Join for FREE
It only takes a minute!
||Thread Tools||Rate Thread|
|Saturday 8th September 2018, 00:05||#1|
Join Date: Sep 2014
Please school me on the Pentax 65
Very experienced with binoculars, but fairly inexperienced with spotting scopes. My personal scope up to now has been an old Bushnell Spacemaster with a fixed 20x eyepiece. It is remarkably good, which is why I haven't bought a new scope in 20+ years. Everything I've compared it to has left me wondering why I need to spend $400+ on a new scope.
However, I have a keen interest in the Pentax, not only because of the rave reviews it receives but also because of the universal 1.25" eyepieces it uses.
Here's where I need help. I know literally nothing about 1.25" eyepieces. I've read a bit, and know that you don't necessarily have to spend a ton on an eyepiece to get a great image, but I don't know how to convert mm focal length to the convetional "power" setting, etc.
I do know I'm a fan of fixed focal length eyepieces. My 20x eyepiece on my Spacemaster blows any variable eyepiece I've ever seen out of the water in clarity and FOV. So I guess my question is, what eyepiece should I be looking at for the Pentax 65 that will give me 20-25X and not break the bank?
Thanks in advance for your help!
|Saturday 8th September 2018, 17:28||#2|
It's just a flesh wound.
Join Date: Sep 2007
To calculate magnification, divide the focal length of the scope by the focal length of the eye piece.
Conversely, to solve for eye piece focal length, divide the scope focal length by the desired magnification.
The focal length of the PF-65ED is 390mm. So, for 20X take 390mm/20x = 19.5mm eye piece focal length.
The Pentax XW eyepieces are fantastic (and waterproof, most astro eye pieces aren't), and there is an XW-20 available. Not cheap, but good deals on used eye pieces can be found.
Latest lifer: #373 Barrow's Goldeneye
Latest Pennsylvania lifer: #340 Western Meadowlark
Latest Lancaster County lifer: #301 Henslow's Sparrow
Use eBird to record your bird sightings.
|Monday 10th September 2018, 13:22||#4|
Join Date: Aug 2015
quite frankly, if you have a scope that is doing 20x well (which is not very difficult) and you only want/need 20x, there is not really a need to upgrade.
Regarding the EP question for the Pentax with a body focal length of 390mm we get 390mm / 20 = 19.5mm or 390mm / 25 = 15.6mm. My recommendation would be to get 30x though - 390mm / 30 =13mm. You will not find astro EPs with the exact focal length - get sth in the ballpark and divide body fl by EP fl for magnification. You want to get wide angle EPs from 60 deg apparent field of view onwards.
Also be prepared to find out that a 3rd party EP you get will not come to focus in your Pentax spotter - they have a lot less focus travel than real astro scopes after all. So either find some friends with astro scopes and EPs to try theirs (the local astro club is a good idea) or get them from a shop with a no questions asked return policy.
|Rate This Thread|
|Thread||Thread Starter||Forum||Replies||Last Post|
|Pupils at Paget Primary School joined world's biggest school wildlife survey (RSPB)||BF Newsroom||Latest news from the RSPB||0||Sunday 8th February 2015 14:33|
|Pupils at Paget Primary School prepare to join world's biggest school wildlife survey||BF Newsroom||Latest news from the RSPB||0||Wednesday 28th January 2015 10:45|
|School bell rings to mark the start of world's biggest school wildlife survey (RSPB)||BF Newsroom||Latest news from the RSPB||0||Sunday 26th January 2014 12:08|
|School bell rings to mark the start of world's biggest school wildlife survey (RSPB)||BF Newsroom||Latest news from the RSPB||0||Sunday 19th January 2014 23:15|
|Current Classic "Old School" vs. Current State of the Art "New School"- Habicht vs SV||stephen b||Binoculars||50||Friday 26th July 2013 20:51|