Barlow for SW 130p dob

[Monstar]

Happy Easter everyone,

Don't know if you remember or not but about a month ago I bought the SW 130p Dob, which as my first scope I must say I'm still amazed at its performance and simplicity. There was at first a bit of difficulty getting used to moving the tube as I found it a bit counter intuitive, especially following objects with the 10mm EP, but that's become second nature with use. I just have a couple of questions you may be able to help me with.

First the RDF, I can't seem to get it on target as the adjustment wheels don't seem to go far enough for me. I've tried it level with the eyepiece and farthest forward and backward. What's the best position, or am I missing something obvious (it wouldn't be the first time).

I only have the supplied 10 and 25mm EPs. I was thinking it would be nice to add 8 and 16mm but have decided on the 16 and a 2x Barlow as I could use the Barlow with the other EPs. The problem is I've read somewhere that you can only use a "short" or "long" type Barlow (can't remember which) with this particular scope. Can anybody help with this or offer suggestions please.

Also any help or suggestions or tips for accessories or learning new stuff would be appreciated.

Enjoy the rest of the holiday breaks, and save some chocolate for me everyone!

[SkyWatch]

Hi Johnny. First the rdf: sometimes you have to loosen the base-screws and move these a bit sideways if there is not enough sideways adjustment, and if vertical is the problem, try putting a small washer underneath to change its vertical angle.
From the photos it looks like you will need a relatively short barlow: otherwise it will protrude into the light-path. Andrews have a GSO one for $29.
All the best,
Dean

[Regulus]

Johnny, RDF's are a pain to use unless they are high quality. An optical finder is so much nicer, even a 6x30 will be easier to use. And because it is a little telescope in it's own right it magnifies the light of stars/planets and makes it easier to find things in the night sky.
Sometimes trying to find things with an RDF is hit and miss if they are not that easily seen naked eye and un-magnified (light-wise), like a globular cluster (Omega Centauri for example). In instances like this the RDF is giving you very little, to no assistance.
Seriously consider getting an optical finder. 6x30 Meade or Vixen etc., or if you want 'easy street' then a 8x50 which can be had from Andrews for $59 with a mounting bracket and foot. Add $10 postage
http://www.andrewscom.com.au/site-section-10.htm
- right near the bottom of the page John.
Trevor

[raymo]

I seem to be alone in that I have tremendous difficulty in locating
objects in my 9x50mm finder by sighting along it. Doing a 2 or 3 star
alignment becomes an exercise in frustration. Using my RDF I go straight to the required stars, and alignment is done in a flash. Once alignment is
done then the finder is, of course, essential for centreing faint objects found by the GoTo system.
raymo

[SimmoW]

Johnny, I was frustrated with my new RDF, no real adjustment, until I took it into Bintel for a review. There's a tiny locknut at the bottom of it, that needs to be released to allow the adjustment to work. I'd also inserted the holder backwards!

So now it works great and I can point and find most large objects and planets etc. So have a look at yours.

[Allan_L]

No you are not alone.
This is a perfect description of how I use the RDF and the magnified finder combination.

And for those without GoTo, the RDF gets you quickly into the area of sky you want, then the magnified finder helps you zero in on your target.

[Renato1]

I concur with the idea of getting a finder for you telescope. But I'd follow the other suggestions and get the red dot finder working and leave it there also.

If you had a straight through 6X30 or 8X50 finder, it's easy enough to locate brighter stars initially by keeping both eyes open when you line up (it's much harder with just one eye open, the way one tends to want to do it, like in aiming a rifle). But there are lots of times where there aren't many bright stars near what you want to observe, or where there are too many, creating confusion. In those cases, it is a lot easier using the RDF first, and then the optical finder.

What I like best is having a RDF with a right angled, Correct image finder that matches one's star atlas.

Very strange about the Barlow, I've never heard of one that doesn't work in a reflector. Generally speaking, the longer ones are considered the better ones, with quality sacrificed slightly in the "shorty" ones, which people don't mind as they are handier to use in telescopes with star diagonals. Also, I'm not sure what is meant by "long" as I have a pretty long Televue one, shorter Televue and Celestron ones (which I still think of as standard long), and a much shorter "shorty" Meade one.

My only eyepiece tips would be that it's nice to have eyepieces that match the size of the deep sky object you are trying to observe. With 1.25" eyepieces, 32mm gives you the widest field - don't buy a 40mm one, as it gives the same field of view. But if you have a 2" focuser, then 40mm does give you a wider field, as does a 56mm eyepiece.

Initially, when viewing the brighter objects, your current collection is fine. But later on, as you try hunt down faint galaxies at a dark site, an eyepiece that gives you a 2mm exit pupil is usually best. Basically multiply the focal ratio of your telescope by 2 to find that eyepiece. So if you have a focal length or say 900mm, focal ratio is 900/130=7 and you'd want a 14mm eyepiece, or the closest you can get to it.

And to make life easier for yourself, try make that 2mm exit pupil eyepiece a wide angle one - it doesn't have to be an expensive one. The inexpensive ones aren't as good at the periphery of the field, but faint fuzzy galaxies will still be spotable there.

Regards,
Renato

[OzStarGazer]

I have the same scope and use a short Barlow. I also have a long one which I bought because it was incredibly cheap and I thought I could use its body for projection in astrophotography one day... I mean, it was cheaper than most projection adapters on the market... If I shorten the tube it even works, but I still prefer the short one.

[CJ]

Hi Johnny,
I had the same problem with the RDF on my 130P. I couldn't figure out a way of shimming it into alignment so, slightly niggled by it, I just compensated by eye for the offset.
Unfortunately of no help to you, it packed up after 8 months and the warranty replacement could, oddly, be aligned accurately.

I bought this barlow with my Heritage
http://www.ozscopes.com.au/skywatcher-2x-1-25-single-barlow-lens.html
It was VERY cheap at the time. Focus wise, it works and has a T-thread, but the quality is probably poor.

[OzStarGazer]

My RDF sometimes works fine and sometimes I have the same problem you have, so I don't know if I should tell the seller? I am just a bit reluctant because sometimes it seems to be fine.

[CJ]

On my RDF the dot intensity would fluctuate. When I decided to try a fresh battery I discovered that the spring contact that holds the battery in place was loose. Cost $8 postage to return it :rolleyes:

[Monstar]

First the bad news, SIMON, I removed the RDF to remove the locking screw but it wasn't there, bugger!

The good news is when I replaced it I was able to correctly place the red dot on the horizontal axis and the vertical is only very slightly off. Dean I was thinking of using a washer to solve the vertical but as it's only very slightly off I've decided to leave it as it is as so far it is working fine with a slight compensation for the difference.

Thanks for all your help, now to think of getting that Barlow!

[SkyWatch]

Well done: glad to hear it is OK.
Have fun with the barlow!

- Dean

[OzStarGazer]

I think slightly off is fine as long as the object is in the FOV. :)

[julianh72]

A little bit of folded-up aluminium foil packed under the spring contact will work wonders - and costs a lot less than $8!

[CJ]

Nah, it was actually broken. It had loads of lateral movement as well as the "spring" being more of a flap. It was only the battery cover holding it all in place. $8 wasn't too painful. :D