Re: [APML] OT? - Parfocal Eyepieces (SB iFocus particularly)

["John Boudreau" <jeboud@comcast.net>]

> My question to the group: does anyone have an SB iFocus eyepiece? (Loke
> Tan - I saw you sell one more recently - I'd welcome your insight) If so,
> are they happy with it; and did they learn anything in its use that I can
> pass to this guy to help him out (or if he wants to return it, that I can do
> to ensure it will deliver a happier result to the next person)?

Hi Stuart,

I use one for my ST-4. I've had the iFocus eyepiece for about 3 years or so, and mine turned out to be a "generic" 10mm Plossl identical to the Orion Sirius 10mm Plossl, but with a large parfocal ring that was tightened onto the optic head assembly. I don't know if the newer ones are any different.

It was OK, but really wasn't critically parfocal with the ST-4. On a night of very good seeing I critically focused my ST-4 in my TV85, then replaced the ST-4 with the iFocus and repositioned it's parfocal collar. It works very nicely now. Using an even faster f/ratio scope than the TV85 to check it would be even better, as the depth of focus would be even more critical. Better still would probably be to adjust the eyepiece after critically focusing the CCD by viewing the target star on a computer monitor.

But even after all that, if your friend uses different filters at times for the CCD, that would throw the focus off some. For imaging, you can only rely on an iFocus to get your focus in the ballpark. Then it's time to fine-tune focus in the CCD's software focusing routine.

Another thing to consider--- My iFocus had a 1.25" barrel, which is what is common for the ST-4. *If* he's using a 2" nosepiece on his CCD and his iFocus is 1.25", could he be throwing things off by using a 1.25 to 2" adapter with a top flange? The thickness of the flange of most such adapters I know of would completely throw off any parfocalization.

John


John Boudreau
http://home.comcast.net/~jeboud/astro.htm

----- Original Message ----- 
From: "Stuart Heggie" <stuart.j.heggie@sympatico.ca>
To: "Discussion of FilmAstrophotography" <astro-photo@seds.org>
Sent: Sunday, November 23, 2003 2:44 PM
Subject: [APML] OT? - Parfocal Eyepieces (SB iFocus particularly)


> Question on parfocal eyepieces for focusing autoguiders hence OT.
> 
> Some time ago I bought an SB iFocus Ocular for my ST-7. Now honestly I was
> not overly impressed but it worked "okay" so I used it to achieve focus for
> my ST-7 in autoguider operation on my guidescope. Having done that, I had no
> use for it so offered it for sale with the same text the person who sold it
> to me used. The person who bought it from me can't get it to work and is
> annoyed with me (sigh). I'm offering him his money back. I'm not sure he
> really tried too hard but in the end, the customer is the final arbiter of
> whether they are happy or not - not the seller.
> 
> My question to the group: does anyone have an SB iFocus eyepiece? (Loke
> Tan - I saw you sell one more recently - I'd welcome your insight) If so,
> are they happy with it; and did they learn anything in its use that I can
> pass to this guy to help him out (or if he wants to return it, that I can do
> to ensure it will deliver a happier result to the next person)?
> 
> The thing was sold to me as being for the ST-7/8/9/10 and of course I have
> an ST-7 so I figured I'd be happy. My actual experience was that it got me
> to a point of focus where the stars on the screen of my computer were
> bloated but obviously there - achieving finer focus using the algorithms
> that come with the ST-7 got me fine focus.
> 
> Help?
> Stuart
> 
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> Astro-Photo mailing list
> Astro-Photo@seds.org
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> 


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