Can’t find a single star

[HydrogenBadger]

All, I have a brand new rig including my first dedicated camera the ZWO 533 mc pro with a Williams Optics GT71. I am using (or trying to) an ASI Air Pro for control. I have spent a week learning how to balance the damn thing as it was not sold with the correct counter weights and last night was the first clear sky to try and polar align. I cannot get an image of anything vaguely resembling a star - out of focus or otherwise. All I have is noise. I have turned the gain down to the minimum settings, up to maximum and everywhere in between and experiment with spacers and focus. Nothing. 
 

Pointing at the same bit of the sky I was able to focus my asi 120 mini guide scope. 
 

Really frustrated by the total lack of instruction available for any of the equipment. 

Help would be very much appreciated. A picture of my rig below. 
 

 

 

 

[Gfamily]

Ah, you've left your lens cap on.

 

Only joking, but - have you tried shining a flashlight down the aperture? That will give you an indication of whether it's a scope issue or a camera issue.

If shining a light down the aperture produces a response, then look at a bright street light, that should let you get an idea of how far out of focus your are and work out what gain setting is needed

Then, if you know your finder is well aligned with the scope, you could try getting focus on Jupiter, or if you're not sure about the finder alignment wait until the moon  comes up.

[Tomatobro]

Stop trying to do this in the dark.

Point the scope at a distant object (pylon, tree top etc) and get it aligned using an eyepiece. Then install the camera and set the shutter speed at something like .025 and the gain low. Then wind the focus in and out till you get an image. If with the focus fully out no image is seen then remove the camera and if you have a diagonal fit that and then the camera and try again. If you do not have a diagonal make up a cardboard tube to excluded the light from the side and hold the camera in position. You might be surprised how far away the camera needs to be held away to get a rough idea of focus.

make a note of this distance and then get a spacer to suit

[teoria_del_big_bang]

I am no expert but looking at the image of your setu I would expect some spacers in between your focuser on the scope and the camera. So probably you cannot move the camera far enough back to get into focus.

You mentioned you have tried with sacers, but what size, I would need to check the specification of your scope but would be expecting something like 50 to 60 mm would be required.

Other possibilities are camera exposure settings.

It would be far easier for first attempts to use it (VERY carefully) in daylight and try to focus on a land based object. I say carefully because you must keep it well away from the sun, I know you are not looking with an EP but the sun could also damage your camera. Something like a tree as far away as possible.

Now when you can focus and get images of a tree (or whatever you choose) the focuser will need to be withdrawn a bit more to focus on stars or DSOs, which are at near infinity, but you have a start, just make sure you have a fair bit more travel outwards of the focusser.

So now for you next clear night you will know your camera can take images and that focus is outwards from the current position.

Steve

[teoria_del_big_bang]

Oh @Tomatobro beat me to it whilst I was typing 🙂

Steve

[michael.h.f.wilkinson]

I would guess spacers would be needed. I need something quite long to get to focus on my APM 80mm F/6 and ASI183MC

[Z3roCool]

I have not got a Telescope yet so could be talking rubbish  (Only use lenses). From all the images of the GT-71 and ZWO cameras they all seem to have more spacing between the camera and back of the scope. As mentioned above, do some testing in the day to see what you can get. Looks to me though that it may be spacing issue.

**3 replies came in as I was typing...I AM SLOW**

Edited August 12, 2020 by Z3roCool

[inFINNity Deck]

Hi HydrogenBadger,

Your scope has a 420mm focal length, so the CMOS surface should be around 420mm behind the centre of the objective, which can easily be measured with a tape measure.

HTH,

Nicolàs

 

[teoria_del_big_bang]

There is a manual here but even that does not tell you much.

GranTurismo_71_Owner_Manual

Again from the image of your setup it looks like you are not using a flattener.

Unfortunately I cannot find any info on spacers required without a flattener and I do not know how much that affects the back focus. But image below shows a setup with a flattener (ringed in red) and with a fair amount of spacers  (ringed in green) in between the focuser and camera. Looks to be nearly 50 mm of spacers.

Also without a flattener you will have a fair amount of distortion of your images so it may pay in the long run to get a flattener then you have all the info you need to determine what spacers are required.

There is 6.5mm between the front of the camera body and the image plane so with a flattener fitted you would need to measure to the front of the camera body and take into account it is another 6.5 mm to the image plane.

