Altair Astro Ultraflat 24mm 65°

[ScouseSpaceCadet]

I'm considering replacing my Celestron 25mm 60° eyepiece. I've owned it two years and now fancy moving up to a more premium eyepiece.

The Explore Scientific 24mm 68° seems to be the one based on price vs performance reviews. To be honest, with the proceeds of the Celestron sale, the ES priced at £155 is the most I can afford.

However, they're out of stock everywhere except Ali Express at cut down prices even but I don't want to go there.

I've noticed Altair have a range of premium eps.The Altair Ultraflats received a favourable review in Sky at Night Magazine. The 24mm 65° caught my eye and at £135 it's £20 cheaper than the ES.

The specs look decent, but do any of the eyepiece gurus here have experience of this Altair range or any clones? Should I just hold out for the ES 24mm 68°? Thanks.

Edited February 13, 2021 by ScouseSpaceCadet
Ali Express...

[Ricochet]

The Altair is the same optically as the APM, so if you search for that you will find more reviews. The general consensus is that they are very good eyepieces and one would be a worthy alternative. 

[ScouseSpaceCadet]

Just now, Ricochet said:

The Altair is the same optically as the APM, so if you search for that you will find more reviews. The general consensus is that they are very good eyepieces and one would be a worthy alternative. 

Thanks.

[Louis D]

Here's my comparison image of ~24mm eyepieces.  Your 25mm Celestron is probably similar to the 25mm Meade HD-60.  The 24mm APM UFF is optically identical to the Altair Astro.

It's a decent eyepiece that suffers a bit toward the edge.  I much prefer my 22mm AT AF70 (Omegon Redline, TS Optics Expanse) for just a bit more TFOV.  However, it does require a 2 inch focuser.

[Don Pensack]

In my f/7 apo, the 24mm APM UFF has a better edge of field than the ES 24x68.

Both are not quite up to the standard of the TeleVue 24mm Panoptic, though.

But the APM is the only one of those 3 24mm eyepieces compatible with glasses.

 

As for true field size, the 22mm 70° eyepiece Louis mentions is a great alternative if you have 2" eyepiece capability.

Now sold as:

Arcturus	Ebony
Astromania	SWA
Omegon	Redline
Skywatcher	SWA
Telescope Service	Expanse ED

They might be available used as an Astrotech AF70, an Olivon 70, or a Celestron Ultima LX

My calculations show a 26.9mm field stop in that eyepiece versus a 27.2-27.3mm field stop in the APM, which is close enough the field size is pretty much the same.

Measurements of the others show 27.0-27.2mm, so all of these can be safely considered to have roughly the same true field size.

 

[ScouseSpaceCadet]

Brilliant chaps. Thanks for your help. 👍

[Louis D]

From my yard stick field stop measurements:

24mm APM UFF: 27.5mm FS

22mm AT AF70: 28.4mm FS

There is a bit of falloff/fuzziness for the APM at the edge, so it's not a good, clean 27.5mm FS.  Measured AFOV=63°, eAFOV=66°

The AF70 has low distortion toward the edge, helping maximize its TFOV. Measured AFOV=70°, eAFOV=74°:

Edited February 13, 2021 by Louis D

[Second Time Around]

The 22mm Astrotech/Olivon/Omegon and clones are excellent and a real steal at the price. It's a real hidden gem.

The only reason I sold my Omegon recently is that it's a 2 inch eyepiece.  Had it been a 1.25 inch I'd still have it.

 

[ScouseSpaceCadet]

Well I gave in and decided on the Altair Ultraflat 24mm. Getting an extra fiver off due to loyalty points sealed it. 😉

[Dantooine]

On 03/03/2021 at 21:29, ScouseSpaceCadet said:

Well I gave in and decided on the Altair Ultraflat 24mm. Getting an extra fiver off due to loyalty points sealed it. 😉

How have you found this eyepiece ?

im thinking of getting one. 

[Don Pensack]

It's not a perfect eyepiece, because the edge deteriorates a tad near the edge at f/6 and faster, but the long eye relief makes it easy to use (effective eye relief of about 18-19mm because the eye lens is recessed),

and the light transmission, when directly compared to a 24mm Panoptic, is excellent.

The star images are very tight out to about the 90% point but don't really get wonky until very near the edge, so it is an excellent full-field 1.25" eyepiece.

In my f/7 apo, it is sharp to just about the very edge, and in anything longer, it should be perfect.

Ackermann designed it for f/5, so it is only a questionable choice under f/5.

It has an effective field diameter of 27.3-27.5mm (different people have measured different diameters in the field), so a little wider than most of the competition.

The 65° field is consistent with 27.3mm

[ScouseSpaceCadet]

3 hours ago, Dantooine said:

How have you found this eyepiece ?

im thinking of getting one. 

Don answered the question admirably!

Eye relief is very comfortable. Paired with the 102mm f7 refractor and 102mm Mak, the view is crystal clear, the field flat and star shapes tight to near the edge. The only other premium ep I've owned is a Vixen Lanthanum 30mm NLVW and this ep is as least as good.

 

Edited May 4, 2021 by ScouseSpaceCadet

[Louis D]

It's not as good as the near perfect 30mm UFF, but it is as good as it gets for eyeglass wearers at this focal length in 1.25" eyepieces.  I've measured the AFOV at 63 degrees, the eAFOV at 66 degrees, the usable eye relief at 17mm, the field stop at 27.5mm with some vignetting, and weight at 12.2 ounces.  I've found the 22mm AT AF70, Redline, Olivon, and other 70 degree 2" eyepiece brands to be better across a slightly wider TFOV (30.9mm field stop), but it is 2" only.

Below is a comparison image of several of my eyepieces in the 24mm range taken through a field flattened f/6 72ED refractor.  It's clear the 24mm UFF is not perfect near the edges, but not bad by any means, either.

[Don Pensack]

The 27mm Panoptic is impressively sharp at the edge, but it does have strong rectilinear distortion in comparison.