Diffraction spikes viewing Jupiter

[bartman (Bart)]

I recently (second outdoor activity) tried my scope out on Jupiter.
Good view through my 28mm SW eyepiece - not so good seeing, but enough for me to appreciate as a newbie.
Then hooked up my Nikon D90 and take some pics. Mmmmmm
Diff spkies....yes I understand that the supports of the secondary mirror causes this.
I could not focus any further 'down' .

a) Does a focal reducer help me focus further 'down' when a DSLR is attached ?
b) OR does a Barlow put the focal plane further back ? in other words , does it reduce the focal length of my scope? ( is that what a focal reducer does?)
c) and would this -either of the above options- reduce the diff spikes?
d) does a smaller eyepiece ( say 10mm) reduce diff spikes?

Grrrr trying to work out focal lengths, FOV, focal planes etc as a noob is frustrating - but rewarding....as I know that in a few weeks i'll be saying to myself "Dooooh that was soooo simple!"

Anyways,
Thank you in advance for any advice!!!!!!

Bartman

[multiweb (Marc)]

Originally Posted by bartman

a) Does a focal reducer help me focus further 'down' when a DSLR is attached ?

No, a focal reducer will shorten your focal length. So your focuser will have to go "up" towards the scope lens or mirror.

Originally Posted by bartman

b) OR does a Barlow put the focal plane further back ? in other words , does it reduce the focal length of my scope? ( is that what a focal reducer does?)

No. The Barlow will magnify your image and increase your focal length. So you'll need to focus further "down", away from your scope mirror or lens. You might need extension tubes if you "run out of focuser".

Originally Posted by bartman

c) and would this -either of the above options- reduce the diff spikes?

No. But if you magnify enough (x3,x5) you will start seeing Jupiter as a disc rather than a point source and your diffraction spikes won't be as overwhelming.

Originally Posted by bartman

d) does a smaller eyepiece ( say 10mm) reduce diff spikes?

No. If the light is close to a point source you'll still see those diffraction spikes with long exposures.

Hope this helps.

[mswhin63 (Malcolm)]

I use a CCD recently and got massive difraction spikes as well. My avitar is a culmination of filter to reduce the light. I also have no tracking as well which alter the final outcome.

My final configuration was IR Filter and double polarising filter adjusted.

I am going to try another method later when the skies clear up.

The DSLR may require faster shutter speed as it looks like you have too much light coming in. I can't help much though if using lenses.

BTW I am a newbie as well. I my advice maybe off a bit.

[bartman (Bart)]

Thanx Marc,
Your reply makes sense!
I used the wrong terminology. I used focusing down instead of up cause I see the focuser going "down" into the tube (newt) but your right that it is going up now that I look at it.
I couldn't get the focuser to go any further "up" the tube. So by reading your reply a barlow would give me the extra travel up the scope...I'm guessing.
However I'm just a little confussed with "No. If the light is close to a point source you'll still see those diffraction spikes with long exposures.".
What do you mean by 'point source'?
thanx Bartman

[multiweb (Marc)]

Originally Posted by bartman

What do you mean by 'point source'?

Means that Jupiter being so small it looks almost like a star. (a point). If you look at it closer it will look like a disc. If you look at the moon, it is a disc.