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2" or 1.25"


Tuda78

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What if any is the difference between 2" and 1.25" eyepieces other than the obvious size difference? Would I be correct in thinking the 2" would have a wider field of view? What do you guys prefer to use?

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Hi there !

The principal advantage of the 2" eyepiece format is that a wider field of view can be delivered, as you say. Because of this, you tend to find that 2" eyepieces are only worthwhile and available in longer focal lengths. Many people end up with a set of eyepieces which are mostly 1.25" but with a 2" or two for the low power, wide or very wide angle views.

My eyepieces have focal lengths of 31mm, 21mm, 13mm, 8mm, 6mm, 5mm, 4mm, 3,5mm and 3mm (they serve 3 different scopes !). Only the 31mm and 21mm are 2" eyepeices because I like ultra wide fields of view and you need to have a 2" barrel to get those over 18mm in focal length.

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As John mentions, 2" is required for wide field, long focal length EPs. I have EPs of 42mm, 31mm, 22mm, and 17mm for wide field work (in part because my main scope is quite slow, at F/10). My 14mm and 12mm are dual fit EPs, and the shorter stuff is 1.25" only, despite being wide-field.

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I prefer 2" EPs for some of the larger deep space targets and the larger clusters.

You just can't get the whole thing into the smaller aperture EPs.

You can struggle with some of them in a 2" EP too mind you.

But then, in my opinion, it is about framing them as best you can, with the kit you have.

A long focal length 2" EP can also be very helpful for star hopping.

The other advantage, but this isn't restricted just to 2" EPs, is that the wider the EP, the longer the drift time when using a dob.

Cheers

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As John mentions, 2" is required for wide field, long focal length EPs. I have EPs of 42mm, 31mm, 22mm, and 17mm for wide field work (in part because my main scope is quite slow, at F/10). My 14mm and 12mm are dual fit EPs, and the shorter stuff is 1.25" only, despite being wide-field.

Michael - presume the 17mm EP you refer to is the Nagler T4? At that focal length does the 2" barrel have any advantages over a comparable wide field 1.25" EP - I suppose the best comparison would be with the 16mm T5 Nagler - apart from the eye relief, which is clearly better with the 17mm?

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Michael - presume the 17mm EP you refer to is the Nagler T4? At that focal length does the 2" barrel have any advantages over a comparable wide field 1.25" EP - I suppose the best comparison would be with the 16mm T5 Nagler - apart from the eye relief, which is clearly better with the 17mm?

It is the 17T4 Nagler. Longer eye relief means several lenses have to be designed a lot bigger, from the eye lens downwards. This is why a 2" barrel is used, whereas the 18mm 82 deg from MaxVision got away with just a 1.25" barrel. That has much less eye relief

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Most of my eyepieces are rather heavy beasts so I tend to use them in 2" mode wherever possible for securities sake. A number of them have hybrid 2" / 1.25" barrels to help with this and at least you have a choice then. The 31mm and 21mm are 2" only though.

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I have 200p dob which has an interchangeable 1.25 and 2 inch eyepiece holder. Is there anything the I can use so I can keep the two inch on the scope but also use 1.25 inch in there? Some sort of adaptor I guess I'm looking for.

Sent from my SM-G920F using Tapatalk

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Hi there !

The principal advantage of the 2" eyepiece format is that a wider field of view can be delivered, as you say. Because of this, you tend to find that 2" eyepieces are only worthwhile and available in longer focal lengths. Many people end up with a set of eyepieces which are mostly 1.25" but with a 2" or two for the low power, wide or very wide angle views.

My eyepieces have focal lengths of 31mm, 21mm, 13mm, 8mm, 6mm, 5mm, 4mm, 3,5mm and 3mm (they serve 3 different scopes !). Only the 31mm and 21mm are 2" eyepeices because I like ultra wide fields of view and you need to have a 2" barrel to get those over 18mm in focal length.

Aren't you forgetting one John? [emoji6]

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I have 200p dob which has an interchangeable 1.25 and 2 inch eyepiece holder. Is there anything the I can use so I can keep the two inch on the scope but also use 1.25 inch in there? Some sort of adaptor I guess I'm looking for.

Sent from my SM-G920F using Tapatalk

http://www.firstlightoptics.com/adapters.html

I assume that anything listed as a  2"-1.25" adaptor should work unless anyone knows of a reason why not for your specific scope. Personally I would recommend the Baader Clicklock as a great improvement over anything with a thumbscrew.

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http://www.firstlightoptics.com/adapters.html

I assume that anything listed as a 2"-1.25" adaptor should work unless anyone knows of a reason why not for your specific scope. Personally I would recommend the Baader Clicklock as a great improvement over anything with a thumbscrew.

I think you need to be careful with the 200p, I don't think you can use a 2" to 1.25" adaptor I the 2" fitting and still reach focus.

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No, you would have to remove the Clicklock or any other adaptor in order to use the 2" eyepiece. However, if Stu is right about the 200p not being able to reach focus using the 2" EP holder plus an adaptor then unfortunately the whole idea is a non-starter really.

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I think the challenge with some of the Skywatcher focusers is that their drawtubes are a little over 2" in diameter so you need to use their adaptors with the flared bit at the bottom for 1.25" and 2" eyepieces and you can't use those together as 1.25" eyepieces won't come to focus.

Thnking it through though, a low profile 2" - 1.25" adapter used in the Skywatcher 2" adapter might be OK if it does not raise the height of the 1.25" eyepiece more than a few mm above the top of the 2" adapter :icon_scratch:

Has anyone tried this ?

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Ah I see, it's fine I'll lost stick with it then rather than faff. It works so I'll leave it at that, it was just more of a convenience idea. Thank you everybody for your input much appreciated, it means whilst we have these wonderful clouds I can save my money to purchase other items :-)

Sent from my SM-G920F using Tapatalk

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What you could do is to put the 2" ep holder in, wind it all the way down and then try holding your 1.25" eyepieces above it at the points at which they focus. If there is a decent gap between the top of the 2" holder and the tops of the ep barrels you will probably be fine using an adaptor. For reference my clickstop protrudes 9.5mm from the top of the 2" ep holder.

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hi,

from here: http://www.altairastro.com/self-centering-extensions-adapters/

I've got the 35mm extension and the 2 to 1.25 adapter, these are twist lock and work well enough. I've got 1 2" eyepiece, and it's a bit of an extra faff swapping out the adaptor, but not more so than changing eyepieces. The 35mm extension stays in all the time and allows all my eyepieces to come to focus. (I have the same scope as you)

EDIT: When using 1.25 eyepieces, I use both the extension and the adaptor

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