Focus problem

[Tony72]

Hi All

I have a Philips SPC 900 NC lens removed and 1.25 adapter.

I can get focus on close terrestrial objects, however at ranges of about 1.5 miles + no go.

I tried on the moon last night, but I could only get to almost focus  as in the attached image.

My thoughts are not enough travel on the focuser i.e fully in, gets to end of travel. 

Scope Meade Polaris 130.

Thanks in advance for all your thoughts and suggestions.

Tony.

[Cornelius Varley]

I don't know the specification of the telescope but generally, for reflectors, you also need to use a barlow lens to achieve focus when imaging.

[Tony72]

4 minutes ago, Cornelius Varley said:

I don't know the specification of the telescope but generally, for reflectors, you also need to use a barlow lens to achieve focus when imaging.

Thanks, will try that next time I get clear skies.

Tony

 

[bobro]

Hi Tony,

As a newbie to astroimaging, I have recently purchased a Meade Polaris 130 Reflector. Whilst my main aim is to attach a DSLR camera, I have started out with a webcam.

Like yourself, I found the (well known) focussing problem with a DSLR (more about that later). However, I didn't have any problem using a  webcam. The reason for this is that my webcam (Microsoft LifeCam Cinema) easily puts the image sensor at the prime focus of the telescope (i.e. at the same place as the focal plane of an eyepiece) as the webcam fits nicely inside the telescope eyepiece holder. Your Philips webcam has the sensor in an external housing that is attached with a mount to the eyepiece holder. To bring the sensor into the prime focus position of the telescope the focuser must move inwards and looks to have run out of travel. With a regular eyepiece there may be only about 25mm of 'spare' inward travel, so it is easy to run out when needing to move the focuser inwards.

As mentioned above, a barlow lens often helps, though I adopted another solution to allow my Canon 1000D DSLR to focus - moving the main mirror up the tube by cutting 40mm from the end of the tube. Seems a drastic mod, but the mod moves the focus point away from the telescope and so the sensor plane of the DSLR can be brought into the prime focus position. The webcam and regular eyepieces then use a barlow lens tube (without the lens) as an eyepiece extender for focussing.

The Meade 130 is very similar to the Skywatcher Explorer 130M and there is lots of info on the web discussing focussing. See the following page for a great discussion :

http://www.alananna.co.uk/blog/2012/using-an-slr-with-a-skywatcher-explorer-130m-telescope/

Note - just tested my shortened scope on the moon by taking some images with the 1000D. Looks OK but there is a long way to go and a lot of learning to be done before I get an image of the Orion Nebula!

Bob

[Atreta]

On 3/21/2016 at 12:18, Tony72 said:

Hi All

I have a Philips SPC 900 NC lens removed and 1.25 adapter.

I can get focus on close terrestrial objects, however at ranges of about 1.5 miles + no go.

I tried on the moon last night, but I could only get to almost focus  as in the attached image.

My thoughts are not enough travel on the focuser i.e fully in, gets to end of travel. 

Scope Meade Polaris 130.

Thanks in advance for all your thoughts and suggestions.

Tony.

what do you mean by end of travel?  did you move the focuser inwards or outwards?  if you need more travel outwards you can use an extension tube or use the barlow with the lens unscrewed. 

[Dutchy]

I do have a simular problem with my 203/1000 bresser (meade) and a dslr canon 1100 is t possible to deattach the ring with the screws of your focusser?  And put an 2" to 1'25" small nose piece  in the focusser something like this 

Notice how thing that ring is of the upper adapter