dreaming of deloi

[Piero]

Last night I had an interesting dream. A elf  came near my bed and whispered on my ear a few things about Delos eyepieces. I don't remember the exact words of his argument (or my argument, as all the people we dream are actually projections of one's self), but I do remember that he mentioned Deloi 14mm and 8mm, and how these could actually replace my set of Naglers.   

I don't have to say that, as soon as I woke up, the first thing that I did was to open my eyepiece spreadsheet, insert the data, and check this out! Retracing the elf's reasons, I think he was right! 

Eyepieces

Although the Delos are 72 deg afov, the Deloi 14mm and 8mm have basically the same field stop as the Naglers 13mm and 7mm. There is an increment of about 0.1-0.2mm in exit pupil with the Delos, making the image a touch brighter. A Delos 8mm + PowerMate 2.5x gives a 3.2mm, which sits right in between my Nagler 3.5mm and Nagler7mm+PM2.5x (=2.8mm), and this is frankly more usable than the latter two on my TV60. A Delos 14mm + PM2.5x gives a nice 5.6mm which is closer to the 200x sweet spot on my Dob. The distance between this 5.6mm and my Vixen 5mm SLV is quite noticeable (214x vs 240x), making the Vixen SLV, which is a great eyepiece to me, more usable. If I use my Bresser SA 2x, I get a 7mm from the Delos 14mm (completely replacing my Nagler 7mm) and a 4mm from the Delos 8mm, which can be the limit on my Dob while observing planets under the steady sky over there near Venice.

Ergonomically, the longer eye relief of the Delos (20mm) would allow me to keep my spectacles on when observing. Not a big deal as I don't suffer from astigmatism, but still more comfortable. Due to the longer eye relief, it is less likely that the eye touches the lens, reducing the introduction of impurities and therefore reducing the need of cleaning the lens. Deloi weigh more than Naglers, but not by much: about 400g-450g vs 200g-240g. Looking at pictures online, it seems to me that a delos 8mm is about as long as a PM2.5x+NaglerT6. All in all, this would make a long term plan in terms of eyepiece quality, decent field of view (to me ~70deg is ideal), potential need to wear spectacles while observing.

Solar

On my TV60, a PM2.5x + Pan 24mm, Delos 14mm, Delos 8mm gives the magnifications of 37x, 64x, and 112x respectively. Now with the Naglers I have 37x, 69x, and 129x which is at the very limit on the Sun. The new magnifications are therefore more sensible. An advantage of using the PM is that I can screw a green filter at the barrel of my PM, so that there is no need to swap the filter between eyepieces every time. With a daystar filter (which I intend to get in the future), Pan 24mm and Delos 14mm give 63x and 108x, again quite reasonable. 

Planets

On my TV60 the Deloi would be used with a PM2.5x on planets. At 64x and 112x they make starting magnifications for planets. Again, an advantage is that the PM is simply left on the diagonal. If I want to further push the magnification when the seeing is steady, I can simply put my Vixen 5 on the PM2.5x getting 180x (0.2mm e.p.), which I found to be usable at the limit.

On my Dob the Delos 8mm gives 150x which can be ideal for Jupiter. Delos 14+PM2.5x gives 214x, which goes closer to the sweet spot of 200x and makes a nicer step from my Vixen 5mm (240x). With my Bresser SA 2x, the Delos 14mm gives 172x, the 8mm gives 300x which I believe can be used in the steady sky near Venice (often no wind at all for days). Reading many posts on this topic, it seems a shared opinion that there is a detectable improvement on planets between Nagler and Delos/Pentax/Ethos. I think the Naglers are very good, but if there is something a touch better with more neutral colour, why not? 

DSO

On my TV60 (F6), the Pan 24, Delos 14 and 8 give the magnifications of 15x, 25.7x, and 45x, and exit pupils of 4mm, 2.3mm, 1.3mm. The Nagler 8mm vs Nagler 7mm would be a bit more useful because offers a touch brighter views. All this without any loss in field of view.

On my dob (F5.9) the 172x above can be the limit for planetary nebulae on my Dob. The 14mm with an exit pupil of 2.4mm is a good choice for moderate size galaxies, globulars, open clusters. Pan 24+PM2.5x and Delos 14mm would be two powerful tools for a wide range of targets. The 8mm can be used for small size dso and for planetary nebulae. Compared to my Nagler 7mm, the images would be brighter (1.4mm vs 1.2mm exit pupil), and therefore nicer. 

