Hello everyone at SGL

[Dave scutt]

Hi everyone I quite new at this. 

I have an 12"skywatcher dob haven't had chance to use it yet weather sucks in Ireland. 

Had a few hours break in the weather during the day so I thought I adjust the finder scope.

I picked an object and adjusted finder scope to what I see in ep. Ep was an celestron 9mm omni  plossol . The image was crystal clear in the centre but was blurred around the sides has anyone have an idea why this is I would appreciate your help thanks

[Sunshine]

Welcome to SGL! as for the issue through the eyepiece I cannot say what would cause that specific issue, maybe collimation is off but soon enough others will weigh in.

Edited August 8, 2021 by Sunshine

[Dave scutt]

Collinmation looks ok round dot in the centre is in the middle of my secondary mirror and I can see the 3 clips holding the primary mirror 

[Pixies]

HI,

Your 300 Dob has a focal ratio of F/5 (focal length divided by aperture). So it's pretty 'fast', meaning it's a light bucket and great for getting bright wide-field views. However, the faster the scope, the more demanding it is on eyepieces. That's because the eyepiece is trying to present a precise image from a wider anglular range of light rays.

The description of the Celestron Omni Plossls at FLO says: "Best suited for telescopes with f-ratios f6 or slower." - so I would say that your F/5 scope is bit too fast for your eyepiece. 

PS - These terms "fast" and "slow" really come from photography, where you are dealing with exposure times. It means less with telescopes and visual observation.

PPS - hope this makes sense and not too much terminology. 

[Dave scutt]

Any advice on a good range of ep for an f5 but not too expensive 

[Pixies]

BST Starguidsers are frequently recommended. Most are good at F/5, although the 18mm is a bit soft at the edges even at F/6. The 8mm and 12mm are the best.

 

[Tiny Clanger]

Welcome !

Do consider making a topic in the 'welcome' section to introduce yourself , folk here are very friendly .

+1 for the BSTs , my little heritage dob is f5 too, and the 8mm, 12mm, 15mm are all pretty good in it. I don't notice any negatives with the 18mm, but I don't get on at all with the 25mm (it is perfectly good in less picky telescopes though)

There's a dizzying range of eyepiece choices out there for a bit more money, but at the price ( just under £50 new) the BSTs have an excellent reputation. Second hand ones quite often come up on the buy/swap threads here at an asking price of around £35 as folk upgrade to more expensive eyepieces, but to get one you need to be pretty quick !

Heather

 

[Dave scutt]

Thanks 

[AstroMuni]

10 hours ago, Dave scutt said:

The image was crystal clear in the centre but was blurred around the sides has anyone have an idea why this is I would appreciate your help thanks

Do you have any other eyepieces that you can try with? How are the views at night of (say) the moon? I have an F/5 too and I dont have such issues with the cheap and cheerful EPs.

[jacobingonzo]

Hi Dave

Do you have the same issue with your other EP's or just the 9mm?

ask 10 different people and you will get 10 different answers-  I have a 24mm for general sky scans then a 10mm and 5mm for closer work- I seriously wish I bought a zoom but where's the fun in getting it right first time? For my  F5 dob I personally prefer the Baader Hyperion EP's not majorly expensive as in Nagler territory , but I would support the BST's too for a relatively inexpensive but well regarded EP.

Keep an eye out on the second hand market and would not be surprised if you snagged a bargain like that big loverly dob you nabbed!

Edited August 9, 2021 by jacobingonzo

[Alan64]

In so far as collimation, your secondary-scene should look like this, or nigh enough...

That's from my 6" f/5 Newtonian, and half as large as your own...

If I'm not mistaken, even though your own is at f/5, in that it's twice the diameter, hence the issue at hand.

But don't let that discourage you, in the least.  You have a portable observatory there, most capable, and it's going to take time to get the best out of it.

Before purchasing additional eyepieces, it may be prudent to look into getting a coma-corrector, then try the 9mm again with that.

[Dave scutt]

Thankyou all with your help . 

Do baader hyperion do a zoom if so what size and in a 2"

[Starslayer]

10 minutes ago, Dave scutt said:

Thankyou all with your help . 

Do baader hyperion do a zoom if so what size and in a 2"

https://www.firstlightoptics.com/baader-planetarium/baader-hyperion-zoom-eyepiece.html

Excellent.  Love mine. 

[Spile]

The BHZ IV is a 1.25" but comes with a 2" adapter and that is what I use. It is worth getting with the matching Barlow.,..

https://astro.catshill.com/the-zoom-eyepiece/

[Starslayer]

2 hours ago, Spile said:

The BHZ IV is a 1.25" but comes with a 2" adapter and that is what I use. It is worth getting with the matching Barlow.,..

https://astro.catshill.com/the-zoom-eyepiece/

I think that is what I just said.  😂😂😂😂😂