I'm most interested in D.S.O and I realize I don't have the best telescope for deep sky viewing but I am not in the financial position to buy a low focal length telescope.
the lowest useful magnification is 29x and I'm pretty sure a wider FOV is important. Is their anything I'm missing? I don't want to make a poorly informed purchase that I may regret.
thank you to you all, this forum has been fantastic for getting me into astronomy, giving me tips and not making stupid purchases.
An 8" Dob is an excellent scope for deep sky viewing!
Understanding Telescope Eyepieces
I'm 17, Edinburgh in Scotland, Bortle 5
My budget is under £130
If the absolute maximum focal length is 40mm, is it worth getting a 40mm or would it be a decrease in quality compared to a lower power since it is pushing the lowest useful magnification?
For each of my scopes I have an eyepiece that provides the widest view I can get with that scope. As you will see when you read the article I posted above, that is based on the AFOV, apparent field of view of that eyepiece. So low power alone is not enough. You want a low power eyepiece that has a wide AFOV.
For my XT8, 1200 mm, F5.0 8" Dob I used a 2" 38 mm eyepiece with an AFOV of 70 degrees which provided about a 2.2 degree true field of view. That is about as wide as you can go in this scope.
Agena Astron Super Wide 38 mm 70 degree
The Orion Q70 38 mm is the same eyepiece
I see. From my experience so far, high power tends to make the image far less detailed and blurry. Is that a problem with my eyepieces or is that because of the Bortle 5 light pollution?
We add magnification until the image degrades. How much we can add depends on the atmospheric conditions and our equipment. My XT8 often topped out at 180X. I could go higher but the image would degrade so there was no point. But on a perfect night I could take it up to 300X with excellent results.
Transparency and Seeing are the key factors here.
What is SEEING and why it can be bad. How it will limit how high you can go.
This is not a problem with your telescope or your eyepiece.
I have an eyepiece that is 42x and another which is 60x. the 60x was a cheep eyepiece that came with my very first 70mm travelscope back in 2017. the 42x however came with my xt8 plus and seems to be a fairly highly rated eyepiece that can be bought separately.
would it be better to get an even lower power eyepiece than my current 42x or to get a higher quality higher power eyepiece?
There are dozens of eyepieces that could produce 42X in your scope. Any 28 mm eyepiece will provide that magnification.
A 28 mm Plossl, 52 degree AFOV, would be 42X but provide 1.2 degree field of view.
A 28 mm 82 degree AFOV eyepiece would also be 42X but would provide a 1.9 degree field of view.
Same magnification but a MUCH larger field of view with the second one.
(see the article on understanding eyepieces)
the 42x is the lowest power I have and it's 54 degree fov.
That is not a wide view eyepiece. A 2" eyepiece of 65 to 82 degrees would be wide.
I think an £100 eyepiece 13mm would be ideal. I don't think I've had a good enough high power eyepiece to be able to reap the true benefits of D.S.O at high magnification as they have always seemed incredibly blurry and undetailed. I was thinking of getting a Baader Hyperion 13mm that was recommended by one of the replies. Would you have any other suggestions around that price range? Thanks for your help.
13 mm in that scope would be 92X. That would be low medium range eyepiece. I used eyepieces from 38 mm to 5.5 mm in my 8" Dob. My 8.8/82 degree, 136X and 6.7/82 degree, 179X were used much more than my 14 mm / 82 degree.
Actually my most used eyepiece is an 8-24 mm Zoom eyepiece.
In your price range, that would probably be a Celestron zoom. I have one and it works well in that Dob.
I also have the Baader Hyperion 8-24 zoom which is a better eyepiece and my most used eyepiece, but it is 3X the price.
Lower cost zoom – Celestron 8-24 – This was my first zoom. Works well at the price and a good way to test your interest in zooms. $85
Higher priced Zoom – Baader Hyperion 8-24 mm – My main eyepiece in the XT8i – $290 There are other choices.
Edited by aeajr, 02 March 2021 - 11:40 PM.