Are big focal lengths available in 1.25"?

[bonox]

Hi All

Newcomer from sydney with an 8" LX90, comes with 1.25" back. I have a 32mm plossl at the moment, and am interested in a really wide real FOV (not necessarily apparent FOV). Guys at Bintel persuaded me to choose the 32 over the 40mm as having the same magnification but smaller field of view - not sure i want what i was pushed into now.

Anyhow, been looking at what's available and there appear to be a number of EP's in the high 40, and mid 50 mm range, but they are all 2" optics - are any available in inch and a quarter, or do you get big vignetting problems? Do i need a special 2" back just for one EP?

Thanks guys

[Starkler (Geoff)]

Its all about field of view . Bintel were right to suggest a 32mm plossl over a 40mm.
The simple fact is that over 32mm with a 50 degree fov plossl, you simply cannot get any greater field as its limited by the width of the barrel.
I have 24mm panoptic which is a wide field eyepiece with the same field as a 32mm plossl. To get any greater field there is no choice but to go to 2 inch format eyepieces.

[shredder]

Have to agree, the limiting factor is the barrel width, which is why you don't see and WA long focal length eyepieces in 1.25". The question is then is it worth getting a 2" focuser / adapter etc for what is likely only to be one or two eyepieces? For me that has so far been no.....not yet....maybe soon....

Anyway the guys at Bintel are very knowledgeable and in my expereince rarely give bad advice, so dont feel like you are pushed into a mistake. I have often asked their advice, gone against it anyway (and bought something else) and then realised they were right....

[acropolite (Phil)]

Shredder, W/O make a 2 inch diagonal that will screw directly on to the back of the LX90 and still clear the forks. trufflehunter, (Wayne) informs me that the Meade s4000 36 mm QX ep performs very nicely with no noticeable vignetting. I suggest you PM wayne for more details if you're interested.

[shredder]

Ahh Phil,

I was just talking generally there about the equipment for a 2" ep. But even just replacing the diagonal and then buying the ep will probably set you back a good $400 for just one ep? For me that a lot to spend for only one ep..... You probably get better value for money buying a good binocular and stand as this gives you comparable magnification and much easier on the eyes (and not too bad at the footy either).

[bonox]

thanks chaps

from what you are saying, in general are there two ways to improve the area of sky you see through the EP?

1. higher EP focal length to reduce magnification (but 40mm shows same actual FOV as 32mm?) OR
2. wider apparent FOV for same same focal length.

this doesn't seem right -> or am i missing something?

[Starkler (Geoff)]

1. You cannot get a bigger FOV in 1.25" format eyepieces than that given by a 50 degree fov 32mm plossl. If you got a 40mm plossl, you would see no bigger true field but the apparent field will be smaller ie like looking through a drinking straw.

2. I mentioned a 24mm panoptic. That has a wider apparent field at 68 degrees, but same true field as the 32mm plossl. ie like looking through a bigger hole but the true field is the same.

[shredder]

Oh just realised you are using a SCT, dolt! There is a much better way to go. Go get yourself a Focal Reducer / Flatener, it will take your scope from F10 to F6.3 and effectively increase your field of view without the need for a new ep, bit like the reverse of a Barlow. I do have one and they are great for when you want that wider view, but can be a bit of a pain to put on in the dark (sits between the Visual back and 90 deg angle). You can probably get one 2nd hand for $100 or so....

[bonox]

thanks for the info

Have a focal reducer on order, part of a meade astrokit I think. Sounds like it will do more than work only as a photographic part.