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Paulhenry85

Realistic/usable sized eyepiece for a 8" dob

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A question for all 8" dob users. What is the shortest focal length EP usable for the telescope, I have a 7mm nirvana which is fantastic, they do a 4mm EP which would give 300x mag, my scope has a maximum potential of 400x but would the 4mm be pushing it?

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Anything over 200x can only be used in good conditions, and only then on certain objects. Mine is not a dob, but my 8" scope has essentially the same limits to magnification. I use 290x (with my 7mm) only on planets, and only then under good conditions. My 10mm (204x) gets a lot more use, as do the 8.5mm (234x) and 8mm (254x). As your Dob is F/6, a 6mm would be great, a 5mm would see quite a bit of use, but a 4mm only rarely, and then only on the moon, Mars, Saturn, and Jupiter, I would guess.

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I get 171x from my 7mm in my scope, so realistically I'm looking at a max of 200x to 250x mag from a eyepiece then?

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When I had an 8" dob my lowest power eyepiece was a 7mm and most of the time the standard focuser couldn't adjust in small enough increments to get good focus easily so it took lots of fiddling.this was a single speed focuser though so with a dual speed 10:1 it would be easier.lots of the time at 7mm the view was shimmering due to bad seeing conditions.I was going to get a 5mm but didn't bother as it would have been wasted.

Edited by crashtestdummy
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I get 171x from my 7mm in my scope, so realistically I'm looking at a max of 200x to 250x mag from a eyepiece then?

Not necessarily. I have barlowed a 10mm to get 406x out of mine on Mars (mainly to test the extremes), but found the result surprisingly usable at times. Though the image was often mushy, from time to time the planet snapped into focus, as seeing temporarily was good. A 4mm at 300 times would see about the same amount of use as my 7mm (290x), and I must say that when I had replaced my good old Vixen LV 7mm and 9mm EPs for Radians at 10 and 8, I started to miss the higher magnification. I would frequently put my Meade 14mm (now replaced by a TV 12mm T4) in a 2x TeleXtender to achieve the same magnification. I am much happier at the planetary end with my 10, 8.5, 8, and 7.  This may seem like a lot (and the XF 8.5mm may be relegated to solar H-alpha duties) but in planetary observing it does pay to have a range of magnifications to match the object and seeing conditions.

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I get 171x from my 7mm in my scope, so realistically I'm looking at a max of 200x to 250x mag from a eyepiece then?

I am still a novice with the 2-month old 82 dob, but that sounds about right.

My most used is the 2.1x barlowed 16mm maxvision at 157x.

I also have a 12mm and 9mm Plossl to give 240x and 280x magnifications.

12mm is slightly blurred, even on the moon / the 9mm is awful - and only used for splitting doubles at the moment.

200x, 210x, or 220x should be a good match for the 7mm at 170x. (5.5mm to 6mm)

240x is pushing it - but is absolutely amazing on the very few occasions when it works.

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PS - wider angled eyepieces will make the high magnification very much more usable.

Don't get high magnification plossls.

They don't let enough light in compared to the more expensive EP's.

And it is like looking down a toilet roll tube with the relatively narrow 52degree field of view.

My plan is to barlow an 11mm ES 82 degree up to 240x,

I can still use it at 109x when high magnification views are impossible (normally 9 nights out of 10)

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At 6mm there are not many EPs with 82 deg FOV. For planets, a more modest 60-70 deg is generally OK. The Delos 6mm stands out of course, but is costly, but you can get second-hand Radians for about GBP100. At the lower end, price-wise, the TMB Planetary could be considered (or its clones, like the TS HR Planetaries). 

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For my scope the 6mm will give 200x and the 5mm 240x so need to have a look what's out there in these sizes, my budget is £150.

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For my scope the 6mm will give 200x and the 5mm 240x so need to have a look what's out there in these sizes, my budget is £150.

You already have a 2-inch 2x barlow.

So you can also consider a decent 11mm or 12mm eyepiece to sit between the 7mm Nirvana and 22mm SWA you have already.

If I hadn't spoilt myself with the Maxvisions already, I would be jumping all over the BST's

12mm barlowed down to 6mm / and their 5mm = 200x and 240x / £49 each / = £98 all in

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You already have a 2-inch 2x barlow.

