Eyepieces for 10" f/5 Dob (first scope)

[jim_bones (James)]

Hi all,

On Tuesday I am picking up my first scope, a BT 252 10" dob (f/5) with Argo Navis The scope doesn't come with eyepieces so I am hunting for some advice on what to purchase. I kinda blew the budget on the setup, so 1-2 EPs for ~$300 would be my max spend! Any suggestions would be welcome.

Thanks all,

Jim.

[jim_bones (James)]

I should add that I don't wear glasses, and am more interested in clusters and nebulae than planets...

[astro744]

If you can stretch the budget to $379.00 then you will enjoy very much the Tele Vue 13mm Type 6 Nagler. You can later add a larger lower power eyepiece for some wider true fields.

[Varangian (John)]

The ES range. Maybe a 6.7 or 8.8 in the 82 series and a 20 or 24 in the 68 series. There are sales in the U.S and you will get two of them for under $300. ES perform very well in fast Dobs.

[N1 (Mirko)]

I got the same scope recently (the GSO version and minus Argo) & am extremely pleased with it. My 2 favourite EPs for deep sky in this scope are the TV 24mm Panoptic and 13mm Nagler. The ES versions of these should perform very well too. So I totally agree with the others here.

[barx1963 (Malcolm)]

My usual advice for first time scope buyers is to use the ones that come with the scope a few times before spending cash. The reason for this is the concepts of eyepiece design and nomenclature can be a little hard to grasp unless you have actually used a couple. AFOV, TFOV, eye relief, exit pupil etc don't make a lot of sense until you have tried to look through a few and even the most basic kit of a pair of plossls at 10 and 25mm adequately demonstrate these concepts. Once a beginner understands how they affect their view in their scope, they are placed to make in informed decision when spending their dollars.
Obviously in this case that is not possible. While I am an unabashed Televue fan and the set of 13mm T6 Nagler and 24 Panoptic is very nice (having used it a lot in my 12") it is a little expensive.
You will need a reasonable low power EP and 24/25mm or thereabouts is about right. The good news is that a 25mm plossl is still a very good EP and can be picked up cheaply (I think the Bintel one is $40?) while a higher grade Televue one is usually about $100. It will give nice wide field, good eye relief and won't break the bank.
For a bit more power, something around 10-12mm is good. At these focal lengths Plossls start to get harder to use with short eye relief and very small eye lenses. Something a bit better may be called for. Unfortunately in the Televue range, you are going to be looking at more than $300 which will blow your budget so a good Explore Scientific may be a good idea. I haven't used one yet to ant extent so will not offer an opinion on them but reports I have seen give them a good wrap.

Hope this helps

Malcolm

[barx1963 (Malcolm)]

Oh, and congrats on the scope BTW!!

Malcolm

[jim_bones (James)]

Hi all,

Thanks so much for taking the time to reply. I think the 24mm Plossl sounds like a good starting point, especially since I can pick one up tomorrow and start using the scope (clouds permitting)! The Televue 25mm goes for $140 new (Bintel) and I was wondering if it is worth spending the extra $100 on this as opposed to the Bintel 25mm ($40)? Also, is the Televue 24mm a better choice than the ES 24mm?

For the more powerful EP, Varangian suggested a 6.7 or 8.8, whereas others have suggested something in the 10-13mm range. What will the difference be between these EPs? I'm assuming the lower the focal length, the greater the power, and thus narrower FOV (this stands for field of view, right?!)

Could someone also please explain what AFOV means?

Thanks in advance,

James.

[Renato1 (Renato)]

For seeing galaxies and other faint stuff (like planetary nebulas and "blinking" them with an LPR filter) a 2mm exit pupil is best. That's a 10mm eyepiece. Make sure it's at least a good quality Wide Angle one, though Ultra Wide would be better.

For bright clusters and nebula, a 4 or 5mm exit pupil is best, which corresponds to 20mm or 25mm eyepiece. Which one depends on how bright your viewing site is. The 25mm will brighten the background more than the 20mm.

