Hi Peeps.
After a very long break from from looking at the sky, I have just got me a small scope a Vixen r150s which uses the older .956 eyeieces, Im looking for 2 new 1.25 eyepieces which i have the adaptor for to use with this scope.
As a good source of information, I would encourage you to go to the Televue website and search for an article about choosing eyepieces...Al Nagler offers some real good advice.
While the Televue gear is wonderful The advice is worthwhile even if you choose another eyepiece manufacture
Hi Peeps.
After a very long break from from looking at the sky, I have just got me a small scope a Vixen r150s which uses the older .956 eyeieces, Im looking for 2 new 1.25 eyepieces which i have the adaptor for to use with this scope.
What would you recomend ?
Hi Graeme,
Is this the type of focuser on your scope ? You can't just use "any" 1.25" eyepiece in that .965" adaptor
Hi John
Yes that is the one.... please tell me what you mean by that.
Hi Graeme,
I will respond in detail within the next 24 hours when I have more time. At this time don't run out and buy any eyepieces. There are some complex issues which I need to explain, before you spend your hard earned coin on eyepieces which may not work in combination with that scope/focuser.
What focal length eyepieces are you considering ?
Cheers,
John B
Last edited by ausastronomer; 15-09-2011 at 06:09 PM.
I will respond in detail within the next 24 hours when I have more time. At this time don't run out and buy any eyepieces. There are some complex issues which I need to explain, before you spend your hard earned coin on eyepieces which may not work in combination with that scope/focuser.
What focal length eyepieces are you considering ?
Cheers,
John B
Hi John
To be honest i have not given any thought to focal lengh, I have not had this scope long Im just getting back into the hobby and have had only one chance to use the scope with the old .965 eyepieces that came with the scope views were very good but you know you can spend $$$ on eyepieces but they cant see past clouds They were a 20mm & 12mm, so i wanted somthing around the same but a bit more modern and that can be used when i upgrade to a bigger scope.
There are some good 0.965 eyepieces around. I sold a few awesome ones here a while back, and you can still get very good brand new ones from Barry Gooley in Japan.
There are some good 0.965 eyepieces around. I sold a few awesome ones here a while back, and you can still get very good brand new ones from Barry Gooley in Japan.
Essentially the FOV of an eyepiece is determined by the field stop. In this situation with a narrow focuser drawtube and the bottom of the drawtube further away from the focal plane than the eyepiece field stop, the bottom end of the focuser drawtube becomes the field stop. If you were to use 1.25" eyepieces in this scope they would have to be short focal length ones. With plossls or othoscopics you could possibly get away with <15mm focal length eyepieces. If you wanted to use wide field eyepieces you would be restricted to even shorter focal lengths of < 10mm. It's very easy to use .965" eyepieces in a 1.25" or 2" focuser, it doesnt go very well the other way around.
I was going to suggest before you buy new eyepieces, you replace the focuser on your scope with a GSO 2 speed crayford for about $100. This would have given you "free reign" with any eyepiece purchase.
Unfortunately, I remembered this scope was one of the very few scopes to be sold commercially with a "sled" or "slide" focuser. A sled focuser, whilst an excellent concept that has some advantages, makes it exceptionally difficult to change the focuser for someone who is not an experienced ATMer. A sled focuser has the secondary mirror attached to the focuser sled by a single spider vane and achieves focus by sliding the eyepiece and secondary mirror (as a single unit) closer to or away from the primary mirror. The only way to change the focuser on this scope is to replace the secondary mirror with a new one with fixed vanes. You would then have a gastly hole in the side of your tube which would need to be repaired.
This is all a bit of a pity really because optically these scopes are very good and are built like a tank. I think your best options are to use the eyepieces you have for a few months and if you are serious about the hobby again sell the scope and buy one with a 2" focuser. Another option is to try and find an ATMer who could change the focuser and secondary mirror for you but this will cost you between $200 and $300 in itself. It may not be worth spending that much money on, I am guessing an early 1980's scope, when you can buy a good GSO or Synta 8" dob with 2 inch focuser for around $400 brand new.
Cheers,
John B
Last edited by ausastronomer; 17-09-2011 at 07:43 AM.
Reason: correct grammar
Hi Nightstalker,
The mount is a Vixen Super Polaris with Dual tracking motors, not sure what the scope is for is for an yes as Jason has said that guy in Japan is looking like he will be getting getting a new customer.
