Parfocal eyepiece for DSI...

[timthelder]

Is there nothing ever simple.....

After doing a jig over precisely polar aligning my scope:Chessy_Smile: ,it was cloudy so I thought I would use the time productively, and make me a parfocal eyepiece to use with my DSI....

Capella was looking good, so I used her to focus my camera to perfection.(bought a GSO Crayford focuser for SCT scopes to solve some mirror slop problems,wonderful piece of equipment BTW.)

I gently ease my camera out of the focuser, grab a 25mm lens and my parfocal ring, and ease them back into the focuser for adjustment and...... the barrel on the lens is too short to use the ring.(star won't focus.)

No problem, I'll grab my 18mm lens.....Hmmm, same problem....grab a 10mm, then a 40mm,.........

To make an eyepiece parfocal with the camera, I have to slide the eyepiece back so far, the barrels of all the eyepiece's I have come out of the focuser!!!!!!Arrrrrrgh!:duh:
The star is perfectly focused in all the eyepieces with them sitting AGAINST the focuser.

I am always open to any helpful suggestions....glue,duct tape,arc welder....
A longer barrel to screw on to an eyepiece would be perfect.

[Tenacious Del]

hi tim, sorry, i have no idea how you could focus an eyepiece with that. i guess others here will be able to shed some more light on this,,,,,much more light. :duh:

[hpcoolahan]

Well What u can do is if u have a 2x barlow, take out the barlow lens and use the setup as a extension, just dont forget u need it there each time to get focus.

Clear Skies
Pat

[timthelder]

I tried the barlow....that's too much extension.If the barrels were just a half an inch/2cm longer any of them would work to use as a focusing eyepiece.

I'm just kind've scratching my head right now trying to figure out what it is about my set-up that is making the focal length different enough that a regular eyepiece isn't working.:hmm:

Here's a thought...Before I do a rough focus with the knob on the back of the scope,I put the adjustment of the crayford close to center so as to leave fine focusing adjustment either way.

If I dial the crayford in some it might shorten the focal length enough to be able to parfocal an eyepiece.(hmm,then that would move the camera out of focus.),Or maybe I could knock the rough focus out a little bit on the scope and try refocusing with the crayford.....sort of find the "sweet spot" so to speak.

Thinking out loud aren't I...(lol)

[Radar]

Hi Tim,

Sounds like a frustrating process. I'll look into this and see what I can find out for you.

Stay tuned.

Ray

[AstroTasmania]

Hi,

What you guys are doing by trial and error is a wonderful way to be gaining knowledge & expertise, and I am pleased to see this happening. You will learn so much in the process, far better than just relying on someone else giving you a solution, in the first instance.

The Meade manuals explain about the par focus ring and how to do it, just take your time and work through it, often in daylight when you can see what you are doing, just to get familiar with the process.

Pat has given you a great clue!!

Clear skies...
Shevill

[Radar]

I think he needs to go closer rather than farther. Which is going to present a problem. Is that right Tim? If you need to go closer, we could maybe find some kind of focal reducing lens so that your eyepieces can still work.

Ray

[hpcoolahan]

Try to unscrew the part on the barlow that goes into the diagonal.
then see if it will screw into the eyepiece as if where a filter,,,might work.

Pat

[Caveman]

I found after some mucking about to what worked that with my GSO Newtonian that at 15mm EP did the trick. I haven't actually used the parfocal ring as yet. I found that once the 15mm was focussed the dsi camera only need some small adjustments to the focuser to bring it into focus.

[timthelder]

Try to unscrew the part on the barlow that goes into the diagonal.
then see if it will screw into the eyepiece as if where a filter,,,might work.

I tried that Pat,but the thread orientation is opposite on eyepieces and barlows.(eyepiece threads on outside of barrel,barlow threads on inside of barrel,or visa versa.)

I even emailed a couple of different barlow manufacturers,same thing.I haven't however checked the barrel on my old stock 1 1/4 diagonal yet.

A very good suggestion though...

I am however,doing ok the old fashioned way,just takes a little longer.

I'll probably just make a note on how many cranks on the focuser I have to make to focus the camera after aligning my scope.

[hpcoolahan]

the way i do it is line up on a bright star with a eyepiece ,swap for the camera, if its out of focus you will see the big dougnut of the out of focus star,, just crank in or out so it gets smaller , and ,,, there you have it ..

Ive never bothered to set up parfocal eyepiece, just do it this way...lol

Good luck
Clear Skies
Pat

[Radar]

This is how I focus to. I don't really trust parfocal eyepieces. Seeing your image on the screen is a sure way to focus a ccd camera.

Ray

[hpcoolahan]

at least some of us still trust our eyes,, you mean..lol


Pat