Personally, I do like a 3mm exit pupil (15mm eyepiece) for areas with lots of faint open clusters - but I seem to be alone in that respect, I've never seen anyone else recommend 3mm exit pupil for that.

Technically, the 6 or 7mm exit pupils (30mm or 35mm eyepieces) give you the widest, brightest fields of view (depending on how big your eye's pupil can actually get). On my 14.5" I even use a 40mm eyepiece which gives a 9mm exit pupil - which I don't mind so long as I stick a broadband filter on to dim the yucky background light.

Good luck with whatever you choose, you'll have fun.
Regards,
Renato

[astro744]

Originally Posted by jim_bones

Hi all,

Thanks so much for taking the time to reply. I think the 24mm Plossl sounds like a good starting point, especially since I can pick one up tomorrow and start using the scope (clouds permitting)! The Televue 25mm goes for $140 new (Bintel) and I was wondering if it is worth spending the extra $100 on this as opposed to the Bintel 25mm ($40)? Also, is the Televue 24mm a better choice than the ES 24mm?

For the more powerful EP, Varangian suggested a 6.7 or 8.8, whereas others have suggested something in the 10-13mm range. What will the difference be between these EPs? I'm assuming the lower the focal length, the greater the power, and thus narrower FOV (this stands for field of view, right?!)

Could someone also please explain what AFOV means?

Thanks in advance,

James.

Firstly Tele Vue make a very high quality product. Secondly see http://www.televue.com/engine/TV3b_p...4#.U4HbIXKSySo for a bit of an explanation on apparent field of view. (AFOV).

The AFOV determines the size of the portal that you look through. The bigger the AFOV the bigger the viewing window. You can get the same true field at different apparent fields (and at different magnifications) provided the field stop diameter is the same. See the column just to the left of column A at http://www.televue.com/engine/TV3b_p...4#.U4HcU3KSySo

e.g. The 24mm Panoptic, 32mm Plossl and 40mm Plossl all give the same true field because they all have the same field stop diameter (27mm) but they all give different magnifications and have different apparent fields. They also give different exit pupils. The view through the 24mm Panoptic is the nicest and well worth the cost of this eyepiece.

In the 2" format there is a hidden jewel in the crown from the Tele Vue range and that is the 20mm Type 5 Nagler. It has a 27.4mm field stop diameter and will give an even more beautiful view than the 24mm Panoptic because of the 82 deg apparent field, higher power, fractionally larger true field and smaller exit pupil for better contrast. It is also a relatively light and compact 2" eyepiece compared to others in the line up.

[jim_bones (James)]

I have settled on 2 Explore Scientific EPs, and am going with a 20mm and a 6.7 or 8.8.

The next challenge was finding a vendor that had them in stock. Many places had one and not the other, which is problematic with shipping costs (around $50 from the US). I found that OPTCORP had both the 1.25" 20mm and 6.7mm in stock for $99 each + postage = $255 USD ($275AU). Any concerns with this choice?

Thanks again for the advice.

- James

[barx1963 (Malcolm)]

James
I would be a little concerned that the higher power ones may be pushing the power a bit. The 6.8mm would give 186x and the 8.8mm gives 142x. When I had my 12" I found that pushing the power beyond the 115x that I could get with a 13mm EP was only rarely possible and even a 10mm ethos giving 150x was viable only on those rare good nights.
Power is not always your friend as it magnifies any atmospheric disturbance.

Just a thought!

Malcolm

[Varangian (John)]

I guess it's a bit of a trade off. Most times my 11 or 14 show good detail but the disc is so small that it renders that detail obsolete. Using the 8.8 or even 6.7 at times shows me a far larger disc but less detail. I'm someone who prefers the compromise of less detail for a larger image but not at the expense of a badly degraded image. The 8.8 is a good FL for my 12" Dob.

