Which 7mm

[scarp15]

Hi

I am currently looking towards starting to save up for one more eyepiece to perhaps complete my set up (damm this addiction!), and I would like to ask opinions on the options available in a 7mm focal range.

This is intended primarily for use with my 12" 1500mm F5 Dob, which will provide a power of 214x.

My current highest power eyepiece is a TV 8mm plossl (188x), which is fine but I like the wider field of view provided by naglers, especially on globular clusters.

I already have several naglers including a 9mm T6 (167x), but I feel I would like to step up the power a bit more without taking the shine off the 9mm. The nagler is perhaps my prefered option because I enjoy using them and they are to an extent parofocal.

I appreciate that there has been some current discusion on the forum of the Pentax XW and I would like to hear views and opinions concerning both the pentax and nagler T6 (or any other) in this focal range. One thing that I am aware of is the fairly wide margin of eye relief between the two.

Cheers,

[Damo636]

Hi Iain. This is an easy one imho. Unless fov is the most important factor, the XW will slightly outperform the Nagler in every other performance criteria. The 7mm is stunningly sharp in my f5 12" dob and at 214x I get to use it most nights :-)

[alan potts]

For this type of quality the TV 7mm Nagler or the Pentax 7mm are all that really come to the fore. The older 6.7mm Meade is a good eyepiece but that has been discontinued, however Ex Sc as fun would have it also started the exact same F/L when the Meade was discontinued. The Vixen is by all accounts very good but at 8mm its to close to the 9mm Nagler you have. I would go for the 7mm Pentax, it's a great eyepiece and may soon be a collectors item.

Alan.

[Naemeth]

You've certainly got a few options in the 7mm range. Either the XW (20mm ER) or a Nagler type 6 (12mm ER), there is also a 6.7mm in the 82 Degree format for an Explore Scientific eyepiece. I suppose an 8mm Delos or 8mm Ethos are out?

Beaten to it by Alan...

[Mike73]

Hi Iain. This is an easy one imho. Unless fov is the most important factor, the XW will slightly outperform the Nagler in every other performance criteria. The 7mm is stunningly sharp in my f5 12" dob and at 214x I get to use it most nights :-)

Completely agree with Damo, just depends on how much FoV you want Iain?

[dweller25]

I use a 7mm Pentax in my Dob and it's sharp, contrasty and Very comfortable to use.

[scarp15]

Thanks all for the comments so far, Clearly after reading some of the comments concerning the pentax, my thoughts for automatically considering yet another nagler had to at least be questioned further. I think that the more comfortable eye relief may compensate a little for the slightly narrower field of view, meaning that I will stay longer at the eyepiece, I find that the tighter eye relief with my plossls results in a succession of short periods spent viewing at the eyepiece.

The 8mm Delos might for the same reason be interesting to look at to. I built up my eyepiece collection for use with a C8 F10, appreciating the constrast and sharp to the edge field. Sharing these with a scope at F4.9, and perhaps investing in the Pentax, may favourably complement my existing set up 'providng stunning sharp views'.

[John]

I've used Pentax XW's alongside Nagler T6's regularly over the past couple of years. Both are very fine eyepieces. I did notice that the 10mm XW had slightly better light transmission than the Nagler T6 9mm but I've not noticed that when comparing the 5mm XW with the Nagler equivalent. I currently use a Pentax 5mm XW and a Nagler 3.5mm T6 but I've considered swapping the XW for a 5mm T6. Personally I really like the Nagler T6 package and, with undriven alt-az mounted scopes, the extra field of view of the Nagler, it's parfocality with my other eyepieces and it's more compact size than the XW do provide some temptation.

I actually find it feels slightly awkward switching from the ultra wide fields and moderate eye relief of my other eyepieces to the long eye relief and 70 degree field of the Pentax. From the other comments posted I may be alone in this but thats how I find it

The Pentax XW's are superb eyepieces though, no doubt about it.

You will get sharp to the edge performance with the Nagler T6's at F/4.9 by the way, or at least I find that I do.

[scarp15]

Thanks John, just an extra question I would like to tag on following on from your comments,

The Nagler T6 & T5 series in medium to high power focal length are all produced in a uniformed 1.25" compact and light weight format . This is a feature I like about them, when changing eyepieces with my dobsonian, (Which I frequently like to do when at medium high power).

Therefore how compact, heavy or light are the Pentax alternatives?

Thanks,

[John]

I've taken a pic of my XW 5mm and Nagler T6 3.5mm to show the size (the XW is extended to the position that I find I need, as a non glasses wearer). The Nagler weighs around 240 grams and the Pentax around 400 grams.

The 7mm XW would be slightly shorter and the 7mm Nagler is pretty much the same size as the 3.5mm. Hope that helps.

[Adrian]

If the Skywatcher Nirvana 7mm is as good as the 28mm & 16mm seem to be then it may be worth a thought (I haven't seen much about their replacements - the sky panorama 7mm?)

[scarp15]

That's great a lot of information (and other options to consider) as always. The difference in scale / weight between the two is quite significant. I wonder if it would be better to build up either one or the other series, so as not to mix up circumstances such as re-adapting your sense of vision between a moderate to a long eye relief, and visa versa, creating a kind of shock effect and

alternating between ultra wide to wide field of view. Concerning the naglers, personally I am quite use to the 12mm of eye relief in the series (especially compared to my plossls)..

Keeping to one series might retain a more consistant level of viewing experience. Anyhow plenty of time to consider as I will need to trade in some items on ebay to help towards raising some funds, pair of nordic skis anyone?