Expectations

BC · #1 10-07-2005, 10:30 PM

Well my new 10" dob is out of the box 4 weeks early and there have been very few clear nights. I must admit to wondering how one ever feels confident about collimation results, I've read endless articles from the web. I haven't a clue whether it's right or not. I'm also just a bit dissapointed with the views. I have pretty dark skies and was looking forward to find a galaxy or 2. I finally found the sombrero (M104) but it was just an angular smudge with a lighter smudge in the middle. I guess all the talk about seeing structure in galaxies with a 10" led me to certain expectations. It all looks so sharp through my 20 x 80 binos or through the finder, but at 40x in the telescope it's all a bit dull. hmmmmm

astroron (Ron) · #2 10-07-2005, 10:42 PM

It all depends what eyepiece you are using, the Sombrero in a 30mm eyepiece even in a 16" scope is not that brilliant but using high manification comes up great, dont get dispondant just yet look at other larger objects to guage the performance of your telescope with different eyepieces and you will learn to appreciate what your scope can do. astroron

RAJAH235 · #3 10-07-2005, 11:18 PM

BC, What does a 'star' image look like at say, 150 x/ 200 x? Do you get good, even diffraction circles either side of focus? If not, then adjust collimation whilst on the star. Try about a mag 3 or 4.
Seeing has a lot to do with how the image looks, & how much mag you can use.
For a simple collimation guide > (http://skyandtelescope.com/printable...rticle_790.asp)
Try 2070 (Tarantula nebula in LMC), as a starter. Should be able to resolve some of the central area.
If you're having trouble collimating, I may be able to assist with the basics,but read/print the article first.
HTH.

L.

ballaratdragons (Ken) · #4 10-07-2005, 11:59 PM

BC,

It could all come down to eyepieces. As I have found, Cheapish EP's give a fairly poor result giving the impression that the scope is no good. Even a moderate scope with very good EP's will give fairly good results.
I know what you mean about Sombrero. I can see it very easy but I see it much the way you explain it. That, I believe, is due to my lower quality EP's. Whereas the Moon give the most incredible views. I can find about 60-80 galaxies from my dark site but my EP's will not show a crisp image and it does get frustrating. My EP's are mainly Series 500's. Not very good. Whereas I can see the Orion and Tarantula nebs extremely clear. The Globulars as well. And yet Joop and Saturn look mediocre.

Dark skies are not everything either. I live in a very dark site and yet lately the seeing (on clear nights) has been terrible.
There is a lot of moisture in the air. Even though I can see the Planets and stars crystal clear with the unaided eye and also in the finder, when magnified through the scope the views are shocking. It is like trying to focus through fog!

Don't despair. Some nights are better than others and you will know when you strike a good night. You will see galaxies everywhere in Virgo for example. The Fornax Cluster of galaxies is excellent too but it is out of range at the moment.

To test the quality of your EP's find Sombrero with a low mag EP. Then place in a higher mag EP. It should appear a bit fainter but clearer. Like I said, it doesn't clear up for me but I know that my EP's aren't all that great. My scope is excellent, I just need to take advantage of better EP's one day.

Two Globs (47Tuc and Omega Cent) are very very clear for me at all mags. Try them too.

cahullian · #5 11-07-2005, 12:27 AM

BC don't expect to see images like those taken by the Hubble telescope it just won't happen.
They arn't called faint fussies for nothing.
Like Ken said you may need to buy a few decent ep's and a UHC or Olll filter to help enhance nebula. These things take time to save for, so in the mean time there are tons and tons of things in the night sky to keep you going for years and years.
Gazz/Irish

asimov (John) · #6 11-07-2005, 12:34 AM

I'm not sure I can agree with that totally Ken....I do to a point..12.5" newt as example.
When it's PERFECTLY collimated, it doesn't seem to matter what quality EP I bung in, weather it's a .965" Huyghenian, Ramsden or a 1.25" UO ortho I get absolutely great views! I'm talking view's that would stun you Ken..Iv'e gone to the extend of purposely putting the scope out of collimation to see what would happen to the view's using these 3 particular EPs. mentioned above.. The result was obvious straight away, Couldn't get a sharp image no matter how much I tried focusing. The 'soft' look.

Now after saying all that, I agree some EPs are total crap! I have 2 of those 500s. The view's I get through them are actually pretty sharp as long as the object is dead centre in the FOV..A lot of flare & ghosting, but if one can look THROUGH that, a pretty sharp image. Put the scope slightly out of collimation though, & it's instant crappy view. Naturally seeing & transparency etc etc all come into play as well.

Anyhow, that's my experience that Iv'e had with my particular scope...Perhaps My Parks mirror is better than what I thought!

?

ballaratdragons (Ken) · #7 11-07-2005, 12:44 AM

John,

Maybe it's just my EP's then (Friday models). My 25mm and 15mm Series 500's have what you call the 'soft look'. Cannot focus to crisp! But my 9mm (not a Series 500) is very good. So I know it ain't the collimation. Also my 2" GS 30mm SuperView is astounding. It's just those rotton Series 500's in between! They won't focus!!

asimov (John) · #8 11-07-2005, 12:59 AM

Oh ok. That's an established fact then. It's your EPs NOT collimation, if your getting the crisp focus with some EPs..

That doesn't explain why I CAN get that crisp focus with the same EPs!!!!!!??????

Any theory's on why??

