9 replies to this topic

[BigBabich]

I recently bought an older [EDIT:] MEADE! 8" F/6 Wide Field SCT. Was wondering if a focal reducer would work on it to make it...wider fielder-er. 
I honestly don't have a use case in my head for this....I'm just wondering.

Edited by BigBabich, 10 May 2025 - 04:38 PM.

[Dwight J]

Didn’t know Celestron made a F6 SCT.

[Jon Isaacs]

Didn’t know Celestron made a F6 SCT.

 

 

Meade made an F/6.3 or something like that but I have never heard of a Celestron F/6.

 

Jon

[hyiger]

Hmmmm... I know years ago Celestron made a C5 f/6 telephoto scope but I don't ever remember seeing/reading about an 8". 

 

Edit: Did a little bit of "googling" https://www.cloudyni...f6-restoration/ still wasn't able to find anything on an 8

Edited by hyiger, 10 May 2025 - 02:38 PM.

[rfcooley]

I recently bought an older Celestron 8" F/6 Wide Field SCT. Was wondering if a focal reducer would work on it to make it...wider fielder-er. 
I honestly don't have a use case in my head for this....I'm just wondering.

I am with the others here. I am unaware of a Celestron f/6 SCT. But if it is an F/6 why would you want to use a reducer? The Meade 6.3 was of questionable performance. Recently received a Meade 6.3  at the observatory but I have not had a chance to play with it yet. I guess I'll  have to play with it and see.

 

RF

[rickmurray1989]

Me neither. Every one that I have ever seen was f/10.

 

Didn’t know Celestron made a F6 SCT.

[BigBabich]

Everyone,
  It is a MEADE Wide Field!  I can either file this under "I was looking at my Celestron focal reducer and wondering if it would work" or "I have the brain of a carrot", your choice!
I honestly don't know what I was thinking. 
I was going to attach a pic, but I'm on my phone and I can't figure it out (Brain of a carrot!).
It's a Meade "Ultra High Contrast" Wide Field f/6/3 8" OTA (year undetermined).

[Airship]

If I recall right the f/6.3 focal reducer/field flattener _will_ work with the Meade f/6.3 wide field SCTs. I used one on a 10" f/6.3 for imaging and an 8" f/6.3 for EAA, but I can't recall if I ever used one for visual.

[carolinaskies]

Everyone,
  It is a MEADE Wide Field!  I can either file this under "I was looking at my Celestron focal reducer and wondering if it would work" or "I have the brain of a carrot", your choice!
I honestly don't know what I was thinking. 
I was going to attach a pic, but I'm on my phone and I can't figure it out (Brain of a carrot!).
It's a Meade "Ultra High Contrast" Wide Field f/6/3 8" OTA (year undetermined).

I have an 8" F/6.3 and have tried various reducer correctors with it.   Be aware an SCT .63x reducer corrector is made to correct the issues of an F/10 SCT so the correction applied to an F/6.3 is going to be less 'perfect' in optical accuracy.  This will often result in aberrations as you move away from the center of the field and will often cause issues on very bright objects at very low power so you may see the secondary mirror as the exit pupil of low power eyepieces will be higher than 7mm. 

[Eddgie]

There are a great many things in astronomy equipment that you can do, but the question is what compromises you face. 

 

The issue that would be most relevant here is the application.  For imaging with a small sensor, such as EAA cameras, this would likely be Ok, but only ok. EAA astronomers stack focal reducers on SCTs to achieve this same kind of fast speed.  

 

For visual use though, based on my extensive, but not professional knowledge of SCTs, the issue most likely to be encountered would be aperture loss. To get the focal plane far enough back to use a 2" diagonal, the primary mirror must be moved forward a considerable amount, and when you use a focal reducer, that amount is extreme. This will cause the axial rays to be clipped off either by the secondary mirror baffle or the primary mirror baffle. You would get a wider field, but that field would be greatly dimmed by the aperture loss, and the contrast would suffer significantly due to the larger percentage of obstruction and the smaller aperture.  You would get a wider field though (assuming you could reach focus). If you used a 1.25" diagonal, then you would not get a field much wider than if you used a 2" diagonal and eyepiece without the reducer. 

 

Aperture loss is not the end of the world, but by the time you run the numbers, you might find that your 8" SCT is working with 6.5" of aperture, and a transmission of maybe  70%, which means it would not likely be better than a 120mm f/6 refractor as a wide field scope. That being said, if you have the 8", it isn't that much to buy a focal reducer.

 

There are a great number of things you can do, but that does not mean that they will all work well, so at this point, it simply becomes a question of what compromises the user is comfortable accepting. 

 

Disclaimer: I do not have ray trace data for the model in question, so I am extrapolating from data that I do have and the general behavior of the moving mirror SCT. I may be way off. 

Edited by Eddgie, 11 May 2025 - 09:08 AM.