Getting Focus

[Carole]

I managed to get out again last night first time since I got my flip mirror repaired which worked nicely last night.

I decided to have a go at the Moon this time.  I could not get any focus at all with the webcam with or without the Barlow x 2 lens (Telescope House were very reluctant to sell me a 3x Barlow even for Astrophotography).  Is it possible that I am pushing the telescope adapter on the Webcam too far into the socket?

Also, if I try to change the controls to reduce the brightness etc I have to take the auto off (there are two auto buttons, one is a tick in a square box (on K3 which you have to UNTICK) and one which gives a selection for auto, night sky, and two other choices which I can't remember).  I am assuming I should be unticking the auto in the square box.

Once I have de-selected auto I can change the controls but then sometimes lose the grey box which shows the image and I can only get it back by ticking auto again which then looses the setting changes.

So what's going wrong guys?

If I can't get this sorted out I think I will have to give up trying on my own and wait for either an imaging session (where we can actually image) or a DSC so one of you can have a look at what is happening/give advice etc.

Carole

[Ian]

Firstly, with the camera control, you need everything set to manual. None of the auto settings work particularly well for astro work, full auto won't work at all. So that's no ticks in auto boxes.

Getting focus is always the trickiest bit (apart from all the other tricky bits). If I remember the ETX focus mechanism is hidden from view which means you can do a rough focus by focusing using an eyepiece and then winding it in approxmately the difference in focus position for the camera. That sounds tricky because it's hard to explain, but much easier to demonstrate... Anyway, you can't do that.

Couple of tips, try and focus on the terminator. Unless the scope is massively out of focus you'll be able to recognise it. The contrast is highest there.

Wind the focusser all the way in (or out, doesn't matter) and then slowly wind the focusser out (at least slowly enough to recognise changes in the image) while watching the laptop screen, recentreing if necessary. You should see the focus improve. If you get the focusser all the way out achieving focus, try the same process with the barlow.

Bear in mind the barlow moves the focus out of the scope, a focal reducer moves it in.

I just googled and have found quite a few people imaging with an etx and a webcam, so focus is possible. You could also have a go during the day time, but again bear in mind that objects not at infinity will move the focus out a bit further. It's best to find something a very long way away to look at, that minimises the focus difference.

[JohnP]

Carole - Try in daytime first. Pick something a long way away - like telegraph pole or tree. I would leave settings in auto during daylight & try to focus. If you can't see anything from your garden why don't you pop across road to Norman park... Just take mount & scope etc. & setup at top end & then look at athletics track at bottom end - if I remember they have some suitable floodlight poles.. If you focus on these the position shouldn't be too far different for moon etc....

John

[mickw]

I also read somewhere about parfocal rings.
When you eventually get the webcam in focus, use a spare eyepiece (about 25mm) and attach a parfocal ring to it.
Remove the webcam, leaving barlows etc. attached to the scope, pop the eyepiece in and slide it up/down to bring into focus, do not use the focusser.  When it's in focus, tighten the ring.
Next time you set up, use the parfocal eyepiece to get into focus, then just swap it for the webcam - should be pretty close to being in focus.
This is all from memory....................

[Carole]

Hi Ian, John and Mick

I turned the focus knob slowly all the way both with and without the Barlow but all I got was a bright shape of the moon with at times something looking like white haze coming off of it.   I couldn't even get an out-of focus view of any craters. 
It could be perfectly focussed in the 25mm eyepiece using the flip mirror so it's not as if viewing conditions were bad.
What sort of magnification would the telescope adapter on the Webcam be do you know?  If I knew it's magnification it would give me some idea of where I was going.  Are these things standard?

Focusing in the daytime sounds a good idea, I'll give that a try.

Parfocal rings sounds a bit like what I was saying when I queried about maybe having pushed the webcam into the scope all the way.  I could have a try with various positions of insertion, then if that works I'll try something like the Parfocal idea. 

I'll also have a look at some ETX Astro-imaging users web sites.

Carole

[Mike]

Carle it sounds to me that your issue might not be focus but that the image of teh moon is far too bright and is beyond the well depth of the CCD. You may well have a perfectly focussed moon that is being viewed with too long a shutter time.

If you have been using auto settings that might be the case. As Ian says, ensure you control the exposure manually and keep the exposure times very short and the gain turned to minimum.

[Ian]

oh, and make sure the corrector isn't covered in dew. Not helpful to focussing, condensation ain't. See the C8n thread...

[Mike]

oh, and make sure the corrector isn't covered in dew. Not helpful to focussing, condensation ain't. See the C8n thread...

