8SE and the Baader Zoom

[jonathan]

Last night I was enjoying observing Mars and discovered something interesting...  My 8SE isn't known for liking my higher power eyepieces, my Celestron X-Cel 10mm rarely is usable (just can't focus, even on bright objects), yet I'd read that the Baader Zoom is excellent with the 8SE so I tried it, and it was indeed excellent.  I went to attemp to zoom up a bit but found it was already at the maximum 8mm stop. 

So what's going on here?  Is it that the zoom eyepiece is a 'slow' eyepiece due to the size and amount of glass it has in it, and thus it matches the 'slow' f10 of the 8SE?  Or is it a quality thing - the Baader clearly outmatches the X-Cel eyepiece, but I thought that eyepiece quality wasn't such an issue with the 8SE.  But then I can never use my 5mm or 3.5mm in the 8SE and those are decent eyepieces.

[John]

It could be down to the seeing conditions, which have been rather mixed of late. Perhaps they were rather good when you recently had the Baader zoom in use and not so good when the X-Cel 10mm was in use ?

I would think that the optical quality of the X-Cel would more or less match that of the Baader zoom.

The 5mm and 3.5mm eyepieces will be giving too much magnification to be useful most nights I think.

 

[AstroTim]

The 9mm X-Cel is my most used eyepiece with my C8 (not that I have many to choose from) and I am able to achieve a good focus. I also have the Baader zoom and would say that they provide similar views. I struggle to get a sharp image at focal lengths below 9mm.

Are you sure it’s a 10mm X-Cel as I thought the range was 7mm, 9mm, 12mm?

Tim

[AstroTim]

To clarify, I was referring to the X-Cel LX range in my post above. I didn’t realise there was an previous X-Cel eyepiece range (with a 10mm). Unfortunately, I don’t know how the X-Cel and X-Cel LX eyepieces compare so my comment regarding the LX and Baader zoom might not apply to the older X-Cel.

[Alkaid]

Also found a 9mm xcel to be sharp  in mine.  
Was the old 10mm the same as the basic eyepieces that get delivered with a scope? If it’s a anything like the SW 10mm, it will be bad...just saying...

[johninderby]

The Xcel-lX eyepieces are an improved design and supposedly the same as the Meade HD60.

When I had a C8 found the Xcel-LXs were very sharp and worked really well.

[jonathan]

I was using both the Baader Zoom and the X-Cel 10mm last night, so same seeing conditions within the space of the time it took to change eyepieces.  My X-Cel is not an LX, it's one of the older range and was always difficult to use with the 8SE from new (both the eyepiece and scope), I just put it down to requiring very good seeing conditions.  By no means would I say the old X-Cel was anything like kit 10mm eyepieces, it looks and feels really nice, a large piece of glass at the eye and straight fixed rubber eye relief, the glass looks the same as my X-Cel LX 5mm.

5 hours ago, AstroTim said:

The 9mm X-Cel is my most used eyepiece with my C8 (not that I have many to choose from) and I am able to achieve a good focus.

I wonder if the C8 is slightly different to the 8SE somehow, or perhaps 10mm is just not a sweet spot for an 8" SCT (maybe why they ditched it?)

To be honest I've been slightly underwhealmed by the X-Cel and LX range in recent times, they only seem to work well in my f5 150P reflector.  Who can say - local conditions, my particular scopes, my eyes...

Edited October 2, 2020 by jonathan

[AstroTim]

From the little I’ve read, the original and LX versions are very similar in observable visual performance. The original has 2 ED elements that the LX lacks, but also has a narrower field of view.

The 8SE is the same optical tube as the other Celestron 8 inch SCT models, of the same generation, just a different colour. There will be some differences from one generation to another. Mine is a couple of years old, but I don’t think much has changed for some years. I think the XLT coating might have been the last change made.

In theory, your f5 scope will be more sensitive to the quality of the eyepiece than your f10 8SE. I don’t have much to compare my LX eyepieces to other than the Baader zoom which I find gives similar views for a given focal length. If your zoom is giving good views at 10mm or even 8mm then that would suggest that it isn’t down to seeing conditions and the 10mm X-Cel should perform well too.

The 5mm and 3.5mm won’t work well in the 8SE as they would give 406x and 580x respectively. For comparison, I can rarely get above 226x. While there are various rules of thumb for the maximum useable magnification, taking in different seeing conditions, you are probably looking in the ballpark of 240x for the 8SE.

Could you see any detail on Mars with the 10mm X-Cel? How did the view differ to the Zoom at 8mm?

[John]

My understanding is that that the older X-Cel line of eyepieces are not as good as the newer X-Cel LX's but even so the F/10 focal ratio of the SCT should mean even a humble plossl should work well.

Some of my best views of Saturn ever were with a Celestron C8 (older one) and an 8mm Tele Vue plossl.