2x Focal Extender or 4mm eyepiece for 80ed?

[Shimrod]

I've got a few bits on order at the moment, one of which is a 7mm OVL Nirvana eyepiece. I've been thinking about whether I should have ordered the 4mm as well (for use with my Skywatcher 80ed) or the Explore Scientific 2x 2" focal extender. I had thought about the latter when placing the original order, but at the time it was 30-40 days delivery - now it is available again in 1-2 days. My thoughts about the Focal Extender are that the 7mm will give me 3.5mm which will give 171x magnification for the telescope, and it will also be useful if I want to try imaging the planets. the 4mm eyepiece will give me 150x, will be lighter but won't really be usable on my other scope (8" EdgeHD).

Any comments or alternative suggestions (up to the budget of the Focal Extender, around £140) would be welcome.

thanks

[Don Pensack]

If the purpose is for lunar or planetary visual use, you won't like the scattered light in the ES focal extender.  The FEs work fine for deep sky, but they aren't well baffled for bright targets like the Moon

or planets.  As for imaging the planets, you should be able to with eyepiece projection, and the focal extender attached to the camera would also work.

I am not certain the correct adapters are available for direct attachment of FE to camera, but a 1.25" nosepiece on the camera will work if the scope has a reasonable amount of in travel available in the focuser.

[Shimrod]

2 hours ago, Don Pensack said:

If the purpose is for lunar or planetary visual use, you won't like the scattered light in the ES focal extender.  The FEs work fine for deep sky, but they aren't well baffled for bright targets like the Moon

or planets.  As for imaging the planets, you should be able to with eyepiece projection, and the focal extender attached to the camera would also work.

I am not certain the correct adapters are available for direct attachment of FE to camera, but a 1.25" nosepiece on the camera will work if the scope has a reasonable amount of in travel available in the focuser.

So the primary aim was to view and image the planets - mostly with the 80ed - as that is my travel telescope and my view of the southern sky from home is obscured by a recent housing development blocking the planets from view. For deep sky I would be using the telescope without the extender and with the skywatcher focal reducer/flattener. Imaging is with a Canon DSLR (unmodified).

Would you recommend a barlow instead?

[Don Pensack]

Depends on the Barlow.  Some of the better barlows (Nikon, AP, Baader VIP, etc) would be great.

But they're not in the same price range.

And you won't get vignetting with the ES Focal Extenders, which might not be important for planets, but could be for lunar shots.

A well-baffled barlow might yield better contrast in the field.

You might see what APM has to offer.

[Ricochet]

On 03/09/2020 at 17:22, Don Pensack said:

If the purpose is for lunar or planetary visual use, you won't like the scattered light in the ES focal extender.  The FEs work fine for deep sky, but they aren't well baffled for bright targets like the Moon

Do you know if the FEs can be easily disassembled or are they sealed like the ES eyepieces? I've got the old Meade branded version of the 1.25" 2X FE and I solved the reflection issue by flocking between the two lens groups. 

[Don Pensack]

You'd lose the seal if the FE is sealed by opening it and flocking IF it's sealed (I don't know that it is), but reassembly would seal it again, just with normal air.

That would not lead to fogging if you did it on a dry humidity day.

[Shimrod]

On 03/09/2020 at 22:02, Don Pensack said:

Depends on the Barlow.  Some of the better barlows (Nikon, AP, Baader VIP, etc) would be great.

But they're not in the same price range.

And you won't get vignetting with the ES Focal Extenders, which might not be important for planets, but could be for lunar shots.

A well-baffled barlow might yield better contrast in the field.

You might see what APM has to offer.

To update on this thread: I did three things in the end. The delivery time for the Skywatcher focal reducer extended to sometime late October, so I cancelled that and bought a cheaper version from Altair Astro - I was also able to buy the Altair branded 2x focal extender, with both items having good reviews and together costing the same as the Skywatcher focal reducer. I also bought a ES 52 LER 4.5mm plossl to support planetary viewing on the 80ed.