[MattT]

Agena Astro in the US have the 8.8mm but not at the sale price. Most of the Focal lengths you want are not available at the moment so what to do? If you have lots of cash (by the sound you don't) then buy TV and you'll never wonder what the difference is, ….on the other hand the best way to find out about eyepieces is to try them. So what to do? Personally I have tried all sorts and can say the difference between Premium (XW's Denkmeier and TV that I have tried) and most of the ES range is pretty small in my scopes. I prefer the ES 68's to Panoptics for example.
If I was you I would buy the 20mm and 16mm ES 68º and the 8.8 82º eyepieces from Agena Astro, and wait for the others to become available which they will. Try VTI optics in Melbourne and see what ES eyepieces they have. My second choice which you can get now is the Agena Astro Dual ED 60º eyepieces at $60 each, haven't used them but by all accounts they work well at f5, all six of them cost US$360 +postage. If you create an account with AA they send out emails when eyepieces are about to become available.
Matt

[AG Hybrid (Adrian)]

Originally Posted by barx1963

James
When I had my 12" I found that pushing the power beyond the 115x that I could get with a 13mm EP was only rarely possible and even a 10mm ethos giving 150x was viable only on those rare good nights.
Power is not always your friend as it magnifies any atmospheric disturbance.
Malcolm

Really? Was that 12" properly cooled and collimated? Because even on the worst nights (short of gail force winds) I can get to 150x with room to spare.

On a side note regarding this thread in general:

*facepalm* at people telling someone with their first scope to buy a Televue eyepiece immediately.

Otherwise good advice here.

[MortonH]

Originally Posted by jim_bones

I have settled on 2 Explore Scientific EPs, and am going with a 20mm and a 6.7 or 8.8.

The next challenge was finding a vendor that had them in stock. Many places had one and not the other, which is problematic with shipping costs (around $50 from the US). I found that OPTCORP had both the 1.25" 20mm and 6.7mm in stock for $99 each + postage = $255 USD ($275AU). Any concerns with this choice?

Thanks again for the advice.

- James

For deep sky observing in my 8" f/5 Newtonian my most used eyepieces are a 14mm Delos and 10mm Pentax XW. I wouldn't normally use my 6.7mm except on the brightest objects.

Not saying you need a Delos or XW, but a focal length or 9mm or 10mm is probably ideal for globulars while for galaxies I prefer 13mm or 14mm.

There's a good reason the 9mm and 13mm Naglers are so popular for deep sky work.

Explore Scientific also does an 8.8mm eyepiece which is similar to a 9mm Nagler.

[Varangian (John)]

Originally Posted by AG Hybrid

Really? Was that 12" properly cooled and collimated? Because even on the worst nights (short of gail force winds) I can get to 150x with room to spare.

On a side note regarding this thread in general:

*facepalm* at people telling someone with their first scope to buy a Televue eyepiece immediately.

Otherwise good advice here.

Not only that 300 bucks won't buy you a new TV anyway.

[David Niven (David Niven)]

Originally Posted by jim_bones

I have settled on 2 Explore Scientific EPs, and am going with a 20mm and a 6.7 or 8.8.

The next challenge was finding a vendor that had them in stock. Many places had one and not the other, which is problematic with shipping costs (around $50 from the US). I found that OPTCORP had both the 1.25" 20mm and 6.7mm in stock for $99 each + postage = $255 USD ($275AU). Any concerns with this choice?

Thanks again for the advice.

- James

Try VTI as thry stock these focals.

[Varangian (John)]

The Optcorp price point seems reasonable. Try Agena Astro as well as their postage is cheaper than Optcorp. Happy hunting.

[jim_bones (James)]

Hi everyone,

Just ordered the 16mm and the 20mm ES from Agena Astro. Came in at $227AU (inc postage) which I am happy about. Will add an 8.8 or 10mm once I have had a chance to check out the view through some other people's EPs, gotten to know my scope, and replenished the funds . I brought the scope home today - my partner almost fainted when she saw how big it was!

Thanks again everyone for your help,

- James.