What is the Widest FOV possible with a 1.25" eyepiece ?

[avtaram]

I've recently taken delivery of a Skywatcher Explorer 150PL, couldn't really resist it for £120 from Astroboot.

I'm using it mainly for double stars and as a quick grab and go for those short sessions where it's not worthwhile setting up the 120ED. It sits in the summer house mounted on an AZ mount and I can take it out all in one go.

I use the Baader Zoom in the 1.25" focuser and that gives me a FOV of about 1 degree at the 20mm setting.

I was just wondering what would be the widest FOV possible and with which eyepiece.

Avtar

[swamp thing]

I may be wrong but I think a 32mm 50degree eyepice gives the maximum FOV in 1.25" format. This same field can be got in a 24mm at 68degree AFOV.

[Dude_with_the_tube]

if to answer to your question directly then the possible widest 1.25" will have to be Baader Eudiascopic 35mm with 45 degree FOV,then you can also have different variety of available plossls in 32 and 30mm range,Baader Aspheric 31mm as it is modular and can be used as 2" and 1.25",then its the array of recently discussed Panoptic/ Meade/Ex Sc/maxvision 24mm in 68 degree range.All these are 1.25"

If you are really after the widest field you will have to jump to 2" barrels to be perfectly honest and looking at your current eye piece set up if it is correct,you already have 24mm UWA and also the 38mm Panaview,dont really need another eye piece in my opinion,unless you do not like them? Issue with the 2" widefields is they share size.Even a 30/31mm UWA would it be Meade or Ex/Sc or even Televue Nagler 31mm will be they massive size and weight of over 1kg.

[John]

The widest that I've owned in the 1.25" format are the KK Widescan III, 20mm, 84 degree AFoV and Celestron Ultima / Orion Ultrascopic 35mm, 49 degree AFoV. Both out of production now though   They would give around 1.4 true degrees in the 150PL which is as wide as you are going to get in the 1.25" format.

The Ultima / Ultrascopic 35mm does turn up on the used market from time to time. To be honest I thought the Baader Eudiascopic was also a 49 degree AFoV but maybe not ?

The Tele Vue 32mm plossl will give you a 1.333 true degree field which is not far off the max.

[nicoscy]

27mm field stop is the maximum in 1.25" format. That would be the 24mm 68 degrees, 32mm 50 degrees and 40mm 42 degrees eyepieces.

So, same FOV, different exit pupil and apparent FOV

[John]

The Celestron Ultima / Orion Ultrascopic 35mm have a 29mm diameter field stop. They managed this by locating the field stop just above the chrome barrel within the eypiece body. The design needs a little more inward focuser movement to reach focus because of this.

[michael.h.f.wilkinson]

A 27mm field stop in a 1200mm focal length scope like the one you have should yield a true FOV of 1.29 deg.

[bingevader]

Too slow!

Steve and John have wrapped it up assuming you're talking 1.25" format.

The only other possibility is to increase the aFOV whilst reducing the focal length of the EP ( and increasing the magnification) as in John's KK Widescan III example, or a 13mm Ethos!

[ronin]

The Antares W70 at 25mm focal length from Rother Valley would give 1.458 degrees.

They are £60 each however, is the small amount extra worth it?

For the maximum you need to work all the figures through, then decide if the small extra bits delivered are worth what will be an increased cost.

[michael.h.f.wilkinson]

The Antares W70 at 25mm focal length from Rother Valley would give 1.458 degrees.

They are £60 each however, is the small amount extra worth it?

For the maximum you need to work all the figures through, then decide if the small extra bits delivered are worth what will be an increased cost.

Not really. I have that EP, and the field stop is 27mm (27.3 if you are generous, I measured it when I inserted cross-hairs for my finder scope). The 70 deg AFOV is in part due to pincushion distortion (a common problem in these EPs), so while if you calculate the true FOV from AFOV divided by magnification you get 1.458 degrees, that would require a 30.5mm field stop. Calculating the TFOV from the field stop you get 1.30 (for 27.3mm)

[Moonshane]

Be interested to hear what you think of this compared with the 120mm ed

[Owmuchonomy]

My favourite for years was the 1.25" Celestron Omni 40mm 43 deg plossl design. A very forgiving eyepiece with good eye relief. I believe there are various copies of it around.

[John]

Be interested to hear what you think of this compared with the 120mm ed

Yes indeed, that would be very interesting

[avtaram]

Be interested to hear what you think of this compared with the 120mm ed

I'm hoping to do a shoot out between these two scopes when the weather allows.

So far I've only managed one short session with the 150PL looking at Polaris and and Almach.

It's been quite a while since I looked at doubles with the 120ED but going by memory I can say that the 150PL really holds up well against the 120ED.

The doubles were easily split and the image produced was bright and contrasty round dots without any spikes. The only time I saw spikes was at the maximum magnification using the Baader Barlow with the Zoom.

When I first received the 150pl I checked the collimation and to my surprise it was spot on.

I'm really happy with this scope and what with the 12" Dob sitting along side it in the summer house, making them both grab and go I'm wondering how much use the 120ed will be getting in the future.

Avtar