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-1-2...4mm-93453.html

Clear Skies

[mental4astro (Alexander)]

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 (Kym)]

Originally Posted by 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-1-2...4mm-93453.html

Clear Skies

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/podcas...=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 (Joe)]

Originally Posted by 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

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 (Alexander)]

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

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

[By.Jove (Jove)]

Originally Posted by 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

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]

Originally Posted by 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.

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.