Astro Eyepieces on spotting scopes? (1 Viewer)

[giosblue]

Any one who's seen any of my post will know I'm not using a Baader Hyperion zoom in my Optolyth TBS80ED and to very good effect.
When you look to buy these, they are specced different to regular scope EP's.
I've been looking at some Pentax EP's, they're expensive, but the quality seems to be top notch. ( are they better than the Baaders? ) On the Pentax website they show the magnification of various EP's with different scopes

With a Pentax 80mm scope a 14mm E is 36x, if I work it out from the info I've got from the forum, for mine it works out at 30x.
To work it out accurately I need to know exact focal length of my scope.
How can I find this out? It's seem all scopes with an 80mm objective lens don't have the same focal length. or do they?
Any advice would be greatly appreciated..

Ron

 

[jring]

To work it out accurately I need to know exact focal length of my scope.
How can I find this out? It's seem all scopes with an 80mm objective lens don't have the same focal length. or do they?
Any advice would be greatly appreciated..

Ron

Hi Ron,

unfortunately no - objective diameter is not correlated to focal length - neither is physical length of the scope due to the fact that the light path inside the scope is folded due to the prisms and effective length in glass is not equal to the length in air.

Henry Link did give an approximation of the TBS80 body at 420mm which sounds reasonable to me. The pt-ducks page mentioned in the other thread also gives the TBS80 at 420mm (implicitly by mentioning a 4mm astro EP gives 105x).

Of course you can always try to ask Optolyth...

Btw. there's always

magnification = objective focal length / eyepiece focal length

So the data on the pentax page allows you to calculate the focal length of all the bodies they give the magnifications for (I assume as an astro supplier they give the EP focal length).

Joachim

 

[kkokkolis]

I answered in another thread you started. Just two points here.
The objective diameter (aperture), unless stopped with a field stop, gives the focal length if you multiply it with the focal ratio. But that's also unknown to you, right?
Another more precise method to find the focal length is to divide the eyepiece field stop (given by most manufacturers) by the TFOV in degrees (measured with star transit) and multiply the result by 57.3.

 

[giosblue]

Thanks Joachim. I have e-mailed Optolyth regarding another matter and I didn't get a reply. I might try again?
The reason I'm asking this question is because I'm thinking about buying a fixed lens as well as the Baader.
Lots of options here, but I think Pentax use the same EP's for their field scopes and Astro scopes, it's the same fitting. Pentax, do a 14mm. it's not cheap, about £350, but by all accounts it's the dogs. I don't mind spending the money. I just want to be sure I'm getting the right thing.

I'm looking to get about 30/35x with the fixed, so the 14mm should be about right.
I might have to get this from the States, I can't find anyone in the UK who has one in stock.

Thanks to kostantinos, but to be honest, you've lost me on that one.

Ron

 

[henry link]

Ron,

I just noticed the Optolyth astro eyepiece adapters at the bottom of this page.

http://www.optolyth.de/english/products/accessories/adapters/index.php

The first one (part # ZUB-24068) appears to adapt 1.25" eyepieces to Optolyth scope bodies. Whether a particular eyepiece can reach infinity focus will still need to be checked.

I have a Pentax 14mm XW. It's OK, but each of the Pentax XWs has its own unique profile of off-axis astigmatism and field curvature (see the chart below), so some will work better than others on your particular scope. They're all quite large and heavy and the short focal lengths are very long.

Henry

 

[giosblue]

Thank Henry, apparently is not as simple as I first thought. I've just bought a Baader 13mm fixed lens, which would have given me a 33.69x Fixed. Hower, it won't fit into the Optolyth hole, it's too big, not by much though.

With the zoom, you have two options, if you unscrew the nose piece, it leaves you with a smaller one, which is too small. That's where the O rings or tape come in. However the Baader 13mm fixed is too big.
I thought it would be the same size as the zoom and have to use O rings, or tape.

Henry, I was thinking about buying a Pentax XW14mm, if you have one could you measure it for me to see if it would fit the Optolyth?

Can anyone throw any light on this.

 

[kkokkolis]

What's pictured at the diagrams? Field curvature?
Whatever it is, it is usual for Newtonian users to favor the 10, 7 and 5mm XWs and for Catadioptric and Refractor users to favor the 20 and 14mm. 30 and 40mm are very rare now and 2", so unusable with a fieldscope. I used the 20, 14, 10 and 7mm in a couple of occassions and liked them but got the Televue Delos 10 and 6mm instead.
I don't remember any astigmatism, just field curvature (as with most astro eyepieces with long eye relief) and the short focal lengths show no coma on Newtonians.
Now there are the Televue DeLites with Ethos technology on a Radian format and the new Baader Morpheus, better than Hyperions according to Baader and therefore direct Pentax XW/Nikon SWA/Televue Delos competitors. But I haven't tried them yet.

 

[henry link]

Thank Henry, apparently is not as simple as I first thought. I've just bought a Baader 13mm fixed lens, which would have given me a 33.69x Fixed. Hower, it won't fit into the Optolyth hole, it's too big, not by much though.

