Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

Widest Practical Eyepiece for a 12" Dob???


AlexxxAA
 Share

Recommended Posts

Hi Guys. Im in the process of purchasing a 12" dob. Should be trying it out tonight if everything goes well. I was just curious what is the widest possible and usefull eyepiece i can get for a 12" with 1500mm focal length? On the product description it says that the lowest power is 43x, which is equivalent to around a 35mm. But there are eyepieces on ebay and on the market all the way down to 40mm, 50mm, 60mm, even 72mm!!!

What is the lowest i should be looking for?

Thanks in advance guys! :grin:

Link to comment
Share on other sites

  • Replies 25
  • Created
  • Last Reply

Top Posters In This Topic

Hi Alex. I personally wouldn't bother with anything lower than a 30-32mm as the exit pupil will be getting quite large beyond this point. I use a 26mm Nagler (5.2mm exit pupil) as my lowest power eyepiece and it works extremely well in my 12" f5 dob.

Edited by Damo636
Link to comment
Share on other sites

Explore Scientific 82° 24 or 30mm would be nice for your scope. I have their 68° 24mm ep which I'm happy with for my 12" dob.

I rarely use any of my 2" narrow field 26, 32, & 40mm Celestron ep's which I received in kit form long ago.

Link to comment
Share on other sites

I think you could go up to 30mm but not beyond. Of course you can stick a larger EP in your scope and it will work, but the images won't be as crisp, and at a certain point, you'll see the "shadow" of your secondary mirror in the image. Up to 30mm should be safe though.

Link to comment
Share on other sites

I have both 27mm and 35mm - 68 degree panoptics, which I use as my lowest power / finder eyepieces. So far with the 12" flextube I have used the 27mm 56x which has worked great. I will also use (try) the 35mm 43x perhaps to frame subjects such as M31. However I can recommend the 27mm panoptic.

Link to comment
Share on other sites

I would also like to point out, that I use these particular eyepieces (with the 12" dob) 56x and 43x under dark skys, as they may otherwise start to produce a greyish sky background under any light pollution. Therefore you might also consider something like a 20mm, 82 degree Nagler @ 75x which might be a little more versatile from a home base and dark location, for creating a dark background and good contrast.

Link to comment
Share on other sites

I find I can already start to see the central obstruction in my 32mm Panaview, so I'm not going to try pushing past the 6.5mm exit pupil this already delivers. If I replace it, it will be because I go for an EP with a wider field of view and more importantly, is better corrected at the edge of the FOV.

Russell

Link to comment
Share on other sites

Thanks guys. This helps alot. I already have a 24mm 68-degree. I like the views it gives me on my 8". But im sure it wont be the same magnification on the 12" since the focal length almost doubles right? The 8" is 800mm, while the 12" is going to be 1500mm. Thus going from 33.3x to 62.5x. So i just wanted to see if getting a wider eyepiece was recommended.

But indeed i will try to stay shy of the manufacturer limit and get something like a 2"-32mm. Im sure the views will be great nonetheless :smiley:

Link to comment
Share on other sites

Tele Vue designed the 31mm Nagler for just this purpose, and it's superb, but the price is very steep. The 28mm Nirvana / UWAN is a great and lower cost alternative though as is (though I've not used one) seems to be the ES 30mm.

Link to comment
Share on other sites

and by the way, besides the weight, what will be the difference in getting a 32-ish mm eyepiece in 2" compared to 1.25" like all my other EP's??? Depending on the AFV, the views should be around the same???

Link to comment
Share on other sites

A 32mm eyepiece in the 1.25" fitting can have a max apparent field of view of 52 degrees wheras in the 2" fitting the max increases to around 80 degrees - over 50% wider.

As for the quality of the views, then it depends on which 1.25" 32mm eyepiece is being compared to which 2" one. A low cost 2" wide / ultra wide field will show some distortion to stars in the outer parts of the field of view in an F/5 scope but the more expensive types show pinpoint stars across most or all of the field. A decent 32mm 1.25" eyepiece (eg: a Tele Vue Plossl) should be sharp right across but you see less sky.

It's a case of "swings and roundabouts" really.

Link to comment
Share on other sites

Larger focal length eyepieces (40mm +) are mostly made for slow scopes. That way, the exit pupil isn't that big (for instance, in an F/10, a 70mm EP would give a exit-pupil of 7mm, right at the top end).

Link to comment
Share on other sites

Hi guys! I love all the options there are... Unfortunately since I just purchased my 12" today the budget is LOW lol

The telescope comes with a 26mm, 2", 70 degree... So let's see how it fares against my explore scientific 24mm, 1.25", 68 degree.

If I still feel like I can use some aperture, maybe I can try one from my local vendor... www.agenaastro.com.

You guys should check them out. They have a 30mm and 32mm, 70degree AFV for only $80 US.

Maybe in a week I'll try one out for myself and ill let you guys know how it compares :)

Link to comment
Share on other sites

The upcoming ES 25mm 100 deg should be really interesting for fast dobs, the FOV of the Nagler 31T5 I have (superb EP), at a 5mm exit pupil in and F/5 scope (vs 6.2 in the Nagler 31T5), or 6.25mm exit pupil (just about OK for me) in an F/4 scope vs 7.75mm (good for aye-ayes :icon_eek: ) with the 31mm.

Link to comment
Share on other sites

A wide field planetary ep is nice too. I use the ES 6.7mm and 8.8mm 82° on the dob.

Without a tracking platform the wide fields give the targets plenty of time to drift across the ep without having to nudge the scope every so often.

Link to comment
Share on other sites

...The telescope comes with a 26mm, 2", 70 degree... So let's see how it fares against my explore scientific 24mm, 1.25", 68 degree......I :)

My prediction is you will prefer the 24mm 1.25" 68 degree eyepiece if the 2" 26mm is a Meade QX .........

Link to comment
Share on other sites

Yes it is a 26mm QX. Is there something negative about the EP?

Several experienced astronomers really wonder why Meade chose to supply that EP with fast dobs that are really good instruments. The QX may be OK in a slow scope like their SCT series, but it not nearly as sharp towards the edges compared to the ES 24mm, or the likes of the Naglers.

There is a review here:

http://www.helium.com/items/1938779-meade-qx-26mm-eyepiece

Link to comment
Share on other sites

As Michael says plus the focal plane of the Meade QX 26mm is in an odd place - I had to have the one that came with my 12" Meade Lightbridge hanging out of the drawtube to get it to focus.

Give it a try though and see what you think.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.