Prime focus on Star Discovery 150p

[Ulysses31]

So, I have gone and got myself a Skywatcher Star Discovery 150p, which has so far proved to be a very good little scope and I've had some very good results.

I have now got the bug for imaging and have gone out and got myself a second hand Nikon D5100 and verious other equipment needed to do this, only to now find I can't get Prime Focus!!!!!!!! So the only way I can image is using a barlow x2 which obviously changes the F ratio from F5.5 to F11 slowing everything x2 this isn't to bad for planetary imaging but for DSO images not so good!!! 

After searching through lots of videos on to do this all I can find is...... 

I can either butcher the standard rack and pinion focuser that's fitted on it by cutting it down and rethreading it or by moving the primary up by 20-25mm,  which seems a shame to do a brand new scope still under warranty! 

The only other option I have come up with is changing the focuser to a Skywatcher Low Profile  Dual Speed Focuser For Newtonian Reflectors. 

Could anyone out there shed any light on this before I spend another £130 on the new focuser. 

Thanks 

[Galen Gilmore]

Normal newtonian reflectors have this problem. The only two ways I've seen to fix this is either use a Barlow lens, or physically move your primary mirror up the tube.

I don't think the star discovery mount is good for DSO's anyway. It is an Alt-Az mount, which means that it only moves up-down, left-right. These mounts do not compensate for field rotation.

[Ulysses31]

Thanks for replying Galen, the mount is a robust upgraded version of the AZ goto and I  have seen it used with great results on Dso's  using lots of short exposures say 100 x 5secs. 

This was using a CCD video camera though!!!! And the results I have had using the barlow at up to 30sec exposures haven't been too bad. 

Here's a link to where I have seen this done.. http://x-bit-astro-imaging.blogspot.co.uk/2015/08/a-ln300-video-camera-was-placed-at.html?m=1 

I'm also thinking of attaching a auto guided scope to help as well. 

[Galen Gilmore]

1 hour ago, Ulysses31 said:

Thanks for replying Galen, the mount is a robust upgraded version of the AZ goto and I  have seen it used with great results on Dso's  using lots of short exposures say 100 x 5secs. 

This was using a CCD video camera though!!!! And the results I have had using the barlow at up to 30sec exposures haven't been too bad. 

Here's a link to where I have seen this done.. http://x-bit-astro-imaging.blogspot.co.uk/2015/08/a-ln300-video-camera-was-placed-at.html?m=1 

I'm also thinking of attaching a auto guided scope to help as well. 

Don't get me wrong, I'm not saying that you can't use it, but it's just not optimal. Normally to get results that are close to what can be achieved with an eq mount, you must put in thousands of exposures (not an over statement).

A guide scope won't really help all that much I don't think, just because the max you will be able to do without any field rotation is 20-30 seconds. And the mount should be able to track for that long unguided easily.

If I were you, don't waste your money for now. You can do some planetary and lunar, and maybe some short exposure DSO. But save your money until you have enough to get a real EQ mount. Most say that an HEQ5 is the minimum for an astrophotography, but if you really are not willing to lay down 900 pounds then an EQ5 with motors will do.

Then eventually you will save enough money for a 130pds, then you will be in business.

 

Now let me let some people who are more experienced have a turn!  

[happy-kat]

You already have your mount, yes you could butcher your focuser but my preference would be take the telescope off and fit the L bracket that came in the box and your DSLR with lens. Even if the kit lens you could get going. There is a massive thread on this The No EQ DSO Challenge. Have a look at what others are doing with a similar mount one member did use your mount with a 135mm camera lens for example and another right now with an ED80 while saving for an eq mount. Don't be put off trying have a read of that thread start at the back for the recent contributions.

[Ulysses31]

Hi everyone just thought I'd say thanks for all the advice.

Finally got myself up and running not the greatest effort but think it not bad for a Manchester back yard!!! 

M42

Skywatcher Star Discovery 150p AZ GOTO V4

Nikon D5100 x2 Barlow 

10x6secs exposures 

ISO 1600

Stack in DSS 

Processed in GIMP 2.8 

[mislav]

hi,i am planing to modify my focuser because i dont want to use barlow anymore...but i want to be sure what i am doing.. questions are on attached picture...please help....  second pciture is with barlow...but i just feel without it thats going to be better, and adromeda will not be so wigneted...

[mislav]

wrong nebula...this is "good one" first try...with full moon...

[Jean-Luc74]

Hello Mislav,

Great work on this Skywatcher Telescope! I'm looking into buying one.

Do you think that prime focus is achievable without voiding the warranty using a raspberry cam, described here: ?

https://www.instructables.com/id/Raspberry-Pi-Astro-Cam/

Is the prime focus location inside the original focuser or just on top of it?

Kind regards,

Jean-Luc

 

[Louis D]

On 30/08/2018 at 01:21, Jean-Luc74 said:

Hello Mislav,

Great work on this Skywatcher Telescope! I'm looking into buying one.

Do you think that prime focus is achievable without voiding the warranty using a raspberry cam, described here: ?

https://www.instructables.com/id/Raspberry-Pi-Astro-Cam/ 

Is the prime focus location inside the original focuser or just on top of it?

Kind regards,

Jean-Luc

 

Prime focus is generally located well above the most inward travel position of a focuser to allow various eyepieces to come to focus.  The problem for the OP was that it wasn't at least 55mm, the required distance for a T-mounted DSLR.  That Raspberry Pi imager should have no problems coming to focus in that scope (or any other for that matter).

