Celestron Astro Fi 127mm WiFi SCT or Celestron Nexstar 4SE

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Re: Celestron Astro Fi 127mm WiFi SCT or Celestron Nexstar 4

Postby dave.b » Fri Dec 08, 2017 12:29 am

The main problems associated with using a Barlow for visual use are:
* Over doing the magnification and reducing the exit pupil of the EP below 2mm. Sure you can use an exit pupil down to about 0.6mm but it's hard work maintaining the alignment and you are not using all of your macular. Compare the detail you can see in a planet like Jupiter or Saturn at different exit pupil sizes and surprisingly the smaller lower magnification will refresh more detail than the image seen with a higher magnification when the exit pupils are in the range 2mm down to 0.6mm respectively.
* Higher magnification produces a dimmer image, which compounds with the exit pupil problem.
* A Barlow adds more elements to the optical path increasing losses and distortion. Price is a good indicator of quality of course. But better IMO to spend the money on good eye pieces.

I've had cheapish Barlows and found then frustrating to use and eventually got rid of them favouring mid range eye pieces such as Hyperions. I now have a mid range Barlow that I use with a dedicated camera for planetary work, although the tiny field of view and dim image are hard to work with. I of course aspire to owning a Powermate (as I do a set of Naglers), but that will require another step up in free time and clear skies to justify (and maybe a lottery win too, esp. for a set of Naglers).

A zoom eye piece is a compromise between image quality and ease of use. Zooming in and out of lunar features is great fun. As it is for deep sky objects such as the Orion Nebula. Moreover, when time and clear sky is at a premium why mess around when just browsing? Better kit for detailed study and imaging when time and clear skies permit.
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Re: Celestron Astro Fi 127mm WiFi SCT or Celestron Nexstar 4

Postby Aratus » Fri Dec 08, 2017 8:38 pm

Its strange, but the best Barlow I ever got came free as a promotion with a eyepiece! However generally speaking you do get what you pay for.
Actually a barlow allows you to use an eyepiece with better eye relief. Eye relief is a component of an eyepiece, not the quality of the image you are looking at.
I use an 11" reflector (Celestron CPC 1100) and a 3" refractor, (Sky-Watcher ST80) mounted on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI 120MM, ZWO ASI1600MC and Canon 1300D for imaging.
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