Best telescopes for photographing planetary nebulae and small galaxies?

Hi Kathleen

I have a Celestron 9.25 (not EdgeHD) and no experience with the Edge, just what I have read and heard. The advantage of the EdgeHD is that the full field is flat, the C9.25 doesn’t give perfect images right the edge of the field.

I do PN, planets, the Moon, and small galaxies to full field larger galaxies, as well as nebula of all sizes.

For planets and Moon close-ups (where you use a barlow) there is no advantage to the EdgeHD since you only use the center of the field anyway. For PN and all deep sky targets and a full image of the moon I use an f6.3 reducer from Starizona, which gives excellent images to the field edges, and obviously the faster f-ratio. My seeing is rarely better than 2” so it makes no sense to over sample with the full FL, the f6.3 is perfect FL for me. For planets one uses lucky imaging where a long FL is critical to take advantage of the lucky seeing, so the full FL and barlow is the way to go for planets.

The EdgeHD is slightly slower if you get the Celestron 0.7x reducer, but not a big deal.

To make a long story short if your seeing is often excellent then you may want an EdgeHD so you can image at f/10 full focal length deepsky targets that are bigger than maybe 2/3 a crop sensor, but not necessary for smaller targets, or planets where you add a barlow to get the FL you want. But note the Edge f10 ratio is high for deepsky objects that are dim. And again if you are mostly looking at small objects, you don’t need an EdgeHD, it only really shines for the full field at the full focal length, especially if you had a full frame camera. And cost is maybe 1.5x higher for he Edge vs the standard. The Edge 0.7X reducer from Celestron is about the same price as the Starizona f6/3 reducer for the standard C9.25, so that is a wash. The Celestron f6.3 reducer is not great, I would not recommend it with the standard C9.25

All this being said, the SCT’s like the C925 is very good for PN and planets. The C11 and C14 would be even better but are very heavy, need a good mount and generally will be more difficult to use. But as you see on AB, these SCT’s are the favorite for planets.

By the way, I have a Celestron CGX mount which I don’t use a lot anymore, it is not a great mount, even though it is supposed to be better than the other Celestron mounts. I have the Ioptron CEM70ec now with encoders for my C9.25 which is so much better. But there are a lot of other good mounts out there too, depending on your price point.

Good luck

Rick

It really depends on your seeing. You want to get the sampling/focal length of the scope in line with the seeing at your site. Being slightly oversampled by conventional standards can be helpful since things like BXT are helped somewhat by better sampling. Typically you will want 3-4 pixels or somewhat more across your typical best seeing. With a standard 3.76 micron pixel camera that means:

Best seeing 2 arcsec = sampling of about .5 to .7 arcsec

Best seeing 1.5 arcsec = sampling of .4 to .5 arcsec

Best seeing 1 arcsec = sampling of about .25 to .3 arcsec

You can figure your focal length from that

You also don’t want too slow, about f7.5 to f8 at the slowest.

Having said that, if your best seeing seeing is worse than 1.5 arcsec, I would not bother with those targets - you will never be able to produce high res images.