the air around the window will also affect the views as it, too, will have thermal currents where the colder air from outside meets the warmer air from inside as well as the heat radiating from the various indoor surfaces. All of these components result in thermal currents. It’s the same principle that impacts observing a planet/DSO which is located close to a roof / building  is not ideal - the roof / building is radiating lots of heat which results in less stable views (even when you are observing from outside).

Edited September 2, 2020 by Rob_UK_SE

[pete_l]

OK, so what you know is that collimation looks good and the focus doesn't seem to be a problem.

The one thing I would strongly recommend is to not go adjusting anything. You say there is another eyepiece(s) on order. I'd wait for that and to try them. It is quite possible that one of the optical elements in the E.P. has come unglued. Aside from shaking it and listening for a rattle (doesn't always work!), you could try to cast an image just through the EP onto a piece of paper.

But to repeat: until you have a good diagnosis of what the problem is, making adjustments just complicates the matter and makes finding the solution many times harder.

[RT65CB-SWL]

6 hours ago, NallyFace said:

It is an SCT yes, thanks for the video also, I looked through the scope with the EP removed and the circles look good to me so maybe it’s not in need of collimation.
 

If you leave an e/p in the defocus, do you see perfect concentric rings around a point of light when doing a star test? - if "Yes!" then you should be good to go - if not then it will need it will/may need collimating.

 

6 hours ago, NallyFace said:

I have, so far, not actually observed outside. I don’t have the garden for it but have a great window from the loft room that has Jupiter and Saturn framed so have been set up there, could the mix of indoor warmth and outdoor cooler air do this? 
 

Maksutov's & SCT's are notorious dew magnets and do require time to acclimatise Being an enclosed tube, hot air and cold air causes dew/codensation. As you are viewing from a window in the loft/attic of your home, is the loft/attic heated and is the window open or closed? - looking through a closed window is not advisable. I leave my C6/SCT-xlt and ETX105 a minimum of 30-40 minutes [outside] to allow any trapped warm air inside the tube to escape, visual back pointing skyward and end caps removed. Yours being a C8, you may need to leave it for a minimum of 60 minutes if outside and maybe longer if your only option is viewing from inside your loft/attic.

[NallyFace]

Thanks all. The circles look aligned. The cold/hot air does make sense and is now number one contender for the issue, I did wonder this when first starting but as I had “beginners luck” it seams I though nothing more. If it turns out like it did the first night of trying is I will be a happy boy, very good sights and so great to see Saturn’s rings! What a view that is. 
 

 

 

[Rob_UK_SE]

Wishing you clear skies in the Lake District so you can test out the scope and, I very much hope, enjoy the darker skies up there. 

Edited September 2, 2020 by Rob_UK_SE

[NallyFace]

2 hours ago, Rob_UK_SE said:

Wishing you clear skies in the Lake District so you can test out the scope and, I very much hope, enjoy the darker skies up there. 

Thank you kind sir 👍

[Highburymark]

You can get away with indoor observing during the warmer summer months when there’s little - if any - temperature difference  outside. But by this time of year I find air currents make it almost impossible. Am sure that’s the culprit here - particularly as these scopes are pretty robust. A small knock would not harm the collimation that badly.