Standard SCT or EdgeHD?

[Darren_S]

I have an Esprit100 for wide field imaging where a flat field to the edge is very important. I want to progress to image small targets at long focal length such as galaxies, planetary nebula, small nebula and planets. If I am only interested in the target and not interested in a wider star field, is an EdgeHD required or would a standard C9.25 or C11 do the job? Big difference in price!! :eyepop: Thanks!

[Dave882]

Hi Darren
I’ve had both edge and non-edge C8 and a standard M10. No identifiable advantage for small targets with corrected optics. But a BIG difference when you go to a larger aperture. Use the extra cash saved on standard non-edge and go big.

A couple of considerations:
Edge scope have vents to help cooling. Try insulating the tube of non-edge
Edge scopes have mirror locks and I reckon less mirror shift on focus. recommend getting a Crayford style focuser

Hope this helps.

[Sitt]

The EdgeHD gives a flat field to the edge of the image (hence its called edge) plus you get mirror locks. Googling comes up with a vast amount info https://www.google.com/search?q=edge+hd+over+non+ehge&rlz=1C1RXQR_en-GBAU967AU967&oq=edge+hd+over+non+ehge&aqs=chrome..69i57j33i160.15093j0j7&sourceid=chrome&ie=UTF-8

[Darren_S]

Thanks David. C11 about $1,000 cheaper than 9.25 Edge so that’s what got me thinking!! Only issue is my 294MC Pro may not be the best match.

[Dave882]

I’ve been using the 294mc in my scts for a while and very happy with it. Just not the best pixel scale for the Hyperstar but apart from that a very good performer. Even goes quite ok with planetary pics too. What was your main concern with using the 294?

[Darren_S]

Basically the pixel scale. Chucked the 294 and the various SCTs in Bintels calculator and it wasn’t the best match, but ok. Your positive experience gives me confidence though! Theory is one thing but the proof is in the results…

[Camelopardalis]

Darren, I think you can probably tell from the above that we all have different tolerances for what we find acceptable at the eyepiece or what appears on the sensor.

Compared to your Esprit (I have one also!), the standard SCT isn’t well corrected once go off-axis i.e. away from the centre. However, there are corrector/reducers that do a better job than the inexpensive Celestron one.

The EdgeHD is good for a full frame sensor, at least the 9.25 and above. I have an EdgeHD 11” which I mostly use for planetary and as a visual scope, but plan to try some “long exposures” soon. FWIW, there are also alternatives to the large and pricey Celestron reducers.

So, for imaging, I’d recommend going for the EdgeHD every day.

I don’t find any major issues with cooling most of the year here in QLD, although in mid-winter we can have 20 degree drops over the course of an evening and nothing short of an open tube copes well with that, but it is manageable.

Of course, this ignores “non-SCT based” options which may suit you equally well…

[Darren_S]

Thanks Dunk, some really good points. Given I will almost solely be imaging, the HD series seems the way to go even if going in tight on a small target.:)

[denodan]

I got the 9.25" was $200, cheaper than the 8" HD, aperture rules for planets, so made more sense bigger aperture cheaper cost. Also you will only getva flatter field if you have decent eyepieces.

The star Arizona reducers are specially made for the SCT And hear with one of these in use work as well as an ED.

Also accessories are far more expensive for the HD series