Extra-light TV60 setup

If I have to be extremely light, the couple Pan24 + Vixen 5mm SLV is a nice combo for DSO and planets on this telescope, aside from being very light and compact. Surprisingly, I do not see much difference in image brightness between my Vixen 5mm and Nagler 7mm, and have used the Vixen a few times on compact dso. Considering the limits of a 60mm, the Vixen 5mm does an excellent job.

Future

Delos 14mm and 8mm are close to Ethos 13mm and 8mm in terms of focal lengths. It seems to me that the latter two are extensively used by the several dob mob gangs, so I think Delos 14mm and 8mm are more than adequate for any future F4-F6 dobson I might get.

 

Conclusion

With this change, I get better eyepiece quality and more comfort. In addition, I can get a touch brighter images, leave the PM2.5x on for high powers (again, less swaps), and get something near 200x on my dob. Why not Pentax? By reading reviews (on SGL there is a very comprehensive one by Alan if I am not wrong) it seems that the Pentax 14mm is not as good as the other Pentax's at shorter focal lengths. As I like to have eyepieces with similar features, then I would go for a Delos. Plus I can get a 7mm with a 14mm+BresserSA2x, so an 8mm would be better.

Now, it's the time to wait  and think that all of this thought really makes sense! 

[Mak the Night]

I love my 10mm Delos. In fact, it's very probably my favourite eyepiece (for high mag).

[scarp15]

Sounds like a good plan Piero and look forward to learning how you get on. I use similar focal lengths, included for my 8" F6 dob on planetary (hopefully to get some use again soon). I switched from nagler T5, T6, to form a combination of Delos and Ethos (and 5mm Pentax). 8mm as you mention at 150X receives a good deal of use, also as you mention, I like the neutral tones that these eyepieces provide.

 

 

[Charic]

........there are not a lot of Delos eyepieces about and when they do appear their gone in an instant?
I just wanted to try one in comparison to my faithful Starguider 8mm, and managed to secure a 6mm (beggars can't be choosers!) but alas, so little time these Days and the poor weather have given little opportunity to test the 6mm with any  anger, just a brief test.
Then I missed the 12mm for £150!!!!!!! and from my home town, was gutted. Then my recent addition the 8mm has arrived, and just this Week, the Moon and Jupiter were neighbours for a brief session, and although  they were both low in my sky-view, meaning Jupiter was not at its best, the Moon gave me some wonderful  images. I compared the 8mm EPs and at the end of the day, the Delos has a wider view, but its still an 8mm and gives 150x power, same as the 8mm Starguider. I also felt the BST was brighter? but I think I was blinded by the light ( not a song!)  causing the pupil to pinpoint to its minimum whilst using the Delos ( I felt, more field of view was causing me to go blind quicker, if that makes sense?) The Starguider seemed brighter in use,  but  as @John pointed out, could have been due to the better optics further  reducing some of the glare. hence my feeling that the 8mm Delos was darker overall?

The Delos were to be bought to compliment my new 300P ( which has not materialised yet ) but when these EPs show up second hand, you cant hang around. One very kind member @ghostdance  has loaned me some TeleVues in the past, and  they were safely returned, but it allowed me to test for myself if the particular EPs were to be of any use too me, not all EPs work for everyone, and your own eyes will at the end of the day,  make the final decision.

For me, the choice of  Delos was for a reason, the 300P f/5 or even the 250P  with its f/4.7 was also on the cards, and at this focal ratio, my Starguiders may have suffered at the field edges, whereas the TeleVues relish in this area by  virtue of their design. I also like the Dioptx accessory, which could be of use to me in the future. I am a spectacle wearer, but not when using the telescope, its just not comfortable.

I'm not sure my requirement for a full set will  be reached either, I think the 8 & 12mm would just suit my needs giving 4,6,8 & 12mm receptively using any one of my Barlow or possibly invest in a Paracorr?

Aside from the 8mm Eps having the same power on my f/6, I did not notice too much difference between the sharpness of either eyepiece, but obviously noted the slightly wider field, which reduces the amount of pushing the scope to keep on axis.

[John]

Sounds like a plan Piero

That Elf can be an expensive visitor though - he keeps talking about more Ethos eyepieces to me !

 

 

[Paul73]

Wow. You really have thought this one through. I have the 8,12 &17.3mm Delos. They are great eyepieces. The 8mm is a good Jupiter  bet. It is incredable on Planetaries and for exploring the detail of the Orion & Veil Nebula(s), it is special indeed. But it isn't much cop on the Solar work. The image is first rate, but it does need exact eye placement which is very dificult with a tiny daylight pupil (no real problems at night).

