Realistic/usable sized eyepiece for a 8" dob

[Paulhenry85]

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

Delos it is then. Off topic but Looking at your kit and previous reviews I don't think there is anyone better to ask. I am now concidering on building a decent set of EP's for my scope, I'm only interested in visual and to keep things simple I'll stick to TV eyepieces, what focal lengths and EP model (ethos well out of range unless second hand) would you recommend me having in my kit to cover everything?

[John]

When I had an 8" F/6 Skywatcher I had an all Nagler set:

- 31mm 

- 22mm

- 16mm

- 13mm

- 9mm

- 7mm

- 5mm

- 3.5mm (rarely used in the 8" F/6 but it provided max power in the 4" F/6.5 ED refractor I also had)

While Naglers may well not be the route for you, the focal lengths (31mm - 5mm anyway) created a pretty useful set. 

[Paulhenry85]

When I had an 8" F/6 Skywatcher I had an all Nagler set:

- 31mm 

- 22mm

- 16mm

- 13mm

- 9mm

- 7mm

- 5mm

- 3.5mm (rarely used in the 8" F/6 but it provided max power in the 4" F/6.5 ED refractor I also had)

While Naglers may well not be the route for you, the focal lengths (31mm - 5mm anyway) created a pretty useful set.

Thanks for the advise its very much appreciated, I'm gone start filling the the gaps in the middle to start. One advantage of having Christmas, birthday and work bonus is I'll be able fill it quite quickly

[Charic]

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?

Paulhenry85.........try this for you maximum, optimal, minimum lenses. Quite a useful tool. Enter your parameters in the green boxes, scroll for the results in the pinks? For practical reasons, some results are un-achievable. That's where you as the user, have to decide as to what extremes your prepared to go to or need.

http://www.stargazing.net/naa/scopemath.htm

[Paulhenry85]

Paulhenry85.........try this for you maximum, optimal, minimum lenses. Quite a useful tool. Enter your parameters in the green boxes, scroll for the results in the pinks? For practical reasons, some results are un-achievable. That's where you as the user, have to decide as to what extremes your prepared to go to or need.

http://www.stargazing.net/naa/scopemath.htm

That's why I use the forums, to help me make the most informed decision before making any financial comitment

[Charic]

That's why I use the forums, to help me make the most informed decision before making any financial comitment

.......I understand, sorry if I offended your intelligence by providing the link, but Your original  question's asked what is the shortest length EP. That link (and others) will tell you the theoretical limit using maths so really no argument there.  The 4mm question! Why not Barlow  your 7mm as a tester? It would be more comfortable to use than a 4mm. At 3.5mm decide if 4mm is pushing it?

[Paulhenry85]

.......I understand, sorry if I offended your intelligence by providing the link, but Your original question's asked what is the shortest length EP. That link (and others) will tell you the theoretical limit using maths so really no argument there. The 4mm question! Why not Barlow your 7mm as a tester? It would be more comfortable to use than a 4mm. At 3.5mm decide if 4mm is pushing it?

No offence taken. I do appreciate any advise, (reading my reply back it does seem a little sharp, it wasn't meant to be.)

It seems from the feedback 5mm is usable in the right conditions and the 6mm is more the realistic size. so I've ordered the 6mm Delos and the 5mm nagler to test myself.

[Charic]

Nice choices,  I`m looking at the Barlow you own, considering the same for myself, although might choose the 2.5x ,or  the BST Starguider at £57+? and the BST 12mm. The 5mm and 15mm BSTs  will come as seconds, when they become available?

[John]

It seems from the feedback 5mm is usable in the right conditions and the 6mm is more the realistic size. so I've ordered the 6mm Delos and the 5mm nagler to test myself.

Thats an interesting choice. The Nagler and the Delos will be quite different viewing experiences I reckon. It will be interesting to see which you prefer 

Did you consider a 4.7mm Delos at all ?

[Reeny]

It will be a while before I can splash out on a Delos.

And I'm desperate to try the 11mm 82 degree Explore Scientific at 109x on nebulae / and barlowed up to 230x magnification on Jupiter.

The 6mm Delos at 200x will be a nice step up to fill the gap when the time (and money) is right.

Charic - I use the 2.5x 3-element Barlow from Revelation on my Maxvision 24mm and 16mm.

The actual magnification is 2.1x, otherwise I have had no problems with it at all.

The sharpness and brightness is slightly reduced due to the normal changes you would expect from doubling the magnification.

The single doublet lens in the 2x Barlows sold under different names is very poor

I think i have a second hand Skywatcher version which is all but useless

The Revelation 2x looks to be the same unit as my duff one - I unscrew the bottom magnifier lens to use at 1.5x, that's all it is good for.

The 2.5x revelation is completely different, and a quality bit of kit.

[Paulhenry85]

Did you consider a 4.7mm Delos at all ?

Thats an interesting choice. The Nagler and the Delos will be quite different viewing experiences I reckon. It will be interesting to see which you prefer 

Did you consider a 4.7mm Delos at all ?

I did have a look but my thought process was that Delos with its narrower afov and shorter focal length maybe "pushing it" in my scope I probably would have been tempted if the Naglers did a 4.7,but saying that I've not owned or had opportunity to compare them up to yet.

[Charic]

How  time flies! 

On 05/12/2013 at 23:10, Paulhenry85 said:

I did have a look but my thought process was that Delos with its narrower afov and shorter focal length maybe "pushing it" in my scope I probably would have been tempted if the Naglers did a 4.7,but saying that I've not owned or had opportunity to compare them up to yet.

Did you ever try the Delos ?

The  £309 Tele Vue Delos EP's (todays price) were nice eyepieces, but I found the 8mm & 12mm  were no better  visually on the Skyliner over my  £47 Starguiders, possibly down to the fact that the Skyliner is not  too fussy about what you put in the focuser, considering the scopes f/6 ratio. 
I'd still have a full set of Delos Ep's if I had waited just a little longer, in the hope that they could have been more beneficial in/on a faster scope >f/5, but side by side, on this f/6, apart from the afov, if the visual details were different, then it was too subtle for my eyes. I'm more than happy to continue using my Starguiders on this scope.

[Stu]

8 hours ago, Charic said:

How  time flies! 

Did you ever try the Delos ?

The  £309 Tele Vue Delos EP's (todays price) were nice eyepieces, but I found the 8mm & 12mm  were no better  visually on the Skyliner over my  £47 Starguiders, possibly down to the fact that the Skyliner is not  too fussy about what you put in the focuser, considering the scopes f/6 ratio. 
I'd still have a full set of Delos Ep's if I had waited just a little longer, in the hope that they could have been more beneficial in/on a faster scope >f/5, but side by side, on this f/6, apart from the afov, if the visual details were different, then it was too subtle for my eyes. I'm more than happy to continue using my Starguiders on this scope.

I guess visual acuity must come into this old discussion . Everyone's eyes are different, and some will be able to see the differences with high end eyepieces and some may not. In an f6 scope, there will still be benefits in terms of contrast and light scatter; increasing scope speed tends to test the edge correction rather than anything else. I think rather than continually discount these differences if you can't see them, it is probably at least sensible not to discourage others who might be able to benefit from them.

EDIT Just to validate what I've said, my eyes are very different. My left, dominant eye gives dimmer but higher resolution views than my right eye. Had both eyes been like my right, I would probably have given up planetary observing by now, possibly even visual astronomy completely. However, my left eye, despite having some annoying floaters, allows me to see fine detail and enjoy the hobby to an extent that I still enjoy premium kit and can tell the differences.