First Light at last.

[alan potts]

Well I got the 17.3mm Delos about two weeks back and due to poor weather and illness have not been able to try it out, last night under testing conditions which I will enlarge on later it got its debut.

Now a good few on site have this eyepiece and it was the only one that I needed for the set which I have to say is a bit of silly reason to buy but it was in the back of my mind. It will have to good into another case as the Delos case is already full so there is a black mark against it to start with. The shorter Delos eyepieces like the 3.5mm and 4.5mm are slim elegent lookers, the Miss body beautiful's of the range where as the 17.3 is a bit like, Miss I ate all the pies. I many respects they follow the the aesthetics of the Pentax XW range, which I guess is no bad thing.

After waiting for what seemed like forever for it to get dark I settled down with the 3048mm F/L Meade as this was the scope it was intended for. Locating Juptier I saw it was right on the sweet spot for magnifcation as I could see more bands than at a rock festival and the Great Red Spot was out to play as well, something that seems to avoid me. It showed nice scatter control and stunning sharpness especially on axis. This was what I had been expecting from this eyepiece and I was not let down.

Moving around to Venus I saw it was about 50% phase, I don't know if it's me but I can never see much on this planet no matter how big the scope, though last night I did feel I could see some shading around the central area of the planet. Again scatter was well in hand as to was any of the abberations, seeing was not at all bad either after such a terrible weather spell. The testing condition got shouted at as Daniel was running around the garden with a torch catching fireflies in a jar and wondering why the ones he had kept escaping.

Moving to the Moon I could see seeing was indeed good as crater stood out with an almost 3D effect, the sharpness was cutting and no sign of any nasties. I did at this point move the Moon ttowards the edge and saw that there was edge distortion though this was not as bad as with some Naglers. I was looking for this a Russwill first pointed out that this eyepiece was not as flat field looking as some of the others. I must say I don't really look for this on these as I use them in driven scope for the most part. Placing the 17.3mm into the 70mm ED topscope showed a fairly egg shaped Moon at the very egdes, this would annoy me in a Dobsonian. I will be checking on the others in the range to where this creeps in as I have not noticed this before.

All in all a fine planetary eyepiece that will be very difficult to better but with edge distortion that may not appeal to some Dob Squad members. 

Alan

[Pig]

Nice report Alan   I used to love the 17.3mm in my 9.25 and found it gave the best dark background of all the Deloi. I didn't use it on planets or the Moon but found it more suited to targets like the Double, wild Duck and Hercules type clusters. However, like you mentioned its the given magnification in the scope that matters.

I don't recall it being so large, its amazing how memories play tricks

[alan potts]

Shaun,

I am sure it would be good on doubles but my first thoughts were for the LX as a planetary eyepiece, of course it will give a lower power in you 9.25. In minw it is giving X176 which for me is bang on Jupiter power, I don't like to over egg the pudding on this planet, many seem to like 200 plus in smaller scope, so I guess it is each to their own.

I did have a look at M13 with it but it was really being ruined by Moon and Daniel and his torch though he was having a great time.

Alan

[Qualia]

I really don't have a lot of experience with eyepieces and for the last few years have just stuck with the Orthos, Panoptics and the 2 Delos (10mm & 14mm).

In the f5, I've noticed pin-cushion distortion (egg shaped Moon) with the Pans but never with the other two types. It's probably due to higher magnification, but I also find the contrast better in the Delos and Ortho. In the 76 f6.3, the Pans perform wonderfully and the only thing missing is perhaps a widerfield of view

With this in mind, it is interesting to read your findings on the 17.3mm and that perhaps as an eyepiece it isn't quite as good as the 20mm XW, for example. Or do you think it is something more than that and would consider the Delos range a close 2^nd to the XWs? Be interesting to hear your thoughts on this Alan.

