High Power for 76mm Frac Conundrum

[scarp15]

Hi

I had recently acquired a Tele Vue 76 and despite the awful winter I have had a few occasions to use and so test out my eyepieces.

A particular favourite with this 480 F/L, F6.3 scope is my Pentax 5mm XW. Whether focused on Lunar, double star, Jupiter or clusters, the image is very sharp, the neutral colour tone is excellent and contrast has great clarity. Initially this eyepiece took a little getting used to (primarily with my 8" F6 dobsonian) as I tend to switch from two Delos and so eye placement  takes some slight readjusting. However it is a clear winner with my TV76.

At x96 it can be considered as a medium / high eyepiece.  I would like to include a fixed focal length high power e.p. Therefore I am considering, as a natural complementary e.p, a Pentax 3.5mm XW, providing x137 with 0.5 exit pupil. However I have read quite a bit concerning the new line of Delite e.p's and that three additional in the short focal  length, are strongly rumoured to be soon announced. This is expected to include a 4mm, which will provide a perhaps  more usable, determined by seeing conditions, x120 and 0.6mm exit pupil. I am not so interested in a barlow or a zoom alternative.

Having both isn't an option, so I would like to ask for opinions, would you wait for the Delite 4mm to become available or consider a Pentax 3.5mm as a logical addition?

Cheers

You may have read, however here is an interesting review on Delites versus Pentax (and others),

Tele Vue DeLite Eyepieces - First Light Review | AstronomyConnect

[John]

I have the 5mm and 3.5mm XW's. They are both superb.

I would have thought that a quality scope such as the TV 76 would be able to handle 50x per inch of aperture well, conditions allowing.

The one drawback with the XW's is that they are not par-focal with the TV Delite's or the Radians, which I currently have in 4mm and 3mm.

This does not really answer your question though but it's vaguely relevent I hope.

[Stu]

I used to have a TV76, they are lovely scopes. I tried many of the high end eyepieces in it and I think 3.5mm is about a good max for the scope.

I ended up with 3.5 and 4.5mm Delos and a 4mm Radian to fill the gap. I even tried a 3.7mm Ethos SX (not bought specifically for the scope but tried in it). Actually 3.7mm is probably around perfect on many occasions but I did not get on with the eye relief and fov of the SX.

I think what I'm trying to say is that ultimately you will end up wanting both but perhaps the 3.5mm will give you more rewards on those nights which can take the mag on planets and doubles.

I know you said no to zooms, but the 3 to 6mm Nagler zoom is very good too.

[scarp15]

Thanks John and Stu. Quite agree and based upon the many reviews I have read, I do believe that 3.5mm - when the seeing is great will be quite rewarding. Additionally that as mentioned 50x per inch of aperture will be feasible on certain nights. I appreciate that the nagler zoom ought be a consideration, yet I enjoy the 20mm eye relief provided by Delos, Pentax and wide field of view, also having invested in 6mm and 5mm.  

Just out of interest here is a scope review by Neil English with emphasis for the high mag capability.

TeleVue 76 Doublet Apochromat Refractor - 60mm - 78mm Refractors - Articles - Articles - Cloudy Nights

   

[jetstream]

More and more reports are coming in about the DeLites and they all sound good- no wrong turn here I don't think. Do you go for the known view of the Pentax XW or do you step out and try the DeLite?

I think your scope will handle either focal length easily as far as your seeing goes.... I'm hoping you try the DeLite so you can tell us how they compare to your excellent arsenal of eyepieces!

[Pig]

I use the 3.5mm XW with my 80mm Esprit 400mm (focal length) the views are nothing short of superb, and are indeed the best I have experienced for lunar and planetary

[Drop Of Sun]

Based on using a Tele Vue 60 and 85, another vote for around 3.5mm eyepiece for the 76. I have 3mm Radian, 3.5mm and 4.5mm Delos, and 5mm Radian. I prefer the Delos but sometimes like the smaller size of the Radian. The 3.5mm Delos is nearly as long as the massive 21mm Ethos when extended!

[Pig]

As the poster above mentions about the length of the eyepieces the 3.5m XW is no shorty either as you can see. ( all eyepieces are all fully extended in the image)

[Stu]

It's also worth considering the 3.5mm type 6 Nagler. These are great eyepieces, nice and compact and obviously 82 degree afov. Eye relief is tighter at 12mm though.

[alan potts]

I have used the 3 shorter Pentax's many times and owned the 5mm, I have yet to see anything actually beat them, Delos eyepieces are as good, some may say better but I have not found this. I also had the 5mm Nagler for a while and did a test against the same focal length Pentax which I never turned into a report purely because I forgot to photograph the Nagler, maybe when I find the time I will write this up as I can't upload photo's now for some odd reason.

I have not had any contact withTV Delite eyepieces yet as they are not available in focal lengths I want. I do not see you are going  wrong with the 3.5mm Pentax and the scope will handle it with ease, I use 3mm on my 70mm APO and that works fine at X140.

Alan.

[GavStar]

I think I would wait for a 4mm delite - better exit pupil and still good magnification - less issues with floaters. I found the Pentax 3.5mm too low exit pupil for my tv85.

[scarp15]

Very interesting comments from everyone, a bit more to consider and clearly both focal lengths would be beneficial. Thanks for highlighting the potential for floaters at this exit pupil, the TV 85 I think is 0.5mm, TV 76 0.55mm.   

[Stu]

Floaters are certainly an issue down at exit pupils around 0.5mm. Depends of course how much you suffer from them. I have a very annoying one right in the middle of my observing eye which I've just learned to look around during planetary observing. It has the habit of looking like a shadow transit on Jupiter, but fortunately moves around so is very obvious!

[scarp15]

Clearly there is no doubt, the Pentax 3.5XW will make for a fine, familiar and complementary addition to the 5XW. Incrementally and perhaps accounting for all the mentioned factors, I feel persuaded to wait for the 4mm Delite to be confirmed and available. I am also curious to trial an e.p from this new line. In the mean time I hope that we all get some badly needed clear skies, many thanks.