With the zoom, you have two options, if you unscrew the nose piece, it leaves you with a smaller one, which is too small. That's where the O rings or tape come in. However the Baader 13mm fixed is too big.
I thought it would be the same size as the zoom and have to use O rings, or tape.

Henry, I was thinking about buying a Pentax AW14mm, if you have one could you measure it for me to see if it would fit the Optolyth?

Can anyone throw any light on this.

If the 1.25" barrel of the 13mm Baader won't fit into the scope body then no other 1.25" eyepiece barrel will fit in there. The Baader zoom only works for you because the 1.25 barrel is removable and the inner barrel just happens to be a snug fit. The 1.25" barrel on the Pentax 14mm is not removable. Presumably the Optolyth adapter has enough stand-off for 1.25 barrels to be inserted into it, but that means that many (probably most) astro eyepieces won't reach focus. I think you should just stick with the Baader Zoom. No other eyepiece will show you anything you can't see with it up to its 55x limit.

 

[giosblue]

Thanks Henry, I just thought a fixed might be a bit brighter for the same magnification.
Do you reckon they would be about the same?


The Optolyth adapter only works if you want to use an Optolyth EP on an astro scope. Not the other way.

Looks like I was just lucky with zoom.

Ron

 

[henry link]

What's pictured at the diagrams? Field curvature?
Whatever it is, it is usual for Newtonian users to favor the 10, 7 and 5mm XWs and for Catadioptric and Refractor users to favor the 20 and 14mm. 30 and 40mm are very rare now and 2", so unusable with a fieldscope. I used the 20, 14, 10 and 7mm in a couple of occassions and liked them but got the Televue Delos 10 and 6mm instead.
I don't remember any astigmatism, just field curvature (as with most astro eyepieces with long eye relief) and the short focal lengths show no coma on Newtonians.
Now there are the Televue DeLites with Ethos technology on a Radian format and the new Baader Morpheus, better than Hyperions according to Baader and therefore direct Pentax XW/Nikon SWA/Televue Delos competitors. But I haven't tried them yet.

The curves labeled "DM" and "DS" are tangental and sagittal foci. Field curvature is not directly shown, but it would be an imaginary curve midway between the two. There's very little astigmatism in the 14mm and 5mm (sagittal and tangental curves track closely together), so in those two field curvature is the main off-axis aberration, but with an opposite sign in each one. It's always seemed odd to me that Pentax didn't design the whole series to the same spec.

 

[henry link]

Thanks Henry, I just thought a fixed might be a bit brighter for the same magnification.
Do you reckon they would be about the same?


The Optolyth adapter only works if you want to use an Optolyth EP on an astro scope. Not the other way.

Looks like I was just lucky with zoom.

Ron

The Baader Zoom's light transmission is right up there with the Pentax XW. The difference is negligible.

Read the text about the adapters carefully. It seems to me to describe an adapter to fit 1.25" eyepieces to the Optolyth scopes (ZUB-24068) as well as adapters to fit Optolyth eyepieces to 1.25" astro scopes (ZUB-24069, ZUB-24070). The Optolyth eyepiece to 1.25" scope is the only one illustrated.

Henry

 

[giosblue]

Thanks Henry, your input is very much appreciated. I still can't see how an adapter would work if the EP won't fit in the hole though? I think I need to do some more measuring.


Ron

 

[mayoayo]

Ron...I have used many astro eyepieces in the kowa 823,i still have some ..The models i use are compatible with spotters,because the astro barrel is removable..These particular models are not expensive,but they are excellent eyepiecs,and they go hand to hand with the nikon fieldscope eyepieces i used to own and i compared side by side with..see Nikon fieldscope eyepieces are every bit as nice as pentax XW or so I have read..these (nikons)are a bit less expensive and i am almost certain you could adapt them to your scope,but again,the astro eyepieces i would suggest ,even being inexpensive,are excellent...I do not use them a lot though ,since the Baader zoom is amost as wide at similar focal and i think better corrected for field curvature...i am using the BST explorer and the BST flat field ..the flat field is easy to adapt,the explorer needs a bit of manipulation,but since you are keen in the use of o rings and self threading patches of insulating tape,you are ready for the challenge...
One thing..Aren't the Baader Hyperions modular eyepieces?...i think you can remove the barrel,although the focal lengh would be altered ,since optical lenses are placed inside

 

[giosblue]

Thanks mayoao, I know where I've gone wrong. or got lucky.
When I measured the aperture on the scope, I measured the threaded part, this is slightly wider than 1.25in, @36mm
So getting an astro eyepeice to fit. seemed easy. When you get the Baader it both 2in and 31.75mm
The problem is the wider part on the scope which is threaded, is only at the very top about 5/6mm deep, 36mm wide. With the correct size O ring this is surprisingly secure, but there was some slight movement if you grabbed the EP and moved it from side to side. To counter this I am using two O rings, one at the bottom and one at the top. This seems to the best way, it's a real snug fit and is going nowhere.
When you remove the 2in, you are left with 31.75, which I tried and it was to big. But this also unscrews to reveal a smaller tube which will fit with O rings or tape. For some reason, I mistakenly thought this was the 1.25in. So I have a 36mm at the top and 31mm on the bottom, so I'm .75mm to narrow.