If you do buy the 14mm and decide that you don't like it, I will happily take it off your hands for £150!!!! That is cracking value for a popular length Delos.

Paul

[Piero]

Another thing that I have to check is the parfocality. I think the 14mm (and the 17mm) are quite different from the rest of the set. I therefore need to make sure that a 14mm reaches focus on my TV60, otherwise this is going to be a serious problem! Also, is the field stop well visible on delos eps as it is on a plossl eyepiece, or it is visible only when one look for it at the corner like a Pan 24mm? 

 

@Paul73 Thanks! Yeah, I do think a bit before really entering in detail (which means read as many comments as possible about the selected choice :)). Could you explain me a little bit more about the eye placement issue you have when observing the Sun? Have you got the same problem with other eyepieces (let's say Naglers)? and what do you think the problem is caused by (design, large lenses..)? 

@John Ethoi must be very good if your Elf friend continues suggesting more of them! 

[John]

1 hour ago, Piero said:

 

@John Ethoi must be very good if your Elf friend continues suggesting more of them! 

If only he would pay for them !

[alan potts]

Firstly,

 

I had all the Delos range and the 8mm and 14mm are as good as the rest, I seem to remember though the 14mm is not parfocal with the 8mm, it also has a little edge distortion but I was looking for it, the 8mm has none I could see. All in all Piero a sound choice and good Elf advice.

Now this Elf must have been the one nagging me for ages about the 4.7mm Ethos, being made of tuff stuff i resisted so he hopped on a plane and went to John, he clearly gave in as he bought the same eyepiece which he had resisted for as long, if not longer than me. I wonder what he is whispering in his ear now, in can only be 17mm 10mm or 3.7mm, maybe all 3.

We should put a Wanted poster up

[Paul73]

Don't worry Piero. The 8mm is a great eyepiece. I have no plans to ever replace the 8mm. The lack of parfocality across the range is a slight an annoyance but not one that should put you off. You can buy an adaptor which sorts that out if you are really worried by the quick twiddle of the focuser.

For night time work the eye placement isn't an issue. The effective twist & lock adjustable eye guard really helps get your head in the right position.

Happy shopping.

Paul

[michael.h.f.wilkinson]

I have the Delos 8, which is superb, I must say, especially now I have made it parfocal with the three Pentax XWs I have. I may well get the 6mm (with parfocal ring), to fill the gap between the XW5 and XW7. I may even replace the Nagler 12T4 and Baader Morpheus 14 with a pair of Deloi: the 12 and 14mm. The 12 can be made parfocal with the XWs, the 14 cannot. As you may have guessed, I am not a fan of using a PowerMate (I have the 2.5x) or TeleXtender (I have the 2x and 3x) for observing, as I find it a bit fiddly, and things are never parfocal. The PowerMate and TeleXtenders are only used for planetary lunar and solar imaging.

[Axunator]

The field stop (i.e. focal plane) of 14 & 17.3 Delos is 0.48 inches higher up (i.e. closer to eye lens) than in shorter FL Delos EPs. Meaning that you need to rack the focuser in about half an inch to get D14 in focus, compared to shorter ones.

The place of the field stop in relation to the shoulder of the barrel in current TV EPs can be found here:

http://www.televue.com/engine/TV3b_page.asp?id=214

[michael.h.f.wilkinson]

Yes, I consulted that table as well. The shorter focal lengths in the Delos range have the effective field stop position 6.3mm in front of the shoulder of the EP barrel, so placing the parfocalizer ring 6.3mm down the barrel makes them parfocal with the XWs. I do not mind the 14mm being off a bit, because that would be used for smaller DSOs, rather than planetary. My collection of DSO EPs requires quite a bit of refocusing, but because focus is less critical in DSO watching compared to planetary, I do not mind so much.

[Axunator]

1 hour ago, michael.h.f.wilkinson said:

Yes, I consulted that table as well. The shorter focal lengths in the Delos range have the effective field stop position 6.3mm in front of the shoulder of the EP barrel, so placing the parfocalizer ring 6.3mm down the barrel makes them parfocal with the XWs. I do not mind the 14mm being off a bit, because that would be used for smaller DSOs, rather than planetary. My collection of DSO EPs requires quite a bit of refocusing, but because focus is less critical in DSO watching compared to planetary, I do not mind so much.