RAJAH235 · #9 11-07-2005, 01:03 AM

A quick story. I recently purchased a *MEADE* WA 18 mm 'Chinese' eyepiece on eBay for $56.00.(Gold Coast). It duly arrived & upon unpacking it, found what looked like a nice E/Pc. taking NO notice of what was written on the box. I 1st lighted it a few days later & found that I could not get all of the image into focus. The centre was O.K. but the outer 20% was blurry/flared. Moon was absolute C**P. I tried it in another guys DOB, but it was pretty much the same. (both fast t'scopes, 4.5 & 5). When it was tried in a refractor,F7, the image was better. I put it away for the night. At home, I noticed that it said > 'ETX T'SCOPES' (OWTTE), on the box. Could I have purchased an E/Pc made for long fl t'scopes???? YEP!
It has been returned for a full refund, thankfully.
Lesson learned.

L.

ballaratdragons (Ken) · #10 11-07-2005, 01:03 AM

No John!

Maybe I just got a bad batch.
Could be my eyes too, that's something I haven't considered.

Laurie, both John and I have similiar scopes. Same EP's. Should be same images.

RAJAH235 · #11 11-07-2005, 01:14 AM

After reading all this, I can honestly say the problem is......... Ken's eyes.

Seriously, if you're getting crisp views with some E/Pcs & not others, then I would suggest a faulty/badly made E/Pc. Maybe a lens has shifted in the E/Pc????? Have you tried anyone else's, Ken?

L.

ballaratdragons (Ken) · #12 11-07-2005, 01:16 AM

No I haven't Laurie.

I've only ever used mine. Looking forward to trying all sorts at the Star Camp.

asimov (John) · #13 11-07-2005, 01:17 AM

Pity were so far apart, I'd love to test those 500s in mine!

RAJAH235 · #14 11-07-2005, 01:19 AM

You'll get jealous!!!! S***F the new comp., give me better E/Pcs.

L.

ballaratdragons (Ken) · #15 11-07-2005, 01:22 AM

John,
I will have to take them to our observatory and test them in some other scopes. I keep forgetting.

Laurie, haha, very funny. Gimmee both!!

ballaratdragons (Ken) · #16 11-07-2005, 01:28 AM

BC,

I hope you are learning something from this conversation. It could be anything, but I highly doubt that it is the scope! (unless the collimation is still out a bit)

RAJAH235 · #17 11-07-2005, 01:46 AM

Yes BC. I too think your collimation may be off a little bit. As you said, if the image of 104? is not up to scratch, then I'd just be checking it out again. You didn't say what mag. you'd been up to. Is it any better at slightly higher mag? So many variables, It's a process of elimination.

L.

BC · #18 11-07-2005, 08:23 AM

Thanks for the input folks. To clarify, I have a Bintel version, thus I got GSO EP's, the 32, 15 and 9mm. I was looking at the Sombrero with all, but the 9mm was still blurry, that obviously takes it up to 138x. The star test was a bit confusing. I could see concentric circles but couldn't tell how perfectly round they were due to the "worms" over the top of the circles (if that makes any sense).

One of my collimation probs is my use of the $29 Cheshire which is much praised on this site (I know, poor workman....). By the doco I've seen, including the one recommended in this thread, I should be sighting using the crosshairs of the tool, not the reflection of the crosshairs in the centre of the picture. My eye simply cannot focus on the crosshairs so close to my eye, even when I put on my glasses. The crosshairs don't focus until I'm about 6" away from the tool, by which time the rest of the picture through that tiny hole is useless. With my eye up to the tool, I can't see the outer edge of the focuser to see how centred the secondary is. I managed to do that by taking the 45 degree piece out of the tool. This gave me the view of the secondary I needed, but I couldn't see the cross-hairs. When I rotate the tool in the focuser, the blurred junction seems to move around. When I take out the tool and view it from the bottom end, the crosshairs appear off centre. ie if I line up the cross hairs and the pin-hole for the eye, the tool appears to be tilted. Isn't it great trying to explain technical things in words. It seems to me I need a longer sight tube with cross-hairs actually in the centre to achieve what I think I need to do.

Starkler (Geoff) · #19 11-07-2005, 09:39 AM

BC what you havent mentioned is how other objects look to you. Do stars focus down to a point or a tiny blob of light?
Galaxies are a challenge and require dark skies and dark adapted eyes to view well. Structure and details are faint and are usually not immediately obvious in a 10 inch scope and require a bit of eyepiece time and use of averted vision viewing the galaxy.
As Cuhullian said "They arn't called faint fussies for nothing."

In collimating my dob I dont use the crosshairs at all and have even considered cutting them out. Mine is the longer type.

If yours cannot function as a site tube just position your secondary as best you can and then adjust tilt so that you can see the reflection of the primary centred in the secondary when looking through the cheshire.

IN aligning the primary mirror you are looking to centre the mirrors centre spot in the reflected view of the ring of light from the 45 degree angled reflective part of the cheshire.

BC · #20 11-07-2005, 10:01 AM

Starkler, your description of centreing (how do you spell that??) the primary on the reflection of the secondary is pretty much how I ended up doing it, followed up by matching the cheshire reflection with the centre spot. Other things I have looked at:
Stars - kind of a point but I'm guessing
Saturn - can see the rings but no Cassini division
Jupiter - can see the 2 main bands but no other detail
Eta Carinae - can see it but is very dull. My 20x binos show it quite bright and while 40x with the scope is 4 times reduced in brighness, I imagined that the light gathering would make it a bit brighter than it is - but of course it seems my expectations were excessive. But no, I realise it would never look like the magazine piccies.
Omega Centauri - quite a lot of resolved stars
Jewel Box - quite a lot of stars and can see the orage colour in one inside the triangle
Anyway, thanks for the input - I think I just need to lower the magnification of my expectations