Focusing Nikon D5300 / Skywatcher Star Discovery 150P Goto

[kevhatch]

Hi

I have had cheapo telescopes in the past for viewing the moon and planets but recently took the plunge and bought myself a proper! scope, Skywatcher Star Discovery 150P Goto. I know that this isn't ideal for photography but it has some capability.

My question, if anyone can throw any light is - Why can't I get the thing to focus?? New scope so I don't want to be getting the hacksaw blades out to achieve prime focus.

I have a Nikon D5300 and a 3 piece adapter - https://www.amazon.co.uk/gp/product/B011U8FU6O/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1  No matter what configuration I use it just doesn't seem to want to focus at night. Viewing through Liveview, even zoomed in, all I see is a black screen. During the daytime with the T ring and small nosepiece attached to the Barlow I can sort of focus (wobbly base! Not where I normally set up) on an electricity pylon a good couple of miles away.

Any tricks/suggestions appreciated.

Thanks

 

 

[Cornelius Varley]

Many reflectors are not designed for photography, they can't reached focus without some form of modification to shorten the distance between the primary and secondary mirrors or by using a barlow lens to move the point of focus outwards.  Barlow lenses are available with a t-thread to which the camera can be attached via a t-ring ie celestron barlow lens .

[kevhatch]

Better focus with just the t-ring on the Barlow but still don't understand why I can't focus / see any stars in liveview at night.

I have tried this set up before.

[Adam J]

If it is literally a new scope then I would send it back if internet purchased, as its not suited to photographic use with a DSLR the model that you want is the 150PDS as opposed to a 150p. 

Its not the correct setup for deep sky but with a 2x barlow it will focus for planetary photography. 

So it really all depends on what you were wanting out of the setup??

[Adam J]

Coincidently you need a very very bright star for focus, look for the brightest star in a constellation and set the camera to its highest ISO in live view. 

[kevhatch]

I didn't originally buy the scope specifically for photography, that is just something I've fallen into since being on this forum ... It's all your fault :-)

I'll have another crack at focusing it tonight.

[happy-kat]

The focus tube is too long. A member did alter their one to to reach focus. However there have been some stunning images taken using this mount a DSLR and 135mm lens. Check out Nigel G on the No EQ DSO Challenge thread.

[spillage]

I could be wrong but if you remove the nose piece from the t-2 ring are you not able to unscrew the ring from the top of the focuser and screw the camera directly to the focus tube?

This is what I did with my old celestron 150 cn-6.

[happy-kat]

You cannot buy a shorter focus tube and you can not buy a low enough adaptor. I've followed the use of this mount and telescope. You either have to do a modification or use a camera and lens instead. Imaging within the capabilities of an altar mount of DSO is possible.

Link

[ronin]

Your problem is one of mechanics. The prime image of the scope will fall at a point that is a little inside the focuser, the DSLR is held further out because of the DSLR body and the attachment tubes and so you cannot wind the DSLR in enough so that the sensor and the prime image coincide.

It arises because the prime image for an eyepiece is a bit outside the eyepiece so the focuser is intended to place the eyepiece further away. In a DSLR the sensor is inside the DSLR body. In effect the scope is set up for visual not imaging.

What people do is release the screws holding the mirror cell in place and move the mirror cell up the optical tube by about 2 or 3 cm. then tighten it all up agian, then recollimate since all the moving will have upset it all.

This pushes the prime image out by the same amount and so it may now coincide with the DSLR sensor. However it will then likely not operate with an eyepiece and you will need a short extension tube - but that is easy.

Common problem as no doubt SW say you can attach a DSLR, you can but you cannot get an image with the attached DSLR, but they never said that, just that you can attach a DSLR.

If just getting used to the scope and what all the bits do then I suggest you leave it and familiarise yourself with it all and especially collimation before you start moving things. Just remember that if you move the mirror then you will need the extension tube for visual.

ES and Bresser seem to supply their scope set for imaging as standard, for visual you have to attach one of the short extension tubes they supply. What happens then is people get scope, put diagonal on, put eyepiece in and scream they cannot see anything as it doesn't quite come to focus. Solution is add in one of the 2 supplied extension tubes.

[happy-kat]

You can not move the mirror in this flavour of 150p because it is not collimated/arranged like the 150p telescope is typically. The 150p used on the star discovery has the same actual 150p mirror just it is housed differently at the bottom of the telescope compared to your usually come across telescope where a DSLR will not reach focus like the 130p which people might move the mirror further up the tube with longer collimation screws.

If you void your warranty the info you to read is here.

link

Personally with an altaz mount I prefer to use a camera with lens on a dove bar attached to the mount. Put a red dot finder in the camera hot flash shoe and you can align the go to and you are away.

Some example arrangements here.

link

 

[Duggyj]

I have a 150pl and had the same  problem with my d3200. I solved it by not using the nose piece and screwing the adapter directly onto the focuser. Problem solved. 

[RAWBob]

I wonder if you would have that issue with a Sony a6000.  I put mine directly on the focuser and have no issues, but it's a far shorter distance from the flange to the sensor.  Works with a 1.25" Barlow or directly attached to the 2" focuser tube.  I will likely use the camera attached to the top of the scope when using my Nikon D610 or D7200.  The Sony seems ideal for imaging though, but I don't have any images to post yet to prove it.  Hopefully I will get some this weekend.

Bob