EdgeHD vs XLT (C11)

[jambouk]

What makes the EdgeHD C11 £1,700 more than the XLT version aside the flat field? Is the field flatter than using an XLT with a field flattener which only costs £100?

This is purely an academic question as I already own a standard C11 and was asked how much "better" the EdgeHD was, comapred to an XLT with a flattener. 

Thanks.

James

 

[Merlin66]

This may help....

https://www.celestron.com/pages/edgehd-optics

[jambouk]

Thanks. That link doesn’t clearly explain the benefits over an XLT with a flatener but the 24 page PDF may do, and I’m planning on reading that tomorrow. Thanks for the link.

James

[Whirlwind]

It depends on what you are intending to use it for.  For Deep sky it allows for a much greater field of view without optical distortions becoming apparent.  Most SCT flatteners have more limited fields in this regards because of limitations of their design whereas the Edge's I believe are corrected for full frame (or close to) cameras which requires a lot more glass and hence expense.  In addition there are mechanical differences between the two.  There is likely also the impact of what the market will pay for an off the shelf design factor and in the UK I think there is a bit of one distributor syndrome that is coming into play.

If you are a deepsky imager with a large CCD then the Edge wins.  For visual, photometry, spectroscopy or solar system imaging the Edge only really has the mechanical benefits (e.g. mirror lock etc).

 

[jambouk]

Thanks. 

The 24 page article is fascinating to read.

Optically, it seems the differences are:

- the EdgeHD is coma free as it has a lens inside the baffle tube

- the EdgeHD delivers a flat field as it has a second lens inside the baffle tube

- the EdgeHD may generate less vignetting as they have "placed the primary and secondary mirrors closer than they had been in the classic SCT, and designed new baffle tubes for both mirrors that allow a larger illuminated field of view."

As you say, mechanically the differences are:

- the mirror lock

- ventilation ports as the baffle tube is now sealed with lenses inside.

 

As I only really use the central part of the FoV for imaging, I can stick with the classic SCT, but can see the advantages of the EdgeHD for full frame deep sky stuff.

James

 

 

[Michael Hogan]

The EdgeHD are much better you can take really good images with SCT with flattener /Reducer but EdgeHD have pinpoint stars and mirror locks

[Ken82]

I think others have covered the differences very well. 
 

The edge hd scopes are mainly for imaging I wouldn’t get one just for visual.
 

Just want to add I’ve recently started imaging with my 11edge and I’ve been very pleased how well the scope covers an aps-c sensor especially at f10. 
 

The mirror locks on mine didn’t stop flexure but that could have been from other causes. An OAG is essential if going over 2min exposures. 
 

unfortunately I’ve only got one mount and at the moment want to concentrate on wide field but I have full confidence the edge hd will give me results in the future. 

[ollypenrice]

The real size of the corrected field of the Edge scopes was initially unclear and Celestron revised it. They now say 42mm without reducer and 26.7mm with it. https://www.celestron.com/blogs/knowledgebase/what-is-the-optimized-image-circle-for-the-edgehd-otas-and-reducers

They claim that this will illuminate a 35mm sensor, unreduced, but it strikes me that this is optimistic. I think my Kodak 11 meg CCD needs about 45mm.

Olly

[coopman827]

With the XLT version, the outer part of the FOV is distorted when the on-axis image is in focus.  With the Edge HD version, the whole FOV is flat and fairly sharp (as sharp as an SCT can get, anyways).  This is my viewing experience (visual only).      

[pete_l]

If a product is skillfully marketed, a higher price on its own is viewed by many customers as a real advantage 🤠
Terms such as "premium" or "for the serious user" imbue an air of exclusivity in their own right.

[Timebandit]

 

 

 

Its probably like most telescope equipment/optics. To get that little bit more performance can cost an awful lot more money. Diminishing rate of increase in performance for an extra lot more money. I suppose the buyer has to weigh up if that extra performance is needed and if the extra cost is really worth it to them. You pays your money and takes you choice

 

 

 

 

[Charles Kirk]

The production cost increases significantly when working to higher tolerances.

That in combination with the additional optical elements in the baffle tube to correct for both coma and field curvature is the reason for the price difference.

Also the margins tend to be higher on premium products.

The white paper makes a good read, a skilfully executed technical sales document.

For Visual some people are more sensitive to the coma in conventional SCT designs which makes the EdgeHD attractive.

Another thing is that as interests evolve over time the EdgeHD is better futures proofed for an observer who starts out main interested in visual but becomes interested in imaging.

The pricing in the UK is incredibly expensive compared to the US it looks as if Celestron want to preserve their profit margins in USD despite the fact that the telescopes are manufactured in China by Syntra.

[Space Hopper]

The C9.25, 11 (and 14) are a big big jump up in price and makes the 8" seem like a good buy in comparison.

I've seen the 8" in the £1000 - £1100 sort of territory at Astroshows. At that price its a good scope and a compelling choice.

[Jane C]

I use an 11" XLT with a 0.63x focal reducer, both from Celestron, and I mainly photograph galaxies, using a camera with an APS-C sized chip (a cooled ZWO ASI2600MC).

My experience is that the stars are good and round all over the image.  

For me the irritants are as follows.

• I need to re-collimate every night, which burns up time, a precious asset in the cloudy climate of South Wales, where I am unlikely to experience a fully cloud-free night.  I probably also need to do this after a meridian flip.
• Because of light pollution I lose a lot of the image space on the chip to reflected rings.

Therefore the Edge HD would have advantages if I didn't have to keep re-collimating and if I could send the reflections to places off the chip by using a higher magnification.

Holding focus is a puzzle to me.  The FWHM I achieve often worsens during a long exposure, but it almost equally often improves.  I put that down to seeing, which is rarely great in the UK, but that's a guess.

Edited February 1 by Jane C
correct misprint

[Louis D]

Visually, at a star party pre-pandemic, I thought that the 8" EdgeHD put up images of Jupiter as sharp and detailed as 8" Newtonians with custom figured mirrors.  Images in standard 8" SCTs on the same night looked mushy and mostly featureless in comparison.  It made me a believer that night.  Basically, that corrector is putting all the photons where they belong in the image, even on-axis.

[900SL]

Didn't Ed Ting do a comparison in one of his videos?