How Would The 24mm Ultra Flat Field Do With A ST80 F5 Achro?

[refractordude]

Hello There

Looking for a wider field than what my 32mm plossl is showing. How would the 24mm UFF do with a f5 80mm achro? I am a little worried about eye relief and edge sharpness with the Celestron 25mm X-CEL. Thanks to you all.
Link to what I want to buy. https://agenaastro.com/celestron-1-25-ultima-edge-flat-field-eyepiece-24mm-93453.html

Clear Skies

[mental4astro]

Well, what do you think will happen with an f/5 achro?

Regardless of the eyepiece that scope has a large amount of field curvature that all eyepieces will struggle with. Increase the AFOV & field curvature will become more apparent too.

I have used this eyepiece (different flavour but same design - same eyepiece is sold under many brands including Celestron, APM, Sky Rover & others) in an f/5 achro. Beautiful image but the edge of the FOV shows some field curvature. Not the fault of the eyepiece but because design of the scope. No free lunch here. In a better corrected scope the eyepiece performance increases too. It's one of my favourite eyepieces.

This eyepiece will not show a wider amount of sky than your 32mm plossl. It will actually show a little less. What it will have is a larger AFOV than your plossl. A 1.25" 32mm plossl will show as much of the sky as the 1.25" barrel size will allow. A 1.25" 40mm plossl will show no more of the sky than your plossl, but in a smaller AFOV. If you want more actual sky you need to move on to 2" eyepieces, whether your scope allows for these is another matter.

[shift8]

A 2-inch 35mm Panoptic can work really well in small achromats. The combination is great for sweeping views of the Milky Way from a dark sky site, especially with larger 120mm apertures. Field curvature can be removed by using a TSFLAT2 flattener.

This approach was discussed in a recent episode of The Actual Astronomy Podcast, namely episode #483 -- Affordable Wide-Field Astronomy with Brian Ventrudo
https://podcasts.apple.com/au/podcast/the-actual-astronomy-podcast/id1508892492?i=1000708999975

[refractordude]

Hello There

The 24mm UFF cost twice what I paid for the scope. So I decided on the Celestron X-Cel XL 25mm. The field of view will be close to what the 32mm plossl provided but wider. I will get a closer view with a darker background. If the eye relief and edge correction is good I will keep it. If not Walmart has a great return it to any store 30 day policy.

Clear Skies

[EpickCrom]

Hi mate.

I think you will like the X Cell 25mm. I had one as Saxon Cielo HD which I believe is identical to X Cell and it was a pleasing eyepiece.

[refractordude]

Hello EpickCrom


Cool

[refractordude]

Hello There

It has arrived. Will let you all know how it does with a F5 80mm achromatic. Hoping for sharpness very close to the edge.

Clear Skies

[mental4astro]

"Hoping for sharpness very close to the edge"...

Yep, you've got field curvature all figured out in an eyepiece.

[By.Jove]

The ultraflat eyepieces have a flat focal plane, they were designed specifically to be used with flat-field scopes used for imaging, such as the quad or quintuplet APOs - not achromats.

Your 80mm achromat has a curved focal plane, like a soup-bowl, so with this eyepiece, if its in focus at the centre, it wont be at the edge, and vice versa.

An Erfle or SWA eyepiece is a better match for a small achromat like yours, as they have curved focal planes approximating that of an achromat.

[Don Pensack]

The 24mm Ultra Flat Field has had its field stop measured to be 27.6mm, whereas the 32mm Plössls out there max out at a 27.0mm field stop, so the 24mm UFF will show a trace larger true field, and at a higher magnification as well.
But, if field curvature is a problem in the 32mm Plössl, it will be worse in the 24mm UFF because the wider the field stop, the more visible FC will be.