Anyway, great report and thank you for taking the time to write this. Sounds like you had a great with your son out under the stars

[alan potts]

Qualia,

I have all the Delos or Deloi as I said and have matched the 3.5mm, 5mm and 7mm XW's against various mambers of the TeleVue family, I think on all occasions I have come down on the side of the Pentax which makes me wonder why I only have the one, 5mm. Pentax have a little CA at the very edges that is there but acceptable, as I see it Delos don't have this. There really is nothing in it, they are good as each other. Some say the Delos has a colour caste but I don't buy into that at all, many said the Radians had and spoke about them as if the Moon was coffee coloured when you looked through an eyepiece. I think I see different things in different scope these days or I am going nuts.

I think the Edge distortion that you see on the Panoptic range and sure enough it is there, is the cost of having tack sharp edges. I noticed on the Meade range of SWA's the edge distortion was not as bad but then neither was it as sharp, and in a faster scope nowhere near as well controlled in just about every other abberation.

I really feel and I am pinching John's thunder here, Pentax XW's and Delos are as close as you can get to orthoscopic eyepiece but with much better eye-relief and wider field of view.

I will be checking the 14mm edge soon for distortion, something makes me think it will be there but very slight and on the next one down which it the 12mm almost invisible. I have never had a 20mm XW in my hands but would not mine betting it has the same issues to some degree.

Alan.

[YKSE]

Nice first light, Alan, I'd say the 17.3Delos performs just as good as I would have expected.

As to distortion in the edge, it just like your comparison of Pan vs Meade SWA, the extra pincusion distortion in 24mm Pan are TV's way to minimize astigmatism. All eyepieces with FOV larger than 1 radian (57.3 degs) will have noticeable distortions to our eyes, either Anngular Magnification Distortion(AMD) or Rectilinear Distortion(RD), this is just simply the law of physics (optics if you prefer), and the wider FOV, the larger distortion, NO eyepiece designer can get rid of that, they can choose different amount of AMD or RD, or make more distortion to minimize astigmatism as TV does.

Pincushion distortion or Barrel distortion (both are RD) are most easily to find out in daytime, just pointing a scope to a telepost, move it to the edge, you'll see the distortion without doubt.

As to Pentax XWs, my wild guess is that they have AMDs instead of RDs, because the mid-range XWs are mostly for spotting scopes, and in daytime use, there're many straight lines in daytime sence, a curved telepost or house in spotting scope doesn't look very good.

Othoscopic view? yes, in the center FOV, not in the edge outside 57 deg FOV, not any eyepiece with spheric lens.

[Chris]

Good read Alan, I've never been tempted by Delos despite hearing mainly good things. They look very tall and slender, how do you think they would fare hanging off the side of a scope?

The new Delite look good but appear to have a silly price tag of 265! 

I think most of us would want to complete a set if we only had one EP remaining, astronomy and OCD go hand in hand

Sounds like a winner in the LX anyway

[RikM]

The 20mm XW doesn't show any eggy-moon distortion at the edge but does show minor field curvature similar or maybe even a bit more than the 14mm.

[alan potts]

I checked last night and the 14mm Delos does have some distortion though not as noticeable in my opinion, it was rather funny plaing Jupiter at the very edge, yes it was still very sharp but it was round. This only seems to happen over the last 5% of the FOV.

Yong the point you make makes perfect sense with the Pentax as you say been designed for daylight, this to was born out by Rik who has this eyepiece. I can see when I can't find anything else to spend money on I am going to have to increase my collection of Pentax XW's, as I said I really don't know why I only have one, still that's a start.

Thanks to all for filling in the gaps in my work.

Alan

[Qualia]

Thanks for the informative and thoughtful reply, Alan. Great stuff. It's interesting you mention some folk noticing a colouring with the Delos. It's something I've never seen, or something I'm just not aware of; funny how different people see different things With all your experience with eyepieces the Pentax range sound supurb but as you say, the owner of either the Delos or XW should feel confident in their purchase: ortho quality with all the extra benefits of eye relief and wider field. Can't really ask for more.

Thanks for a great read

[alan potts]

Not being able to keep paper in my wallet or more to the point in a bank account, I have a 5mm Nagler coming mid next week so I will put that against the 5mm Pentax XW just for somethig to do.

