How useful actually are 2" barlows?

[badhex]

7 hours ago, Alexis said:

If you get a 2" BarAdv from A-P that fixes itself -- you can install it as a screw-on barlow

I believe the GSO one does the same although I have never tried it. 

[Alexis]

Correct, and I've used it as such as well (also to yield much less than 2x -- if you screw it onto a 2"-1.25" adapter it's a very convenient 1.5x-ish barlow for most 1.25" eyepieces.) And it has filter threads for 2" filters too, which sadly the BarAdv does not have (and having to screw filters in between the BarAdv and eyepieces is a pain in the behind, certainly given the T2 thread of the BarAdv that sticks out means you need a 2" extension to make it filter-safe).

 

Edited June 3, 2021 by Alexis

[noisejammer]

First time post here but some might recognise me from the other side.

I have an AP Barcon and a Tak 1.6x extender. My principal use is in increasing the f-ratio so that my ADC works properly. Since I use binoviewers almost exclusively, the optical train needs to be fairly robust to handle the ~2kg load. The T2 thread on the Barcon allows versatility but I concur, it would be better if it had a M48x0.75 thread for filters. Other applications include boosting the focal length so that I can comfortably use 10mm ortho's on the moon and achieve a smallish exit pupil.

I've also used my Tak extender before my Herschel wedge / binoviewer combination when making white light solar observations. It tolerates the light beam from my refractors without obvious difficulty. This is probably because I use it a long way (~220mm) inside focus.

[Robindonne]

This is one of the few rare threads where we all agree NOT to buy a piece of astrogear🙂

Edited June 8, 2021 by Robindonne

[Alexis]

Well, I only agree because for me it's too late ;-).

[badhex]

10 hours ago, Alexis said:

Correct, and I've used it as such as well (also to yield much less than 2x -- if you screw it onto a 2"-1.25" adapter it's a very convenient 1.5x-ish barlow for most 1.25" eyepieces.) And it has filter threads for 2" filters too, which sadly the BarAdv does not have (and having to screw filters in between the BarAdv and eyepieces is a pain in the behind, certainly given the T2 thread of the BarAdv that sticks out means you need a 2" extension to make it filter-safe).

 

I guess if one were feeling so inclined, the Barlow end could be screwed direct into the scope end of a diagonal, yielding perhaps 3.5x ish and allowing one to use both 2" and 1.25" EPs at leisure. Would be a bit tricky to know the exact change to FL of the scope but it could be worked out. 

[badhex]

6 hours ago, Robindonne said:

This is one of the few rare threads were we all agree NOT to buy a piece of astrogear🙂

Oh no, what I have done?! 😂

[badhex]

9 hours ago, noisejammer said:

First time post here but some might recognise me from the other side.

I have an AP Barcon and a Tak 1.6x extender. My principal use is in increasing the f-ratio so that my ADC works properly. Since I use binoviewers almost exclusively, the optical train needs to be fairly robust to handle the ~2kg load. The T2 thread on the Barcon allows versatility but I concur, it would be better if it had a M48x0.75 thread for filters. Other applications include boosting the focal length so that I can comfortably use 10mm ortho's on the moon and achieve a smallish exit pupil.

I've also used my Tak extender before my Herschel wedge / binoviewer combination when making white light solar observations. It tolerates the light beam from my refractors without obvious difficulty. This is probably because I use it a long way (~220mm) inside focus.

Robustness of the optical train does seem to be a good reason, provided the Barlow/extender itself is sturdy of course! 

[John]

In the 2 inch format, the stack can be quite tall and heavy. This ES 20mm / 100 + 2x Powermate combo weighed close to 1,500 grams:

 

[badhex]

12 hours ago, John said:

In the 2 inch format, the stack can be quite tall and heavy. This ES 20mm / 100 + 2x Powermate combo weighed close to 1,500 grams:

 

That is quite something! I was thinking how my Panoptic 41mm would look with a Powermate attached... There are smaller setups including the scope in the "Small can be beautiful" thread! 😂

[rwilkey]

2" ep's are generally used for low power, why the hell would you want to Barlow a low power ep, that defeats the object of buying low power ep's.  I got rid of my 2" almost as soon as I bought it.

[Louis D]

4 hours ago, rwilkey said:

2" ep's are generally used for low power, why the hell would you want to Barlow a low power ep, that defeats the object of buying low power ep's.  I got rid of my 2" almost as soon as I bought it.

For fun to change things up.  I love the enormous eye lenses and long eye relief of my giant 2" eyepieces when wearing eyeglasses.  It's very relaxing to use them because I don't have to touch the top of the eyepiece with my eyeglasses to take in the entire FOV.  It's nice to use them at a larger image scale once in a while with a telecentric Barlow/magnifier.  Don't use a non-telecentric 2" Barlow with widest field 2" eyepieces.  They'll hard vignette ruining the whole experience.

[John]

One issue with barlowing a long focal length eyepiece is that the eye relief is extended by the barlow. With a long focal length eyepiece the eye relief is usually quite long anyway so pushing it out even further can cause eye positioning challenges and the need to "hover" the eye well above both the eye lens and the eye cup.

Telextenders and Powermates usually leave the eye relief more or less unchanged. They also have less tendency to vignette a large AFoV than barlows do.