Michael, maybe a silly question but I'll ask it anyway: how do you fix the parfocalizing ring 6.3 mm down the barrel in the Delos? Doesn't that cursed "safety" undercut make it wobbly? (One more reason to hate undercuts...)

[michael.h.f.wilkinson]

20 minutes ago, Axunator said:

Michael, maybe a silly question but I'll ask it anyway: how do you fix the parfocalizing ring 6.3 mm down the barrel in the Delos? Doesn't that cursed "safety" undercut make it wobbly? (One more reason to hate undercuts...)

I was worried about that too, but actually, the ring sits in the safety undercut (just below its upper edge) and is fixed securely with 3 grub screws, as can be seen in this image. It actually means the safety undercut is less of a problem

[Axunator]

Good to know, thanks! 

[michael.h.f.wilkinson]

BTW, the Delos-type undercut isn't too bad, as the lower part is tapered. As undercuts go, the XWs are clearly better, as they are very, very shallow

[John]

This thread has left me wanting to add the 10mm and 7mm XW's to the 5mm and 3.5mm that I already have. And I don't even need them really ........ they are just such nice eyepieces

[jetstream]

The Delos are excellent eyepieces with high transmission and great planetary color, can't go wrong with one.

[michael.h.f.wilkinson]

2 hours ago, John said:

This thread has left me wanting to add the 10mm and 7mm XW's to the 5mm and 3.5mm that I already have. And I don't even need them really ........ they are just such nice eyepieces

They are indeed. Can't fault them

[Mr Spock]

That 10mm Pentax does look tempting...

[Piero]

10 hours ago, Paul73 said:

Don't worry Piero. The 8mm is a great eyepiece. I have no plans to ever replace the 8mm. The lack of parfocality across the range is a slight an annoyance but not one that should put you off. You can buy an adaptor which sorts that out if you are really worried by the quick twiddle of the focuser.

For night time work the eye placement isn't an issue. The effective twist & lock adjustable eye guard really helps get your head in the right position.

Happy shopping.

Paul

Thanks Paul for reassuring my doubts. Of course I would prefer them to be parfocal, but my real concern is whether it reaches focus on my TV60. The focuser travel is about 1 inch if I remember correctly. I could ask a vendor to kindly let me know this. Alternatively, a call to televue.

6 hours ago, Axunator said:

The field stop (i.e. focal plane) of 14 & 17.3 Delos is 0.48 inches higher up (i.e. closer to eye lens) than in shorter FL Delos EPs. Meaning that you need to rack the focuser in about half an inch to get D14 in focus, compared to shorter ones.

The place of the field stop in relation to the shoulder of the barrel in current TV EPs can be found here:

http://www.televue.com/engine/TV3b_page.asp?id=214

Thanks very very much for sending me this link. I will look at it carefully when at home.

 

 

And gentlemen, don't send me any elves suggesting me to go for ethos! Thanks!  

More seriously, thanks everyone for your comments! Very helpful

[jetstream]

The Ethos Piero.... if it is possible for you to acquire a low power Ethos the views will be taken to another level IMHO, in dark skies of course and with your 200mm dob.

[Paul73]

Wot. Like this??

Go on. You know that you want to.........

[Piero]

1 hour ago, jetstream said:

The Ethos Piero.... if it is possible for you to acquire a low power Ethos the views will be taken to another level IMHO, in dark skies of course and with your 200mm dob.

No no, Gerry! I'm immune to UWF syndrome!  

BTW, that's Massive! It makes the deloi look like small! I believe you guys that the 21E offers dreaming views. Still remember the thread by @swamp thing and the shock he had after viewing through @estwing's one! A really impressive description! 

Luckily for my wallet, I do prefer 70 deg. I wondered about the reason quite a lot.. I think it is just that I achieve more observation control by knowing where the field stop is. I mainly observe nearly on axis and found out that even with my Naglers, I tend to re-position the target about half the way away from the centre. So, although their views can be really immersive, I don't really use those extra 10-15 degrees. I have never felt my Panoptic 24mm missed anything from the Naglers I own, whereas I actually prefer the more neutral colour given by the former. Another thing is that I prefer to maintain my eye on position rather than turning it around at the edge. I find this more relaxing and helps focus to me. All the points above are a personal and picky consideration of course. The Naglers are very good eyepieces and I consider that buying them as second hand, it's a good bargain for what they offer.