I did see one account of a claim of a slightly coloured image when compared against XW count against the Delos but I believe that is it. A good few years back now I did a massive eye test aimed at colour, a sort of colour perception test, they tested 300 people in all, at the time I did a lot of work with colour of our products and came top. with one fault that accutally was two errors the way the test worked. Interesting the worst was one of our inspectors, the tester wondered how he got to work in the morning. Prior to being 50 I had eyes like a hawk but now I need glasses to read but only a low diopta, I'm well looked after as a good friend is an eye surgeon and she checks me out often, and I have been under her knife .

As ever these review and bits I write are only using my eyes and I try to be as accurate as I can and we always have the likes of Yong who helps out no end with some optically information that has taught me a good deal. Not everyone will agree with what I have to say but it is done with a honest mind though I am sure I have made mistakes in the past, if only on terms used.

[Pig]

Alan,

I always find your reviews very enjoyable to read and your sense of humour comes out in them

The very most anyone can do is write down what they see and this will almost certainly be different to some if not many people. Honesty is all that is important

[Scooot]

Great stuff Alan, thanks for the review, as you know I have the 17.3 so found it very interesting. I havent noticed any particular distortion on the edge, but then I haven't looked for it, and if "Edge Distortion" has any particular characteristics, other than what it says, I wouldn't know how to recognise it. However I always view through a Paracorr, and wondered whether this would affect it any way, either reduce it or get rid of it? Probably not as it's only meant to help with coma but I thought I'd ask

[alan potts]

Richard,

A good question, I would have thought that a coma corrector only effects the coma from the mirrors of Newtonians, the scopes I were  using were of course a SC 12 inch and 70mmED refractor (maybe not the best on the market) and last night a Mak 180mm, I will try it in my Sumerian with the Paracorr but when the Moon moves on. I would have though it will still be there, I am now looking for these things which is difficult to stop. I can also give it a try in my M/N190mm which is a flat field scope, don't know if that makes a difference, we will have to wait and see in the words of SPM.

Alan

[estwing]

nice report Alan.....I think i'll stick with the ethos...

[YKSE]

Here's the info about distortion in Televue's homepage

Quote :""Distortion becomes especially important in wide-field eyepieces.  In discussing distortion, however, one must clearly distinguish between rectilinear distortion and angular magnification distortion. ", meaning that distortion is directly conneted to wider FOV, the wider FOV, the more distortion.

Quote :"For astronomical observation, however, it is important that the angular magnification remains constant over the field." Since the center of FOV has zero angular magnification, it means Televue eyepieces have extremely low AMD, thus much more RD.

Quote: "With zero angular magnification distortion, straight lines on a focal plane appear curved in a pincushion fashion, with the curvature becoming greater the farther they lie from the center.  It is impossible to correct an eyepiece simultaneously for rectilinear and angular magnification distortion."

[Paul73]

Thanks for the detailed write up.

I think that this is a cracking eyepiece. My bugbear is that fact that it isn't even close to being parfocal with the rest of the range.

It will be interesting to hear your thoughts after trying it in you big dob.

Paul

[Scooot]

Thanks for the detailed write up.

I think that this is a cracking eyepiece. My bugbear is that fact that it isn't even close to being parfocal with the rest of the range.

It will be interesting to hear your thoughts after trying it in you big dob.

Paul

Hi Paul, I use the telvue high hat with it which makes it parfocal. It also means I can use the same paracorr setting as the other delos range. Additionally I now use it as a 2" eyepiece and as I mostly now use 13mm eyepieces and upwards with the 16" I'm not changing the 2" to 1.25" adapter so often.

[Paul73]

Thanks Scoot, that might be the answer!

Paul

[alan potts]

Paul,

I tidied up the double post. The 17.3 is parfaocal with the 14mm as I found out last night. I am fairly sure the rest 12mm and down are all parfocal with each other. I guess that even with TeleVue we can't have everything. I imagine this gets to some more than others as it is not the first instance that I have read of dislike of this, personally I don't find it annoying but we are all different. It's a bit like the edge distortion on some eyepieces it really gets me where as on others I could care less, different targets I think

I will report on the Dob but as I said when the Moon clears off. It sort of points out how poor things have been here, normally with the Moon almost full I wouldn't bother, tonight the scopes are already out.

Alan