It's only luck that the Baader zoom will fit, so for the moment I'm sticking with that, with the O rings. I had hoped to try a more expensive zoom, but from what I'm hearing there's no need, the Baaders pretty good and stands up well against more expensive EP's.

Ah! I think I know what you saying now, If I can find an EP that you can remove the 1.25 inch barrel it would fit like the Baader does now, is that correct?

Thanks to everybody for all your help and if you know of any EP's that are smaller in diameter that 36mm. please let me know.


Ron

 

[DRodrigues]

Thank Henry, apparently is not as simple as I first thought. I've just bought a Baader 13mm fixed lens, which would have given me a 33.69x Fixed. Hower, it won't fit into the Optolyth hole, it's too big, not by much though.

So you have an "old" Optolyth that don't accept 1.25" astro-eyepieces...
The only premium eyepieces you can adapt are the Nikon fieldscope ones. However is better to have an astroadapter for the telescope in order you can fix the ep to the telescope - without it the ep lens reach the lens of the telescope... Nikon fieldscope eps have a section similar to 1.25". The correct Optolyth adapter can be purchased at http://www.astroshop.eu/miscellaneous/optolyth-astroadapter-f-eyepieces/p,1180#tab_bar_2_select - the Product description text is wrong... But I recommend one with screws - see the info at http://www.pt-ducks.com/cr-telescopes.htm#Test%20of%20100mm%20telescopes - the link of the Austrian producer is not updated but you can ask for one based on the info of the text.

 

[giosblue]

Hi Thanks, yes I've seen that, I'm not sure how it could possibly work though.
At the end of the day you have to get the Eyepiece into the scope and on my scope it's .75mm too wide, maybe the later scopes are different, I don't know?
Anyway, I've found an even better way of fitting the Baader. I now have so it screws on, so I'm sticking with this at the moment.

Ron

 

[DRodrigues]

Yes, Ron, the latter versions have wider internal diameter - exactly the 1.25" size - I suggested that to Optolyth after purchasing my first 100 sample. The second I purchased already had the 1.25" internal diameter.
The Nikon fieldscope eps have less diameter - just a very small portion is 1.25".
I agree with Henry that in terms of light transmission you will not gain much with a fixed ep, compared to Baader zoom, only wider FOV at lower mags or higher mags - this last one only to more recent models...

 

[giosblue]

Thanks, looks like the Baaders as good as anything, so I'll stick with that. (for the moment) lol
Looks like I could have fitted an Opticron SDL v2, would this have been a better choice?

Weathers still not good, rain all weekend in the NW, so STILL not had a chance to have a proper look though it.
The sun came out yesterday so I nipped home at lunch time to have a play. Not a lot to look at from my back garden, but it was excellent. A vast improvement over my old lenses.

 

[Bencw]

Thanks, looks like the Baaders as good as anything, so I'll stick with that. (for the moment) lol
Looks like I could have fitted an Opticron SDL v2, would this have been a better choice?

Weathers still not good, rain all weekend in the NW, so STILL not had a chance to have a proper look though it.
The sun came out yesterday so I nipped home at lunch time to have a play. Not a lot to look at from my back garden, but it was excellent. A vast improvement over my old lenses.

Ron how are you getting on with your Optlyth scope now? I bought an Optolyth astro adapter, but it's no use, the 1.25" celestron zoom EP I tried will not fit through the scope hole as you rightly supposed, so I did not go for the baader as it might be the same. I was going to cut the nose back but now I think I will give up trying to fit a non Optolyth EP, I have found an used, but good condition, Optolyth 20x-60x zoom, not arrived yet, to compliment my 20x and 30x fixed EP's and will stick with them I think.

 

[giosblue]

Hi, because I had a small financial windfall,I decided to sell the Optolyth and treat myself to a new scope.
The Baader on the Optolyth was excellent, the only thing I wasn't happy with was, it was quite dark at full mag (about 54x) I tried a few scopes over the last couple of months, initially I wanted a smaller scope and I tried a Pentax 65ed, nice little scope, but the zoom it came with was poor a full mag. It worked well with the Baader, but was still a bit dim. So I tried a Kowa TSN883, Hawke Sapphire, Opticron ES80ED, Opticron, HR66ED and an Opticron HR80ED with SDLv2 Zoom. I sold the Baader and the Optolyth and bought the HR80ED with the SDLv2 zoom. I also bought the 27x and 37x fixed EPs. The SDLv2 is excellent, not as good as the fixed though.
BTW, you can use Opticron EPs on the Optolyth using rubber O rings.

The Optolyth zoom I had was 22x60, the older version of the one you're getting. The 22x60 zoom I had was hopeless, but the fixed EPs were very good. The zoom you're getting should be much better and I am keen to know what you think of it. Please let me know when you have had a chance to try it out.

If your not happy with the Optolyth zoom, try the Optiron SDLv2, you can always return it if your not happy.

Ron