Ooh yeah good point. Shouldn't be any moistrue inside there if Carole has stored the unit correctly, but it would be a bugger to get out once it got in !!

[Ian]

Shouldn't be any moistrue inside

true, but I was think more along the lines of it being on the outside of the corrector... However, I don't believe the tube on an etx is particularly well sealed. Don't keep your scope in the bathroom folks!

[MarkS]

Carole, Mike,
I did EXACTLY the same thing last night with Mars.  I moved the focus in and out, in and out, in and out but Mars remained a featureless white blob on the screen. I then realised the image was totally saturated because the camera controls were in auto mode.

[Carole]

You're all giving me good input, but unfortunately I tried all this with auto on, auto off, brightness down, gain up AND down (as I was not sure which way it had to go), but it didn't make any difference either way.

I must say I was wondering along the same lines as Mike, whether the Moon was just too bright a subject for the CCD as it was still very bright even with brightness turned down to minimum.  should I have a Moon filter on to image the moon?

I don't know what bit of the telescope is the corrector, does it have another name?  There was a small amount of dew on the "glass aperture" end of the scope when I brought it in, but nothing to write home about, and that made no difference to normal viewing through the eyepiece.  I think the only sin I committed was not having the telescope in a cold room for more than about 1/2 hour before using it.

I never even got as far as taking an image as there seemed no point until I got something worth taking on the CCD screen. 

I am wondering whether it would be a good idea to try to focus the moon during the day time, as this will have the distance and not be as bright as night.

I normally keep my scope in it's padded carrier bag (having waited for any moisture from previous use to evaporate before putting the dustcap on and the scope away), and then keep this in my 3rd bedroom which is an office/Astronomy/sewing room, so no moisture in there.

I don't know whether I am being completely daft here, but is the telescope adapter on the webcam supposed to have any magnification in it at all as I've just had a look through it and it seems to just be a plain bit of glass to me.  I can't see how it can focus without something equivalent to an eyepiece or are we just relying on the Barlow for this at only 2 x magnifcation.  Or have I got a piece of kit missing that no-one has told me I need!!

Carole

[Ian]

the bit of glass in the adaptor is hopefully an IR filter, and you don't need any sort of lens to get an image on the ccd.

The moon isn't too bright, I have imaged the moon with a webcam on my 8" and that has a much brighter image than your ETX. Focussing on the moon during the day wouldn't be much different to during the night, it's just as bright (the sky's just caught up with it during the day). In fact, it's much lower contrast during the day which won't help.

If you can see the moon in the eyepiece you really aught to be able to get something, so I would suggest trying again, being methodical (which is a good habit have anyway when astroimaging) and adjust only one thing at a time.

Any dew on the corrector (the first bit of glass you see when you look down the business end of the scope) will affect focus. It's best to get rid. A hairdrier is the best for that.

Finally, there's a chance that you were trying to focus on an internal reflection in the scope, not the moon proper. It's easily done (I've done it) as they can be very bright. Might be worth double checking that the moon is in the middle of the eyepiece.

Once you get it, there'll be no stopping you...

[Mike]

Like Ian said, with teh gain at minimum and the shutter speed at its fastest (60fps?) you will get a nice DARK image of the moon if it is all set up correctly. If it is still too bright there is something seriously wrong somewhere.

[JohnP]

Carole - I know it's crap weather at the moment but you need to try it during the day - at least if you can focus on a distant object you know issue is with not having the right settings & not to do with the fact that you can't reach focus... it'll only take 5mins to test if we ever get a break in the clouds or you could even try pointiing the scope through an upstairs window if you have a reasonable horizon...

John.

[Carole]

John,

I certainly wasn't looking at an internal reflection of the Moon through the eye piece, and when I flipped the mirror over I could see the shape of the Moon against the dark sky on the CCD which was very bright, but other than that and the wisps of haze, nothing else whatever I did, focus and fiddling with controls gave any clearer picture.

I will check that what I am getting through the rear port is the same as the right angled eye piece (since the flip mirror has just been repaired) and also try to focus it during the day time.

Incidentally I did not bother to switch the motors on on the scope as really all I wanted to do on this occasion was find out how to get a good image on the screen(!!) using focus and controls, as Mike says - one thing at a time.

Since Ian has previously imaged without using drive I assumed it would not make any difference to the image on viewing, just on capture and I did not want to go through all the rigmarole of aligning the scope just to end up with nothing (once again!) at the end of it.  Had I managed to achieve this then I would have aligned the scope and taken an image.

Maybe this is what is wrong.

Carole