Enjoying my TV 32mm plossl

[ColHut (Colin)]

Just sharing (because I care)

I recently acquired this second hand (thanks Eric).

It shows notably less astigmatism in my f5 dob than the 25mm GSO plossl (which was not at all bad) both at the edge of view and at the same apparent field of view, and outstanding sharpness and light transmission. It's really for the 4.5" f8 newt though to give the maximum TFOV I can get.

I am a happy camper. Next stop a Nagler or similar when the readies build up!

regards

[erick (Eric)]

Fantastic news Colin. It had sat, unused, far too long in my eyepiece case. I've a few other 2" eyepiece options now at that focal length and I cannot see myself needing a 1.25" in the 30mm range any more. Ain't IceTrade Classifieds fantastic!

[Tallstock (Peter)]

Eric,

Putting aside all the technical jargon could you please comment on the benefits of using a 2" ep against the more commonly supplied 1.25" ep? My tired old eyes (with multi focal specs) suffer after only a short time observing. Just when things are getting interesting, I have to take a break to rest my eyes.
The inexpensive possls that came with my SW dob are OK but do you think a 2" would be benefical?
Peter

[erick (Eric)]

For the longer focal lengths, if you want a wider apparent field of view(AFOV) than the plossls which are around 50 deg, I'm fairly sure that the eyepiece has to have a 2" barrel. Eg, the 100 deg Ethos is a 2" in the 17mm focal length version. I have a 35mm Panoptic (68 deg AFOV) and a 30mm Chinese clone (80 deg AFOV) and both are 2".

Plus, it saves having to fiddle with the 2"--> 1.25" adapter when you have a 2" focusser.

[ColHut (Colin)]

Really thats the only reason for the 2" barrel - it allows a larger true field of view(TFOV). A 1.25" eyepiece resticts the TFOV to about 1.3 degrees compared with a just over 2 degrees with a 2" eyepiece.
For plossls apparent field of view(AFOV) about 50 degrees) in my 10" f5 dob the largest eyepiece in 1.25" would be 32mm, for a "super wide" (about 68 degrees) it is about 24mm, an "ultra wide" (about 80 degrees) it is about 20mm, an ethos about 16mm.

regards

[Tallstock (Peter)]

To a complete novice like me, I think what you are saying to me is that I will "see" more through a 2" ep. Therefore, can I assume it will make it easier for me to find objects?

I have tried using Stellarium v 0.10.3 Ocular module to mimick my viewing. It doesn't seem to use any 2" eyepieces.

Currently, I use Stellarium v 0.10.3 to check for targets. At the telescope I then use the 1.25" adaptor with my 25mm ep to get the widest possible view. Next step is to swap to my 10mm to try and fine tune my viewing. This is where the eye strain kicks in.
Adding a 1.25" (2x) Barlow makes tracking the object even harder.

Would having a 2 degree view instead of the current 1.3 degree make all that much difference?

I can't find much discussion on 2' versus 1.25' on the forum although I am sure it has probably been common.
Peter

[erick (Eric)]

Might be some reading for you on the Televue site, Peter? maybe:-

http://www.televue.com/engine/page.asp?ID=311

[ColHut (Colin)]

Originally Posted by Tallstock

... At the telescope I then use the 1.25" adaptor with my 25mm ep to get the widest possible view. Next step is to swap to my 10mm to try and fine tune my viewing. This is where the eye strain kicks in.
Adding a 1.25" (2x) Barlow makes tracking the object even harder.

Would having a 2 degree view instead of the current 1.3 degree make all that much difference?
...
Peter

A couple of things here. you might benefit from eyepieces that have more eye relief - it would be pretty short on that 10mm plossl.

A wider field of view will enable you to see more of the sky but the issue may be the tracking bit that you refer to. Dobs do take some getting used to IMHO.

You could try making sure that the finderscope is aligned as well as possible with the scope as this will really help seeing things at higher mag in a small field of view. Then you need to get used to tapping the dob the right way as the planets etc will appear to move more and more quickly across the field of view the higher the maginfication.

The only other option is a tracking mount of some kind.

Apologies if I am telling you how to suck eggs.

regards

[Tallstock (Peter)]

Colin,
Many thanks for your comments. My Dob moves smoothly enough and the Finderscope is aligned as well as possible.
I have experimented with different "eye relief" combinations through Stellarium but, in real life, can only play with my 25mm and 10mm ep's.
So that I see more of the sky I have been thinking about upgrading to the wider field of view available through a 2" ep.

Erick,
Your preference(?) for a range of 2" ep's (rather than 1.25") prompted my question.
I will study the Televue link in due course.

Thanks for your help.
Peter

[erick (Eric)]

Originally Posted by Tallstock

Your preference(?) for a range of 2" ep's (rather than 1.25") prompted my question.

Peter, it is in those longer focal lengths that I have 2". I use Vixen LVs at 10mm and 6mm and they are 1.25" I also use an 8-24mm zoom which is a 1.25". And I won't give away my TV 20mm 1.25" plossl.

But for wide AFOV, it's 2". I have a cheap 15mm and then 30mm 35mm and even a 40mm (but narrower AFOV for this one) in 2".

Look at the "Eyepiece family" thread

http://www.iceinspace.com.au/forum/s...ad.php?t=19917

and you'll see some people sticking entirely to 1.25" eyepieces.

[Tallstock (Peter)]

Thanks Eric, I now understand a lot more about eyepieces.
At the cheaper end of the market (where I am) it seems that Suppliers keep costs lower by marketing entry level telescopes solely with 1.25" eps.
The option of a wider field of view 2" ep was not even mentioned when I researched purchasing my SW 8" Dob. An in-shop comparison would probably have seen me upgrade. A 30mm 2" cheapie might now be worthwhile.
Peter

[erick (Eric)]

Try the 30mm 80 deg Chinese clone. See the Andrews version here:-

Andrews 80° UltraWide (UW) Eyepieces
http://www.andrewscom.com.au/site-section-10.htm

Probably buy the 20mm type. You just unscrew that barlow lens and it becomes the 30mm type, is my understanding.

Your scope is an f6 I expect. For a cheap eyepiece, I think you'll find the view quite exciting. I did when I moved from the standard GSO 26mm Kelner (?) to this 30mm 80 deg eyepiece. I still use it regularly in the C8 for public viewing. At that price, I guess there might always be a few duds shipped? Query your supplier if you are not happy with it.

[Tallstock (Peter)]

Excellent. Thanks Eric. Much appreciated.
Peter

[GrahamL]

Hi Pete Imo eye relief is always going to be your main consideration when shelling out for an eyepiece, theres quite a few offerings that are 1.25" that will do the job well , some cheap , some not.

[tempestwizz (Brian)]

Tallstock's quote
"Putting aside all the technical jargon could you please comment on the benefits of using a 2" ep against the more commonly supplied 1.25" ep? My tired old eyes (with multi focal specs) suffer after only a short time observing. Just when things are getting interesting, I have to take a break to rest my eyes."
I am under the impression that if you are either short, or long-sighted, adjustment of the focus on your telescope will correct for your viewing. (no good if sharing with another viewer at the same time).
If astigmatism is a problem ( which it is with me), Televue make an add-on Doptrix that can correct for astigmatism. For me, I have used my right eye forever for critical viewing, and my brain just can't adapt to using the left, which doesn't suffer from astigmatism. The Dioptrix changed that foe me, I now get pin-point stars on my retina, and the brain can absorb the detail.

Maybe there is a way for you to get quality viewing without your daytime glasses.

HTH,

BC