Jump to content
  • Join the online East Midlands astronomy club today!

    With active forums, two dark sites and a knowledgeable membership, East Midlands Stargazers has something for everyone.

focusing problem with DBK and Powermate


Guest greencorner
 Share

Recommended Posts

Guest greencorner

My scope is a Skyliner 250 Go To Dob: 1200mm focal length and f4.7 f ratio.  I’m attempting to image Jupiter with a f ratio around f25-f30. 


 


I managed recently to obtain some good images of Jupiter with 4 moons at prime focus using my Imaging Source DBK21AU618.AS  camera.  However, when I tried to raise the f ratio with my TeleVue Powermate 5x to get a decent image size of the planet on its own, I was unable to obtain focus on my lap top screen. Can anyone please advise how best to can connect my DBK to my Powermate.


 


I have heard that this can be done via a PTR-1250 Powermate adapter (which I have) and a C-mount to T2 adapter.  Is this correct?  I've seen some excellent images of Jupiter on the web taken with this scope, camera and Powermate so I assume it can be done.


Link to comment
Share on other sites

Guest Kheldar

If it's physically getting to focus, where are you out - in or out travel?


 


If you've got travel either side of the focus point then I fear my conclusion is you're just pushing it too hard - f25 on a Dob is a pig to focus and will only really work on the best of nights. Maybe consider backing down to f20 for more regular useable nights?


Link to comment
Share on other sites

Sorry to tell you I have a x5 power mate and managed to use it only twice as the seeing is not normally up o it in this country(I have had it about 5 years)


 


the x 2.5 is much more useful IMO


 


Steve

Link to comment
Share on other sites

Hi Tony and a warm welcome to EMS. :)


 


The problem with focusing a newtonian for imaging is usually to do with not enough "in focus" or not enough "out focus". If it's "in focus" causing the issue there's two common solutions. Either change the focuser to a low profile one like this:


 


http://www.firstlightoptics.com/skywatcher-focusers/skywatcher-dual-speed-low-profile-1252-inch-crayford-focuser.html


 


Or a bit of jiggery pokery with longer mounting screws to move the primary up the tube a bit so it's closer to the secondary. If it's "out focus" causing the problem then an extension tube usually solves it (much cheaper too). Hope that helps.


 


Please feel free to leave a brief intro in the Welcome Section so everyone can say hi - hope you enjoy the forum. :)


Link to comment
Share on other sites

You should just bung the DMK into the powermate via the 1.25 nosepiece on the camera, any increase in distance from the powermate lens to camera chip will increase the powermates effect!


Most planetary imagers use a motor focus as it does away with the scope shake caused by manual focusing.


 


But sorry to say I agree with Steve (Ibbo) 5x is rarely useable in this country.


Link to comment
Share on other sites

Guest AstroOlly
You should just bung the DMK into the powermate via the 1.25 nosepiece on the camera, any increase in distance from the powermate lens to camera chip will increase the powermates effect!

Most planetary imagers use a motor focus as it does away with the scope shake caused by manual focusing.

 

But sorry to say I agree with Steve (Ibbo) 5x is rarely useable in this country.

I don't think that is strictly true of the Telvue powermate, correct me if I am wrong but I think the design of them means you can lengthen or shorten the distance between sensor and lens and it won't make any difference in mag

But like I say I could be wrong, I know the meade telex tender work like that

Olly

Link to comment
Share on other sites

I don't think that is strictly true of the Telvue powermate, correct me if I am wrong but I think the design of them means you can lengthen or shorten the distance between sensor and lens and it won't make any difference in mag

But like I say I could be wrong, I know the meade telex tender work like that

Olly

It doesn't increase the magnification but does increase the focal length which has an effect on the image size on the chip

Link to comment
Share on other sites

Guest AstroOlly
It doesn't increase the magnification but does increase the focal length which has an effect on the image size on the chip

We'll looking at that graph I am getting mixed up,with the 2.5x powermate, I thought they were all the same

I Stand corrected, sorry for the duff information

Olly

Link to comment
Share on other sites

Guest greencorner

Thanks for your views, guys.  I'm assuming I was out of focus as my laptop screen was lit across the screen but neither focussing in or out made any difference: no detail of any kind (BTW, I do have a motor focusser)  Maybe the gain was too high.  I thought that Jupiter was central but could have been wrong at such a mag.  Maybe a flip mirror would help here.


 


I have seen brilliant images of Jupiter, taken with identical equipment to me (inc the Powermate x5), taken from Cheshire - so I assumed I could too, from Derby!  Any comments on this would be most helpful as this point seems to run against what Steve, Andy & Felix have said about the Powermate x5 in the UK.


 


I'd rather not loose my Powermate x5 - it was expensive!


Link to comment
Share on other sites

Yes the flip mirror is lovely, one of my fav things.

If you've seen results with exactly the same kit there is hope.

Is the scope collimated optimally?

Keep an eye on the jet stream (http://www.netweather.tv/index.cgi?action=jetstream;sess%3D) if it's over head it might contribute to poor "seeing" and mean getting sharp focus seems more tricky than normal.

It sounds like you will only get this set up to work on the very best of nights (which don't happen often); so it might be worth while dropping down the multiple of any powermate/barlow to 4x, 3x. 2x to see if that means you can do some imaging on less favourable nights (which are the normal).

Jd

Link to comment
Share on other sites

Guest greencorner

Thanks Steve - do you know whether a flip mirror works on f4.7 newt?


 


Thanks for the link, Kim.  Not sure if you've seen this image from Cheshire - Congleton I think - taken with the same equipment as mine...


http://www.flickr.com/photos/42079393@N05/8060748846/in/photostream/


 


As you say James, there's hope.  What I really need is a clear night now!!  I would say collimation is good, yes.  I'll keep an eye on the jet stream, thanks.


Link to comment
Share on other sites

Thinking about it, the flip mirror will add a fair amount of length onto the focuser. I'm not sure what the comined lengths and optics of a flip mirror and a powermate will result in.


 


Again it woul dbe useful if you could try someone elses before you comtted to buy. A flip mirror on its own would prevent you from achieving focus I suspect as you normally need more inward travel with a Newtonian and this will add a greater outward distance at the start.


 


JD

Link to comment
Share on other sites

Hi Tony


That is a good question that I don't have the answer to


 


as I say I use the x2.5 (mainly)on an SCT so have longer native FL and no problems with the focus, but I do use that adaptor you mentioned as it means all the "plumbing" is screwed together


 


Can you get focus without the powermate in the mix? if you can you may have to use an extension piece (do you have anything ?)


 


I would check that you can achieve focus with the x5 on the moon as its easier to get in the FOV


 


if you can get focus with x 5 as the scope is you would I believe struggle with the flip mirror unless its a long travel focuser.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.