Steve

Edited August 12, 2020 by teoria_del_big_bang

[HydrogenBadger]

Thanks for all the replies. 
 

I have a field flattener - this again arrived without a single instruction. I found some instructions online. As I am on holiday I do not have the tools to fit it. 
 

I really hope that I don’t need any additional spacers. I bought the setup as a ‘job-lot’ from a supplier with the specification being I wouldn’t need to go out to buy a single  extra component, nut or bolt to get started. I have already had to spend £80 on the correct counter weights. I will be pretty disappointed if I also need more spacers. I think I have around 50-60mm of spacers. 
 

 

Edited August 12, 2020 by HydrogenBadger
Sorry, loads of typos first time round.

[teoria_del_big_bang]

50 to 60 mm should be easily enough, try focussing on a land based object during daylight. I am sure you will need some spacers.

[teoria_del_big_bang]

Also you should be able to fit the flattener without tools, well on my WO 73 I can.

Steve

[HydrogenBadger]

1 hour ago, inFINNity Deck said:

Hi HydrogenBadger,

Your scope has a 420mm focal length, so the CMOS surface should be around 420mm behind the centre of the objective, which can easily be measured with a tape measure.

HTH,

Nicolàs

 

 

Edited August 12, 2020 by HydrogenBadger

[HydrogenBadger]

47 minutes ago, teoria_del_big_bang said:

Also you should be able to fit the flattener without tools, well on my WO 73 I can.

Steve

Unfortunately not on this model, it requires an extremely small hex drive for 3 screws to be removed. 

[inFINNity Deck]

Strange, in my mailbox I see that you wrote:

Quote

Excuse my ignorance but I don’t understand this. From my primary lens to the aperture where is would install the camera is only around 280-300mm.  

So apparently there is 120mm of 'material' missing between scope and camera. The flattener is 11mm, add to this 50-60 spacers you have, makes 61-71mm, so still 49-59mm needed. I have no idea how much the focuser extends, but if that is 60mm or more it should be fine to get things into focus.

Nicolàs

[TerryMcK]

Your camera will have the necessary spacers to make up to 55mm. All ZWO cameras come with them. Once you've fitted the field flattener you will find that focus on that scope is roughly 46mm extension. If you don't fit the flattener then focus will be around 54mm extension.

[HydrogenBadger]

Thanks all, I will try again this evening. I don’t have any eyepieces with me which is a bit annoying but I am hopeful I can point it at a street lamp. 

[teoria_del_big_bang]

If you can try it while still light, I am sure you will find it easier

[HydrogenBadger]

Looks like 100% cloud cover tonight! I will be happy if I can set up around 7 or 8 pm and see something other than white noise. Fingers crossed!

[HydrogenBadger]

All, just managed my first photo with my new rig. It is of a tree. Most importantly however, it is a nearly focussed tree. I am a happy boy.

I need to buy extra spacers (which is annoying). Needed around 70mm from the end of the telescope to the camera body. 
 

Will I need to increase that to focus on stars or will 70mm distance decrease slightly?
 

 

[teoria_del_big_bang]

How far out is the focusser itself ?

 

[teoria_del_big_bang]

So long as there's some movement outwards then you may be able to focus on the stars but how much more movement you need I cannot say.

At the moment without the flattener the focal point is just dependent on the focuser position itself plus the length of the spacers. Hence the focuser could be almost all the way in with say 150 mm of spacers, or almost all the way out and only 50 mm of spacers (these figures just examples not necessarily for your scope and camera setup)

When it comes to fitting the flattener then it gets a bit more complicated. You need an exact amount of spacers between the flattener and the camera to give the desired "Back-Focus" as dictated by the flattener you have bought. The flattener is designed to give a flat field at a certain back focus, if this is not correct then the flattener will work to a certain extent but will not be perfectly flat.

Steve

 

[HydrogenBadger]

“When it comes to fitting the flattener then it gets a bit more complicated”. 

More complicated! 

I have 15mm of outwards movement left. 
 

 

[teoria_del_big_bang]

15mm may be enough but I really cannot say for sure,

Steve

 

[HydrogenBadger]

If it isn’t enough are there generic spacers I can buy? I guess it is worth getting a few spare to deal with when I try to fit the flattener.