The news I bring isn't what you want to hear. Essentially the FOV of an eyepiece is determined by the field stop. In this situation the bottom end of the focuser drawtube essentially becomes the field stop. If you were to use 1.25" eyepieces in this scope they would have to be short focal length ones. With plossls or othoscopics you could possibly get away with <15mm focal length eyepieces. If you wanted to use wide field eyepieces you would be restricted to even shorter focal lengths of < 10mm. It's very easy to .965" eyepieces in a 1.25" or 2" focuser, it doesnt go very well the other way around.
I was going to suggest before you buy new eyepieces, you replace the focuser on your scope with a GSO 2 speed crayford for about $100. This would have given you "free reign" with any eyepiece purchase.
Unfortunately, I remembered this scope was one of the very few scopes to be sold commercially with a "sled" or "slide" focuser. A sled focuser, whilst an excellent concept that has some advantages, makes it exceptionally difficult to change the focuser for someone who is not an experienced ATMer. A sled focuser has the secondary mirror attached to the focuser sled by a single spider vane and achieves focus by sliding the eyepiece and secondary mirror (as a single unit) closer to or away from the primary mirror. The only way to change the focuser on this scope is to replace the secondary mirror with a new one with fixed vanes. You would then have a gastly hole in the side of your tube which would need to be repaired.
This is all a bit of a pity really because optically these scopes are very good and are built like a tank. I think your best options are to use the eyepieces you have for a few months and if you are serious about the hobby again sell the scope and buy one with a 2" focuser. Another option is to try and find an ATMer who could change the focuser and secondary mirror for you but this will cost you between $200 and $300 in itself. It may not be worth spending that much money on, I am guessing an early 1980's scope, when you can buy a good GSO or Synta 8" dob with 2 inch focuser for around $400 brand new.
Cheers,
John B
Hi John
Thankyou so much for all you information i just have 2 more questions.
1 will this scope still be ok to use with a webcam using the 1.25 adaptor.
2 Can i use the the 1.25 to use a collimator to allign it.
I will stick with the .965 for viewing but need to find out those questions as im trying to get my son interested in the hobby as well.
cheers
Graeme.
Last edited by Saturn%5; 17-09-2011 at 06:48 AM.
Reason: Spelling
1 will this scope still be ok to use with a webcam using the 1.25 adaptor.
Hi Graeme,
I am not am imager so not an expert about about these cameras and imaging. What it will come done to is the chipsize of the camera you plan to use and the focuser travel range. A camera with a small chip (<12mm) will probably work fine. The second problem will then be if the focuser has enough downward travel to reach focus on the camera chip. You need more infocus for imaging than you do for visual astronomy.
Quote:
Originally Posted by Saturn%5
2 Can i use the the 1.25 to use a collimator to allign it.
Any form of 1.25" collimation devise (laser, cheshire, sight tube, autocollimator etc) should work fine in the adaptor.
Those .965" orthos from KK in Japan will cost you about $80 each plus shipping. They are very good quality optically but the FOV is fairly narrow by modern standards and the eye relief on the shorter focal lengths is tight. They should be somewhat better than the eyepieces you already have.
Hi Nightstalker,
The mount is a Vixen Super Polaris with Dual tracking motors, not sure what the scope is for is for an yes as Jason has said that guy in Japan is looking like he will be getting getting a new customer.
Cheers
Graeme.
Hi Graeme,
I don't know what the design objectives of this scope were, particularly with a .965" focuser drawtube. Although that size was common 30 years ago on smaller commercially built scopes.
The main advantages of a sled focuser design are in fact for photography. It allows for a much greater focuser travel range than is possible with a vertically moving focuser tube. It also allows the focuser tube to be much shorter in length and closer to the telescope tube making it stronger and able to support the weight of the camera better. Also the design makes it very easy to incorporate a filter slide into the back of the focuser.
The negatives, and they aren't really negatives for photography, is that you need to use a larger secondary mirror than what is required with a vertically moving focuser. This is because you need to size the secondary to fully illuminute the field at the bottom end of the focuser travel range, at which point the light cone is wider. The second one is that you have one fairly think spider vane.
They were a 20mm & 12mm, so i wanted somthing around the same but a bit more modern and that can be used when i upgrade to a bigger scope.
.