So you can also consider a decent 11mm or 12mm eyepiece to sit between the 7mm Nirvana and 22mm SWA you have already.

If I hadn't spoilt myself with the Maxvisions already, I would be jumping all over the BST's

12mm barlowed down to 6mm / and their 5mm = 200x and 240x / £49 each / = £98 all in

I really don't like to barlow EPs. I'm slowly trying to build a set of dedicated EPs as for the gap my wife has bought me the 16mm nirvana for Christmas.

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Just had a quick look into the vixen lvw and they pretty much the same EP as the baader Hyperion but cost under £100 new

The Vixen's are much better optically despite looking a little like the Hyperions. I've compared sets of both "back to back" some time back. The Vixen's are really high quality Japanese made eyepieces, similar to Tele Vue and Pentax quality. 

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The Vixen's are much better optically despite looking a little like the Hyperions. I've compared sets of both "back to back" some time back. The Vixen's are really high quality Japanese made eyepieces, similar to Tele Vue and Pentax quality.

Are you the same john who did the review on the first light optics site?

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Are you the same john who did the review on the first light optics site?

Yes  :smiley:

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+1 for Vixen LVWs, right up there with the best, in terms of correction in fast scopes.

Regards, Ed.

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I use the 6mm quite a bit on Saturn and Jupiter. The 5mm only on the moon so far, but for £42 second hand it was definitely worth it, it's been spectacular.

Cheers

(Sorry, on the same 'scope as you. So, 200x and 240x)

Edited by bingevader
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I have the same scope as you and for me the 6mm William Optics is a fine eye piece. It's shown me some glorious views of Jupiter, so much better than the Celestron Omni 6mm plossl I shouldn't have bought with it's poor eye relief.

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Yes  :smiley:

I'm now thinking to put towards my own Christmas present and going for either the Nagler 5mm or the 6.0mm Delos Eyepiece but can't decide which one will best suite my scope

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I'd go with the 6mm rather than the 5mm, just because you'll be able to use it more frequently.

Cheers

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I also have an 8 inch DOB, and at one time or another I have fed it a 4mm, 4.3mm, 5mm, 6mm and so forth. Truth is that these eyepieces are for my shorter focal length APO. It is rare to use these in the DOB as the seeing does not usually allow it. Normally, the 7mm works best, and often as the high mag piece, followed by the 8 and then on up. I see by your equipment that you already have the 7mm -   7mm Skywatcher Nirvana, 22mm skywatcher SWA and a 32mm skywatcher PanaView. I personally think that you would be better served by dropping in a quality eyepiece in the 10mm or 11mm range. It is a range that will always be used in a 8 inch DOB no matter what the conditions. My 22 Pan finds what I want, and the 10mm Delos at 120X will really let me explore it. If it's a planet, in goes the 7mm XW at 171X. That 10mm or 11m is the most important hole to fill with that scope, in my opinion.

David

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I would certainly go for the Delos rather than the Nagler on planets. The Delos is much more comfortable to use, and is a smidgen sharper. If you want a 5mm, go for an XW

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I'm now thinking to put towards my own Christmas present and going for either the Nagler 5mm or the 6.0mm Delos Eyepiece but can't decide which one will best suite my scope

I used to use a set of the Nagler Type 6's for planetary use when I had an 8" F/6 dobsonian. I was very fond of them and they performed really well and the ultra wide view helped tracking. I was loaned a 10mm Pentax XW and had the chance to compare that to the Nagler 9mm T6 and found the Pentax was just a touch better at controlling scattered light around bright objects (eg: planets !) which helped bring the contrast of subtle features out a little and enabled me to see faint Saturnian moons like Enceledus a little easier. 

I've not used a Delos but I believe that their characteristics are very similar to the Pentax XW's so, if I was choosing between a Nagler and a Delos for high power viewing I'd probably go for the Delos for this reason. 

The additional eye relief of the Delos and Pentax XW's was less of a factor for me but does make viewing more comfortable and, combined with the slight optical improvements described above, offset the loss of the FoV of the Nagler I reckon.

This doesn't make the Nagler T6's bad in any way though - they are excellent and compact UWA eyepieces  :smiley:

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I use a 6mm & 8mm Delos on the planets and are very good ergonomically and optically excellent.The 8mm is used more often,but when conditions allow the 6mm is wicked @200x(1200mm FL)

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