6 replies to this topic

[extragalactic]

Hi folks!

 

A 102/460 refractor without flattener will show field curvature.

 

Is there a rule of thumb like "field curvature will become very apparent with an afov of xy" or something like that?

Are there heuristics or ways to calculate?

 

I'd like to observe in prime mode without flattener. How bad is FC going to be?

 

A number of you are using the TSFLAT2 with fast refractors with great results, for now I'd like to observe without flattener though.

 

Comments appreciated!

[bobhen]

Even when I used 82-degree Nagler eyepieces and observed visually, I never used a flattener with my 102mm F5 achromat. In prime mode with my intensifier, I believe the field of view is around 40-dgrees and I never saw the need for a flattener or noticed field curvature.

 

I also use a .7 reducer in prime mode, getting the 102mm F5 down to around F3.5. I see some slight falloff at the edges caused by the reduce but it does not impact the view and it is not noticeable unless you look for it. As a matter of fact, most of the time I use the 102mm F5 reduced to around F3.5. 

 

The NV, wide field views are much too captivating to care or notice any very slight distortions.

 

Bob

[extragalactic]

Okay. You say I shouldn't worry too much about FC in this case.

 

The 31mm Nagler has an apparent field of 82 degrees.

So, in prime, the 27mm 40 degrees NV lens only shows the center area (with little FC) of a potential >82 degrees field.

[slavicek]

Yes, you should not worry too much...

However, another way to observe (and to get flat field) is to use camera lens. I and many here on CN use different camera lens. You can find ton of info about it here on CN.

I have 31 mm Nagler and I never use it with NV. Ploslls is all you need for 40 deg FOV of the NV in afocal mode. So 67/50/40/32 mm TV ploslls all work well.

My "favorite" "ultra wide FOV" set up is Canon 200 mm f/1.8 with 40 mm plosll which makes it like f/1.2. I can see "half of the sky" with it! 

GL.

[bobhen]

Okay. You say I shouldn't worry too much about FC in this case.

 

The 31mm Nagler has an apparent field of 82 degrees.

So, in prime, the 27mm 40 degrees NV lens only shows the center area (with little FC) of a potential >82 degrees field.

I observe in prime mode and I never saw the need. I wouldn't worry about FC with NV and prime observing mode. You could add the flattener later, if you felt the need. 

[Joko]

Hi folks!

 

A 102/460 refractor without flattener will show field curvature.

 

Is there a rule of thumb like "field curvature will become very apparent with an afov of xy" or something like that?

Are there heuristics or ways to calculate?

 

I'd like to observe in prime mode without flattener. How bad is FC going to be?

 

A number of you are using the TSFLAT2 with fast refractors with great results, for now I'd like to observe without flattener though.

 

Comments appreciated!

No worries in prime mode, there should be no issue.

You can also add a Barlow for more magnification.

Edited by Joko, 07 July 2024 - 05:54 PM.

[extragalactic]

bobhen, slavicek, Joko, thank you for your help!