[Matnb]

I think that this telescope would be very good for beginners, especially for teenagers thanks to the new wifi goto system manageable on smartphones. It's a shame that it cannot reach prime focus with a dslr. 

I was thinking there should be no problem with recent mirrorless camera, because Sony or Fuji mounts have a flange focal distance of 16, 17 mm insted of 44, 46 like Dslr...

...Unfortunately it seems all T mounts for  Fuji and Sony are made to bring that distance to 55 like in Dslr!

Having a fuji xt-20 I am curious to know  if someone made it, either by cutting the adapter or finding a short adapter because I am thinking to buy this telescope to use it in camping with my children 

[happy-kat]

Perhaps there is a thinner adapter say on thingverse for 3d printing

[Matnb]

I didn't find anything ready made. I am scared it would cost more than 50$.

Looking at the measurables given in the video above, I think one could buy a Sony or Fuji T adapter (15$) then unscrew the T ring (6 mm), cut away almost all the tube and keep just the flange (7-8mm), glue the flange to the T ring. The piece should be short enough to go directly on the scope eyepiece holder which is free to rotate, so non need to have a rotating T ring.

The resulting adapter would be long as a standard Canon T adapter but the sensor is only 16-18 mm deep instead of 44 as in Canon Eos. That's a few mm more than the 1 inch required to achieve prime focus according to the very clear video fron Nige.

Wondering if someone tried. And if someone sells fuji mount flanges, just the flange.

[happy-kat]

You could probably take this designed part link here and change it to have an inbuilt T mount instead of the T2 male thread bit.

[Matnb]

I think I found it for sale. It's the same piece hand made in the video of Nigel G but for Fuji mirrorless, and technical specs says that it adds only 10mm to the camera flange focal distance which is 17.7

I guess we are quite inside the focal range, nevertheless I will try to check on the OTA before buying it.

I must say that italian Sky Watcher client service was wonderful. They gave me hints and found me the piece itself.

That basically would mean that all new mirrorless camera can achive prime focus on this tube

[mislav]

what is max subexposure for primefocus thst is achiavable with stardiscovery 150p when is tracking (when is goto on)... with sony nex and lowprofile adapter focus is achiavable   

[happy-kat]

The exposure time will vary by the direction the telescope is pointing and the altitude. The range might be anything from 10 seconds to 45 seconds. East or West 0-60 degrees altitude are the best directions and altitude range to point.

[Grahlom]

On 05/12/2018 at 12:47, Matnb said:

I think I found it for sale. It's the same piece hand made in the video of Nigel G but for Fuji mirrorless, and technical specs says that it adds only 10mm to the camera flange focal distance which is 17.7

I guess we are quite inside the focal range, nevertheless I will try to check on the OTA before buying it.

I must say that italian Sky Watcher client service was wonderful. They gave me hints and found me the piece itself.

That basically would mean that all new mirrorless camera can achive prime focus on this tube

Hi guys, first time posting here. My apologies if I was supposed to introduce myself as a new member, but as I didn't see that requirement I decided not to.

Anyway, I am also an owner of SD 150p, aforementioned telescope, and as well have an urge to take a few pictures. As I don't want to have a laptop with me, or own one just so I could take a picture of the night sky, I was looking into getting a "standalone" camera. 

You guys got my attention with mirrorless camera, which could possibly get into prime focus on this telescope. If I was to buy for example Canon M100, which part would I need to buy to be able to attach it to my telescope in prime focucs?

Matnb, you said you found an attachment for sale, do you have a link for it maybe?

 

[Swoop1]

I have an SW Explorer 150P and had similar issues with my Sony a350- couldnt achieve prime focus with a T ring inserting the tube into the draw tube on the focuser.

I then found that if I unscrewed the nose piece off the T ring and did likewise with the focuser- unscrew the draw tube (if that is what the bit you insert the eyepiece into is called), I could screw what was left of the 1 1/4 EP adapter to the T ring and bingo- prime focus achieved.

[Grahlom]

Yeah I guess my telescope has different kind of threading because people say we need that "nose" part of the adapter. Not sure why there isn't an adapter for that type of threading ? Correct me if I'm wrong

[alberto91]

On 02/05/2019 at 11:56, Grahlom said:

Yeah I guess my telescope has different kind of threading because people say we need that "nose" part of the adapter. Not sure why there isn't an adapter for that type of threading ? Correct me if I'm wrong

 

[Charis]

On 01/12/2017 at 15:45, Ulysses31 said:

Hi everyone just thought I'd say thanks for all the advice.

Finally got myself up and running not the greatest effort but think it not bad for a Manchester back yard!!! 

M42

Skywatcher Star Discovery 150p AZ GOTO V4

Nikon D5100 x2 Barlow 

10x6secs exposures 

ISO 1600

Stack in DSS 

Processed in GIMP 2.8 

Hello, I am in the same exact position as you were 4 years ago. May i ask you what did you do to counter the prime focus problem?

Edited June 17, 2021 by Charis

[Peter Munkholm]

On 21/10/2019 at 15:33, alberto91 said:

 

Thank you SO much for the video. I managed to replicate your modification with some card-board tube and gaffer tape. And it works SO muc better than with a X2 Barlow.

I attached my Andromeda and Double Cluster from yesterday.