1 reply to this topic

[Cielo_nocturno]

Hello, I use an Arcturus binoviewer with an 2” 2x barlow (equivalent of 2.75x Barlow in real life) to reach focus with my 12” f5 dob. I use it mainly for planets and the moon but also for stars clusters and bright/small DSO.

 

Due to the 22mm clear aperture of the bino and the high magnification that the focal length + Barlow gives me, the biggest eyepieces field stop I can use are:

 

-25mm plossl 48º (165x)

-18mm APM UFF 65º (230x)

-14mm ES 82º (295x)

 

But in the real world: all those 3 eyepieces gives me the same real TFOV (~0.28º) with different magnifications. And my goal is always to stay at that maximum field stop range, as the magnification is already considerably high. So the question is, should I just keep one of them as they gives me “the same”?

 

I’ve been using the bino for almost a year and almost every time the 14mm 82º is the one in the bino.

 

The 18mm and 25mm are a different experience, as the magnification is lower, but the amount of sky I see is the same, and changing eyepieces in the bino is a bit of an inconvenience… (And someone just have offered me $160 for the 18mm pair).

 

So, should I just keep the 14mm 82º and say (just because they’re cheap), the 25mm plossl?

Also, if I want more magnification (which I rarely do), i can increase the distance from the bino to the barlow.

 

Do any of you follow the same strategy? I see multiple people with a dozen eyepieces for the bino, and I won’t want to be like that hahaha.

 

For monoviewing I’m served with 25, 14 and 9mm ES100 + barlow.

 

Note: I DO like big AFOVs as you can see, and I find the 14mm 82º really comfortable on my binoviewer, even more than the UFF 18s due to the bigger width of the last one.

 

Thank you.

 

Edited by Cielo_nocturno, 21 February 2025 - 04:51 AM.

[betacygni]

Even though they are giving you the same true field of view, the exit pupils and therefore brightness will be quite a bit different. Depending on the object and your level of light pollution certain exit pupils will be more optimal.

The 14mm with an effective 2.75x amplifier would give you about a 1mm exit pupil, that’s good for planetary/double star but quite small for a lot of deep sky.

Have you considered instead getting a lower power binoviewer amplifier? Depending on your scope’s back focus most reflectors can achieve focus with a 2x effective amplifier (Televue 2.5x powermate for example gives 2x in binoviewers).